I'm only guessing but I would imagine you are using a much heavier walled pipe in the boiler room thus mitigating arc burns as a major factor. On a pipeline, the energy companies use the thinest pipe possible to save money on material costs. It also makes the welding quicker since there is less bevel to fill up an therefore greatly reduces labor costs. That having been said, there is little room for error in the quality. The one I'm on now X-rays every single joint and has a very low defect tolerance. A strict application of the API 1104.
Boiler tubes are very thin! This enhances heat transfer. Scrappy will have to help my bad memory on this but on the power boilers I used to run (never welded on) two of them had tubes of about 0.125" and the third one's tubes were about 0.090". Give me a little leeway on the dimensions as it has been 6 years since I left that PowerHouse.
For those that have never seen the inside of boiler these tubes are virtually side by side and next to the wall.
Griff
we do alot of heavy wall tubes .250", but the waterwalls where I work are .140" wall thicknest down to .040" with the scale on the inside. Try putting a padweld on that thin crap, needleast to say it sucks. We do have on one unit a main steam header in the penthouse with a 7" wall thickness. We shoot to B3.3 Boiler and Pressure Vessels code. Yes the tubes are max. 2" edge to edge, but usally there is a 1/2" membrane in between the tubes, can be side by side(no space) have to wedge them apart to weld.
Thanks for the additional info.
Griff
I believe it was John Wright wrote about a demonstration he has performed for his welders to show the affects of an arc strike.
He described dragging the electrode over the surface of a plate and then bending the plate so that the arc strikes are within the bend radius and subjected to the tensile loads. The results are typically cracks due to the microstructure resulting from the arc strike. I tried the experiment and it worked as predicted.
As Metarinka stated, the rapid cooling of the metal melted by the momentary arc results in a hardened heat affected zone under the visible arc strike. The higher the strength of the steel alloy, i.e., higher carbon equivalency due to alloy additions, the sensitive the HAZ to the hardening effects of the rapid cooling.
In the early days of pipelining the steels used were essentially low carbon steels. As such, the materials did not develop the very hard heat affected zones under the arc strikes such as we experience with today's high strength, high performance steels. The newer line pipe materials, having higher carbon equivalencies are also more susceptible to delayed hydrogen cracking, thus low hydrogen electrodes that have been properly stored are required.
The Navy requires the arc strike and the adjacent HAZ to be ground out and blended. If the the carbon content is above a certain threshold, the blemish has to be etched with acid to ensure the HAZ is completely removed.
Times and technology are changing. We in the welding industry have to keep up with technology. We need to be aware of how our daily practices may have unexpected consequences. It is better hear about and learn about the possible consequences here in the Forum than on the job site. Welcome to the School of Hard Knocks were we learn from each other's mistakes. Hopefully, we won't repeat them.
My apologies if it wasn't JW that told us about the demonstration I mentioned in the first sentence.
Best regards - Al
Al,
That demo is pictured, and post you speak of, in the thread that I cut and pasted in my post above. It was what I pictured in my mind when this subject came up again..... a very vivid image - one I'll probably never forget. I think it will make a believer out of you.
To save some searching for anyone looking for it. LOOK UP. :)
Jenn
Thanks Jenn;
That is the thread I had in mind.
Best regards - Al
1/32" huh OK I'm revising my standards arc strikes are now allowable. Just not very big ones, I love it. That will be right up there with "allowable porosity" I get into it all the time with welders who actually are somewhat versed in the code(s). But a certain amount of porosity is allowable, and yes it is. . . . . but not according to my companies standards. We are instructed to not allow any, period. And I agree with that because you never know how deep it can be.
Let me give a little background. I have both inspected and welded a few boiler tubes. And though there is a considerable skill involved, the margin of safety built into a tube is probably much greater than that of a pipeline. I do not have any idea what pressure they operate under but a 42" diameter pipe with a 3/8" wall would have the same unit stress as a 2 1/2" od boiler tube with a .015" wall thickness given the same internal pressure. Leave an arc strike on THAT ! I am not sure if the formula is the same for small heavy wall pipes as it is for large thin wall so I may be way off.
If the above is true, an arc strike or any discontinuity for that matter could have a far more serious impact on the large diameter pipe in comparison to the small tube.
Its my opinion that you REALLY have to do something bad to make a waterwall tube fail because of a circumferential butt weld. I have cut out a few waterwall tubes and even SH tubes with 30% of the joint penetrated and the rest unwelded.
I have no pipeline experience at all but would love to get some. If one ever comes through Northeast Mississippi, let me know. I may make a decent helper.
"I may make a decent helper."
Smarta**!! LOL :-)
None the less, a good post.
jrw159
I was kinda serious. The pipeline industry is something I have never worked in. I have put up structural steel (for boilers), welded tubes and pipes in various settings, nuc work, fab shops for structural, fab boiler parts, fab pressure vessels, fab heat exchangers, chemical plants, food plants, gas turbine rebuilds, blah blah blah
Much of that experience is probably much different than pipeline work (im guessing). Without seeing what goes on and how things work, I would be feel awkward saying I would like to "go try pipeline welding to see what its like" without clarifying that I would start at a position that reflects my abilities. I would feel like making light of the special skills needed by welders and fitters in that industry. I am pretty sure with all of my experience, I would be of fairly low value as a helper which I am sure has a special set of skills and knowledge that makes "good ones" and "bad ones".
I am pretty sure I could pick it up. Of course those times welding tubes when I looked like Darth Vader with a 3/32" 7018 light saber swinging around would have to be overcome.
Thanks for the reponse though !
Pipewelder,
I am quite sure you would pick it up quickly. :-) I would venture to say you would be a helper for a very SHORT period of time, unless that was where you wanted to stay.
jrw159