Safety in LPG Design 2000

ExxonMobil

Safety in LPG Design

min. 15 m from Fence

Removable Fill Distance Valve to Fence15 m

Removable Part to ESS TI

PI

First Edition by

Exxon Company, International Florham Park, New Jersey  ExxonMobil

Fairfax, Virginia

ExxonMobil Proprietary Information

This manual was produced using Doc-To-Help® Version 4, WexTech Systems, Inc.

Revision History

First Edition - January, 1996 Second Edition –October, 1999

Third Edition ExxonMobil – March, 2001 now including Mobil EPT 15-T-02 and Mobil SCS Volumes 1 and 2

For future additions, suggestions and changes please contact either: Detlef Robertz/CentralEurope/ExxonMobil@xom or

Contents

1

PREFACE

1-1

1.1 Introduction 1-1

1.2 Objectives for Safety in LPG 1-2

2

PLANT SITE

2-1

2.1 Exposures from and to the Site 2-1

2.1.1 Planning Considerations and Criteria 2-1

2.1.2 Topography and Prevailing Wind 2-2

2.1.3 Road Access and Traffic Situation 2-2

2.2 LPG Plant Layout 2-2

2.2.1 Space Requirements 2-3

2.2.2 Equipment Spacing to Maximize Separation 2-4

2.3 Electrical Equipment Specifications 2-9

2.3.1 Electrical Area Classification 2-9

2.4 Emergency Shutdown System 2-15

3

BULK STORAGE

3-1

3.1 Storage in Plants and Industry 3-1

3.2 Mounded and Above Ground Storage 3-2

3.2.1 Dimensional Sizing of Drums 3-2

3.2.2 Materials Selection for Tanks 3-3

3.2.3 Design Basis for Mounded Drums 3-6

3.2.4 Testing Requirements 3-11

3.2.5 Horizontal “Bullets” and Spherical Tanks 3-12

3.2.6 Spill Containment 3-14

3.2.7 Vacuum Conditions 3-15

3.3 Refrigerated LPG Storage 3-15

3.4 Overpressure Protection for Tanks 3-16

3.4.1 Contingencies to be Expected 3-16

3.4.2 Refinery and Upstream Pressure Relief 3-17 3.4.3 Pressure Relief in Marketing Terminals 3-17

3.5 Emergency Block Valves on Bulk LPG Tanks 3-23

3.5.1 Tank EBV's in Liquid Service 3-23

3.5.2 Tank Shutoff Valves in Vapor Service 3-25

3.6 Tank Instrumentation 3-26

3.6.1 Tank Level Measurement 3-27

3.6.2 Pressure and Temperature Indicators 3-28 3.6.3 Grounding Connections for Tanks 3-29

3.6.4 Product Odorization 3-30

4

PUMPS & COMPRESSORS

4-1

4.1 Pumps 4-1

4.1.1 Pump Types Commonly Used 4-1

4.2 Compressors 4-11

4.2.1 Compressor Types Used 4-12

5

PIPING AND VALVES

5-1

5.1.7 Small Piping Connections 5-7

5.1.8 Installation 5-8

5.2 Valves in Piping 5-9

5.2.1 Valve Integrity 5-9

5.2.2 Shutoff Valves 5-9

5.2.3 Backflow Check Valves 5-10

5.2.4 Thermal Relief Valves 5-10

5.2.5 Emergency Block Valves for Piping 5-11

5.2.6 Valve Packings 5-11

6

PRODUCT TRANSFER

6-1

6.1 Principles of Product Transfer 6-1

6.1.1 Loading or Unloading with Pumps 6-3

6.1.2 Loading or Unloading with Compressors 6-4

6.1.3 Using Pumps Versus Compressors 6-5

6.1.4 Static Electricity in Unloading and Loading 6-6

6.1.5 Hard Arms 6-6

6.1.6 Hoses in Product Transfer 6-8

6.2 Loading and Unloading 6-10

6.2.1 Truck Loading and Unloading 6-10

6.2.2 Rail Car Loading and Unloading 6-13

6.2.3 Marine Loading and Discharge 6-15

6.2.4 Marine Pier Installations 6-15

6.2.5 Pipeline Dispatch and Receipt 6-21

7

LPG CYLINDERS

7-1

7.1 Cylinder Purchasing Specifications 7-1

7.1.2 Cylinder Specifications 7-2

7.2 Cylinder Valve Purchasing Specifications 7-8

7.2.1 Manufacturing Design Standards 7-8

7.3 Regulator Purchasing Specifications 7-10

7.3.1 Manufacturing Design Standards 7-11

7.4 Hose Purchasing Specifications 7-13

7.4.1 Hose clips 7-14

7.5 Cylinder Filling Plant 7-15

7.6 Cylinder Filling 7-15

7.6.1 Cylinder Processing and Filling 7-16

7.6.2 Manual Filling System 7-17

7.6.3 Automated Filling System 7-17

7.6.4 Integrated Automated Filling Plant 7-22 7.6.5 Purchasing Guidelines for Filling Plants 7-30 7.6.6 Third Party Cylinder Filling Plant 7-33

7.7 Cylinder Distribution 7-33

7.7.1 Distribution Center 7-33

7.7.2 Dealer and Reseller Cylinder Storage 7-35

8

FIRE PROTECTION

8-1

8.1 Passive and Active Fire Protection 8-1

8.1.1 Fireproofing, a Passive Fire Protection 8-1

8.2 Fire Protection System Design Philosophy 8-7

8.2.1 Firewater System, an Active Fire Protection 8-8

8.2.2 Protection Requirements 8-16

8.2.3 Flammable Gas Detectors 8-19

8.2.4 Fire Detectors 8-20

9

TRANSPORTATION

9-1

9.1 Means of Product Movement 9-1

9.2 Road Bulk Transportation Equipment 9-1

9.2.1 Truck Design and Procurement 9-1

9.2.2 Basic Design Considerations 9-2

9.2.3 LPG Truck Discharge System 9-7

9.3 Road Cylinder Transportation 9-11

9.4 Rail Tank Cars 9-12

9.5 Marine 9-13

10 CUSTOMER INSTALLATIONS

10-1

10.1 Cylinder Bank Installations 10-1

10.1.1 Design of Cylinder Banks 10-1

10.1.2 Installation of Cylinder Banks 10-2 10.1.3 Vaporization Rate in Cylinders 10-2 10.1.4 Icing or Sweating on Cylinders. 10-5

10.2 Containers at Customer Sites 10-5

10.2.1 Spacing and Location of Containers 10-5 10.2.2 Designing Customer Storage Systems 10-7 10.2.3 Sizing Of Containers and Vaporization Rates 10-8 10.2.4 Sizing Containers for Vaporizing Liquid 10-9 10.2.5 Enforced Vaporization by Means of Vaporizers 10-12

10.2.6 Installation of containers 10-14

10.2.7 Container Fittings and Piping 10-17 10.2.8 Container Valves and Accessories 10-18

11 AUTOMOTIVE LPG

11-1

11.1 Automotive LPG Stations 11-1

11.1.1 Design of Automotive LPG Equipment 11-1

12 LPG PROPERTIES

12-1

12.1 Product Properties 12-1

12.2 LPG Hazards 12-5

1 PREFACE

1.1 Introduction

The manual is primarily intended for assisting managers and engineers responsible for design, construction, or modification of LPG facilities. It should also be useful as a ready reference for members of management who have a need to understand LPG equipment and design practices.

