I have encountered a recurring event among some welders. It seems that after completing the 2nd pass on ss pipe they have burned through the first pass . I have rejected 100% of these welds stating that the technique needs to improve for subsecuent passes, due to basicly weld burn through. This is my basis, and also, since the acceptance criteria doesn't address this issue especificly I automatically assume that it is not accepted.
These welds are recurring in smaller Diameter pipes (i.e. 1/2" 3/4") ...
Has anyone tackled this in any other way (has any accepted these welds and why).
Regards
Raul Vidal
Raul:
1.) If the code, standard or specification does not address the issue how can you reject it?
2.) When you do reject and document this condition, what do you use as acceptance criteria?
If this is pipe and not tubing, many pipe welders run their second pass as the "hot pass" to ensure CJP at the root. Most seasoned welders can accomplish this with just enough internal reinforcement to satisfy code requirements. Thats why their pipe welders. Most are very good at their trade.
Unless your engineer has a problem with the internal reinforcement...
Raul,
I agree with what DGXL has stated, if the code doesn't address it you cannot automatically reject it.Have you got the correct code for the application you are using.?
A common problem with s/s welding is that some people assume that once the root run is completed purge gas is no longer required. If the second run is welded hot (hot pass) with no purge gas there is a possibility of "burn through" which will cause oxidation if oxygen has managed to enter pipe.If purge gas is still being applied while hot pass is being run it is acceptable to "melt" the root run as long as internal protusion does not exceed code requirements.
Hope this helps,
Regards,
Shane Feder
Everyone , great feed back:
Shane,
1-Doesn't burn through affect the mechanical properties(soundness) of each weld , and subsequently the weldment?
2- Doesn't it also reflect excess heat input, or too slow of a travel speed? (heat input = a great concern )
3- So if there isn't a specificification on the contract document addressing this issue that I have, your basicly telling to me that the weld is acceptable and to disregard #1 and #2 above?
4- shane, you mentioned "If purge gas is still being applied....it is acceptable to "melt" the root run ..." Where can I find this basis that it is correct. Could you point out to me the code where this is in? I would appreciate it.
PD - after going through the visual inspection workshops ( hands on) and a review . There is not a "scale" visually or written on what is an acceptable burn through on a weld. extent nor width.
More feed back please =)
Thanks
raul
As someone above stated, if the visual acceptance criteria is silent on this topic you should not reject the weld.
As for the mechanical properties of the weld being adversely effected due to burn through, I have never heard any technical commentary on that (other than excess burn through). The heat input argument is also not valid. Heat input is calculated based on a formula that takes into consideration current voltage and travel speed. It doesn't address burn through (which could be the result of a relatively thin root pass).
Your third comment implies there is an obligation to consider 1 & 2 in spite of the fact that the acceptance criteria does not address them. I think a more reasonable approach is to apply the acceptance criteria as it is. If you have a concern, address it in a request for information to the client or your own engineering department.
We have found that when backing gas is not used on the hot pass the biggest potential problem is oxidation, not burn through.
Charles
Charles,
My apologies, we have different terminology in this "neck of the woods".
My interpretation of "burn through" is when the "hot pass" actually changes the physical appearance of the root run by melting and blending it.
We have a term called "blow through" which is generally used to describe a hole blown through the root run from excessive heat/excessive grinding etc.This can lead to excess penetration if it happens on the top half of the pipe or a blow through cavity if happening on the underside of pipe.
Not sure which one of these Raul is meaning but I agree with all your remarks.
Regards
Shane Feder
1- I was under the impression that the first pass was to ensure CJP. and thats why it is considered a hold point in most inspection programs, and welder qualification ( to ensure (s)he has the proper technique).
"if and only if" IJP is allowed to a tolerance (CD, acceptance criteria,code) it is the only way that I understand that a welder qualifies with an IJP on the first pass.
2 - Is there anywhere written that Burn through can be a means of completing an IJP to a CJP?
3 - If it takes a welder 2 passes (the second one a "hot-pass) to ensure CJP, there is a problem then with the technique, or the variables are not set accordingly.
please tell me what code or standard I need to attain. Because I would like to enhance my ability to address specifically this issue.
Gracias
Raul
I have experience some "melt-thru" as I like to call it where the cap on a stainless steel pipe weld and have never had a rejection (per ASME B.31.1 or B.31.3 code) with either a visual or an x-ray. I would think that you would have to use 1/16" for the cap to avoid this condition. Mostly this (condition) occurs with a fusion root where little (if any) wire is added to the root pass. In an open root procedure, I have personally never had this happen.
I have been a pipe welder for over 20 years. I work alot in the bio-tech and pharmasuedical industry where ss tubing is welded with the automatic orbital machine. I was told by an outside CWI that (say an oversized tack) which has been fused, but not necessarily consumed is acceptible as long as it is not contaminated. This is per BPE code which governs that industry.
Because the heat transfer is so rapid (in smallish bore piping) it would be difficult to eliminate this condition altogether and maybe you should consider the logic used in rejecting welds with this phenomenom.
As I said, if open root is the procedure then "it" can be avoided, but if fusion roots are allowed, then so should this (melt-thru).
Just my opinion, for what it's worth.
Raul:
I am NOT being disrespectful here with this reply.
You are not that familiar with pipe welding?
What do you note in your report as the rejection criteria?
Where does your criteria mention the root pass reinforcement must be performed on the 1st pass?
Many welders deposit a small root pass bead and burn it in on the second pass. I do this regularly and not just with GTAW and teach those who cannot run their 1st pass w/out achieving the required reinforcement. This technique is very common in pipe welding and other industries. It does not mean "... the variables are not set accordingly" simply due to you have never seen this technique used.
I noted in the other forum I recently qualified numerous AWS D1.2 aluminum WPS's. I used this techique on 1 WPS with GMAW on the second pass to achieve CJP on an open root butt joint. The root reinforcement is very nice & uniform. I need to get some fotos before the parts go out the door.
Again, not being disrespectful, but all of your concerns appear to be speculative only.
I beleive no one has been disrespectful...thank you very much for the replies. this is a great forum.
I have learned plenty today!
just trying to get better!
again, thank you
Raul
By -
Date 03-18-2005 17:03
Raul,
I know of no code book that states "burn through" is an unaceptable condition. If it is no repaired and leaves code non-compliance results, then you have a problem. Liquation, or re-melting of a previous weld pass, on thin walled stainless steel is not really uncommon, but it is easily repairable. An experienced welder can have a burn through, but he will know how to repair it and go on to finish the weld and have acceptable properties and corrosion resistance. A burn through is a discontinuity if repaired correctly. A burn through is a defect if not repaired properly. To reject a weld solely because a welder had a burn through is being a little too strict. Regardless of the welding process, small diameter stainless isn't the easiest thing to weld on. If I were you, I'd more concerned in his ability to correctly fix the burn through than reject his weld strictly because he did have a burn through.
