What is Hot Bolting?
Hot Bolting is the practice of removing and replacing or freeing and re-tightening bolts on live piping and equipment.
It is potentially hazardous and the utmost caution needs to be exercised when planning and carrying it out. It is not recommended as best practice although it is widely carried out. However, any potential benefits arising from hot bolting should be carefully weighed against the risks encountered.
Why Use Hot Bolting?
Hot bolting is practised for several reasons, including:
- For replacing corroded or damaged bolts
- For upgrading the material specifications/grades of bolts
- To minimise the time spent freeing bolts during plant shutdown
The Engineering Equipment Materials and Users Association (EEMUA) publish an information sheet called Guidance Procedures for the Removal and Replacement of Flanged Joint Bolting on Live Piping and Equipment. This is essential reading before carrying out any bolt work on live plant.
Things to Consider Before Hot Bolting
When contemplating hot bolting a number of factors need to be considered. These include, but are not limited to:
- The operatorís own working procedures and guidlines
- The piping system and the system's operating pressures and temperatures
- Flange joints considered for hot bolting should have a minimum of eight bolts. The bolt material should have a minimum strength equal to or greater than grades B7/2H
- Prior to the commencement of work, the site supervisor should review the maintenance history of the joint under consideration, and any joints of a similar type which have been hot bolted in the past. Is there any history that should be considered?
- The supervisor should also carry out a visual assessment of the joint. Hot bolting should not be carried out on joints which show significant signs of corrosion or necking, or which have worn or cracked threads on the fasteners
- Hot bolting should only be attempted under operating conditions when the history of the flange assembly is known, ie records exist for the bolt load
- The consequences of joint leakage during hot bolting should be considered (for example, toxicity, flammability and temperature of escaping fluids) and all necessary precautions taken. Contingency plans should also be put in place for an escape or emergency, e.g. means of communications and provision of standby equipment
- Pipework within the vicinity of the joint to be hot bolted should also be reviewed. Pipe supports for the local section should be checked to ascertain whether they are taking the load on the pipe, along with their overall condition. If the pipework displays any significant signs of vibration around the specific flange, then hot bolting should not be considered as an option
Performing Hot Bolting
Assuming permits are in place, and all necessary safety talks (e.g. toolbox talk) have taken palce then:
- The site supervisor shall check that all the necessary personnel, materials and equipment are at the worksite
- Each bolt shall be checked for tightness, with any abnormal conditions, such as loose bolts, reported to the supervisor
- Carry out hot bolting on one bolt at a time in accordance with the operator's correct sequence
- Remove, examine, clean and lubricate each bolt, complete with nuts, for reuse. Any damaged bolts or nuts shall be disposed of and replaced with new items to the correct piping specification. If there is any doubt, the materials shall be replaced. All exposed flange surfaces must be cleaned and the area under the nuts lubricated
Note: Bolt cutting by any hot methods, including burning and grinding, is not usually permitted during hot bolting operations. Any cold bolt cutting, including hydraulic nut splitting, is usually only permitted by specific approval of the relevant Technical Authority
- Ensure that the bolt has been correctly tightened before moving onto the next bolt in the sequence. Initial retightening of refitted bolts shall not introduce additional local compression of the gasket
- After all the bolts have been replaced, a final tightness check shall be carried out again using the specific operatorís sequence for hot bolting