RERATING.pdf

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4.1 Rerating Piping and Pressure

Vessels

• Overview

• Guidelines

• Minimum Required Thickness Determination

• Regulatory Requirements

Major Piping Inspection Codes

API 570 Piping Inspection Code

Underlying Corrosion Underlying Design Standards New Construction Corrosion Mitigation

Standards Quality Safety

Other Inspection Codes / Documents ASMEB16.34 Valves - Flanged Threaded and Welding ends API 651 Cathodic Protection of Aboveground Storage Tanks NACE RP0169 Control of External Corrosion on Underground or Submerged Metallic Piping Systems

ASME BPVC Sec IX, "Welding and Brazing Qualifications" API RP 750 Management of Process Hazards Of Materials API 510 Pressure Vessel Inspection Code

ASME BPVC Sec VIII, Division 1 & 2 Pressure Vessels

R:0170 Protection of Austenitic Stainless Steels from Polythionic

Acid Stress Corrosion Cracking During Sh d f NACE RP0274 High-Voltage Electrical Inspection of Pipeline Coatings Prior to CP-189 Standard for Qualification

and Certification of Nondestructive Testing

Personnel

NFPA 704 Identification of the Fire Hazards of Materials API RP 574 Inspection of Piping System Components Shutdown of Refinery Equipment Coatings Prior to Installation ASME B31.3 Process Piping Application of Organic Coatings to the External Surface of SNT-TC-1A API 598 Valve Inspection and Testing

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Piping System Management Cycle

Prioritize Pipes For Analysis Monitoring Techniques Inspection Techniques Repair Rehabilitate Replace Inspection And data Gathering C t f Data Gathering Methods Probability Of Failure Decision Making Condition Assessment Consequences Of Failure Available Funds Cost of Renewal Deterioration Rates Failure Mechanisms

Rerating

• Rerate. A change in either or both the

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design temperature or the maximum

allowable working pressure.

• Existing piping systems or pressure

equipment might require rerating to

accommodate new operational needs (or to

accommodate deterioration that cannot or

will not be repaired).

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Rerating - 2

• Frequently when debottlenecking process plant

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th

equipment, the possibility of increasing the

equipment's design temperature, design

pressure, or both comes up. This process of

re-evaluating the equipment for more severe

design conditions is usually referred to as

uprating.

Rerating - 3

• In other cases, after a piece of equipment or

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piping system has been in-service for a number

of years and corrosion has taken its toll, it may

be necessary to re-evaluate whether the

equipment has sufficient corrosion allowance

until the next inspection or whether the

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Rerating - 4

• Rather than assuming that the piece of equipment must be replaced when its corrosion allowance is must be replaced when its corrosion allowance is used up, it may be worthwhile to investigate derating the equipment to allow its continued use although at somewhat less severe design conditions.

• In some cases the term rerating of the equipment may also be used to cover changing the throughput or also be used to cover changing the throughput or service of the equipment.

Rerating of Piping Systems

• API 570 Piping inspection code: Inspection, repair,

alteration and rerating of in-service piping systems alteration, and rerating of in service piping systems covers the inspection, repair, alteration and re-rating procedures for in-service metallic piping systems. • The code establishes the requirements and guidelines

that allow the owners and users of piping systems to maintain the safety and mechanical integrity of systems after they have been placed into service systems after they have been placed into service

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Rerating Definition

• Section 3 of API 570 - “Definitions” states the definitions that apply to this code They include the definitions that apply to this code. They include the following definitions that pertain to rerating:

“Rerating [3.39]: A change in either or both the design temperature or the maximum allowable working pressure of a piping system.

A rerating may consist of an increase a decrease A rerating may consist of an increase, a decrease, or a combination of both. Derating below original design conditions is a means to provide increased corrosion allowance”.

MAWP Determination - 1

• Maximum Allowable Working Pressure: (MAWP) [3 21]: The maximum internal pressure permitted in [3.21]: The maximum internal pressure permitted in the piping system for continued operation at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service.

• It is the same as the design pressure, as defined in ASME B31 3 and other code sections and is subject ASME B31.3 and other code sections, and is subject to the same rules relating to allowances for variations of pressure or temperature or both

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MAWP Determination - 2

• MAWP for the continued use of piping systems shall

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be established using the applicable code.

• Computations may be made for known materials if all the following essential details are known to comply with the principles of the applicable code:

a. Upper and/or lower temperature limits for specific materials. b. Quality of materials and workmanship.Q y p

c. Inspection requirements. d. Reinforcement of openings. e. Any cyclical service requirements.

