socket weld maximum gap
socket weld maximum gap
(OP)
Dear All,
I need to know the maximum gap between a nipple and a coupling before welding. ASME B 31.3 calls for 1.5 mm minimum, but what about maximum?. Attached, a sketch for clarifications.
Thanks a lot.
I need to know the maximum gap between a nipple and a coupling before welding. ASME B 31.3 calls for 1.5 mm minimum, but what about maximum?. Attached, a sketch for clarifications.
Thanks a lot.





RE: socket weld maximum gap
RE: socket weld maximum gap
Keep the gap near the specified minimum. Structurally, you want enough pipe penetration in the socket to get stability and maintain alignment, which is probably about 1/2 to 2/3 of the socket length.
The minimum allows for expansion of the pipe from the weld point to the socket end.
RE: socket weld maximum gap
RE: socket weld maximum gap
Thanks
RE: socket weld maximum gap
RE: socket weld maximum gap
His response was that as long as the length of pipe inserted into the socket was sufficient to prevent the fillet weld from burning through, it was acceptable.
Good, bad, indifferent, or ugly, that was the response.
Best regards - Al
RE: socket weld maximum gap
RE: socket weld maximum gap
Be prudent.
RE: socket weld maximum gap
Best regards - Al
RE: socket weld maximum gap
BOYWELD
RE: socket weld maximum gap
These types of welds are not generally x-rayed. They are either checked with dye-penetrant or magna-flux.
RE: socket weld maximum gap
RE: socket weld maximum gap
Some Owners and Engineers require random radiography of a percentage of socket welds to confirm the minimum gap. A single shot is used for verification. Some demand that the gap between the pipe and coupling shoulder be measured and be not be less than 1/16"; some demand that a gap simply be detectable. If the pipe end is observed to be in contact with the shoulder or the gap is less than that permitted by the Owners' specifications, the weld is considered defective and must be removed and the joint remade. These requirements are beyond those of the ASME B31 Piping Codes.
RE: socket weld maximum gap
It always makes me scratch my head when owners spec this stuff, though, as code specifies a minimum BEFORE welding and no minimum after welding. Given the limited size range of SW, doing RT on these joints is silly in my opinion.
The maximum gap after welding is a total judgment call. If turbulence, dirt, debris, crevice corrosion or a need for true free-draining are valid concerns for small lines in a particular service, you shouldn't be using socket welding.
RE: socket weld maximum gap
Our requirements based on experience are one wall thickness for both the minimum and maximum with a two pass weld.
Our requirements are based on the fact that one cup of heat transfer fluid vaporized, or ignitied can level a large building. With the majority of our system being in a building with people and essentially a confined space where have required 100% RT since 1990.
Based on a incident where we vented 22 gals of medium as a vapor due to a bad weld we went back and did 100% RT on every weld in each system in a 18 month long project. I forget the total number of welds but I remember that we made about 200 repairs and re-piped 4 systems.
RE: socket weld maximum gap
RE: socket weld maximum gap
Another reason for the 100% inspection was that two independent experts on explosions and detonations concluded that we sitting on a time bomb as the majority of our piping was in confined space. Therminol and Dowtherm will detonate at 927F and there is the big possibilty of BLEV. Then alone cam OSHA and lower the limit of Therminol vapor release to about 1 tablespoon full. Also during this peroid we have the big leak leak mention in the last post, Fortunately this was before the lowering release limits. Another problem we encounter was welder apathy, they either didn't like making socket welds or just couldn't.
Normally Leaks caused by porosity are small enough to be penned shut.
Our process areas are very confined spaces with very little room to manipulate pipe, 3/4" to 2", so the use of socket welds were deemed the most expedite way to accomplish the piping installation. A secondary factor not normally considered is that during the initial construction the majority of small CS pipe was welded by acetylene torch. It was a lot quicker to make a fillet weld on a socket than using the existing electrodes or acetylene torch of the day to make a butt weld.
We look at the gap. If the pipe was cut with a pipe cutter or portaband. The portaband cut are normally the ones that caused problems as a lot of cuts are biased by as much as 1/4" so one side has the proper insertion and the other is flush with the end of the fitting. We require that the inside edge of the fitting and the pipe be fused, no bridging of the fillet weld. No discernible porosity. Two passes on the fillet weld. Fitters using the fitting as a crutch, no insertion of the pipe in the fitting.
We have both a primary vapor heating system system, 70 psig and 650F, and a secondary system, 30 psig @ 600F. Each line has 6 reboilers that are feed primary system condensate and the primary vapor is used as the heating media to make the secondary vapor use to heat our process vesssels. We only use the latent heat of vaporization of the heating media.
RE: socket weld maximum gap
The proper pipe insertion will keep weld stresses down but its a matter of degrees. I looked at this a few years ago and its not linear. As the insertion gets really poor, weld quality will be impacted. I remember reading work done as part of an EPRI effort that showed really poor insertion would result in sugaring at the ID.
RE: socket weld maximum gap
Preferred gap/withdrawl is 1/8" to 3/16", because weld shrinkage will decrease the final gap. If a 1.5mm / 1/16" gap is used, X-ray will seldom show a remaining gap. Minimum insertion was 2 x wall thickness of pipe.