ASME PCC-1, Guidelines for Pressure Boundary Bolted Flange Joint Assembly, is a MUST have (and read) for process safety professionals managing piping systems that have bolted flanged joints. In fact, Chapter 15, JOINT DISASSEMBLY, has some specific requirements that a facility should adopt as part of its Line Break SWP for flanged joints.
HINT: the old trick of the first nut loosened being down and away from the worker is no longer a “trick” it has become part of the RAGAGEP
(emphasis by me)
Before any joint is disassembled, it is essential that assurance be obtained from personnel in responsible charge of the management of the system that all pressure, including that due to a liquid head, has been removed from the system and that proper procedures have been followed to ensure that joints may be safely opened. A sufficient number of loosened nuts SHOULD BE LEFT IN PLACE UNTIL ALL TENSION HAS BEEN RELIEVED to guard against falling components, pipe springs, or other unanticipated movements. Due to the possibility of residual liquid in the pipe and any unrelieved pressure, the first bolts loosened should be in a location that will direct any pressure release AWAY from the assembler.
NOTE: This used to be a “trick of the trade,” but now that ASME has it in their RAGAGEP, one could argue this needs to become a standard practice in the procedure and Line Break training.
When significant numbers of bolts are loosened, the elastic recovery of the clamped parts can result in excessive loads on the relatively few remaining bolts, making further disassembly difficult and sometimes causing thread galling between the nut and bolt sufficient to result in torsional failure of the bolt as further loosening is attempted.
NOTE: Thread galling occurs during installation when pressure and friction cause bolt threads to seize to the threads of a nut or tapped hole. It is also known as “cold welding”. Once a fastener has seized up from galling, removing it is typically impossible without cutting the bolt or splitting the nut.
The reported incidents of disassembly difficulties have typically involved
(a) flanges larger than DN 600 (NPS 24)
(b) flange thicknesses greater than 125 mm (5 in.)
(c) bolt diameters M45 (13∕4 in.) and larger
Accordingly, the use of a joint disassembly procedure may be desirable for joints involving components meeting all the criteria of (a) through (c) above or where thread galling of the bolts has been or is found to be problematic. Also, using a joint disassembly procedure may be prudent for joints involving components for which high local strains could be detrimental (e.g., glass-lined equipment, lens ring joints) or joints where the gasket is to be removed for analysis.
1) When a joint disassembly load-control procedure is deemed appropriate, start by loosening one bolt completely while noting the amount of nut turn it takes to fully relieve the bolt load from assembled to the finger-tight condition.
2) Retighten the loose bolt to approximately 7∕8 of the turn to fully relieve the load (e.g., if the nut comes loose after two flats of movement, then retighten by turning the nut 7∕4 flats from finger tight, i.e., to a position 1∕4 of a flat less than the original amount of nut turn).
3) Proceed in a circular pattern around the joint and loosen each bolt by approximately 1∕8 of the turn of the nut required to fully relieve the load (e.g., if the nut comes loose after two flats of movement, then loosen each nut by 1∕4 of a flat).
4) For particularly problematic joints, continue to proceed in a circular pattern around the joint and loosen each bolt by a further 1∕8 of the turn of the nut required to fully relieve the load (e.g., in the above example, a further 1∕4 of a flat)
5) Proceed with bolt loosening and nut removal in a circular pattern, remembering to reaffirm that all pressure on the joint has been released and that the joint has separated before removing all bolts and nuts.
An aid such as a hydraulic or manual flange spreader may be used to separate the joint if necessary.
6) If the bolts start galling during final disassembly (i.e. when performing step 5), then retighten all loosened bolts (if possible) to the position obtained after performing steps 3 or 4 and then recommence at step 4.