The LPG guidelines included in this manual are intended for application to new construction or alterations to existing facilities. The manual covers guidelines for the safe receipt, storage, loading, transport, and unloading of LPG for refining, upstream, and marketing bulk storage, as well as marketing cylinder filling plants and depots. The manual is not intended to cover refinery onsites, upstream gas plant facilities, or offshore platforms. Design practices among the functions are quite similar, although in a few cases some differences appear due to the scale of operations in refineries or upstream plants compared with marketing plants. These are noted. When deviations from the guidelines become necessary they should receive safety review and approval by the country/cluster.

If local regulatory requirements or current country/cluster practices are more restrictive, however, they will of course supersede the guidelines described herein. Local regulations have to be followed as a minimum.

The manual references EMRE Global Practices (GPs), EMRE Design Practices (DPs) and ExxonMobil Engineering (EMRE) reports. GPs are typically referenced to provide detail on the implementation of design concepts. Within GPs, individual paragraphs are identified as to their purpose, i.e. safety, operability, reliability, maintainability, etc. Deviation from “safety” paragraphs should receive formal safety review and approval. The lead design engineer would control deviation from “other” paragraphs. DPs are referenced to provide considerations for design. Their application requires engineering judgment and the lead designer should determine when deviations require formal safety review. EMRE reports are referenced to provide additional design considerations on special topics. The lead design engineer should determine their applicability by reviewing or contacting EMRE.

Industry standards used in this manual include NFPA (National Fire Protection Association), LPGA (Liquefied Petroleum Gas Association), API (American Petroleum Institute), NPGA (National Propane Gas Association), and IP (Institute of Petroleum, UK).

The material contained in this manual is considered “Proprietary” and its distribution limited according to company procedures for safeguarding proprietary company information. If there is a strong business reason to give portions of the material to customers or contractors, only the minimum portion containing pertinent information shall be released.

Quality Assurance

Whenever possible, equipment for LPG Marketing applications should be purchased from manufacturers who have submitted their product to a recognized governmental or independent laboratory for analysis, evaluation, and performance testing in LPG service, and have been granted approval as indicated by listing and/or labeling. Organizations performing or sponsoring the type of testing recommended include US Underwriters Laboratories, the UK Board of Trade, Lloyds Underwriters, the German BAM (Bundesanstalt für Materialprüfung) or similar institutions, which are widely recognized. It is desirable to have selected equipment covered by a testing program that provides periodic quality assurance of the manufacturer that design, materials, and procedures are unchanged from the initial approval. The Underwriters Laboratories listing program incorporates this feature.

Approved LPG equipment will often be available for standard Marketing equipment, e.g. cylinders, cylinder valves, filling equipment, small pumps and seals, and regulators. Equipment for larger scale LPG operations in refining and upstream is often not submitted for formal LPG approval, because it is manufactured in accordance with industry standards for hydrocarbon service, which includes LPG. When equipment has not been approved for LPG, its mechanical design and materials of construction reviewed by the project engineer, with input from specialists when necessary, to determine suitability for LPG use, and to ensure that the device will function satisfactorily for the intended service life.

The conversion of valves and accessories originally designed and fabricated for another service is not recommended. All valves and accessories shall be supplied by the manufacturer as assembled and tested at the factory, without subsequent modifications

1.2 Objectives for Safety in LPG

Following are objectives to maintain high standards of equipment design and operations. 1. Minimize or eliminate LPG incidents

2. Develop and coordinate inter-functional LPG safety training programs. 3. Monitor regulatory trends.

4. Update manuals at regular intervals.

5. Publish information on lessons learned from incidents that occurred in the company or industry.

Procedures for LPG

Inter-functional training programs for LPG safety have been developed and coordinated through the LPG Safety Network.

The LPG design guidelines contained in this manual are based on current ExxonMobil and industry design philosophy and practices, and on the results of company LPG risk assessment programs. Where differences exist between country/cluster design practices and those presented in this manual, it is suggested that country/cluster management consider adopting the practices described herein. ExxonMobil issues this manual to its country/clusters for suggested use in design of Liquefied Petroleum Gas (LPG) facilities used in Upstream, Refining and Marketing operations. Relevant aspects of safety for LPG design are documented in this third edition (2001) of the “Safety in LPG Design” manual. LPG safety design and operations manuals will be updated on a 3-yearly basis. More urgent updates will be communicated through the LPG Safety Network and through the BestNet. Recommended changes to guidelines and practices will be developed as appropriate.

New directives and standards are coming from legislative bodies and industrial associations, which every nation is directed to follow. Regulatory developments will be controlled by following the OIMS systems.

Distribution of industry and company incidents and lessons learned will be done on a timely basis through the LPG Safety Network.

Responsibilities

ExxonMobil LPG Technical Advisors provide guidance and assistance to help plants to implement procedures and practices described in the LPG manuals and solve their problems. The ExxonMobil LPG Advisors are primary contacts for Marketing country/cluster LPG issues such as incidents and lessons learned, training needs, suggested revisions to LPG safety manuals. They attend industry LPG meetings, monitor technical and regulatory trends, evaluate changes in industry procedures and practices for applicability. They communicate to the country/clusters as appropriate. Representatives from Upstream, Refining, Marketing, and Marine will have an influence on company LPG standards reflected in the “Safety in LPG Design” and “LPG Safe Operations Guidelines.” Ultimate decisions on technical issues will be made by the ExxonMobil LPG Technical Advisors and ExxonMobil Research and Engineering.

Verification and Feedback

Yearly verification of SHE performance of LPG operations by the SHE organization. Summary of incidents, lessons learned. Identify areas for system improvement and implement.

2 PLANT SITE

2.1 Exposures from and to the Site

Before choosing a plant site it is important to study all relevant facts that may be of influence on the choice. Such items of influence are exposure to and from the

neighborhood, topography, prevailing wind direction and the road traffic situation.

It is considered appropriate to locate an LPG plant in an industrial zone. The plants in the neighborhood may preferably be refineries or storage plants or similar industries where ignition sources are rare or under control. Therefore, neighborhood to any type of facility which incorporates obvious ignition, sources, or which employ hazardous processing methods (e.g. storing powerful oxidizing agents), shall be avoided. If known exposures are more severe, increased clearances may be necessary.

Warning signs “NO SMOKING,” “FLAMMABLE GAS” shall be posted at all LPG handling areas and outside the gate. The locations of the signs shall be

determined by local conditions, but the lettering shall be large enough to be visible and legible from each point of transfer.

2.1.1 Planning Considerations and Criteria

The input data required to start the design of an LPG system shall be available from the ExxonMobil marketing unit responsible for the proposed facility. This data shall include the following:

1. Products to be handled and peak volumes in bulk and in cylinders. 2. Total storage capacity required for each product.

3. Requirements of local government agencies with jurisdiction. 4. Allowances for future expansion.

5. Product sampling requirements. 6. Toxic materials in plant.

7. Site data including limitations or restrictions.

8. Possibility of storage and handling of other petroleum products within the facility.

9. Evaluation of any surrounding external hazards at the site.

10. Capacity and frequency of each type of LPG delivery to the site from tank trucks, railroad cars, marine vessels and pipelines.

11. Number of tank truck or railroad tank car unloading positions required. 12. Maximum and minimum flow rates for each type of equipment.

13. Method used to verify quantity of shipment: weight, volumetric measurement or meters.

14. Types of unloading pumps or compressors carried by transporting equipment. 15. Number, size and type of connections on transporting equipment.

16. For cylinder filling, the type, number and layout of scales, and the size, number and type of cylinders to be filled.

17. Cylinder painting, stenciling, washing and testing facility requirements. If possible, this task should be contracted to third party companies.

18. Method of receipt, storage and handling of cylinders: Manual handling or palletization, forklift, hand truck or other.

