Socket weld size limits

[DRight]

According to B31.1 what are the size and classification limits for socket welded valves and fittings
B31.1 references both B16.11 and B16.34 ( which also references B16.11 )
B16.11 limits end at 2" for a 6000 class as no values are given for 2-1/2" class 6000
From a valve manufacture " Refer to Table 4 of B16.34, attached. The wording is tricky, but it requires that only the socket diameter, depth and end surface be to B16.11. Everything else is to be to B16.34, including wall thickness".
111.3.4 Drains and bypasses may be attached to
a fitting or valve by socket welding, provided the socket
depth, bore diameter, and shoulder thickness conform
to the requirements of ASME B16.11

If this is correct why would a socket weld valve be allowed in a service condition that a fitting would not be allowed

 

[nickelkid]

Is this a general question or do you have a specific design problem?

 

[DRight]

This is a general question . Typically the valves and fittings are used in 2500 psi design and temperatures from 750F to 1000F and what to understand the code requrement .
I know thatSWs are susceptible to erosion due to the discontinuity of the pipe internals.
2. Fatigue cracking can be a concern due to temperature fluctuations and stress concentrations on the fillet welds.
3. Fillet welds only permit a surface inspection of the weld .
Butt-welds are the "best" in terms of strength, fatigue, corrosion, erosion, and temperatures - however, they are more difficult to fit-up and weld properly

 

[nickelkid]

The B31.1 SW limitations for piping service I interpret are:

- SW branch connections cannot exceed is smaller of NPS 2 or 1/4 of the run

- In toxic fluid service SW shall not be greater than NPS 2 1/2

- In toxic fluid service (piping for refillable storage and associated equipment application) SW shall be a maximum of NPS 2 when pressure is 50 psig or greater.

IMO for NPS 2 and above butt welding has minimal fit up issues with qualified craftsman and should be utilized for the reasons you have stated.

 

[JohnBreen]

Excuse my nit picking - Fluid Service is a B31.3 exclusive.

The most limiting issue with socket weld fittings has been the tendency to undercut the fillet welds. SW fittings are limited to NPS 4 and less and the welder usually has to stop and start several time as he welds around the small circumference to change his access to the weld. This (stop and start of the arc) tends to facilitate undercut. Notice that the stress intensification factors are rather large unless the fillet weld profile is "improved" per B31.1, paragraph 127.4.8 (figure 127.4.4(A)(d)) concave. The weld can be improved with a grinder to get a concave profile with NO undercut at the toe.

 

[nickelkid]

John,

Point well taken. Instead of "In toxic fluid service", "With toxic fluids" would have been a better reflection of B31.1

 

[JohnBreen]

.......and I hope I am not going too far "off topic" here you might want to read via the Internet:

Vibration Fatigue Testing of Socket Welds (PWRMRP-07)

mydocs.epri.com/docs/public/TR-113890.pdf

Regards, John