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Socket Welding 8
- Thread starter klkweld
- Start date
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2
- #2
klkweld-
It's good practice since if you bottom out the pipe in the socket then when the piping is put into service and heats up it will try to expand but be restrained by the socket. Failure of the fillet weld is one possible outcome.
If you're working to B31.3, take a look at Fig. 328.5.2B which calls out a 1/16" approx. gap.
There's a product called a gap-o-let which I couldn't find on google, but we use it often in our socket welded construction. The other option is to RT the finished socket welds to confirm the gap.
jt
It's good practice since if you bottom out the pipe in the socket then when the piping is put into service and heats up it will try to expand but be restrained by the socket. Failure of the fillet weld is one possible outcome.
If you're working to B31.3, take a look at Fig. 328.5.2B which calls out a 1/16" approx. gap.
There's a product called a gap-o-let which I couldn't find on google, but we use it often in our socket welded construction. The other option is to RT the finished socket welds to confirm the gap.
jt
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2
- #3
When bottomed out, cooling during welding produces contractive forces which can press against the socket fitting. This in turn produces a shear load across the weld, which when great enough promotes hot cracking of the weld. Similarly, if the material is hardenable and a suitable martensitic microstructure is obtained, hydrogen induced cracking may also occur.
redandysafc
Mechanical
I f you check ASME b31.3 the information is 1/16" gap after welding.
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stanweld,
There MAY be some piping Codes that do not REQUIRE (and quantify) the subject gap but I can assure you that the ASME B31.1 and B31.3 Codes ABSOLUTELY DO REQUIRE a 1.5 mm (1/16 inch) gap (see, e.g., B31.3 Figure 328.5.2C).
Regards, John.
There MAY be some piping Codes that do not REQUIRE (and quantify) the subject gap but I can assure you that the ASME B31.1 and B31.3 Codes ABSOLUTELY DO REQUIRE a 1.5 mm (1/16 inch) gap (see, e.g., B31.3 Figure 328.5.2C).
Regards, John.
JohnBreen
Please refer to B31.3 Fig 328.5.2C "1.5 mm (1/16in.) approx. gap before welding". Also refer to B31.1, FIG. 127.4.4(B)"Approx. 1/16" (2.0 mm) gap before welding".
APPROXIMATELY is not exactly! Before welding is not after welding when measured by viewing a radiograph! As previously stated weld shrinkage will generally cause the approximate 1/16" gap prior to welding to be reduced. There is ABSOLUTELY NO REQUIREMENT to meet the 1/16" gap after welding.
Please refer to B31.3 Fig 328.5.2C "1.5 mm (1/16in.) approx. gap before welding". Also refer to B31.1, FIG. 127.4.4(B)"Approx. 1/16" (2.0 mm) gap before welding".
APPROXIMATELY is not exactly! Before welding is not after welding when measured by viewing a radiograph! As previously stated weld shrinkage will generally cause the approximate 1/16" gap prior to welding to be reduced. There is ABSOLUTELY NO REQUIREMENT to meet the 1/16" gap after welding.
stanweld,
When we (at B31, MDC) put those rules in the Codes the "approximate" in the gap was a round-up, based upon our calculation of how much expansion would result from the welding process (heating the weldment). We based that upon the expansion coefficient of stainless steel. So, what we intended was that when at ambient temperature, before the welding process, (i.e., before the components were heated to welding temperature) we would have a big enough gap such that the end of the pipe would not "bottom out" at the base of the socket when the weldment was AT welding temperature. Of course upon cool down after the weld was made, the gap would be approximately the original 1/16 inch. It is implicit in the rule that upon fit-up the gap would be approximately 1/16 inch (cold) and after the weldment had cooled (after welding) the gap would return to approximately 1/16 inch.
If you think it is something that needs the full Committees to interpret, I would be glad to sponsor an inquiry to B31.1 and B31.3. I would ask them to add words that unambiguously specify that the gap should be approximately 1/16 inch after the weldment has cooled.
Regards, John.
When we (at B31, MDC) put those rules in the Codes the "approximate" in the gap was a round-up, based upon our calculation of how much expansion would result from the welding process (heating the weldment). We based that upon the expansion coefficient of stainless steel. So, what we intended was that when at ambient temperature, before the welding process, (i.e., before the components were heated to welding temperature) we would have a big enough gap such that the end of the pipe would not "bottom out" at the base of the socket when the weldment was AT welding temperature. Of course upon cool down after the weld was made, the gap would be approximately the original 1/16 inch. It is implicit in the rule that upon fit-up the gap would be approximately 1/16 inch (cold) and after the weldment had cooled (after welding) the gap would return to approximately 1/16 inch.