2.1.2 Topography and Prevailing Wind

Considering the basic characteristics of LPG vapor, it is desirable to locate a plant in an area which is free of depressions and contours radiating from the plant which might convey vapors to a point of exposure.

In the event of an accidental discharge of product within the plant, LPG tends to vaporize rapidly. Dissipation of vapors below the lower flammable limit develops more rapidly if the plant site is elevated slightly above the general terrain, or is slightly inclined. Dissipation of vapors in a flat location will mainly depend on wind or time. In low-lying areas vapors may stay trapped despite wind. This potential shall be considered in connection with gas leaks.

Any site considered for a marketing plant shall be analyzed with respect to the prevailing wind direction. Prevailing winds may have an influence on potential exposures. Based on prevailing wind, sites shall, whenever possible be located down wind (meteorological data) of population centers or known ignition sources. Tanks shall always be located downgrade and downwind from possible ignition sources.

2.1.3 Road Access and Traffic Situation

Any streets adjacent to the plant site shall be analyzed to determine that a safe traffic flow in and out of the plant is possible. The access road shall be of such width that vehicles could enter and leave the plant without creating a hazardous condition. Consideration shall be given to the traffic conditions on the access road during peak traffic flow in and out of the plant. Visibility, which is influenced by road curves etc., may play an important role in these considerations.

2.2 LPG Plant Layout

Following are some concepts that govern the layout/plot plan of the bulk LPG storage facilities.

Bulk LPG Tanks shall be located together to minimize piping and general site size.

Before the final location for bulk storage is selected, a site survey shall be conducted and if deemed necessary, soils investigation shall be done. It should be defined whether the storage is above or below ground and whether cylindrical or spherical tanks shall be used. These investigations shall provide sufficient data on the bearing capacity, drainage characteristics, estimates of settlement, and remedial measures, if necessary. Future expansion plans shall also be considered. Bulk transports that discharge or receive product within the plant shall be provided with a clear access through the plant, which can be negotiated without, at any time, reversing the unit. Sufficient space shall be provided at a loading or unloading location to allow for positioning the transport with minimal chance of collision with other vehicles or fixed objects. Loading or unloading

facilities shall be protected with guardrails or stanchions to prevent damage from vehicles. Vehicles shall be facing an exit while loading or unloading.

Pipeline or marine loading and discharge operations will utilize the least amount of

land since pipelines need only metering and control equipment and ships need only shore-based compressors for the unloading operation. However, a considerable amount of waterfront space shall be allocated for marine berth(s). With product delivered by

rail tank car, sufficient space shall be allotted to the rail line and the racks and

compressors for the unloading operation.

Pumps and compressors shall be grouped together and arranged such that the piping

is as simple and direct as possible. Electrical control panels and other support equipment shall be located in accordance with the electrical area classifications.

Figure 2.1 a: - Example for plant layout in sloped terrain

The Cylinder Filling Plant, with storage area, loading dock and access area, shall be laid out to ensure:

1. Optimum traffic pattern/parking for cylinder transport trucks. 2. Minimum interference between truck and fork lift traffic. 3. Clear separation of filled/empty cylinders.

4. A minimum of necessary cylinder handling. Cylinders should “flow” from the empty to filled area.

5. Optimize natural ventilation by positioning the cylinder filling plant such that natural air currents will be utilized in the most effective manner.

6. A separate area is designated for cylinders requiring repair or refurbishment.

2.2.1 Space Requirements

Space requirements will normally incorporate the following functions: 1. Gate house and security fence.

2. Administration and Control Building.

3. Bulk product receiving and dispatching areas, including weighbridge. 4. Tank truck loading and unloading area with access roadway.

5. Railroad siding, including loading and unloading area. 6. Tanker or barge loading or unloading facilities. 7. Stenching facilities for odorization of the LPG.

8. Bulk product storage.

9. Cylinder handling and storage (new, empty, filled, scrapped, truck parking). 10. Cylinder filling and inspection processes.

11. Other fuels storage or manufacturing facilities.

12. Pumps and compressors for loading and unloading trucks, rail cars, tankers and barges.

13. Pumps normally used for filling cylinders.

14. Cylinder repair and re-qualification processes (if located in filling plant). 15. Maintenance shop and warehouse.

16. Storage area for reserve supply of cylinders and customer containers. 17. Staff, customer and plant vehicle parking areas.

18. Fire water systems. 19. Firefighting access.

All of the above should be interrelated to the spacing requirements which are discussed below. A qualified company outside the filling plant may preferably carry out the cylinder repair and re-qualification process.

Figure 2.1-.b: Filling plant with unloading rack, tanks, pump/compressor house and filling area

2.2.2 Equipment Spacing to Maximize Separation

The most important objective of spacing is to separate risks by zoning. The higher a risk, the larger the spacing. Spacing requirements between tanks will help to limit the spread of fire, should it occur. In case of accidental leakage, spacing between equipment and the fence will help to disperse flammable mixtures below lower

flammability limits (LFL) such that ignition by uncontrollable external ignition sources

(e.g. passing cars) may be prevented. Another aspect that influences spacing is the requirement for safe access of the operator to perform an emergency

shutdown/activities but also for normal operations and maintenance. Also traffic

patterns for truck and rail loading shall be considered. The safe location of the control room and firefighting pumps may be of importance during an emergency.

The equipment spacing requirements detailed below are minimum figures, which in general will satisfy the above objectives. Whenever a special consideration or particular factors (e.g. plot space available) require deviation from the spacing rules a safety

specialist shall perform a risk assessment. Additional safety and firefighting

equipment requirements may compensate for a lack of spacing. So, if for instance, LPG is stored in vicinity to housing, passive fire protection may be the answer to reducing the risk. This may be achieved by mounded storage of the tanks.

Where sufficient space is available, the ground can be contoured and sloped such that the liquid from a potential leak will flow away from the storage tank to a remote

location. In case of a subsequent fire, this would be desirable since the liquid from the

leak would burn at a place away from the tank. Admittedly for Propane and hot climates this is not a major mitigation factor since the bulk of the leaking gas will flash right at the leak. But for Butane and colder climates it may mitigate the situation considerably.

2.2.2.1 Spacing at Refining and Upstream Gas Plants

Spacing of storage and loading and unloading facilities at Refining and Upstream Gas Plants shall be in line with spacing requirements documented in the Design Practices DP XV-G, “Equipment Spacing” and GP 9-1-1, “Spacing and Dikes for Storage Vessels and Tanks.”

2.2.2.2 Spacing Requirements for Marine Berths

Planning for Marine berths requires considering a number of issues affecting spacing. Generic marine issues such as berth layout, approaches to the berth, dredging etc. may affect the location of the berth and spacing requirements regarding other shore-based facilities. Information on such issues is available in the Marketing Engineering Standard EE.3M.86 “Marine Facilities, Design, Specification and Evaluation.” If multiple LPG berths are planned, additional spacing considerations between berths shall be taken into account. The minimum spacing criteria for fire and safety considerations is 30 m. However, in most cases, other plant design considerations shall require berth spacing greater than 30 m. More detailed descriptions of such considerations and additional commentary is provided in the ERE report EE.131E.79 “Suggested Design Considerations for Refrigerated Liquefied Gas Facilities.” Additional clarifications are provided in “Clarifications of Recommendations Arising from the ‘Betelgeuse’ Incident” (83 EEEL 514 or 83 CMS3 R9). EMRE's Marine Section should be consulted from the early stages of the project to ensure that the appropriate issues have been considered regarding berth layout and spacing.

2.2.2.3 Spacing at Marketing Plants

Spacing to the property line for Marketing Plants is consistent with API 2510, as indicated in the table below. Marketing plants may store considerably smaller volumes of LPG than Refineries or Upstream sites.

