Stress critical line list is developed by Stress Engineer based on stress design criteria for the particular project. A typical Stress Design Criteria specifies following types of lines to be critical from stress point of view.

The Critical line list should include following lines:

• 4” to 14” : Operating Temperature beyond 175°C;
• 16” to 18” : Operating Temperature beyond 120°C.
• 20” and above.
• If pipe stress calculations compel the national approval or client authorities, this shall be implemented by the procedures as required by the respective authorities.
• 3” and above sized process lines connected to rotating Equipments.
• Piping fastened to air cooled Heat Exchangers, Pulsating equipments, inlet and outlet of boilers and Heaters.
• Unacceptable stresses and reactions caused by external displacements.
• Lines of cycling services eg. Batch process or regenerations.
• Locations of snubbers, spring type support, expansion joints.
• Specific piping for slug flow/water hammer/ double phase flows.
• 4” and above diameter flare lines, Relief loaded lines.
• 8” and above lines with operating temperature above 200° C, in case of toxic services.
• Glass reinforced plastic piping.
• Steam outlets, jacketed piping.
• Cryogenic lines below -46° C.
• Lines connected to Solenoid Pumps (X’mas trees) and well heads.
• Lines in which bolts joints do not comply with ASME B16.5/B16.47
• Piping’s in, in and on derrick and flare structures.

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Prior to the computerized analysis the following minimum analysis shall be carried out manually

• Lines with operating temperatures 100° C (210° F) to 175° C (350°F) of pipe sizes 4” to 14”.
• Calculations of forces, moments and stresses caused by the expansion strains shall be formally analyzed by means of analytical and chart method
• All critical lines must be highlighted in both project line list and PEFS/ P&ID’s. The integrity of non-critical lines must be ensured by the piping stress engineer, whereas the non-critical lines shall be flexible or natural flexibility shall be achieved by pipe work configuration.

Synopsis

Critical lines include piping systems of 4” to 14” with temperature above 175°C, 16” to 18” with operating temperature of 120°C. Whereas the non-critical piping system come under pipe sizes 4” to 14” with operating temperature of 100° C to 175°C.

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