Structural design 1 General

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a. Structural design of elevated flares, whether guyed, mast (self supported), or tower supported, shall be performed by specialists in this field with proven record of experience.

b. Single Vendor should be responsible for design, detailing, supply, and erection. Materials of construction, standards for fabrication, inspection, and nominated fabricator shall be subject to BP approval.

c. Self supporting stack for facilities located within North America Region shall be designed in accordance with API Std 560.

d. Facilities located outside of North America Region shall be designed in accordance with ISO 13705.

e. Unless specified otherwise, to lengthen period between inspections, the following constructional requirements shall be satisfied:

1. Load carrying connections shall be bolted.

2. Steelwork and bolting shall be galvanised or aluminium sprayed after fabrication. 3. Design of flare stack shall take into account proposed method of transportation and

erection.

4. Specification for bolting of flanges shall take fatigue into consideration.

f. Structural calculations shall be submitted to BP for review and shall demonstrate that in proposed design Vendor addresses design requirements that are listed in equipment data sheets.

g. The following are some aspects of design that shall require consideration: 1. Static wind loading.

2. Dynamic effect of wind, including effect of wind turbulence on dynamic response of structure.

3. Earthquake loads.

4. Internal pressure and sudden internal pressure.

5. Vortex shedding phenomenon.

6. Dynamic response of guys, including “galloping” response.

8. Local stress at guy attachment points and local stress due to choice of structural element, i.e., in the case of tubular joints, punching shear stress.

9. Radiant heat and its effect on riser, guys, upper guy fixings, and upper members in the case of a structure.

10. Effect of fatigue. Analysis shall be performed in accordance with Department of Energy guidance notes - Offshore Installations: Guidance on design and construction - using n/N no greater than 0,5 for design life. Fatigue design shall take into account full extent of allowable misalignment of circumferential seams.

11. Shell and strut buckling for static and dynamic loads.

h. Foundations

1. Foundation design should be by main civil contractor to loads and moments specified by supporting structure designers.

2. If guys are used, specific attention shall be paid to possibility of differential settling of main foundation and those of concrete block foundation.

3. Earthing (grounding) of flare structure and riser shall be independent of foundation reinforcement and piling.

4. Templates for anchor bolts shall be supplied and delivered to site in a timely manner to enable associated civil works to commence.

5. Templates for anchor bolts and design details of concrete block foundation shall be provided by Vendor to site in time for foundation construction. This requirement shall be written into contract of supply to ensure compliance.

i. Guylines and terminations

1. Radiation shield in type 321 SS shall be provided if effect of incident heat flux will reduce termination efficiency by more than 5%.

2. Sufficient articulation shall be provided in connections between guy rope terminations at one end and rigging screws at other end to ensure that no bending moment is transmitted to their respective attachment points.

3. In light of experience, guys and associated equipment (i.e., shackles, turnbuckles, anchor points) should be checked and regreased every 4 yr to 5 yr.

4. Guys should be retensioned after first year of operation and every 4 yr to 5 years thereafter.

j. Effect of temperature

1. Structural components shall be designed to ensure that allowable stresses will not be exceeded at temperatures that may be reached due to thermal radiation, hot gas flow, and, if applicable, flame impingement.

2. In performing this analysis, specific attention should be given to wind effects. Analysis should address:

a) Flame tilt due to high winds and radiation levels on structures below height of tip. b) Radiation levels on guy supported structure and guy ropes on downwind side of

c) Account should be taken of minimal wind speed case if flame is vertical or near vertical, and incident radiation on flare tip and structure is usually higher than in high wind speed case.

k. Flanges for guyed flares

1. Flanges for risers of guyed flares shall be of forged weld neck type with flat faces. 2. Jointing faces of flanges should be machined after welding flanges to pipe.

3. Accuracy shall be such that, after assembly, deviation of centreline from vertical shall not be greater than 30 mm in 100 m (0,36 in in 100 ft).

4. Gas inlet to guyed flares should be of same size as riser and may be in form of either “tee” branch or bend.

5. In both cases, sufficient reinforcement shall be provided to transmit vertical loads in riser from above inlet to below inlet without exceeding allowable stress levels.

6. Near atmospheric pressure in riser does not demand use of raised face flanges. 7. Full face gaskets with supporting inner and outer rings should be used. 5.6.4.2 Design loads

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a. Structure or part of structure shall be designed to resist applicable dead and live loading, including the following:

1. Structure dead loads (including fireproofing and insulation).

2. Imposed loads.

3. Weight of process contents of test fluids, also process contents resulting from credible maloperation.

4. Lifting equipment, including dynamic effects.

5. Dynamic or periodic loads resulting from operating machinery. a) Wind, snow, and ice loading.

b) Seismic loading.

c) Settlement.

d) Thermal loading - particularly for structures subject to high temperature variation and long structures.

e) Pipe anchor and surge condition loads.

f) Loads arising during construction and erection. g) Lack of fit.

h) Flare platform shall be sized and structurally suitable for maintenance activities. b. The following imposed loads shall be used in design of structures:

1. Platforms, walkways and stairways (not supporting any equipment and not intended as working platforms): 2,5 kN/m2 _{(36 750 psi).}

2. Working platforms and platforms over which heavy equipment may be transported or stored: 5,0 kN/m2 _{(73 500 psi) or the actual superimposed equipment load, whichever is}

the heavier.

3. Earthquake loads.

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1. If appropriate, seismic loads shall be calculated in accordance with national standards or codes applicable to site of works.

2. If such standards or codes do not exist or, with approval of BP, are considered

inappropriate or if these do not refer to specialised and hazardous items of plant, a study shall be performed to determine potential risk and level of seismic activity, to determine appropriate design loading.

3. For loading combinations with seismic load, increase in permissible stresses may be allowed. However, proposals shall be submitted and shall be subject to BP approval.

i. Special loads

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Unique design problems, such as transportation loads during shipping, shall be taken into account.

5.7 Knock-out drums and liquid seals

5.7.1 Knock-out drum Add Refer to 4.6.1.3. 5.7.2 Liquid seal Add Refer to 4.6.1.4.3.

5.8 Blowers and drivers

5.8.1 General description Add

a. If approved by BP, forced draft air can be used to achieve smokeless flaring. Two speed air blower or multiple blowers shall be provided as follows:

1. Low speed shall be for continuous operation.

2. High speed shall be actuated by pressure switch from flare header, with manual override. 3. Damper on blower discharge can be used for flow variation requirements.

4. Blower unit shall include inlet screen, removable for maintenance. b. Air intake for fan shall be ducted from safe area.

c. Ducting shall be sized and provided by Vendor.