Individual Tank

Capacity, m3 8 - 110 < 260 < 340 < 450 < 760 < 3800 > 3800

Spacing to

Property Lines, m 15 20 30 40 60 90 120

Table 2.2.2.3-a: Spacing to property lines

At some locations, where risk exposure is considerably lower than usual the design engineer may deviate from the spacing requirements. A typical example would be a marketing plant on a riverbank surrounded by industrial plants (no housing). When additional storage is required at existing sites, and the spacing guidelines cannot be met, risk assessment techniques may be used to evaluate reduced spacing. As explained earlier, compensation for reduced spacing may be achieved by adding active/passive fire protection. The ExxonMobil LPG Technical Advisor or an EMRE Safety Engineer should be consulted when planning to deviate from spacing requirements. The rationale for deviating shall be documented in the design memorandum.

In addition to property line spacing, Marketing sites have other spacing guidelines not covered by DP XV-G. Additional guidelines, as well as spacing from DP XV-G commonly applied at Marketing plants, are covered by the following table.

Spacing Distances,

in Meters

Property

Lines

Office

Building

Cylinder

Filling

Loading,

Unloading

Sphere

Horizontal

Bullet

Mounded

Tank

Pump or

Compressor

Horizontal Bullet Note 1 30 15 15 Note 3 Note 4 Note 7 Note 10

Mounded Tank Valving 15 15 15 15 Note 3 Note 5 Note 8 5

Mounded Tk. Covered Part 3 3 3 3 Note 6 Note 7 Note 8 3

Truck Loading/Unloading 30 30 30 15 30 15 3 3

Rail Unloading/Loading 15 30 30 15 30 15 3 3

Cylinder Filling 30 30 Note 11 30 30 15 Note 12 5

Firewater Tank or Pump Note 11 Note 11 30 30 30 30 Note 12 30

Table 2.2.2.3-b: Spacing within Marketing LPG bulk storage plant

1. Note 1: Above ground tank spacing from property lines according to the above Table 2.2.2.3-a: Spacing to property lines.

2. Note 2: ¾ Diameter of larger sphere. 3. Note 3: ¾ Diameter of sphere.

4. Note 4: 1 Diameter of larger bullet (or 1.5 m min.). 5. Note 5: 1 Diameter of bullet.

6. Note 6: At sphere bund wall. 7. Note 7: Next to bullet toe wall.

8. Note 8: Spacing between mounded drums does normally not involve any fire hazard considerations, therefore, the following is recommended:

a. Tanks up to 135 m3 _{water capacity shall have a minimum}

spacing of 1.5 m between the tanks.

b. Tanks over 135 m3 _{water capacity: The site conditions and}

the needs for safe installation, testing, maintenance, and removal shall determine the spacing between adjacent tanks.

9. Note 9: Pumps, compressors, and other equipment (including piping not related to LPG tanks) shall be outside bund walls.

10. Note 10: Pump drawing from individual bullet may be outside toe wall and minimum 3 m from bullet. Other pumps or compressors 5 m.

11. Note 11: No minimum. Provide spacing appropriate for access. 12. Note 12: From drains, vents, and valving or flanges 15 m; from

covered part of mounded drum 3 m.

For spacing to atmospheric storage of other fuels or refrigerated storage see GP 9-1-1. Spacing of groups or “stacks” of cylinders to the property line is discussed in Chapter 7. Dikes spacing to spheres shall be according to GP 9-1-1 “Spacing and Dikes for Storage Vessels and Tanks.” Toe wall spacing to shell of bullet shall be 3 m. Also refer to section 3.2.6 “Spill Containment.”

Minimum Distances Flammable Liquid

Storage Tank

Bullet up to 135 m3 Bullet over 135 m3

Flash Point lower than 37 oC

6 m to bund wall 15 m to bund wall

Flash Point from 37 to 65 oC. Tank size up to 3,000 liters

Safety distances for LPG tank or 3 m to the tank / bund wall, whichever is the less

6 m to tank, bund wall or diversion wall

Tank size over 3,000 liters

3 m to bund wall or diversion wall and 6 m to tank

15 m to tank, bund wall or diversion wall

Table 2.2.2.3-c: Minimum separation distances for LPG horizontal tanks (bullets) from other flammable liquid storage

Non pressurized hazardous and Flammable Storage Tank Type and Product

Minimum separation distances

Refrigerated LPG Tank ¾ diameter of the larger

tank or sphere

Storage Tank with product flashpoint 37 oC

or less

1 diameter of the larger tank or sphere

Storage Tank with product flashpoint more than 37 oC

½ diameter of the larger tank or sphere

Table 2.2.2.3-d: Minimum separation distances for LPG sphere tanks from other flammable liquid storage.

LPG tanks shall not be installed within the bunded area for flammable or combustible liquid storage tanks. The minimum distances of separation between a LPG horizontal tank and a storage tank containing a flammable liquid shall be according to Table 2.2.2.3-c. For LPG spherical tank and a tank containing flammable liquid, Table 2.2.2.3-d shall be used. Open drains, gullies or ducts located within the tank safety distances in Tables 2.2.2.3-a and b, carrying water runoff from the ground underneath aboveground LPG tanks shall be provided with an LPG trap or be sealed to prevent LPG liquid and vapor from passing through.

No permanent source of heat shall be located within 1.5 m of a LPG tank. LPG tanks shall not be located directly beneath electrical power cables. LPG tanks shall be located such that a break in overhead electrical lines shall not cause exposed ends to fall onto any tank or equipment. No horizontal separation shall be required between an aboveground LPG tank and underground tanks containing flammable or combustible liquids installed in accordance with NFPA 30.

If, in industrial installations, LPG and oxidizing gases or hydrogen are stored on the same premises, the following minimum distances shall be observed:

Chlorine LPG 300 m

Oxygen* (> 0.75 t) LPG (> 1.9 m3) 15 m

Gaseous Hydrogen* (> 7 kg) LPG (> 1.9 m3) 15 m *see NFPA 58 for smaller capacities

RAILWAY GATE OFFICE BUILDING FIRE PUMPS FIRE W A T E R TANK Propane Loading SPHERE Dike RAIL CARS 15 m Butane Loading One Way EMPTY CYLINDERS FILLED CYLINDERS CYLINDER FILLING min. 3 m MOUNDED TANK Distance depends on drum size Earth Mound min. 15 m Depending on Tank Size 15 m 3/4 Sphere Diameter

one bullet diameter

BULLET

min. 15 m from LPG bulk storage min. 30 m from

Sphere or Bullet

min. 15 m from manhole of Mounded Drum

min. 30 m from Sphere/Bullet or Cylinder filling

30 m

30 m

30 m Pumps or compressors must be outside spill containment and may be 3 m away from tanks they take suction from, but 5 m from other tanks (like next bullet or next sphere dike)

min. 15 m

MOUNDED TANK

BULLET

Toe Wall

Depending on Tank Size Depending on Tank Size

Electrical Insulation

Remote Impoundment

Figure 2.2.2: Spacing in marketing LPG bulk plant with cylinder filling

2.2.2.4 Siting of Aboveground Tanks and Equipment

Pressurized LPG tanks shall not be located within buildings, within the spill containment area of flammable or combustible liquid storage tanks as defined in NFPA 30, or within the spill containment area for refrigerated LPG tanks.

Rotating equipment and pumps taking suction from the LPG tanks shall not be located within the spill containment area of any storage facility.

Horizontal tanks used to store LPG may be oriented so that their longitudinal axes do not point toward other tanks, process equipment, control rooms, loading or unloading facilities, or flammable or combustible liquid storage facilities located in the vicinity of the horizontal tank.

Horizontal LPG tanks shall not be stacked one above the other. Horizontal tanks used to store LPG shall be grouped with no more than six tanks in one group. Where

multiple groups of horizontal LPG tanks are to be provided, a minimum horizontal shell-to-shell distance of 15 m shall separate each group from adjacent groups.

2.3 Electrical Equipment Specifications

Electrical equipment and wiring shall comply with the specifications of, and be installed in accordance with the requirements of the local electrical codes. For reference on reliability in electrical design, see the related electrical GPs.

2.3.1 Electrical Area Classification

Normal electrical equipment can be considered an ignition source. Therefore, where flammable liquids, gases or vapors are handled, or stored, special electrical equipment shall be installed, which normally will not serve as an ignition source. The industry has produced standards to differentiate the ignition potential of electrical equipment. Following are the levels of protection:

1. Equipment that will never produce a spark, even if it fails.

2. Equipment that, when operating normally, will not produce a spark, but may do so if it fails.

3. Equipment that will produce a spark during normal operation.

The likelihood of encountering flammable vapors in plants governs the level of equipment needed. Plants shall be divided into separate areas according to the likelihood of flammable LPG vapors being present.

FILLING HOSE

FLAMMABLE VAPORS

FLAMMABLE

Figure 2.3.1-a: Example for Zone 1 area

Based on experience, minimum distance requirements between points of potential gas release and electrical installations have been developed. These minimum distance requirements are defined in both NFPA 497A and API 500. Classifications used in LPG and other Hydrocarbon service are called Zone 0, Zone 1 and Zone 2 distances. Zone 0 is an area where an explosive gas atmosphere is continuously present, or present for a long period. Definition of Zone 1 and 2 follow below. Different Zones require different quality electrical installation. Areas that require no special electrical equipment are called “Unclassified.” Following are definitions for the electrical classification areas.

Zone 1 areas are defined as locations where ignitable concentrations of flammable gases

pits and sumps are typical Zone 1 areas. This may be by frequent releases or by infrequent releases or small releases combined with inadequate ventilation. The Example in Figure 2.3.1-a shows a solvent drum filling area, for LPG it would be around the filling nozzles.

FLAMMABLE VAPORS

PUMP SEAL LEAK

VAPORIZING LIQUID

Figure 2.3.1-b: Example for Zone 2 area

Zone 2 areas are defined as locations where an ignitable concentration of flammable

gases or vapors is not likely to occur in normal operations. If it does occur it will be infrequent and will exist for a short period. Examples for Zone 2 are areas adjacent to Zone 1 (and not separated by a vapor barrier), areas normally prevented from explosive mixtures by positive ventilation, and areas where abnormal operation or equipment breakdown might create an explosive mixture.

Figure 2.3.1-c: Example for Unclassified area

Unclassified is defined as locations where there are little or no hazards from flammable

gases or vapors under normal or abnormal operating conditions. Plant roads, adequately ventilated LPG cylinder storage areas, and maintained, adequately ventilated piping systems, which may include valves, fittings, meters and flanged or threaded connections (per GP 16-1-1) are examples of unclassified areas.

Following selected example drawings from NPFA 497A showing how the electrical classifications apply. It is important to notice that they also include the space above the potential leak source. The hatched areas indicate that in these spaces only certified (Zone 1 or 2) electrical equipment can be installed.

7.5 m 15 m 30 m 0.6 m 7.5 m 7.5 m

BELOW GRADE LOCATION SUCH AS A SUMP OR TRENCH

SOURCE OF POTENTIAL LEAK UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED ADDITIONAL ZONE 2 AREA ZONE 1 ZONE 2

Figure 2.3.1-d: Electrical classification area around pump seal.

The contour of the envelope roughly approximates the flow that gases may follow in case of leak. It is important to notice that the complete area below a potential leak is considered classified. However, if a vent exits through a roof the hemisphere of a 7.5 m radius may be considered Zone 2 area. Pits and trenches, unless ventilated by force, shall be considered as Zone 1 areas. The outer 0.6 m Zone 2 region in the figure above is additional area to reflect crawling of heavier-than-air vapors along the ground. This area would normally be included for LPG applications, as explained in NFPA 497A.

7.5 m 15 m 30 m 0.6 m 7.5 m 7.5 m

BELOW GRADE LOCATION SUCH AS A SUMP OR TRENCH

SOURCE OF POTENTIAL LEAK UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED ADDITIONAL ZONE 2 AREA ZONE 1 ZONE 2

Figure 2.3.1-e: Electrical classification area around an elevated source of potential release

Notice that a sump on a pier is a Zone 1 area due to potential collection of vapors. At a Pier the Zone two area extends to the water level. Electrical installations are rarely found below the pier level but this may be important for small vessel traffic.

The area around the valves of rail cars and trucks is Zone 1 because of frequent making and breaking of loading and unloading connections. Depending on conditions, a 7.5 m diameter zone may be required around the pressure relief valve as indicated in the truck drawing. 7.5 m 15 m 7.5 m UNCLASSIFIED UNCLASSIFIED ZONE 1 ZONE 2 15 m 7.5 m 15 m SUMP 7.5 m 0.6 m PIER WATER LEVEL

Figure 2.3.1-f: Electrical classification area around marine unloading facility

2.3.1.1 Electrical Codes

The US National Fire Protection Association Codes #70 (National Electrical Code) and #58 (LP-Gas Code), or UK Institute of Petroleum “Model Code of Safe Practices in the Petroleum Industry,” Parts 1, (Electrical) and 9, (Liquefied Petroleum Gas), supplemented by Health and Safety Executive publications HSG 34, “The Storage of LPG at Fixed Installations” and HSG 22, and British Standard 5345 are commonly used as the design basis for electrical systems.

7.5 m 1.5 m

UNCLASSIFIED

ZONE 1 _{ZONE 2}

. Truck ESS EBV EBV Electrostatic Bonding Cable Truck ESS Truck PRV UNCLASSIFIED ZONE 1 ZONE 2 1.5 m 7.5 m 7.5 m

Figure 2.3.1-h: Electrical classification area around LPG truck

Standard Continuous_Hazard Intermittent_Hazard

Hazard under abnormal conditions IEC/CENELEC/

EUROPEAN Zone 0 Zone 1 Zone 2

NORTH

AMERICA Division 1 Division 2

Table 2.3.1.1-a: Comparison of Area Classification

GAS IEC / CENELEC / EUROPEAN NORTH AMERICA (CLASS 1) Acetylene II C A Hydrogen II C B Ethylene II B C Propane/Butane II A D

Table 2.3.1.1-b: Gas Grouping for Area Classification Protection Techniques

2.3.1.2 Electrical Installations

Both European and American practices are acceptable. The requirements for electrical installations shall be in accordance with NFPA 70 or equivalent. Current-carrying

conductors shall be made of copper. Electrical wiring shall be installed such that the system is free from short circuits and from grounds. All protection devices shall be properly sized, selected and installed. An overall electrical study for the entire electrical system shall be undertaken by qualified electrician or electrical engineer. Internal parts of electrical equipment shall not be damaged or contaminated by foreign materials. There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment. Conductors of dissimilar metals shall not be inter-mixed in a terminal or splicing connector where physical contact can occur between the dissimilar conductors.

Live parts of electric equipment shall be designed to guard against accidental contact using any of the following means:

1. Approved enclosures.

2. Locations in a room or similar enclosure accessible only to qualified persons. 3. Suitable partitions arranged so that only qualified persons will have access to

space within the reach of live parts.

