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Un undercut having depth 0.8mm is identified at all the long of a butt weld at the toe. Is it acceptable per ASME VIII Div 1?

RE: Undercut

See UW-35
undercut: a groove melted into the base metal adjacent to
the weld toe or weld root and left unfilled by weld metal.


RE: Undercut

The answer is dependent upon your inspection method, application and to an extent, its length.

The requirements of UW-35(a) and UW-51(b) shall be met except that for SA-517 material the maximum weld
reinforcement shall not exceed 10% of the plate thickness or 1/8 in. (3.0 mm), whichever is less. The edge of the weld
deposits shall merge smoothly into the base metal without undercuts or abrupt transitions; this requirement
shall apply to fillet and groove welds as well as to butt welds.

44-6.1 WELDING AND EXAMINATION (a) For all Category A joints, the reinforcement shall not
exceed 10% of the plate thickness or 0.125 in. (3 mm), whichever is less. The weld deposits shall blend smoothly
into the base metal without undercut or abrupt transition. All attachment welds shall be continuous and have a
smooth contour with no undercut permitted.

RE: Undercut

This case is for carbon steel sa516gr70 pressure vessel nominal thickness of shell 20mm

RE: Undercut

Yes it is acceptable for most applications of Section VIII, Div 1 butt welds.

RE: Undercut

1/32" (1mm) maximum - UW-35(b)

Interpretation: VIII-1-86-217
Subject: Section VIII, Division 1, UW-35
Date Issued: February 18, 1988
File: BC88-029

Question: Is "reduction in thickness due to the welding process" as used in UW-35(b) synonymous with the term "undercut"?

Reply: Yes; see UW-35(b)(1) and (2) for the tolerances.

RE: Undercut

Thank you all.

RE: Undercut

For undercuts the inspection is VISUAL.


RE: Undercut

if undercut having depth 0.8mm is identified at all the long of a butt weld at the toe, hence the welding process should be investigated.

RE: Undercut


The weld having that undercut is acceptable by visual as per Code. Why should the welding process be investigated?

RE: Undercut

As UW-35 say .."A reduction in thickness due to the welding process is acceptable provided all of the following conditions are met:…..”., hence your welding process should be investigate to reduce all imperfections.
UW-35 nothing say about the extension of undercuts. In your case “…at all the long of a butt weld at the toe”
is excessive.
The undercut 0,8 mm ( imperfection, not repair needed ) is in the limit of tolerance, almost a defect (imperfection not allowed and need repair)
Undercut, either continuous or intermittent should be minimized
Undercut serves no useful purpose. Therefore, no reasonable effort should be spared to eliminate it or at least minimize it.
Undercut are usually caused by the welding technique used during welding, incorrect electrode positioning and/or incorrect travel speed. High currents and a long arc length can increase the probability for undercut.

See more in THE PROCEDURE HANDBOOK OF ARC WELDING, The Lincoln Electric Company.


RE: Undercut

UW-35 and the interpretation forwarded by David confirm that Code accepts the undercut regardless of its length provided the depth is less than 1mm or 10%.
Since the purpose of the Code is safety, Comity should know that this defect is not harmful to the pv integrity before issuing the above interpretation.
I agree that it seams strange by experience.

RE: Undercut

Firstly - what are you measuring undercut with ?
The difference between 0.8 mm (acceptable) and 1.1 mm (not acceptable) is miniscule.
Secondly - a good weld should have zero undercut.
If you have undercut for 100% then you have problems with your parameters (not your process).

I have not mentioned manipulation of the electrode by the welder as you must be welding with a robotic process.
Otherwise, it is impossible to get 0.8 mm undercut over 100% of the weld with manual or semi-automatic welding.

RE: Undercut

The undercut is identified all the long of the weld but with maximum depth 0.8mm measured by weld gauge and strip standard gap gauge.

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