Welder qualification for 8ft penstock

[ingsergiogarro]

Good morning.

We are welding 8ft diameter penstocks, 1-7/16" thick, with SMAW, in a 35° slope. We have K-type bevels so we have to weld externally and internally.

Our inspector is requesting 6g certified welders, but we have only 4g welders.

Does a 3g and 4g welder are certified to weld this pipe diameter, with this conditions? taking into account that it is a big diameter and I think that is more similar to a plate that to small diameter pipes that are used for 6g qualifications. How can I support this argument?

really appreciate your help.

Thanks

 

[ColonelSanders83]

What is your code of construction?

My experience has been in AWS D1.1 and ASME section IX codes.

If either of these codes apply, on this matter I would side with your inspector. Although I can see your argument and why you are making it, A 3G and 4G weld qualification is not representative of a 6G Pipe weld (your weld is much closer to 6G than 3G and 4G).

The reason for performin a weld in the 6G position (45 Deg incline) is to ensure your welders are capable of controlling thier weld in all positions. There is no allowed equivalent to a 6G weld in the codes I am familiar with.

Just my two cents worth.

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.ap-dynamics.ab.ca/

 

[qcrobert]

We have always been required to have 6G certs for Penstock piping, in my experience in dam building.

 

[qcrobert]

Spec per Corps of Engineers in contract that is....

 

[racookpe1978]

Physically, what position is your welding actually being being done?

That is, are you welding down-hand across the lower arc of the penstock, rotating the penstock so the inside weld is always "down"? Are you welding the outside weld from "above" (from outside the pipe) as the penstock slowly or incrementally rotated below the welder?

If your welding position is not "up and around a stationary pipe" then you only need the "flat plate" (or vertical plate) welding positions. The diameter is so large and so thick-walled that "thin-walled, round pipe" (compare your situation to a 2 inch diameter, 1/4 to 5/8 thick pipe!) all-position pipe welding certification comparisons are irrelevant. But weld position is critical.

 

[ingsergiogarro]

Thanks for your opinions. Here are your answers:

ColonelSanders: You´re right, we are regulated here with AWS D1.1 and ASME section IX codes. I have both right here.

Racookpe79: The penstock is already on its field final position when have to weld it, so we cannot rotate it. The penstock is completely stationary. The welder has to move around the pipe using scaffolds. The pipe has a 35° slope, cause it is the final drop to the Power House. But as you indicate, that is my question, the diameter is so large and the wall so thick that i don´t think a 6g qualification meets the actual welding conditions on the field. Starting with that I would have to qualify our welders in 6g with a pipe that has to have a minimum of 3/4" of thickness, like a schedule 160 to meet the maximum thickness of 1-7/16" that we have to weld here in the project.

 

[ColonelSanders83]

From the look of it it appears you need both procedure and welder qualifications for these welds. This is not the end of the world.

First look at your welding process and determing the thickness range you qualify for.

Once you have that piece of information select out a piece of pipe with wall thickness inside that range, chances are 24" SCH 80 (1.219" wall) should be a good place to start. The wall thickness is quite representative of what you are welding and should fall within the required thickness qualification range (confirm this with the code, I don't know your exact conditions, materials, or weld process). The diameter is selected to give you substatial internal and external access for welding. I would confrm these selections witht the welding crew you plan to use and see if they have any comments befoer proceeding with your qualifications. If you have a labor pool of skilled welders none of this should pose any problems.

Keep in mind the ultimate purpose of a 6G test is to ensure your welders are capable of controlling the weld puddle and obtain appropriate weld strenth under flat, vertical, and overhead welding positions while the material itself is sloped (i.e the weld puddle wants to ESCAPE in two planes instead of only one.

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.ap-dynamics.ab.ca/

 

[Kiwi2671]

ingsergiogarro,
Plate qualification is fine for what you need - 3G and 4G covers you for all positions to both ASME IX and AWS D1.1.
ASME IX QW 461.9 - 3G & 4G plate qualifies you for Flat, Vertical and Overhead on Plate and Pipe over 24".
AWS D1.1 Table 9 - 3G and 4G plate qualifies you for all positions on Plate and Pipe over 24".
ASME IX QW 452.1(b) - qualify on 1/2" and over with a minimum of 3 layers and you are qualified "Maximum to be welded."
AWS D1.1 Table 10 - qualify on 1" plate and it qualifies you for Unlimited Thickness.

If you have to qualify procedures it is a whole different ballgame but to qualify your welders it is pretty basic,
Regards,
Kiwi

 

[ingsergiogarro]

Thank you all for your precious points of view.

The solution was right there on qw461.9!...


“Engineers like to solve problems. If there are no problems handily available, they will create their own problems.” Scott Adams

 

[racookpe1978]

Definitely. As noted above ... "Keep in mind the ultimate purpose of a 6G test is to ensure your welders are capable of controlling the weld puddle and obtain appropriate weld strenth under flat, vertical, and overhead welding positions while the material itself is sloped (i.e the weld puddle wants to ESCAPE in two planes instead of only one."

If your pipe is sloped at 35 degrees, and it's fixed in place, my "approximations" of a flat plate are not good enough. The 6G test (sloped 45 degrees, all around/all position welding) is proper.

The best answer is what you found above in the last few replies.

 

[ingsergiogarro]

Ok. I indicated the inspector that with 3G and 4G welder qualifications we´re fine and ready to go. But now he's asking why there are 6G qualifications for pipes over 24in of diameter on table QW461.9?.

Let me see if I can explaing myself. He's asking if there's a diameter limit in which over that certain diameter the pipe is taken as a plate and the qualification can be made on a plate. And under this certain diameter the 6G qualification must be made.

It is a very difficult inspector. He wants me to certify all the welders in 6G, taking the test on a pipe, not on a plate. The issue here is that it must be a pipe big enough that allows to weld inside the pipe and the thickness must be at least 3/4", to meet the maximum thickness of 1-1/16" that we have on field. And then cut the specimens and run the bend tests.

Help anyone! thanks

 

[ColonelSanders83]

1) 3G and 4G are not enough, to qualify for the "All" position criteria for pipe over 24" your welders need to be 2G, 3G, and 4G qualified.

2) The dual listing requirement are such that multiple qualifications are not neccessary. The intent is to qualitfy on what you plan to be welding. In my case we only ever weld pressure piping, consequently I would qualify my procedure and welders in the 6G position on a Pipe coupon. Per code this gets me qualified for all. In your case you qualify for "all" position pipe welding in diameters over 24" if you have 2G,3G,and 4G position qualifications.

3) The reasong why mutliple qualification are allowed is not within you inspectors realm of authority, his job is to determine whether or not your work qualifications meet the requirments. Other allowance are not material to the conversation. If everyone agrees 2G,3G and 4G is code compliant then thats that.

Just my two cents worth.

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.ap-dynamics.ab.ca/

 

[ingsergiogarro]

Thank you ColonelSanders83!

Much clearer now.

Have a good day!