MAWP Determination - 3

• For unknown materials, computations may be made assuming the lowest grade material and joint

assuming the lowest grade material and joint efficiency in the applicable code.

– When the MAWP is recalculated, the wall thickness used in these computations shall be the actual thickness as determined by inspection (see 5.6 for definition) minus twice the estimated corrosion loss before the date of the next inspection (see 6.3).

• Allowance shall be made for the other loadings in accordance with the applicable code.

– The applicable code allowances for pressure and temperature variations from the MAWP are permitted provided all of the associated code criteria are satisfied.

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Retirement Thickness

Determination - 1

• The minimum required pipe wall retirement

q

p p

thickness shall be equal to or greater than the

minimum required thickness, or retirement

thickness, and shall be based on pressure,

mechanical, and structural considerations

using the appropriate design formulae and

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code allowable stress.

• Consideration of both general and localized

corrosion shall be included

Retirement Thickness

Determination - 2

• For services with high potential consequencesif failure were to occur, the piping engineer should consider increasing the required minimum thickness

above the calculated minimum thickness to provide for unanticipated or unknown loadings, undiscovered metal loss, or resistance to normal abuse.

• In this case, the retirement thickness shall be used in , lieu of the minimum required thickness in 7.1.1 for remaining life calculations

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Rerating Requirements

API 570 - Sub-Section 8.3

• Rerating piping systems by changing the temperature rating or the MAWP may be done temperature rating or the MAWP may be done

only after all of the following requirements have been met:

a. Calculations are performed by the piping engineer or the inspector.

b. All reratings shall be established in accordance with the requirements of the code to which the piping system q p p g y was built or by computation using the appropriate methods in the latest edition of the applicable code. c. Current inspection records verify that the piping system

is satisfactory for the proposed service conditions and that the appropriate corrosion allowance is provided.

Rerating Requirements

API 570 - Sub-Section 8.3

d. Rerated piping systems shall be leak tested in d i h h d hi h h i i

accordance with the code to which the piping system was built or the latest edition of the applicable code for the new service conditions, unless documented records indicate a previous leak test was performed at greater than or equal to the test pressure for the new condition. An increase in the rating temperature that does not affect allowable tensile stress does not require a leak test allowable tensile stress does not require a leak test. e. The piping system is checked to affirm that the required

pressure relieving devices are present, are set at the appropriate pressure, and have the appropriate capacity at set pressure.

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Rerating Requirements

API 570 - Sub-Section 8.3

f. The piping system rerating is acceptable to the inspector or piping engineer.p p g g

g. All piping components in the system (such as valves, flanges, bolts, gaskets, packing, and expansion joints) are adequate for the new combination of pressure and temperature.

h. Piping flexibility is adequate for design temperature changes.

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i. Appropriate engineering records are updated. j. A decrease in minimum operating temperature is

justified by impact test results, if required by the applicable code.

Use of API 579 Procedure For

Rerating

• For rerating pressure vessels and piping, the following expressions apply:

following expressions apply:

MAWPr = MAWP (RSF/RSFa) for RSF < RSFa MAWPr = MAWP for RSF ≥ RSFa

• RSF is the remaining strength factor , which is defined as:

RSF = LDC/LUC

• LDC is the limit or plastic collapse load of the damaged p p g component, and

• LUC is the limit or plastic collapse load of the undamaged component.

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Use of API 579 Procedure For

Rerating

• MAWPr is the reduced maximum allowable working pressure,

• MAWP the original maximum allowable

working pressure, and

• RSFa is the allowable remaining strength

factor (typically 0 9)

factor (typically 0.9).

Evaluation of Inspection Data

MAWP Calculations Using Corrosion Half-life Concept

Example 1:

Design Pressure: 500 psigg p g Design Temperature: 400°F Pipe Material A 106 Gr. B Pipe Size: NPS 16

Allowable Stress: 20,000 psi (from B31.3)

Longitudinal Weld Efficiency: 1.0 (A 106 Gr. B is seamless pipe)

Thickness Measured During Inspection: 0.32 in. Observed Corrosion Rate: 0.01 in./year

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Evaluation of Inspection Data

Estimated thinning until next inspection = 5 x 0.01 = 0.05in. (5 x 0.254 = 1.27mm)

MAWP = 2SEt/D (From ASME B31.3)

= 2 x 20,000 x 1 x (0.32 – 2 x 0.05) /16 = 550 psig (3747 kPa )

Since the MAWP > 500 (system design pressure), the system may remain in service at the design pressure without repairs, replacements, or rerating.

