Bolt-Load Considerations Associated with ‘Hot Bolting’

In some situations, it might be necessary to remove or replace a bolt during operation. This article shows how to determine the proper bolt load to prevent leaks Bolted flange joints (Figure 1) are part of pressure vessel and piping components and are extensively used in the chemical, petrochemical, fertilizer and the oil-and-gas industries. They are simple structures and offer the possibility of disassembly, which makes them attractive to connect pressurized equipment and piping. In addition to being prone to leakage, they often require maintenance while in operation, in which case, the bolts are either re-tightened as in hot torquing or un-tightened to be replaced. Although costly shutdowns are avoided, such maintenance work exposes the operator to a potential risk because bolt load alteration can produce a gasket load unbalance, which results in the local gasket contact stress to drop below some critical value, causing a major leak and hence jeopardizing the life of the worker. The distribution of contact stress has a dominant effect on sealing performance, while the sealing capability of joints is related to the contact pressure (gasket stress) during operating conditions, providing possible leakage and ultimately joint failure.…