Inspection Criteria for Welding Arc Burns

There are a lot of codes that had its "Welding Discontinuities and Acceptance Criteria", that differ from code to another, such as ASME, AWS, BS, .... etc.

For ASME BPVC : the acceptance criteria is ASME Section IX, in addition to the mandatories of the fellow code of pipe or vessel.

For AWS : the acceptance criteria is AWS D1.1, AWS B1.10, AWS B1.11, AWS B2.1, ... etc.

1^st I recommend that you have to define the job activity and the code which you like to fellow, then look for its welding discontinuities and acceptance criteria.

Arc burns (or) stray arcs on carbon steel pipes occurs due to negligence on the part of the welder either due to dragging a electrode / holder with live cable connections (or) poorly insulated cables on the pipe surface and are generally not allowed as they do not deposit any significant weld metal and may have an effect as severe as a notched brittle weld, more so when the steel is high tensile grade and my record as service failures.

Due to sudden raise in heat input and instant cooling factors, they may form hard zones (depending upon the carbon and alloy contents in the pipe materials) and may turn into stress raisers.

They may in the future course may form starting points for corrosion depending upon the project ( say petro chemical , fertilizer, thermal stations etc ) sites.

Hence they are considered as dangerous and completely removed. Voids are filled up by welding using preheating if necessary. Light fillet welds and thin single pass welds in heavy plates must also be discouraged unless adequate pre –heat is used.

Use of low hydrogen electrodes with proper moisture control for above has distinct advantages from view point of avoiding brittle failures .

No code gives allowable limit for stray arcs for its depth or width.

Sridhar – Welding Technology & training Centre – Chennai / India.

How can we positively convince Plant Owners that arc burns cause stress risers, hence cracks, and are very detrimental to the lfe of the affected component?

This is a very hot topic all of the time and especially so now with RBI and Plant and Pipeline Failures here in US.

Thanks for the post, we are thinking along the same line.

There is plenty to say about the subject, but limiting to certain factors given below..

As mentioned earlier, the stray arcs are momentary , localized hardness zones (or) starting points for cracking. They will open out to form small cracks or holes when guide bend tested. It is attributed to formation of unbalanced thermal stresses and forming of marten site zones.

Hot or cold cracks occur due to ductility of the steel is not sufficient to with stand localized stresses without fracturing.

In the case of stray arcs, it is possible that that stresses are of lesser magnitude, insufficient to cause Instantaneous failures , but may generate minute cracks in the

(depending upon many factors including alloy content, thickness, environmental conditions etc.,) arc strike zone , allow it enlarge, spread gradually cause the weld structure to fail subsequently in service.

That is why it has becomes neglected topic / subject, but opens out only at the time of

(after a gap of few years) catastrophic service failures and too after the guarantee period of the fabrication is over.

Due to this complex thermal cycle ( sudden heating followed by rapid cooling), in which all temperatures from melting range of the steel to mere warming are involved may influence the grain to enlarge and form coarse grain ( from micro) structure and can readily transform to brittle martensite, which is most potentially dangerous area. Many failures have originated in Welds / HAZ at points of geometrical discontinuity.

These stress raisers, when exposed to corrosive attacking compounds – interaction of water th' moisture in the air and sulphur (hydrogen sulphide) and phosphor (phosphoric acid) and become more concentrated or temperatures increases (thermal stations) may develop cracks due to (a) residual stresses at the weld, (b) hard micro structures both in the weld and HAZ of ferritic steels, (c) thorough any corrodent like hydrogen sulphide.

We do not say that all the arc strikes ( a part of weld defects) are very detrimental to the life of the affected component but since no chances are to be taken during service, we expect to take maximum possible precautions during welding / fabrication and to give a longer service life for the pipes and vessels.

sridhar.

Go to this site and join the group. http://www.aws.org/w/a/

dear sir,

please send to me arc strike size.