Safety issues with compression bolts

It is recommended to use an explosion-proof wrench, or a C-clamp to assist with tightening.

During normal production, tightening bolts under pressure is strictly prohibited (as required by laws and regulations). However, in some chemical industries (such as oil refining plants), thermal tightening is required during operation, and thorough operating procedures must be established before such actions can be carried out, following approval.

Bolting under pressure is common in enterprises; many pipes and tanks need to be preheated before being tightened again. When tightening the bolts of the ammonia system, explosion-proof tools must be used. Tightening should be done carefully to avoid compressing the gaskets beyond their limit. Try to keep sensitive parts of the body away from the area where tightening takes place, to prevent sudden increases in leakage that could cause injury.

No matter how secure the tools are or how many safety measures are taken, using tensioning bolts is definitely not something that our technicians recommend.

Tightening bolts under pressure is indeed a commonly used method in production, but it also poses a safety hazard. **Article 122 of the \"Regulations on Safety Inspection of Pressure Vessels\" issued by the Bureau of Technical Supervision (which have been in effect since January 1, 2000) stipulates: \"No repairs shall be carried out on a pressure vessel when there is pressure inside it.\" For special production processes that require bolts to be tightened under temperature and pressure conditions ； In the event of an emergency leak that requires plugging it while the system is under pressure, the user entity must follow the specified operational requirements and safety measures as outlined in the design. The personnel carrying out these tasks must have received professional training and hold the necessary certifications, and their actions must be approved by the technical supervisor of the user entity. In actual operation, the safety department of the using unit should send personnel to supervise on site. ” Flange bolts shall comply with the **standard GB150-98 “Steel Pressure Vessels”** during their design, manufacturing, and installation. The original flange bolts have had their strength calculated under specified operating conditions; they are capable of withstanding the prescribed preload and system pressure, along with a certain safety margin. However, it is absolutely not permissible to apply additional loads to them. Especially after long-term use, when the bolts are subjected to corrosion and fatigue, their strength inevitably decreases, and no one can know exactly how much load they can still withstand at that point. Therefore, tightening bolts blindly may cause them to break, leading to an escalation of the accident with unpredictable consequences. In the event of flange leakage, it is absolutely forbidden to tighten the bolts blindly. The correct approach is to use a G-type clamp separately for reinforcement, or to first reinforce with the G-type clamp and then replace the original flange bolts with new ones.

I often encounter this phenomenon; I really didn’t think it was a potential problem. Thanks for the reminder

If torque wrenches are used to tighten the bolts, in accordance with the procedures specified in ASME PCC-1, a \"re-tightening\" operation, also known as thermal tightening or tightening under pressure, must be carried out within a certain period of time after the unit is brought online. Because after the bolt is tightened, compression causes a decrease in preload.

Article 122 of the \"Regulations on Safety Supervision of Pressure Vessels\" (which have been in effect since January 1, 2000) stipulates: \"No repairs shall be carried out on a pressure vessel when there is pressure inside it.\" For special production processes that require bolts to be tightened under temperature and pressure conditions ； In the event of an emergency leak that requires plugging it while the system is under pressure, the user entity must follow the specified operational requirements and safety measures as outlined in the design. The personnel carrying out these tasks must have received professional training and hold the necessary certifications, and their actions must be approved by the technical supervisor of the user entity. In actual operation, the safety department of the using unit should send personnel to supervise on site. ” Emphasized again! !