seal weld definition
seal weld definition
(OP)
An internal standard prohibits GMAW due to fear of "Short-circuiting metal transfer" GMAW-S / MIG.
GMAW is barely allowed on "seal welds."
I'm wondering if there is a definition somewhere of when a weld is a "seal weld."
Our weld prep has been defined for decades like the attached jpg. Pretty much full penetration, on a 3/8 inch thick pipe (8 to 22 inch) with design code requirements of 50 psi, or possibly even much less.
thanks
Dan T
GMAW is barely allowed on "seal welds."
I'm wondering if there is a definition somewhere of when a weld is a "seal weld."
Our weld prep has been defined for decades like the attached jpg. Pretty much full penetration, on a 3/8 inch thick pipe (8 to 22 inch) with design code requirements of 50 psi, or possibly even much less.
thanks
Dan T





RE: seal weld definition
Regards,
Mike
RE: seal weld definition
RE: seal weld definition
seal weld - any weld designed primarly to provide a specific degree of tightness against leakage.
RE: seal weld definition
And I fully concur with your "internal standard". GMAW-S is too easy for a welder to turn from a 'cold' weld into a hot braze. Nothing wrong with brazing, unless the joint was calculated to provide a weld strength, not the lower strenght of a braze. Happens way too often to allow GMAW-S on items requiring 'real' welds, not 'some weld, some braze'.
RE: seal weld definition
I may have not described our internal standard clearly. Actually it is NOT real clear, so it may be impossible to describe it clearly.
In more than one of our stds, the entire broad category of SMAW/MIG is forbidden for structural parts, engineered parts, or "pressure" containing parts.
Unfortunately, at the same time, some of the same stds say GMAW-S >>may<< be approved for "seal welds" or possibly low stress welds.
So we occasionally specifically forbid GMAW-S welds, but also forbid GMAW welds for fear they "might" be GMAW-S welds.
AWS structural codes have a bunch of prequalified structural joints that are OK for GMAW, but carry a note that not for GMAW-S. Maybe it their industry bias, but that seems to imply there are ways to avoid accidently create GMAW-S welds in production.
Our rational reportedly is, there is no on-off switch for short circuit mode. If volts or amps or whatever are cranked down a little low, the process changes to short circuit mode, and aside from the sound, there is no convenient way to know it. Google searches suggest the concern about poor fusion using GMAW-S on thick sections is not unfounded.
============================
Did you mean to refer to a P1 TO P1 weld (steel>steel with steel filler) with poor or incomplete fusion as "brazing?"
thanks
Dan T
RE: seal weld definition
The welder should be following a WPS that stipulates the welding parameters to be used. The parameters, i.e., voltage, wire feed speed, electrode extension, and shielding gas will determine the transfer mode.
The welders must be trained to work within the welding parameters listed by the WPS and it is incumbent on the individual developing the WPS to understand how to control the transfer mode via the welding parameters. There are references available to that can serve as useful aids when writing the WPS to ensure the appropriate parameters are provided to produce the desired transfer mode. AWS publishes a Recommended Practice for GMAW and many manufacturers such as Lincoln and ESAB have information available on their websites.
If the WPS is written to ensure spray or globular or pulsed transfer is used, short circuiting transfer should not be an issue if the welder is working within the permitted ranges of voltage, wire feed speed, etc. listed on the WPS. Dropping the welding parameters to the point where short circuiting transfer mode is produced indicates the welder is not following the WPS.
The fabricator/manufacturer should make a surveillance program part of any QC program to check the welding while it is in-process. The surveillance program will help to ensure the welders are following the approved WPS.
Best regards - Al
RE: seal weld definition
Dan T
RE: seal weld definition
http://www.jflf.org/pdfs/papers/design_file6.pdf
RE: seal weld definition
RE: seal weld definition
For an ASME threaded connection [NPT or similar], the seal weld cannot be counted as contributing any strength to the joint. Officially, the strength member is the threads. Same thing under AISC for structural; on a bolted plus welded connection, you can only take credit for the bolts OR the weld(s). No combinations permitted.