Does low-temperature LPG pipeline require pre-cooling when put into operation for the first time?

Low-temperature LPG (propane -43°C, butane -7°C) pipelines usually require pre-cooling when put into operation for the first time, and a special pre-cooling plan should be prepared. Requires pre-cooling: Because pipelines are operated at room temperature with low-temperature liquids (such as propane boiling point ≈ -42°C), a temperature difference exceeding 40°C will cause severe thermal shrinkage (the shrinkage rate of carbon steel/austenitic stainless steel can reach 0.3%~0.4%), resulting in flange leakage, weld cracking or support instability. ； Especially when the system contains butane (boiling point ≈ -0.5°C), if it is designed for full liquid phase low-temperature transportation, it still needs to be pre-cooled according to the most stringent component (propane). A special pre-cooling plan should be made: It includes step cooling (such as pre-cooling with nitrogen or a small amount of LPG to -30°C and then gradually reaching the operating temperature), rate control (≤10~15°C/h), stress monitoring, material low-temperature toughness verification and anti-frost injury/leakage emergency measures, and complies with pressure pipeline and low-temperature process safety regulations (such as GB/T 20801, ASME B31.3). If the pipe material is 304/316L stainless steel and the design includes expansion compensation, slight butane working conditions or short-term low-temperature charging may simplify precooling, but it is still recommended to implement standardized precooling procedures for the first operation to avoid thermal stress failure. Whether it is actually "mandatory" depends on the design documents, owner standards and local special equipment supervision requirements. It is recommended that the approval conclusion of the HAZOP/commissioning plan shall prevail.