4. Location on platform so elevated and arranged as to exclude unqualified persons.

5. Elevation of 2.5 m or more above the working surface.

Parts of electric equipment which in ordinary operation produces arcs or sparks shall be enclosed or separated and isolated from all combustible material. Circuit breakers for electrical equipment shall be legibly marked to indicate its purpose.

2.3.1.3 Emergency Shutdown Systems

The emergency shutdown system in a liquid transfer operation shall close all emergency shutoff valves and stop all pumps when activated. The location of Emergency Shutdown Pushbuttons is described below under “Emergency Shutdown Systems.” The shutdown buttons shall be RED in color of the Push-to-Activate, Pull-To-Reset type. They shall be clearly marked for the purpose for which it is intended and protected against accidental activation. All emergency shutoff valves shall be provided with both open and closed position indicators. All wiring and logic diagrams shall include a written description of the proposed operation. Each sequence trip and alarm shall be described in detail.

2.3.1.4 Instrumentation

Instrumentation shall meet the requirements of the applicable national codes. All instruments, pneumatic or electronic, shall fail to the safest position or lock in place upon air or power failure. Enclosures and cabling for all instrumentation shall conform to the requirements of the electrical area classification of the area of installation. Instrument installations shall meet all area classifications and code requirements. All electronic instrumentation shall be grounded at a single, common point separate from the plant ground grid.

Cable and conduit shall be routed in underground trenches where practical. Armored cable may be installed by direct burial methods. Where underground routing is not practicable, overhead cabling shall be routed in cable racks. All terminal strips used shall be of modular construction. Electric terminals shall be of the pressure-plate type, with all “live” parts recessed into the insulated block.

2.3.1.5 Lightning Protection

Aboveground LPG tanks do not require lightning protection for tank integrity. However, it is common practice in refineries and production plants to ground all towers and drums. This is done to protect electronic instrumentation and control systems. Therefore, grounding is recommended when electronic instruments are on the tank, but

is optional if the tank has no electrical instruments or control systems. Grounding rods shall be provided for tanks supported on non-conductive foundations.

2.3.1.6 Plant Lighting

Adequate lighting is needed for security as well as operations. It shall be provided to illuminate operating facilities such as walkways and essential control valves and devices. Any loading or unloading facility to be used after daylight hours shall be provided with adequate lighting, as well as gates within the plant fence area. The quality of the lighting installations as well as all other electrical installations shall comply with the Electrical Area Classifications.

Adequate lighting shall be provided for the following:

1. All storage and operating areas for normal operation.

2. To illuminate storage tanks, tanks being loaded, control valves and other equipment.

3. Facility gates.

In addition, sufficient emergency lighting shall be provided to allow safe operations during an emergency. Lighting shall be designed to provide the average maintained illumination in Table 2.3.1.6.

Location Lux Footcandles

Cylinder inspection and filling 540 50 Cylinder processing plant (general) 320 30 Tank car, tank truck, loading point 320 30

Piers, loading point 110 10

Entrance gate 55 5

Table 2.3.1.6: Average maintained illumination

2.4 Emergency Shutdown System

There shall be an Emergency Shutdown System (ESS) by which the facility can be shut down in case of emergency. At the following strategic locations throughout the plant, emergency push-buttons shall be installed which relay a signal to the central emergency shutdown system.

1. One in a central area which is at least 15 m from LPG tanks. 2. One at each loading or unloading position.

3. One, located 15 m from each loading or unloading position.

The actuating system shall be designed to close valves upon failure of any system component. More information on Electrical requirements are described under “Electrical Classification” above. When one of these push-buttons is activated the following shall happen:

1. Shutdown power to all product pumps, compressors, and cylinder filling. Rundown streams from processes are not included in this requirement. They shall be handled individually based on “fail safe” considerations.

2. Closing of all Emergency Block Valves (EBV) at unloading, loading, tankage and cylinder filling. EBV’s in rundown streams from refinery or gas plant process units are not included in this requirement. They shall be closed or kept open individually based on “fail safe” considerations.

3. An audible alarmshall be activated.

4. The power to the firewater system shall be maintained throughout the emergency/alarm.

5. Emergency push buttons at the pier may shut down the pier lines only or they may be tied into total plant shutdown. This may depend on distance to the pier and on other factors. The necessity shall be determined in a Hazard and Operability Analysis (HAZOP). In any case, the closure of the pier valves shall result in an alarm at the plant.

6. When the loading/unloading area is part of a refining or upstream site, activation of the ESS shall not necessarily require a shutdown in the process area. This shall be confirmed during the design.

E B V E M E R G E N C Y P U S H B U T T O N E M E R G E N C Y P U S H B U T T O N E M E R G E N C Y P U S H B U T T O N E M E R G E N C Y P U S H B U T T O N E M E R G E N C Y P U S H B U T T O N E B V E B V E B V

EBV EBV EBV

E B V ESS EQUIPMENT SHUT DOWN EMERGENCY SHUTDOWN SYSTEM POWER TO FIRE PUMP NOT INTERRUPTED FIRE WATER

MOUNDED DRUMS SPHERE

BULLETS RAIL CAR TRUCKS CYLINDER FILLING OFFICE ALARM

MARINE PIER EBV

EBV SHORE E M E R G E N C Y P U S H B U T T O N E M E R G E N C Y P U S H B U T T O N

3 BULK STORAGE

3.1 Storage in Plants and Industry

This chapter is intended to provide general technical guidance to engineers who are responsible for the design and installation of bulk tanks for Liquefied Petroleum

Gas (LPG). The guidelines are intended to assist engineers in the development of

technical specifications, which meet company and industry standards for design, fabrication, installation, and testing of such facilities. These specifications aim to maximize the integrity and safety of these facilities. Achieving this objective is dependent upon using design concepts, which are proven to be safe and conform to good operating and maintenance practices throughout the operating life of such facilities. In developing these specifications, designers shall also follow Global Practices (GP's), Design Practices (DP's) specified in this section, and local regulations.

This guide tries to use consistent wording for LPG storage. “Tanks,” “mounded drums,” “spheres” and “bullets,” are used for bulk storage at company plants or industry. “Vessels” means ships and barges only. Note that the GP's, DP's and other codes do use “vessel” for refining drums and towers. “Containers” are used in small bulk and domestic use. “Cylinders” (also often called “bottles”) are used for small portable LPG containment.

If LPG tanks for commercial, utility, or industrial customers are as large as plant bulk LPG tanks they shall be designed to the same principles. Typically commercial consumers or domestic users require containers. Such containers may be designed according to requirements in the chapter “Customer Storage” of this Guide.

For all new designs or design modifications in LPG storage service, a review of all applicable local regulations, codes, standards, practices and operating permits is needed. Major pressure tank manufacturers have developed standard designs for different tank capacities, permitting the purchaser to specify only the code required at the proposed plant site, and the tank openings and fittings required. Standardization can provide substantial savings over development of an individual design. However, the standard shall meet all the requirements of the GPs specified in this section.

For new designs the use of “mounded drums” for pressure storage is required for some countries (Europe). These are horizontal tanks placed on above ground foundations or on sand beds but thereafter completely covered by an earth mound. This type of storage is inherently safer since its passive fire protection makes it not vulnerable to external fires.

The most frequent tank types used in the past and still in use in many countries today are the horizontal cylindrical (“bullet”) tank and the sphere. These are above ground tanks on concrete foundations. The horizontal “bullet” tank was the most common design in the past for tanks sized between 28 and 282 m3_{. For larger capacities, often}

the most economic solution was the spherical tank. Depending on location and exposure in some cases it may still be appropriate to use this approach for new designs, however, more and more regulations ask now for retroactive passive fire protection by fireproofing.

Vertical “bullet” type tanks have also been installed by industry. They may have their merits when spacing is tight, however, from a safety and firefighting standpoint this is an undesirable configuration and shall be avoided.

