Welded pipe seams in orientation

[LittleInch]

I've seen since I started in pipeline engineering some decades ago (cough), a requirement in construction specifications to avoid lining up the weld seams and offsetting them by a certain amount (this varies but is typically min 100mm or 10 degrees). My understanding of this has been that when seamed pipes were first mass produced, a number of weld seam failures occurred and the thought was that you didn't want to line up welds exactly to prevent long running fractures.

Now I have a situation where for a number of reasons I might not be able to do this and some occasions where the weld seam could align or be very close to alignment.

So the question is:

Given modern welded pipe production, is this still a valid concern?
Is the non line up just a preferred action or "mandatory"?
Have there been any failures where lining up the weld seams on adjacent pipes caused an issue / more damage
Is this requirement now out of data and just a hang up from the past?

This is for a liquid pipe at about 60C so I don't have the same running fracture properties you have with gas.
Design code ASME B 31.4
Pipe is 18" 5L X65 with wall thicknesses between 8 to 15mm

Your thoughts, links and past experience would be helpful.
I'm going to ask materials engineers, but they always tend to be a bit conservative and like I said at the start, this requirement has been around for a long time so maybe no one has really questioned it properly.

Thanks

LI


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[Dhurjati Sen]

Dear LittleInch,

Shell DEP says the following:

"Longitudinal welds in two adjacent pipes should be 180° apart, but in any case shall be
separated by at least twice the wall thickness of the thicker pipe. When pneumatice leak
test in accordance with ASME B31.3, para. 345.4 is performed in lieu of hydrostatic leak
test, the minimum spacing of the longitudinal welds SHALL [PS] be followed.
If the pipe contains a longitudinal weld, this weld SHALL [PS] not be located at the bottom
of the pipe after installation; it should be located at least 45° from the bottom of the pipe."

PS is process safety.

The weld seams and the circumferential weld together act as a notch and we do not want stress raisers in the system.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[LittleInch]

Thanks.

This is my point - It appears in a number of company practices and specs, but it not clear why and whether in modern manufacture it still applies.

I don't really follow your notch comment. There shouldn't be a notch.

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Also: If you get a response it's polite to respond to it.

 

[weldstan]

The notch is a metallurgical notch due to the differences in strength, hardness and toughness of the base metal, HAZ and weld metal. Not all pipe is manufactured to the same standards by each Manufacturer. With proper specification requirements by the Purchaser and inspections thereto, I would not have a problem with some joints aligning in a liquid containing pipeline operating at temperatures as you described.

Many of the Owner specifications like those of Shell have not much changed during the past 40 plus years. Some have and reference API Recommended Practices, which have incorporated many of the Exxon, Shell, Chevron and other Owner requirements.

 

[EdStainless]

LI, Where are you guys buying pipe these days?
I have seen some stuff recently that would have gotten you kicked off of an AVL 20 years ago.
The worst case is when the welds 'almost' align. Then you get the highest strength location of one piece lining up with the lowest strength location of the next one. This is fine until something begins to yield.
A separation is best practice.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[brimmer]

It's listed in the code: AWS D1.1 Structural Welding Code- Steel, 5.22.3.1 Girth Weld Alignment (Tubular), as 90 degrees as standard, which may be the basis for it and people doing it? As for why, your reasoning is the only rationale I've heard for this,to stop very long fractures in brittle, low toughness longseams of the past, to stop the hundreds of feet rupture scenario. At your temperatures I'm not sure this would be a concern. In transmission pipelines today there can be other reasoning to stagger seams related to maintenance etc., such as in ILI tools staggering seems makes it easier to tell what joint you're on when excavating rather than having them all at the same position. Other reasons I've seen for longseam placement, at the top for example, again for ease of finding your targeted joint when exposing, or even related to what type of coating was used (tapes the seams would always be between 10:00 & 2:00).

 

[LittleInch]

Thanks for the response - Just as I asked the question I ended up on a loooong trip without time to respond.

I agree it is generally good practice, but was trying to find out if, for whatever reason, I had to align two seams either exactly or within a few mm whether pipe made now compared to 40 years ago, this is an issue or not.

The message I'm getting is one of the extra hardness / toughness of the weld / HAZ, but is this an issue?

It would be only the odd couple of pipes in tern.

If not that then what is the min separation - I've heard 5t mentioned before now. I have some pipe which is only 8mm thick.

LI

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