Checklist for Chapter VIII of ASME B31.3 Piping for Category M Fluid Service


1. This checklist shall be used only when CLIENT/COMPANY has designated Category M fluid service for any piping class.

2. Following points are applicable for metallic piping components only. Please note that the checklist shall be filled in preferably by Lead Engineer.

3. The check points listed below are not comprehensive, for detailed description please refer cross-referenced paras of Chapter VIII of ASME B31.3



1.01 Consideration shall be given to the possible need for engineering safeguards (see Appendix G para. G300.3) in addition to the safeguards already provided (paras. G300.1 and G300.2) [M300 (d)]
1.02 Piping system designed for Category M service fluid preferably shall not go under severe cyclic conditions [M300 (e)]
1.03 Design temperature considered same as the fluid temperature [M301.3]
1.04 Design, layout and operation of piping shall be conducted so as to minimize impact and shock loads (including changes in flow rate, hydraulic shock, liquid or solid slugging, flashing, and geysering) [M301.5.1]
1.05 Dynamic stress analysis carried out, to avoid or minimize conditions which lead to detrimental vibration, pulsation, or resonance effects in the piping [M301.5.4]
1.06 Design temperature and pressure based on coincident pressure–temperature conditions requiring the greatest wall thickness or the highest component rating [M302.2.4]
1.07 No variations in design pressure and/or design temperatures shall be considered even in occasional cases [M302.2.4]
1.08 When two services that operate at different pressure–temperature conditions are connected, the valve segregating the services shall be rated for the more severe service condition [M302.2.5]
1.09 Allowable stress considerd in the design as per stress tables in Appendix-A [M302.3.2]
1.10 Fitting conforming to MSS SP-43 and MSS SP-119 and propietary “Type C” lap-joint stub-end butt welding fittings shall note be used [M306.1.3]
1.11 Creased or Corrugate type of bends shall not be used [M306.2]
1.12 Miter bends shall not make a change in direction at a single joint greater than 22.5 deg [M306.3]
1.13 Flared laps shall meet the requirement of para306.4.2. In addition, [M306.4.2]

a) pipe size shall be less than or equal to DN 100 with wall thickness before flaring great than or equal to the value of T for schedule 10S.

b) P-T rating shall be less than or equal to ASME B16.5 Class 150, Group 1.1 flange

c) service tempertaure shall be less than 204 deg C

1.14 Fabricated Branch Connections design shall consider the following [M306.5]

i) para 304.3.1(a), subpara. (3) may be used only if (1) and (2) are unavailable.

– para 304.3.1(a)(1) – states that fittings (tees, extruded outlets, branch outlet fittings in accordance with MSS SP-97, laterals, crosses)

– para 304.3.1(a) (2)- unlisted cast or forged branch connection fittings (see para. 300.2), and couplings not over DN 80 (NPS 3), attached to the run pipe by welding

ii) 304.3.2 (b) and (c), those having threaded outlets are permitted only in accordance with para M314 and those having socket welding outlets are permitted only in accordance with para M311.2

1.15 Metallic Valves having threaded bonnet joints (other than union joints) shall not be used [M307.2 (a)]
1.16 Special consideration shall be given to valve design to prevent stem leakage to environment [M307.2 (b) (1)]
1.17 The following shall be considered for Metallic Valves [M307.2 (b) (2)]

Bonnet / cover plates shall be flanged, secured by atleast four bolts and gaskets conforming to M308.4 or

– properiety or attached by bolts, lugs or other substantial means and having a gasket design that increases gasket compression as fluid pressure increases or

– secured with a full penetration weld made in accordance with para M311 or

– secured by a straight thread sufficient for mechanical strength, a metal to metal seat and a seal weld made in accordance with para M311, all acting in series

3) Body joints, other than bonnet/cover plate joints, shall conform to para M307.2 (b)(2) [M307.2 (b) (3)]

