Twice recently I have come across fabricated storage tanks where I felt there was excessive weld distortion on the vertical seams.
One tank was 30 ft dia, the other was 16 ft dia, both with 1/4" wall. In both cases, the drawing called for complete penetration weld with a bevel (one was 45 degrees, the other was 60 degrees) on the outside, followed by backgouging and welding the inside. The finished weld was around 3/4" wide on the outside.
The tanks are mild steel. One was welded using 7018 rods, the other was made 20 years ago so I have no idea what was used.
At most of the seams, the weld pulled in, in some cases up to 1".
Am I correct in assuming that a good welder should be able to make these welds without this distortion. Is the problem with the type of weld
or is it lack of skill on the part of the welders? Or am I being too picky.
Any comments would be appreciated.
There are things that can be done to reduce distortion on tank seams. Usually careful joint prep, avoiding wide weaves on welding, and weld sequencing help. But many things can go astray too. Sometimes the pre-bend of the shell ends wasn't right. Or the fit-up wasn't what was intended, leaving the welder with a wide gap to fill. Or the fit-up was too tight, limiting 1st pass penetration and requiring deeper back grinding to compensate. It can make a difference whether the inside or outside was welded first. And 1/4" thick material will distort a lot.
It sounds like the outside was welded last with a wide weave but the welder may not have had control over the situation. And somebody rightly or wrongly must have accepted it at some point. Although the seam could have been pressed out, either somebody didn't know how or may have felt the additional cost wasn't worth it. But it isn't necessarily the welder's fault.
CHGuilford
I wasn't necessarily trying to blame the welder. What I want to know is if the distortion on the weld seams is in the order of 1/2" to 1", am I justified in telling the fabricator that this is not a good quallity product, and that with proper procedures/fit-up/welding/post weld straightening etc, a skilled fabricator could have producted a tank with minimal distortion on the vertical seams.
Let me clarify my answer with some backround. I am an Owner, a Welder, a Purchaser of weldments, my own Inspector and I write most of my own procedures with input from engineers. With that said I would like to ask you is the tank functional? Will it perform its required duties? Will it or does it pass all tests? Including visual? How is the procedure written? Is there an allowance for distortion? How is the contract written? You are asking whether or not to reject this weldment, that is a very difficult decision without answers to the above questions. However, you are correct in your assessment that with proper procedures this could have been avoided. But, does that mean that the tank will not perform its required duties?? You may be in a bind if the contract has no reference to distortion and the tank is still functional. Perhaps if this is the case, you can negotiate a better price.
Respectfully,
Mike Sherman
Shermans Welding
I am asking the question more for future guidance. One tank was supposed to be fabricated according to API 650, which it did not meet due the weld distortion and a number of other reasons. After several reworks, it was eventually accepted with some weld distortion remaining in the vertical seams. The other silo is 20 years old, and obviously has been functioning satisfactorly.
After seeing what I felt was excessive distortion twice in a short period of time, I started wondering if my expectations were maybe too high
I don't believe your expectations are too high. Anyone paying for something should be able to get exactly what they order. This could be viewed as a lesson in how to write a contract to get "exactly" what you want though. Good luck in the future.
Respectfully,
Mike Sherman
Shermans Welding
H. Dibben, weld distortion is the curse of all weldments. When a weld is made mostly from one side, you will almost always have distortion. A better way to weld this would have been to bevel both sides and either weld both sides simultaneously or jump from side to side (perhaps impractical when welding a tank). This requires less filler metal than a single bevel. Strongbacks are often used as is post heating with a rosebud to keep things in line, you can also prebend the steel in the opposite direction before welding. Sometimes the skill or lack thereof on the welders part will cause an excessive amount of distortion but welders are usually not in charge, if a good and knowledgeable welder were allowed to make his own decisions you are correct that it probably would not have as much distortion but, someone else has usually chosen the procedure for them. Whether or not you are too picky depends on what the owner or contractor of the tank wants. If the tank is functional and passes all testing than I would accept it. I personally would blame the procedure and whoever developed it.
Respectfully,
Mike Sherman
Shermans Welding
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