Examining the Process of Hot Bolting
Hot bolting is a controversial approach to tightening or replacing a bolt or flange on a pipe that is live - full of hot liquid or gas. The dangers of hot bolting at the very least is a severe injury. In many documented accidents where hot bolting failed, there have been fatal casualties, fire, explosion, and loss of equipment and plant. This discussion is a guide to hot bolting so that safety is a primary concern.
When to use Hot Bolting
The best answer to this question is never. The process is dangerous. With that being said, and when there is no other choice but to replace bolts or flange bolting on life pumps or pipes, then you should only do so when a permit is in place and with the utmost care given to safely. The reason for the permit is that every piece of equipment is different, as is every situation where hot bolting occurs. Every hot bolt operation needs to be fully reviewed and planned before it is attempted. That evaluation should always follow protocols that consider the contents of the line or the type of equipment that is involved. Those include:
Operating pressures and temperatures - Because hot bolting weakens the structural connection between two piping units or between pipe segments and industrial pumps, the pressure within the pipe must be a prime consideration before hot bolting occurs. Follow the protocol for pipe pressure before attempting to hot bolt. Also, the temperature of the liquid or gas in the pipe must also be considered as both the pressure and temperature change the behavior of the pipe, flange bolting, and the integrity of the pipe joint. For most pipes, hot bolting should never occur when the pressure within the pipe is above 60 percent of the safe recommended pressure of the pipeline or for the liquid involved.
Potential for hazards or upset conditions - Part of the engineering process for evaluation of each hot bolting application must include the assessment of those outside conditions that can cause the process to fail or injury to occur.
Position and functionality of piping supports - Piping supports help to stabilize the pipe joint during maintenance. A pipe segment that is not supported should never be approved for hot bolting as the torque from gravity can cause the joint to separate enough for the hot liquid or gas to escape, especially when those contents are under pressure.
Flange and flange bolt inspection - An inspection of the joint, the flange bolts, and the flange itself should be inspected as part of the engineering review before hot bolting is begun. Never use hot bolting if the flange bolts or the flange show signs of corrosion as those pieces are weak and may not support the added pressure when a single flange bolt is loosened or removed. Other issues that should always prevent hot bolting, include bolt necking or if the bolts or the flange show signs of metal fatigue and cracking.
Position and type of expansion bellows fitted - Not all expansion bellows allow for safe hot bolting to occur. The engineering review must consider both the position of the expansion bellows and the method by which they are fitted.
Joint maintenance history - Because hot bolting is a last resort, the maintenance of the joint must also be considered. A joint that is problematic should be replaced and redesigned, so that future issues are resolved rather than extended.
Contents of the system - Piping systems that contain toxic substances or radioactive substance must never be hot bolted.
Safety Concerns and Protocols
In every hot bolting situation, safety must trump all other concerns. When hot bolting is permitted, it should only occur when there are safety routes and escape routes easily accessible from the site. Further, hot bolting should not occur in any location where access is restricted, and emergency personnel or equipment cannot gain access.
In every hot bolting situation, make sure that the right tools are available so that the job is handled quickly and efficiently. Industrial torque tools should never be substituted for a tool that "might" do the job. Always use industrial torque tools. Reach out to the professionals at Aztec Bolting for all your industrial torque tools and replacement bolts, flanges, and expansion units.