1.18 Single-welded slip-on flanges, Expansion-joint flanges shall not be used [M308.2 (a) (b)]
1.19 Slip-on flanges used as lapped flanges shall not be used unless the requirements in para 308.2.1 ( c) are met [M308.2 (c)]
1.20 Threaded metallic flanges shall not be used, except those employing lens rings or similar gaskets and those used in lined pipe where the liner extends over the gasket face [M308.2 (d)]
1.21 All blanks shall be marked with material, rating and size [M308.5]
1.22 Welded joints may be made in any metal for which it is possible to qualify welding procedures, welders, and welding operators in accordance with para. M328 [M311]
1.23 Split backing rings shall not be used [M311.1 (a)]
1.24 Socket welded joints greater than DN 50 (NPS 2) are not permitted [M311.1 (b)]
1.25 For Taper-Threaded Joints the following shall be considered [M314.2.1] para 314.2.2 applies except that components suitable for Normal fluid service in sizes DN 8 to equal to or < DN 25 can be use. Sizes smaller than DN 20 shall be safeguarded
1.26 Calked Joints shall not be used [M316]
1.27 Soldered, brazed and braze welded joints shall not be used [M317]
1.28 Adhesive joints and bell type joints shall not be used [M318]
1.29 Simplified rules related to piping flexibility studies in para 319.4.1 are not applicable [M319]
1.30 Supporting element shall be of listed material [M321]
1.31 Instrument piping in which signal lines are in contact with process fluids and process temperature-pressure conditions the following shall be considered [M322.3]

a) tubing shall not be larger than 16mm (5/8 in) OD and shall be suitable for the service.

b) an accessible block valve shall be provided to isolate the tubing from the pipeline.

c) joining methods shall confirm to the requirements of paras 315.1 and 315.2

1.32 Design Pressure shall not exceed more than 10% during operation of a pressure relieving system [M322.6.3]


2.01 Pipes made of ASTM A134 made from ASTM A285 plate and ASTM A139, API 5L, Furnace Butt-Welded ASTM A53, Type F should not be used in Category M [M305.2.2]
2.02 Unknown material shall not be used [M323.1.3]
2.03 Reclaimed Materials can be used when material certification records are available for the specific materials employed and the designer is assured that the material is sound and free from harmful defects [M323.1.4]
2.04 The low-stress exemption from impact testing is not permitted i.e following is not applicable.
Impact testing is not required if the design minimum temperature is below −29°C (−20°F) but at or above −104°C (−155°F) and the stress ratio defined in Fig. 323.2.2B does not exceed 0.3.”” [M323.2]“
2.05 Cast Iron other than ductile iron shall not be used for pressure containing parts and lead and tin shall be used only as lining[M323.4.2]
2.06 Metallic Cladding and Lining Materials shall comply with para 323.4.3 requirements, in addition to that wherever other material listed in 323.4.2( c) and 323.4.3 are used as lining or cladding which serves as a gasket or as a part of flange, the design of the flange joint shall be such as to prevent leakage to the environment [M323.4.3]


3.01 While welding of materials split backing rings shall not be used, and removable backing rings and consumable inserts may be used only where their suitability has been demonstrated by procedure qualification [M328.3]
3.02 No requirements less stringent than those of Table 331.1.1 shall be specified for heat treatment of metals [M331]
3.03 Any bending or forming required for alignment and fit-up shall be heat treated if required by para. 332.4 [M335.1.1]


4.01 All fabrication shall be visually examined (100%) [M341.4 (a)(1)]
4.02 All threaded, bolted and other mechanical joints shall be visually examined [M341.4 (a)(2)]
4.03 Min. 20% of circumferential butt and miter welds and of fabricated lap and branch connections welds comparable to those shown in fig 328.5E and 328.5.5 sketches (d) and (e) shall be examined [M341.4 (b)(1)]
4.04 The in-process examination alternative in para 341.4.1 (b) (1) may be specified on weld-for-weld basis in the engineering design or by the inspector but it shall be supplemented by appropriate nondestructive examination [M341.4 (b)(2)]
4.05 A sensitive leak test in accordance with para 345.8 shall be included in the required leak test along with hydrostatic leak test [M345 (a)]
4.06 Initial service leak test (para 345.7) shall not be considered [M345 (b)]

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