= 550 psig (3747 kPa )

Evaluation of Inspection Data

Example 2:

Next planned inspection 7 yrs. Ne t p a ed spect o 7 y s. Estimated corrosion loss by date

of next inspection = 7 X 0.01 = 0.07 in. (7 x 0.254 = 1.78mm) MAWP = 2SEt/D

= (2 x 20,000 x 1 x (0.32 – 2 x 0.07) /16) MAWP 450 i (3104 kP )

MAWP = 450 psig (3104 kPa)

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Rerating a Piping System

• Operators may reduce the maximum allowable operating pressure of defective pipe to a safe level instead of permanently repairing the pipe This is instead of permanently repairing the pipe. This is conditional on demonstrating that a safe operating pressure can be calculated under accepted

engineering guidelines based on the remaining strength of the corroded pipe (e.g., ASME B31.G) • Rerating can be used both to increase design

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pressure and temperature, and also to decrease design pressure and temperature to increase the available wall thickness for corrosion/erosion allowance.

Rerating a Piping System - 2

• Inspection, repair, alteration, and rerating of in-service piping systems are normal activities that p p g y must be dealt with in process plants.

• Requirements and procedures are necessary in carrying out these activities to ensure that piping system integrity is maintained.

• API 570 is the industry standard that is used to 7 s e dus y s d d s used o form the basis for more detailed procedures that must be developed by process plant owners.

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Rerating a Piping System

• Rerating an existing piping system is

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essentially redesigning the system for new

design/service conditions.

• The new design and service conditions must be

specified.

• The anticipated new corrosion rate must be

determined.

Fluid Properties and Characteristics

The following information must be specified: • Chemical composition, material safety data sheet

(MSDS) chemical formula (MSDS), chemical formula.

• Chemical reaction. If the fluid involves a reaction, note whether the reaction is exothermic or endothermic.

• Moisture content in the fluid. Design value and normal range.g

• Characteristics of the feed. Viscosity, cohesion,

flowability, reactivity, change in composition, toxicity, flammability.

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Service and Design Conditions

Design pressure - As defined in ASME 31.3 para. 301 2: The design pressure of each component in a 301.2: The design pressure of each component in a piping system shall be not less than the pressure at the most severe condition of coincident internal or

external pressure and temperature (minimum or maximum) expected during service, except as provided in ASME B31.3 para. 302.2.4. See also

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ASME B31.3 para. 301.2.1 and para. 301.2.2.

Service and Design Conditions - 2

• Design temperature - As defined in ASME B31.3 para. 301.3: The design temperature of each component in a piping system is the temperature at which, under the

p p g y p ,

coincident pressure, the greatest thickness or highest component rating is required in accordance with para. 301.2. (To satisfy the requirements of para. 301.2 different components in the same piping system may have different design temperatures.).

• In establishing design temperatures, consider at least the fluid temperatures ambient temperatures heating or fluid temperatures, ambient temperatures, heating or cooling medium temperatures, and the applicable provisions of ASME B31.3 paras. 301.3.2, 301.3.3 and 301.3.4. See also ASME B31.3 para. 301.3.1.

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Use of API 579 Procedure For

Rerating

• For rerating pressure vessels and piping, the following expressions apply:

following expressions apply:

MAWPr = MAWP (RSF/RSFa) for RSF < RSFa MAWPr = MAWP for RSF ≥ RSFa

• RSF is the remaining strength factor , which is defined as:

RSF = LDC/LUC

• LDC is the limit or plastic collapse load of the damaged p p g component, and

• LUC is the limit or plastic collapse load of the undamaged component.

Use of API 579 Procedure For

Rerating

• MAWPr is the reduced maximum allowable working pressure,

• MAWP the original maximum allowable

working pressure, and

• RSFa is the allowable remaining strength

factor (typically 0 9)

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Piping Stress Analysis

• Performing a piping stress analysis is not normally a part of inspection and maintenance. However,

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stress analysis considerations must still be kept in mind.

– The pipe must be adequately supported to carry its weight. Locations where supports have become damaged or are otherwise ineffective should be identified for further evaluation or repair.

– Adequate flexibility to accommodate thermal displacements must be provided. Identify situations where thermal expansion might be restricted (e.g., due to interference by adjacent items).

Piping Stress Analysis - 2

– The pipe must not vibrate excessively, since this could cause leakage at flanged joints and threaded could cause leakage at flanged joints and threaded connections, or cause a fatigue failure.

– A new stress analysis may be required if the design conditions are changed (e.g., due to equipment rerate) or if the system is modified (e.g., adding a new equipment item with associated piping to the new equipment item with associated piping to the system).

