What is the Limited Pressure for Hot Bolting?

Hello Thieumy,

Notwithstanding stud relaxation and differential expansion between the bolts and the flanges, "Hot Bolting" is often the last step used as an attempt to ensure joint integrity.

Hot Bolting at any time can be quite dangerous since it can actually cause loss of joint integrity. Obviously, at higher pressures and temperatures the ramifications of creating an unexpected leak will be more serious

Let's assume that the engineer responsible for the joint had designed it properly. Rather than specify a dubious and potentially dangerous procedure intended to address possible leakage, perhaps it may be a better idea to ensure that everything has been done properly before the joint is pressurised.

Your procedure should ensure that the following are addressed before even putting tools onto the joint:

• verification of proper bolt and nut materials
• verification of proper gasket material
• verification of suitable flange surface finish
• verification of flange geometry

The actual bolting process must also be controlled:

• define proper gasket handling
  
• ensure calibration of torque wrenches
• describe applicable torquing pattern
  
• insist on elimination of torque error by verifying bolt elongation
  
• specify use of Bolt Tensioners on large critical flanges
• suitable waiting period before re-measuring bolt elongations and "tuning" fasteners as needed

Although there are many variables, addressing the main issues ahead of time should result in there being be no need to risk interrupting production or harming personnel by "hot bolting" when the unit is under pressure.