If you think it is something that needs the full Committees to interpret, I would be glad to sponsor an inquiry to B31.1 and B31.3. I would ask them to add words that unambiguously specify that the gap should be approximately 1/16 inch after the weldment has cooled.
Regards, John.
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Welder4956
Materials
John,
It's interesting to hear the background for how this requirement came to be part of B31. I've welded many socket welds for Navy nuclear and non-nuclear applications, and it was also a MIL-STD / NAVSEA requirement to have a 1/16" gap before welding. For those standards, we had to qualify separately for socket and groove welds. The socket welder test coupons were required to be examined by PT, then cut into quarter sections for macroetch examination. Many times the NDE shop would try to hold us to the 1/16" minimum gap AFTER welding. If we set the gap at 1/16", the weld shrinkage would always close the gap to almost zero. To get 1/16" after welding, we would have to set it at 3/32"-1/8" before welding.
I don't see the logic in requiring any gap to be present after welding, except for disimilar welds where thermal expansion could cause the pipe to grow at a different rate than the socket fitting.
It's interesting to hear the background for how this requirement came to be part of B31. I've welded many socket welds for Navy nuclear and non-nuclear applications, and it was also a MIL-STD / NAVSEA requirement to have a 1/16" gap before welding. For those standards, we had to qualify separately for socket and groove welds. The socket welder test coupons were required to be examined by PT, then cut into quarter sections for macroetch examination. Many times the NDE shop would try to hold us to the 1/16" minimum gap AFTER welding. If we set the gap at 1/16", the weld shrinkage would always close the gap to almost zero. To get 1/16" after welding, we would have to set it at 3/32"-1/8" before welding.
I don't see the logic in requiring any gap to be present after welding, except for disimilar welds where thermal expansion could cause the pipe to grow at a different rate than the socket fitting.
John
If it is truly the intent of B31.1 and B31.3 that the 1/16" minimum gap is required and is to be demonstrated after welding, then amend the Code accordingly. Require RT of 5% (or more) of the socket welds to confirm this workmanship standard; noting that there is no current requirement to do so. As I have stated and Welder 4556 has noted, weld shrinkage will most often reduce the original gap; it will not return to the orignal gap prior to welding.
If it is truly the intent of B31.1 and B31.3 that the 1/16" minimum gap is required and is to be demonstrated after welding, then amend the Code accordingly. Require RT of 5% (or more) of the socket welds to confirm this workmanship standard; noting that there is no current requirement to do so. As I have stated and Welder 4556 has noted, weld shrinkage will most often reduce the original gap; it will not return to the orignal gap prior to welding.
Gentlemen,
That IS very interesting. Maybe 1/16 inch after welding is not enough (?).
Perhaps the best approach is to sumbit inquiries to B31.1 and B31.3 and have them provide a formal interpretation. I will send inquiries to these Committees and see if we can get a fast interpretation or Code Case. By the way, anyone who has a question can submit an inquiry. If you look at B31.3 Appendix Z, it provides guidance for submitting inquiries. I will post updates on this thread if I can.
Regards, John.
That IS very interesting. Maybe 1/16 inch after welding is not enough (?).
Perhaps the best approach is to sumbit inquiries to B31.1 and B31.3 and have them provide a formal interpretation. I will send inquiries to these Committees and see if we can get a fast interpretation or Code Case. By the way, anyone who has a question can submit an inquiry. If you look at B31.3 Appendix Z, it provides guidance for submitting inquiries. I will post updates on this thread if I can.
Regards, John.
The 1/16 inch is before welding, as stanweld states, and there is no code requirement for a gap after welding. Weld shrinkage will tend to close the gap. If you need to see a gap for quality control purposes after welding, you would need to specify that as an additional requirement of the engineering design. There are existing B31.3 interpretations on this issue, and they confirm the gap is before welding, and that there are no requirements for after welding.
See also the discussion in section 12.12 of the book, Process Piping, by Becht.
See also the discussion in section 12.12 of the book, Process Piping, by Becht.
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