Socket Weld vs Butt Weld
Socket Weld vs Butt Weld
(OP)
Hello everyone,
There is a significant difference between the two welds regarding cost and inspection. Does anyone know where I can quickly source requirements for capping a 4 inch steam line at 600 psi? Am I required to use one weld in favour of the other and what is maximum pipe size requirement?
Thanks,Tom
There is a significant difference between the two welds regarding cost and inspection. Does anyone know where I can quickly source requirements for capping a 4 inch steam line at 600 psi? Am I required to use one weld in favour of the other and what is maximum pipe size requirement?
Thanks,Tom





RE: Socket Weld vs Butt Weld
Yes. Butt welds require more effort and welder skill to complete. Socket welds by design are simply fillet welds.
Regarding inspection - butt welds in most service conditions are inspected by surface and volumetric methods, again more cost.
Regarding design use, butt welds are treated differently in comparison to socket welds for specific service applications.
Review ASME B31.1 Power Piping Code.
RE: Socket Weld vs Butt Weld
Yes, there are some difference between butt and socket.
There more cost in butt weld than in socket, usually the welder is more expensive for butt weld and the inspection too.
The END are more demanding for butt than socket, for example you may need to do a 10% of RX in buttweld and a 2% in socketweld. It depend of specific service, the product and the material of the pipe, in some cases you must check all the welds, but in this case is cheaper socketwelds.
I don´t be sure, but usually in refineries you can use socket welds for pipes since 3 inch, for diameters aboves you need butt welds. Of course it depend the specific service.
This is only my opinion.
RE: Socket Weld vs Butt Weld
I would never employ a socket weld on a 600 psig steam service weld cap - or any other type of fitting. This is just a fillet weld - something a high school welding school can easily handle. I consider this type of weld merely one of aesthetics and never meant to lend mechanical strength to a joint.
For strength and integrity you have little choice but to opt for a 100% penetration, butt weld. For this type of service (where the end cap may be subjected to steam or condensate hammer) I seriously recommend a butt weld.
And I haven't even gotten to the part where you suffer crevice corrosion within the socket joint - especially under certain steam services.
RE: Socket Weld vs Butt Weld
It is still true - "you get what you pay for". The (expen$ive) well executed girth butt weld is stronger than a fillet weld. For 600 psig steam I would always use a girth butt weld. Generally, this would especially be true where there is any bending moment as the girth butt weld will give you better fatigue life.
ANSI B16.11 Socket Wekding Fittings are made up to NPS 4 size so you are looking at the largest of these. If you use socket welding fittings make sure that the design/analysis includes the larger Stress Intensification Factor that the Code recommends for the fillet welds where the pipe meets the B16.11 components (reference B31.1, Table D-1, note 11). Remember, by far the most common mode of failure that we see in the field with socket weld fittings is fatigue - crack propagation that begins with a crack at the toe of the fillet welds (usually at a fillet weld undercut stress riser). If this is a system that would be expected to see vibration or if it is B31.3 “cyclic service” (also see B31.3 severe cyclic conditions), don’t do it. Specify a weld profile like the illustration in B31.1 Figure 127.4.4(A)(d). Specify the examination of all finished fillet welds with repair for any undercut. Make sure that the welder provides the 1/16-inch gap shown in B31.1 Figure 127.4.4(B)(c).
Ed Wais developed a report for Epri that you might find interesting - go here and download:
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(Stress Indices for Circumferential Fillet Welded and Socket Welded Joints)
Regards, John.
RE: Socket Weld vs Butt Weld
For smaller dia pipes, it is difficult to align the pipes for a butt weld, so for smaller pipes, the socket weld is usually preferred.
RE: Socket Weld vs Butt Weld
RE: Socket Weld vs Butt Weld
RE: Socket Weld vs Butt Weld
RE: Socket Weld vs Butt Weld
The design concept of a butt weld is that you want to achieve 100% fusion in the weld joint to assure no reduction or penalty in load carrying capacity in service. Fillet welds by design are subjected to significant reduction factors for shear and tension.
Yes, you can account for socket welds in piping design. However, my experience has been that if you have unaccounted for thermal/mechanical bending stresses, the socket welds may be the first to develop problems in cycling related service. So, for components subjected to cyclic service stresses the fillet weld just doesn't exhibit the fatigue strength endurance as a full penetration butt weld. Whereas, under static load conditions or few cycles, socket welds may be appropriate.
It really comes down to design philosophy and past experience.
RE: Socket Weld vs Butt Weld
Hydrae
RE: Socket Weld vs Butt Weld
RE: Socket Weld vs Butt Weld
Thanks for all the great info and your time.
Tom