Recently I was asked if “torquing” threaded pipe is required by code. I answered the inquiry by referring the client to ASME B1.20.1-2013, which states:
1.4 Sealing (NPT and NPSC Only)
…
1.4.3 Tightening Torque.
Due to application-specific variables such as materials, wall thickness, operating pressures, etc., no guidance is given in this Standard regarding joint-tightening torque. However, joints should be tightened beyond the hand-tight engagement position. Advancing the joint past hand-tight creates interference between external and internal thread flanks, produces a seal (with the use of a sealant), and helps prevent loosening of the joint. Overtightening may be detrimental to the sealing function of the joint.
However, ASME B31.3 offers the following regarding Threaded Flangers when used in “Normal Fluid Service”. Refer to Section 308.2.3…
(emphasis by me)
308.2.3 Socket Welding and Threaded Flanges.
A socket welding flange is subject to the requirements for socket welds in para. 311.2.2 . A threaded flange is subject to the requirements for threaded joints in para. 314
314 THREADED JOINTS
314.1 General
Threaded joints are suitable for Normal Fluid Service1 except as stated elsewhere in para. 314. They may be used under severe cyclic conditions only as provided in paras. 314.2.1(c) and 314.2.2 .
(a) Threaded joints should be avoided in any service where crevice corrosion, severe erosion, or cyclic loading may occur.
(b) When threaded joints are intended to be seal welded, thread sealing compound shall NOT be used.
(c) Layout of piping employing threaded joints should, insofar as possible, minimize stress on joints, giving special consideration to stresses due to thermal expansion and operation of valves (particularly a valve at a free end). Provision should be made to counteract forces that would tend to unscrew the joints.
(d) Except for specially designed joints employing lens rings or similar gaskets, threaded flanges in which the pipe ends project through to serve as the gasket surface may be used only for Category D Fluid Service.
314 .2 Specific Requirements
314.2.1 Taper-Threaded Joints.
For joints in which the threads of both mating components conform to ASME B1.20.1
(a) the minimum thickness of components with external threads shall be the greater of tm in accordance with para. 304.1.1 and the schedule shown in Table 314.2.1
(b) threaded components shall be checked for adequacy of mechanical strength as described in para. 302.5
(c) threaded components of a specialty nature that are not subject to external moment loading, such as thermo wells, may be used under severe cyclic conditions
A coupling having straight threads may be used ONLY for Category D Fluid Service, and ONLY with taper-threaded mating components.
314.2.2 Straight-Threaded Joints.
Threaded joints in which the tightness of the joint is provided by a seating surface other than the threads ( e.g., a union comprising male and female ends joined with a threaded union nut, or other designs shown typically in Figure 335.3.3) may be used. If such joints are used under severe cyclic conditions and are subject to external moment loadings, safeguarding is required.
- ALL fluid services are considered “Normal” unless the owner designates them as other categories. ↩︎