The following International Codes may be applicable to the design of pressurized LPG tanks:

1. The United States American Society of Mechanical Engineers, “ASME Boiler and Pressure Vessel Code, Section VIII” Section VIII is subdivided into Division 1 “Unfired Pressure Vessels” and Division 2 “Rules for Construction of Pressure Vessels.” To be more economical, LPG horizontal tanks shall be designed and fabricated according to ASME VIII Division 1 while LPG sphere tanks shall be designed and fabricated according to ASME VIII Division 2.

2. API STD 2510 and NFPA 58.

3. BS 5500 Specification for Unfired Vessels.

4. BS 1501 Steels for Fired and Unfired Pressure vessels - Plates, or Equivalent. 5. BS 1502 Specifications for Steels for Fired and Unfired Pressure vessels

-Sections and Bars.

6. BS 1503 Specifications for Steel Forgings (including semi-finished forged products) for Pressure Purposes.

7. Finnish Standards (SFS) 3205, 3339, 3340, 3341, and 3342. Finnish Government Statues 98/73, 636/77, 257/84, 258/84, 312/79, and 1106/81. 8. Japan High Pressure Gas Law (HPGL). Japan Industrial Standards (JIS). 9. Australian Pressure Vessel Code AS 1210.

3.2 Mounded and Above Ground Storage

The guidelines and technical considerations discussed below refer to facilities, which utilize large horizontal mounded drums for storing LPG. Storage in aboveground tanks presents the risk of a BLEVE. Storage of LPG in mounded drums avoids the risk of external fire exposure. Mounded drums are long horizontal cylindrical tanks, with dished heads, which are installed above grade level and covered completely with sand bed fill and general fill material. The mounding of drums permits reduced spacing when compared to the space needed for spheres/bullets, which is mandated by regulatory requirements.

As of 1993 there are several mounded drum installations in company Refining and Marketing facilities in Europe and the Asia Pacific region. These tanks have been used to store LPG since 1982-83. Operating experience with the installations during the years has been good.

3.2.1 Dimensional Sizing of Drums

The specific dimensions for the drums are based on LPG storage requirements, available space on site, safety considerations, spacing from buildings, facilities, and other equipment, orientation, and the costs associated with fabrication, transport and installation. The capacities of the drums should be based on planned sales. However, shipment parcel size, transport delays, seasonal effects, future business outlook or other factors may have an influence on the capacity.

Mounded drum sizes vary substantially in diameter and tangent length. The drum sizes that are currently in use have diameters in the 4 to 6.5 meter range and tangent lengths of 34 to 88 meters. The diameter and length chosen are dependent upon transportation and site spacing. In addition, considerations such as field assembly and fabrication of drum sections should be used to optimize LPG storage and inventory needs at specific installations.

LHHA(CO) if filled by Pipeline or by Ship EBV Tank Slope 1:100 min. 0.9 m LPG LPG Filling PRV LHHA LI LHA

Water Draw-off to Location min. 15 m from Fence

LPG Vapor Return

Removable Fill Distance PRV to Fence15 m

Removable Part with Sleeve to ESS

TI PI

Concrete Wall

Figure 3.2.1-a: Typical LPG mounded drum

Tank Slope 1:100 PI TI min. 0.9 m PRV LHHA LI LHA Water Draw-off to Location

min. 15 m from Fence Distance PRV to Fence 15 m to ESS Submerged Pump Distance to Fence 3 m LHHA(CO) if filled by Pipeline or by Ship

Figure 3.2.1-b: Mounded drum, spacing alternative with submerged pump

In general, it is preferable to have the drums fabricated in the manufacturer shop and transported to site. However, due to the large sizes involved, transportation, site access and off-loading at the plant usually dictate the feasibility of shop manufacture or the need for site assembly of major drum sections. Recent LPG mounded drum installations have used both shop fabrication and field construction practices.

3.2.2 Materials Selection for Tanks

All materials of construction shall meet the requirements of Section II of ASME “Boiler and Pressure Vessel Code”, or equivalent national code. Low melting point materials of construction such as aluminum and brass shall not be used for LPG storage drums. It is recommended that the drum materials consist of fully killed, grain refined and

normalized carbon steel plates and forgings, with adequate mechanical strength and

toughness properties for the storage of LPG. The presence of H2S in has led to wet H2S

cracking problems associated with hard welds (> 225 Brinell Hardness). The tendency for in service cracking increases as the H2S concentration and strength of the material

contents by specification is in the order of magnitude of 1 ppm. Minimum specified tensile strength of the tank steel historically has been below 483 MPa. However, with more recent technology development higher strength steel is used to keep the thickness of spheres below 38 mm, so PWHT can be waived per ASME Code. Experience shows that if a proper procedure is taken (e.g. pre-heating 90-150 ºC), high strength steel can provide satisfactory service. The amount of H2S in the product to be stored is a very

important factor to determine metallurgic characteristics of the material of construction. Steel specifications shall include chemistry control per GP 9-2-1, and requirements for impact properties at the Critical Exposure Temperature (CET), and heat treatment per GP 5-1-1. Impact Requirement for Materials shall follow GP 18-10-1 "Additional Requirements for Materials." Additional information which may be useful to the designer is available from GP 18-7-1 “Welding Procedures,” GP 5-3-1 “Hydrostatic Testing of Vessel,” and GP 5-2-1 “Internals for Towers & Drums.”

Material of construction for the pressure parts shall comply with ASME Sec II D Appendix 5. Alternative materials equivalent to the ASME Code material specification may be used. However, alternative materials shall be provided with the following to EMRE for approval:

1. Nomenclature and complete chemical and physical properties of the proposed material stated along with ASME equivalent. Any additional requirement necessary for equivalence shall be stated.

2. Where necessary to demonstrate the equivalence of alternative material, test specimens shall be provided for Charpy V-Notch testing according to applicable ASME material specification.

3. Quenched and tempered steel is limited to a maximum tensile strength of 690 Mpa and an actual yield-to-tensile ratio of < 0.85.

The following shall NOT be used as material of construction for pressure parts: 1. SA36, SA283 and other structural grade steel.

2. Steel casting.

3. Low melting point materials such as aluminum and brass.

3.2.2.1 Minimum and Maximum Design Temperature

The principal purpose for specifying impact requirements is to ensure that a catastrophic brittle fracture of the drum will not occur during hydrotesting, start-up, shutdown, and normal operations throughout its service life. Impact requirements are based on the

Critical Exposure Temperature (CET, also “Minimum Design Temperature”),

metal thickness of the drum component, and the material specification selected.

The CET for a LPG pressurized storage drum or sphere shall be based on the lower of the following:

1. Lowest one-day mean temperature. This would account for filling the drum or sphere up to the safety valve pressure limit on the coldest day.

2. The temperature equivalent to 25% of the design pressure on the vapor pressure curve for the material to be stored.

The minimum design temperature shall be the minimum metal temperature expected in service, taking into consideration ambient temperature and auto-refrigeration of the stored product when it flashes to atmospheric pressure. For storing Propane, this temperature will be –42 °C. In no case shall the minimum design temperature be higher than –18 oC. In many situations, the owner prefers to set the minimum design temperature at the lowest possible temperature due to depressurizing the LPG to atmospheric pressure (–42 °C). This is almost always more conservative than the criteria provided above. It adds an extra safety margin for protection against brittle fracture and is recommended. Using modern carbon steels, this should not significantly add to the cost for the drum, bullet or sphere.

