紧固件螺栓拧紧吐出线要求.doc

Thread Protrusion Charlie Chong How much protrusion is acceptable for fastener assembly? On the question raised on amount of thread protrusion above the nut to be considered as acceptable; Specific requirements were not mentioned in the standards (API / ASME) as far as I know. By common sense, the all the threads of the nut shall be engaged by the bolt or stud. Thus a minimum thread protrusion length is given to ensure that all the threads are engaged! (we do not need to convince this point by showing code requirements because this is required to ensure a full strength fastener assemblies as given in the design itself) At site, when installed and tightened, the nut shall protrude a distance of at least one thread beyond the top of nut as sign of full thread engagement. Two threads engagement is usually adopted for double sure. Excessive protrusion should be avoided in view of clearance, accessibility and safety is important and this could damage to machinery, hinder operation or harm to personnel. Full engagement of threads could not be positively ascertained. Full engagement of threads could not be positively ascertained on the left fastener assembly. On the right fastener assembly full thread engagement ensuring full fastener assembly capacity can be positive ascertained, thus acceptable. Some Codes and Standards Requirements. API RP 686-2009 “Recommended Practice for Machinery Installation and Installation Design”- 11.10 Anchor bolts shall project a minimum of 2 threads above the fully engaged nut(s). API 570-1998 Piping Inspection Code Inspection, Repair, Alteration, and Rerating of In-service Piping Systems 5.11 INSPECTION OF FLANGED JOINTS…Fasteners should extend completely through their nuts. Any fastener failing to do so is considered acceptably engaged if the lack of complete engagement is not more than one thread. What if the threads were not fully engaged? API 570-1998 Piping Inspection Code Inspection, Repair, Alteration, and Rerating of In-s