How critical are full penetration butt welds in joining two pipes for low pressure systems? 1

[Headphone5]

We had a vendor construct a small 2in piping system spec'd to ASME B31.3. MAWP is 200psig.

The pieces came back and didn't have full penetration welds for joining things like elbows and T-sections. Meaning they had a solid exterior weld but on the inside you couldn't see the weld, only the seam where the two pipe sections meet. This stood out to me but I'm not an expert by any means.

ASME B31.3 seems to require full penetration. But our vendor, whose expertise we trust and have a good relationship with, says it is pretty difficult to get full penetration on sch40 2". I kind of find this hard to believe. But since we're only at 200psig I'm wondering how necessary this is.

So I guess those are my 2 questions,
1. Is full penetration overkill for 200psig?
2. Is it pretty common to forgo full penetration when trying to meet ASME B31.3?

 

[jmec87]

Review B31.3 Table 341.3.2. Some incomplete penetration may be allowed as long as the piping is not required to meet Severe Cyclic requirements.

 

[Headphone5]

Thank you,

What I'm reading there is for Girth welds in normal service incomplete penetration is acceptable as long as it less than 1.5" of the length of the weld.

These pipes don't have any complete penetration. They are nicely welded on the outside, but on the interior there is just a seam where the two pieces of pipe meet.

The interior seam looks like the below picture, although without the rust and rough edges.

 

[XL83NL]

ASME B31.3 seems to require full penetration

No it doesnt. Slip on flanges, for example, w/ fillet welding is allowed, for certain Fluid Services or situations. However, acceptance criteria for welding differ between the weld joint type. What should be a butt weld, has to be a butt weld, and cant be downgraded on a Fitness For Purpose assessment. Thats not how the Code works, regardless of the application.

As per your questions;

1. Is full penetration overkill for 200psig?

It depends on the application. Whats the medium, what temperature do you have? Etc.

2. Is it pretty common to forgo full penetration when trying to meet ASME B31.3?

forgo? I.e. go without? Full pen is pretty common for butt weld fittings. Fillet weld is pretty is pretty common for socketweld fittings. Non pean welding for butt weld fitting would be a no go for me, regardless of application. 2" 40S full pen welding isnt hard, even though Im not a welder, Ive and inspected 1000s of full pen butt weld piping welds. Not that special ...

Huub
- You never get what you expect, you only get what you inspect.

 

[Headphone5]

Gotcha, so this would be for O2 at ambient temperature.

As for the type of weld in question it is just for circumferential or girth welds connecting various butt type pipe pieces together.

But it sounds like in your experience full penetration in this situation is both common and easy to do.

 

[EdStainless]

So if you have all of these crevices how are you going to clean for oxygen service?
No, lack of pen on butt welds is clearly a no-no.
I recently inspected a SS system that was sch40 and all of the welds looked nice on the ID as well as the OD.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Headphone5]

Yeah I agree on the O2 clean.

I actually just got off the phone with our vendor (I made this post ahead of our conversation with them)
This is for a small contained piping system where each piece would 1.5 feet or less long, and their take was that with such small pieces they wouldn't be able to keep the parts concentric doing full penetration. And for the gaps affecting O2 clean, their take was that we have much bigger crevices at all of our flanged connections.

I can understand those points. Not sure how much truth there is to them, maybe people in this thread with more experience will know.

 

[1503-44]

Very creative welders. I've not heard that excuse in 50 years.

Seriously. Think about including a welding spec in your project docs.

https://www.lanl.gov/orgs/eng/engstandards/esm/welding/welding_specs/3001-1-SC Rev_2.pdf

See p21
API 1104

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[weldstan]

Your vendor is just fooling you trying to get out of remaking the pipe spools to meet the Contract and Code. As a contractor we made tens of thousands of 2" and under piping systems in the field and most required 5% RT and some 100% RT. We made repairs when required under B31.3 or cut them out and rewelded with RT and never had the incidents described by you and the balony spewed out by your vendor/contractor.

 

[GBTorpenhow]

These pipes don't have any complete penetration.

B31.3 requires full penetration for butt welded joints. It does give a certain length of incomplete penetration as an allowable level of imperfection, but the joints you describe are very much not acceptable. If your vendor is trying to argue that a butt weld without any penetration at all is even remotely OK then they are either brazenly blowing smoke or are vastly, immensely incompetent. Either way, find a new vendor ASAP.

Were these welds X-rayed? B31.3 Normal Service requires a minimum of 5% random radiographic inspection on butt welds. If they were, find a new NDE vendor, too.

 

[LittleInch]

"Not sure how much truth there is to them,"

Errrr. None is the polite reply.

Reject it all.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

For cleaning the difference is that you can clean flange faces before you make them up.
You can never clean these crevices.
Have you ever seen steel pipe burn in pure O2?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Headphone5]

Thank you for all the input, it is really helpful because these codes are not my bread and butter so I don't know how much adherence is status quo.

I'm looking at alternative vendors today.

 

[TiCl4]

Run, don't walk, away from any fabrication contractor that says it is "difficult" to get full pen on a 2" schedule 40 line.

 

[DekDee]

Agree with all the comments - especially TiCL4.
Would love to see the WPS used (or not used) for these joints.

 

[1503-44]

Ask them if they have any problems welding full pen 2"

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[r6155]

This vendor is a traitor.
You paid full penetration and you get socket weld!!!

I suggest RT of all butt welds.

Regards

 

[Headphone5]

Last question but does anyone have good resources, like a forum or what to search for, when looking for high quality small job stainless steel pipe fabricators? I think we need more than just a machine shop who also welds, we need someone who specializes in this stuff. We are west coast.

 

[1503-44]

The better pipe fabricators ones are usually found in the areas surrounding a refinery/chem plant complex.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

I know of a company in CA that welds a lot of SS pipe.
And he does good work.
You can email me at my 'posting name'atearthlinkdotnet
He is a character, but welds are great.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed