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Min spacing between 2 welds
4

Min spacing between 2 welds

Min spacing between 2 welds

(OP)
Hi everyone,

I have noticed that many clients ask for a min weld spacing of 1.5 - 2 time the thickness of the shell. Although ASME Sec VII Div.1 mentions about 1.5 time the thickness there is no hard and fast rule to maintain this.

Can anyone provide me and research papers or any article son why it is a good practise to maintain a min distance between two welds.

Thank You

RE: Min spacing between 2 welds

You don't want overlapping weld heat affected zones, which could effect fatigue performance in service and to avoid problems with interpretation of volumetric examination results for each weld. So, keep the welds separated by some distance.

RE: Min spacing between 2 welds

(OP)
@metengr , thanks.

I want some article/case studies which can shed some light on how interlapping HAZ can cause problem.

RE: Min spacing between 2 welds

HAZ tends to be harder than base metal. If oevlaping HAZ, it could loose some ductitivity. Hardness test is the way to check. So you try to avoid HAZ getting too close. That is only my thinking. I always keep weld toe to toe minimum 2" apart. Thay way, HAZ won't overlap. But many times, we have pads or internal support rings welded over long or girth seams. And it seems it is not a big deal. Why ?

RE: Min spacing between 2 welds

Why? Because in certain situations it is unavoidable. For pipe welds it is avoidable and should be considered based on good engineering judgment.

RE: Min spacing between 2 welds

In non-stress relieved welds, you also want to avoid the high opposed tensile stress applied to the narrow member due to weld shrinkage of the adjacent welds.

RE: Min spacing between 2 welds

(OP)
@jtseng123 thats very interesting what you have said, can you provide me more info on the hardening concept that you have explained, any articles.

RE: Min spacing between 2 welds

roystercabral,
I've been very patient (for me) for two days now. You have gotten a lot of information from VERY experienced engineers and you keep demanding documentation. My standard answer to that is "I provide references to paying clients, for free you get opinions." You've gotten opinions from folks that don't owe you anything and have given freely of their time.

You have reached a point where you should say "Thank you" (preferably with stars) and get on with your life before people start getting unpleasant.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Min spacing between 2 welds

roystercabral,
I am not a welding or material engineeer, so I have no article for your reference. The point is, you do want to keep welding zone ductile.

RE: Min spacing between 2 welds

(OP)
@zdas04 the only reason i ask for articles/papers is that i need to present this concept at my company. Since i thought there are experience people in this forum they can suggest me some papers to read. I could not find much on google, i guess my googling skills are bad.

Anyways thanks to all you guys @jtseng123, @stanweld, @metengr, @zdas04

RE: Min spacing between 2 welds

"Pressure Vessels- the ASME code simplified" authored by Robert Chuse and Stephen M. Eber,PE will give most of the answers.

RE: Min spacing between 2 welds

zdas04,
David,
I think you have been overly harsh here.
I regularly give people "a serve" on the AWS forum similar to what you have done but that is because I hate people who are to lazy to do the research themselves.
However, this is a different case - we are all in agreement that no major codes stipulate a minimum distance between welds - but why is it listed on just about every O&G specifification I have been involved with for the last 15 years ?
Where do the design engineers who write the specifications get their information from ?
Roystercabral asked that question and I will second it.
Metengr and co gave valuable replies as to why the HAZ shouldn't be too close but where is it documented in recommended piping design literature ?
Regards,
Kiwi

RE: Min spacing between 2 welds

I'd have to go digging but I think there might be something addressing this subject for piping in one of the Pipe Fabrication Institute Standards (ES-7 is minimum spacing between branch connections and it may be mentioned in there else it may be in one of their other standards) and I think it is mentioned in the PIP (Process Industry Practices) standards (either for piping, vessels or both).

RE: Min spacing between 2 welds

The distance mentioned is for structural attachment welds.

Which is the minimun separation distance between category A to B welds?: RIDICULOUS.

See PIP VESV 1002

Regards

rhg

RE: Min spacing between 2 welds

FYI, B31.3 had a minimum distance specified for adjacent butt welds many years ago. It was deleted at least 30+ years ago.

RE: Min spacing between 2 welds

ASME VIII Div 1 doesn't address distance between welds at all.

And the answer is different for every material.

For instance Aluminium 5083 is not affected by welds being close together or on top of each other.

Carbon steel is a different story. And then PWHT can be taken into account.

Distance between welds can be a very complex topic. Without needing to become a Yoda of Metalurgey, I use the PD 5500 rule of thumb that covers all materials: 2 thicknesses or 40mm between the toe of the welds, which ever is less.

Maybe the question you are asking is much more detailed then you think.

RE: Min spacing between 2 welds

(OP)
@Kiwi2671 thank you for the support.
That's what i have been telling, there has to be some research or literature (at least for carbon steel) which can validate the use of a 1.5 factor.

Thank you @rneill, i saw the PIP standards but sorry i could not find any info, could you be more specific.

@Karloss12 there is a requirement in ASME Section VII Div-1, UG-36(c)(3).

If i know how the factor has been considered then may be we can take quick decisions while fabricating.

RE: Min spacing between 2 welds

Hi roystercabral,
If you were talking about pipe then BS2633 states:-

Para 11.2 The toes of adjacent butt welds shall, whenever
possible, be no closer than four times the nominal
thickness of the pipe.

And for attachment welds it states minimum distance between toes of welds S to be the smaller of 2 times the pipe thickness or 40mm.

Hope this helps.



RE: Min spacing between 2 welds

(OP)
@DSB123
Thank you
But i was referring to the welds in pressure vessel

RE: Min spacing between 2 welds

See PD 5500
3.10.1.2 It is permissible to weld nozzles, pads, branches, pipes and tubes and non-pressure parts to
pressure parts, provided that the strength and characteristics of the material of the pressure part are not
influenced adversely. Attachments of non-pressure parts by welds which cross, or for which the minimum
nominal distance between the edge of the attachment weld and the edge of the existing main welds or
nozzle welds, is less than the smaller of twice the nominal thickness of the pressure part or 40 mm, shall
be avoided; if this is not possible, such welds shall cross the main weld completely rather than stop abruptly
near it in order to avoid stress concentration.

rhg

RE: Min spacing between 2 welds

The comments by DSB123 and rhg are basically the same as the Australian standards for pressure equipment (piping and vessels), so if your code doesn't specifically address this then it would be considered good practice to follow instead.

RE: Min spacing between 2 welds

(OP)
@rhg thanx mate this is gold.

This sentence "shall be avoided; if this is not possible, such welds shall cross the main weld completely rather than stop abruptly near it in order to avoid stress concentration" is very interesting. I want such details so that i can decide for myself if any distance between weld is ok, or if not what can be done to counter affect the damages.

Would appreciate if any one has literature regarding the effect of proximity of HAZ due to welding.

RE: Min spacing between 2 welds

MPI or DPI of the full HAZ in this region would be sufficient.

RE: Min spacing between 2 welds

per Rhg citing PD5500 "...if this is not possible, such welds shall cross the main weld completely rather than stop abruptly near it in order to avoid stress concentration. ", Does it mean it's bettter we completely weld the pipe/ladder/platform support clips over the girth seams ?
For tall towers with hundreds of suppport clips, many times clips will cross over girth seams. What we have done is to notch out a small raduis on clip to clear the girth seams. If that is not neccessary according to PD5500, that will be great news to save time and money. Your thought.





RE: Min spacing between 2 welds

(OP)
@rhg
see attached, most of our clients specify a similar weld arrangement for cases where pad is overlapping on the weld seam.

How Come PD5500 say that the welds crossing is better than being near, what is the basis for such a statement.
Most of the petroleum company standard specify welds to not cross each other.

RE: Min spacing between 2 welds

There is no mention of distance between welds in UG-36(c)(3). The only mention is in UW-14(d), which says any small openings that haven't had a reinforcing calculation must be atleast 13mm from from Catergory A, B or C welds in a shell thickness less then 38mm. But it can be within 13mm if you carry out a UG-37 reinforcement calculation.

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