3.2.2.2 Post-Weld Heat Treatment

For aboveground bullets with a plate thickness below 38 mm Post Weld Heat Treatment (PWHT) is not required. However, Post-Weld Heat Treatment is recommended for mounded drums due to service considerations. These requirements are independent of PWHT that may be required from Code considerations of plate thickness, and material specification. The preferred method of PWHT for shop fabricated drums is to heat treat the entire drum or major sections of the drum in a heat treating furnace. This minimizes the thermal stresses, which can be introduced by local PWHT, which typically involves banding the weld seams with electric resistance heating jackets. If this capability is not available in the shop or if PWHT in the field becomes necessary, then local Post-Weld Heat Treatment of the individual seams may be done, subject to careful control of temperature and temperature gradients.

3.2.2.3 Materials Specifications

The recommended materials specifications for bullets and mounded drums are identical to ASTM Specifications as follows:

SA 516 Grade 70 normalized for the shell and heads SA 333 Grade 1 or 6 for nozzles

SA 350 Grade LF2 for flanges & fittings SA 352 Grade LCB for fittings

SA 334 Grade 1 or 6 for tubing

Substitute Materials specifications may be made provided they meet with the requirements in GP 18-1-1. Materials not covered in GP 18-1-1 should be evaluated on a case by case basis.

3.2.2.4 External Corrosion Protection

The earth mounds used on mounded LPG Drums increase the potential for soils induced corrosion and holing through. In addition, the design does not permit on stream thickness measurements and/or visual inspection of the drum surface. Shop fabrication is preferred when drum size permits. Any damage during transport to the coatings on shop fabricated drum shall be repaired. It is extremely important, therefore, to consider the following:

1. Develop an earthwork specification for the mound. Specify sand bed fills, general fills, and acceptance tests, in accordance with ASTM Standards and Global Practice GP 4-9-1.

2. Provide an adequate corrosion resistant coating on the external surface of the drum per GP 19-1-1. Shop-applied coatings are preferred, but field applications are also acceptable. Irrespective of type and application method of coatings, a holiday test on the coating shall be carried out immediately prior to back-filling on site. The following specification is the normal requirement:

Surface Preparation: Abrasive Blast Clean to SSPC SP-10 Near White

1st Field Coat: Coal Tar Epoxy @ 6-8 mils DFT 2nd Field Coat: Coal Tar Epoxy @ 6-8 mils DFT 3. Install a cathodic protection system utilizing sacrificial anodes. Permanent

reference electrodes shall be buried along with the drum at each end of the drum and above and beneath the drum at its midpoint.

4. Requirements for a cathodic protection system are a twenty-year life and a maximum exposed steel surface of 10%. Insulating flanges shall separate permanent lines connected to plant piping from this cathodic protection

system. The cathodic system may be used to protect short runs of buried pipe provided the pipe coating is equal or better than the tank coating.

5. Any special plant refinery/production applications where the LPG is expected to contain wet H2S, shall have the drums lined internally.

The exterior surface of aboveground tanks, including the steel supports, shall be grit blasted to SSPC SP-10 standard or chemically treated and adequately painted.

After grit blasting horizontal LPG storage bullets and LPG sphere tanks, shall be painted with a primer coat of alkyd zinc phosphate (75 microns dry film thickness), build-coat of alkyd micaceous iron oxide (50 microns dry film thickness) and topcoat of

white alkyd enamel (30 microns dry film thickness).

1. Sphere legs shall be fireproofed and left unpainted

2. Bases and saddles of bullets that are concreted shall not be painted.

3. If bases and saddles on bullets have exposed metal, they shall be painted with same primer coat, build-coat and finished with topcoat.

The exterior of aboveground LPG tanks shall be inspected every 2 years. Repainting shall be carried where necessary.

3.2.3 Design Basis for Mounded Drums

The mechanical design of large mounded drums is complex, due to its mounded configuration, internal pressure, nozzle geometry and piping loads, type of support, foundation pad design and soils settlement characteristics. In addition, if these facilities are located in earthquake zones, the seismic loads substantially increase the complexity of mechanical design considerations.

Most national codes entrust the responsibility to users for defining and specifying the loading mentioned above. Therefore, it is recommended that users develop Mechanical

Specifications (MSpec) for these drums and ensure that all pertinent design criteria and

loads are specified.

The following guidelines are intended to assist users when developing MSpecs for mounded drums.

3.2.3.1 Design Conditions for LPG Drums

Design conditions for LPG drums should preferably be based on Propane storage. This will allow the flexibility to switch to Propane and will provide protection against inadvertent loading of Propane to a lower design pressure drum. Based on local regulations in several countries, the minimum design pressure is specified as 17.2 bar gauge with a corresponding design temperature of 55 °C. Under design conditions, 1.6 mm corrosion allowance shall be added to the design thickness of a drum. In addition, external pressure of 1 bar gauge is used to allow for the soil pressure from the earth mound. In the absence of local regulations, the maximum design temperature shall be taken as the highest ambient temperature that has been recorded over the last 10 years at the nearest meteorological station. In no case shall this temperature be lower than 38 °C.

3.2.3.2 Design Codes Applied

Most nationally recognized Codes can be used for the design of mounded drums. However, design, fabrication, inspection, and testing requirements shall be based, as a minimum, on the requirements of Global Practice 5-1-1. Design and fabrication inspection of LPG tanks shall be carried out by an internationally recognized and EMRE Engineering approved third party inspection agency.

3.2.3.3 Permanent Identification is Needed

For continuous reference, a non corrosive identification plate shall be fixed to the drum in a suitable and clearly visible location. It shall be stamped with the following information as a minimum:

Drum Serial Number: Owner’s Name: Designer’s Name: Design Code:

Manufacturer’s Name:

Design Pressure, min./max.: Design Temperature, min/max: Product Stored:

Water Capacity in volume units: Date of test and test pressure:

3.2.3.4 Earth Mound Design

The following supplementary requirements shall apply to mounded drums:

1. Partial mounding is not recommended. Partial mounding continues to have the design considerations of storage in aboveground bullets so that little or nothing is gained.

2. The depth of the mound over all surfaces of the drum shell shall be a minimum of 0.9 m. The mound cover shall include the heads of the drums, which shall not be exposed.

3. The backfill used for mounding shall consist of washed sand totally free of rocks or abrasive materials likely to damage the drum coating. The mounds shall have good stabilization to prevent erosion by firewater or heavy rain. Furthermore, it shall be capable of withstanding prolonged heat radiation or jet flame impingement. This is important since the pressure relief valves on such drums are not designed to provide protection against heat input by external fire. Therefore, if the drum is being uncovered later, e.g. for external inspection, LPG shall be taken out of the drum before it is uncovered. If a drum has to be removed and the adjacent drum is still filled with LPG the side of the filled drum shall still be covered by a mound of 0.9 m thickness.

3.2.3.5 Nozzles on LPG Drums

As a matter of principle the number of nozzles on mounded drums shall be kept to the necessary minimum. This pertains in particular to the lower part of the drum. Following nozzles are considered necessary:

1. Pressure relief valve (PRV) connection to the vapor space.

2. Water draw-off connection via the top (similar to GP 9-2-1, para. 9.5). 3. Connection for the level indicator with high level alarm.

4. Connection for the independent high level alarm. 5. Connection for the fixed level gauge.

6. Filling connection at the top of the drum.

7. Withdrawal connection at the top or bottom of the drum. 8. Vapor return connection at the top of the drum.

9. Vent connection to atmosphere.

10. Connection for the temperature indicator.

11. Pressure indicator connection to the vapor space.

Careful engineering may permit the combination of some of the above fittings to

reduce the number of nozzles on the drum. The preferred location for nozzles is at the

manhole (see below). All nozzles on new drums are preferred to be flanged and not