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Pressure Testing

• Except where local jurisdictions require it, pressure tests are not normally done as part of a routine inspection. When pressure tests are done (e.g., after alterations) they should be based on the following:

– Must meet (e.g. ASME B31.3) requirements.

– Test fluid must be water unless this would have adverse consequences (e g freezing process contamination consequences (e.g., freezing, process contamination, water disposal problem).

– Stainless steel piping requires special attention (e.g., potable water and blown dry).

Requirements for Rerating

• The following requirements must be met to

permit rerating a piping system to a new

design temperature or MAWP:

– Design evaluations must be done by the piping engineer or inspector to verify the system for the new conditions.

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– The rerating must meet the requirements of either the original construction code or the latest edition of that code.

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Requirements for Rerating - 2

– Current inspection data must verify that the system is adequate for the proposed conditions and has is adequate for the proposed conditions and has sufficient remaining corrosion allowance.

– The system must be pressure tested for the new conditions, unless records indicate that a previous test was done at a pressure that was greater than or equal to that required for the new conditions

equal to that required for the new conditions.

Requirements for Rerating - 3

– The safety valves must be reset for the new design pressure and confirmed to have adequate relieving pressure and confirmed to have adequate relieving capacity.

– The rerating must be acceptable to the inspector or piping engineer.

– All components in the system (e.g., valves, flanges bolts gaskets etc ) must be checked and flanges, bolts, gaskets, etc.) must be checked and found to be acceptable for the new design

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Requirements for Rerating - 4

– Piping flexibility is adequate for the new design temperature New calculations may be required to temperature. New calculations may be required to confirm this.

– The engineering records for the system must be updated.

– A decrease in the minimum operating temperature is justified by impact test results (or exemptions) if is justified by impact test results (or exemptions) if required by the code.

Temperature Uprating

Considerations

• The flange pressure-ratings may decrease too • The flange pressure-ratings may decrease too

much as the temperature increases.

• The higher temperature may cause problems with:

– thermal expansion of the piping and related stresses. – Corrosion rates may also go up as the temperature is

increased.

– In some cases temperature limits on various types of construction should also be considered, such as

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Rerating Documentation

• The old and new design conditions

• The Code used for the rerate

• The allowable stresses and joint efficiencies

• The minimum required thicknesses vs. the

existing thicknesses for each component

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affected by the rerate

Rerating Documentation - 2

• The remaining life of each component

• The required inspection interval determined

• Any physical modifications required

• Any requirements for pressure testing, such as

test pressure and temperature

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TSSA Guidelines for

Registration of Piping

• Anyone, or any company, intending to design, fabricate and/or install a piping assembly in fabricate, and/or install a piping assembly in Ontario should first refer to the Ontario

Regulations made under the Technical Standards and Safety Act, 2000, which govern such actions. The Act and Regulations require compliance with the applicable CSA Standards, ASME and ANSI Codes and reference should also be made to these Codes and reference should also be made to these standards.

• Modification or alteration (rerating) to an existing system that include a change in design pressure and temperature requires re-registration.

TSSA Guidelines for Registration

of Piping - 2

• Submissions:

• Drawings (flow diagrams, piping and

installation drawings) shall be submitted in

triplicate, together with one copy of the

system specifications and a letter of

application requesting registration.

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TSSA Guidelines for

Registration of Piping - 3

• General Inromation:

• Construction Code Information latest Edition andConstruction Code Information latest Edition and Addenda (i.e. ANSI B31.1, B31.3 or B31.5) (excludes B31.9 Building Services Piping); • Design Pressure;

• Design Temperature;

• Test Pressure and Type of Test;yp ;

• Service Fluid Information (e.g. Air, Water, Steam or specific Gas or Liquid);

• Safety/Relief Valve Setting and Location; or • Statement regarding overpressure protection

TSSA Guidelines for Registration

of Piping - 4

• Specifications:

• Pipe specification shall indicate, as a minimum, the following:

• Pipe line identification; • Pipe size and schedule;

• Pipe material (in accordance with ASME or ASTM p ( material specification);

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TSSA Guidelines for Registration

of Piping- 5

• Fitting(s) classification, identification and rating (for details see TSSA’s Guidelines for the Registration of Non-Nuclear g Fittings in the Province of Ontario, also note Appendix “E” of this Guideline, for the requirements for flexible hose

assemblies);

• Statement attesting that only registered fittings are used; • Pipe joining methods and details (welding, brazing, or others); • Non-destructive examination (NDE);

• Statement describing maximum support spacing and type, and anchor location.