Class 600 Slip-on flange with B31.1

[KevinNZ]

Can we justly using a class 600 DN400 slip-on flange in B31.1 piping, if the weld detail is not two filet welds? e.g face and back welds?

Class 600 slip-on flanges are used by many other piping and vessel codes. B31.1 seem to be concerned with stress risers and weld faults when two filet welds are used. B31.3 allows higher class SO flanges with two filets (even only one weld), But B31.3 also requires more NDT and HT.

 

[XL83NL]

There are 2 sides to this question; is it allowed by the Code, and is it good engineering practice. I cant help you with the latter as Im not experienced with B31.1, I can only point you to Code sections which I found through a simple Crtl + F in B31.1:2016;

104.5.1 Flanges — General
(A) Flanges of sizes NPS 24 (DN 600) and smaller,
that are manufactured in accordance with ASME B16.1
and B16.5, shall be considered suitable for use at the
primary service ratings (allowable pressure at service
temperature) except the slip-on flanges to ASME B16.5
shall be limited in application to no higher than Class 300
primary pressure service rating. Refer to para. 127.4.4.

PART 6
SYSTEMS
122 DESIGN REQUIREMENTS PERTAINING TO
SPECIFIC PIPING SYSTEMS
Except as specifically stated otherwise in this Part 6,
all provisions of the Code apply fully to the piping
systems described herein.
122.1 Boiler External Piping; in Accordance With
Para. 100.1.2(A) — Steam, Feedwater, Blowoff,
and Drain Piping
122.1.1 General. The minimum pressure and temperature
and other special requirements to be used in
the design for steam, feedwater, blowoff, and drain piping
from the boiler to the valve or valves required by
para. 122.1 shall be as specified in the following paragraphs.
Design requirements for desuperheater spray
piping connected to desuperheaters located in the boiler
proper and in main steam piping are provided in
para. 122.4.
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(F) American National Standard slip-on flanges shall
not exceed NPS 4 (DN 100). Attachment of slip-on
flanges shall be by double fillet welds. The throats of
the fillet welds shall not be less than 0.7 times the thickness
of the part to which the flange is attached.