This question comes up all the time especially when dealing with piping contractors.  I'm not sure if a code addresses this or not.  If so, I'd sure like to know which one.

The rule of thumb I was taught is that the minimum distance between adjacent buttwelds was one pipe diameter IF it could be done that way.  If not, it was never to be closer than 1-1/2".  This is supposedly to prevent the overlap of HAZs.  Practically speaking, on big-inch pipe it's mighty hard to get a pup piece that short and still end up with a decent bevel and land.  There are others here who know more about this than I - hopefully they'll contribute.

Thanks!
Pete

I agree with 74Elsinore but to the most ideal & common practice regardless of pipe size is 3" min.

I am not aware of any code but as usually industrial practice 200mm is sugusted

I have seen owners who have specified the minimum clear distance between edges of butt welds was to be four times the wall thickness or 1", whichever was greater.  This seemed awfully close, so we "encouraged" our piping designers to keep the minimum distance to four inches.  (In other words, we told them they needed approval for closer than four inches, and then took two weeks to approve it.  They got the message that we really didn't like it.)  Where it really is necessary, you need to be cautious about the heat affected zones of the weld overlapping.  Any time we went under the 4" rule of thumb, we had the design reviewed by a welding specialist.

I recall trying to find code that specified a minimum distance, but the job was really hectic and I can't remember if I actually found one.  (One of the disadvantages of working for many different owner's, occasionally owner's specs and industry codes will start to overlap in your brain!)

Good question...

The British Standrd BS2633 for Class 1 pipework states :-The toes of adjacent butt welds shall, whenever possible, be no closer than four times the nominal thickness of the pipe.

Because you dont want HAZs clashing.

Regards

John www.gowelding.com

You must use the ASME B31 Standard where are posted all the certified answers to this kind of questions. It is the best and more professional way.

ferdy,

Your suggestion is good.......however not very practical or timely. You should know the following about questions posed to the ASME B31.1 committe:

-    They do not answer all questions,...only the ones they like, or find interesting.

-    They do not respond very quickly....you may, or may not get an answer in six months or so....

-    They lack the brutal humor, brilliant insights, and acerbic sarcasm of the participants of this superb forum (did I mention that we are modest, too ?)

-    They require all questions to be posed as "yes" or "no" so you cannot ask for questions like minimum distances between components...... you can ask any kind of question on the eng-tips forum (even personal relationship questions...... we will try to answer these too..... although you probably won't get very good answers)

My thoughts only.....


MJC

i fully agree with 74 elsinore regarding the spacing between two welds. his answer is very good and highly convincing.

Hey MJC,

Here's a question for you.  Does the First Law hold for my relationship with my girlfriend?  

Thanks!
Pete

Pete!

Reluctantly I am joining the fray of eng-tips.com grandparents. Is your question an academic one or a professional one?

Note: To me it really doesn't matter(I mean academic vs professional)

Cheers,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

Hello All,

Mike Cronin knew he would draw me out of the woodwork with his comments regarding Code Committees:

-    They do not answer all questions,...only the ones they like, or find interesting.

Actually, we are required by our charter to answer all question (inquiries) addressed to us that are of a technical nature.  We will NOT provide engineering services in answer to questions however.  Inquiries may ask for interpretations to the existing Code documents and these will result in "Code Interpretations".  If the Code (per se)does not address the issue, the response of the Committee will say so.  If the Committee feel that the issue is one that should be addressed by the Code, they MAY put it on their agenda for rulesmaking.  Also, the Committee may write a "Code Case" to address the issue until it is addressed by the subsequent editions of the Code.

-    They do not respond very quickly....you may, or may not get an answer in six months or so....

The reason for the six month wait is that the "Book Section" Committes meet every six months.  After the specific "book section" Committee addresses the issue and proposes a response (interpretation) it must go through the review and approval stage.  If there is a negative vote from someone "up the line" the negative comment must be addressed - these are consensus codes.  It might get addressed in less than six months if everything falls into place with the schedule.  The procedure is very rigorous in an effort to assure that the response is truly representative of the entire Code Committee.

-    They lack the brutal humor, brilliant insights, and acerbic sarcasm of the participants of this superb forum (did I mention that we are modest, too ?)

Mike needs to go to more Code Committee meetings.

-    They require all questions to be posed as "yes" or "no" so you cannot ask for questions like minimum distances between components...... you can ask any kind of question on the eng-tips forum (even personal relationship questions...... we will try to answer these too..... although you probably won't get very good answers)

You can ask the question in any way you wish.  Because many questions are ambiguous or are asked by a person who has English as a second language, the Committee will try to rephase the question relative to the specific part of the Code to which it refers.  The Committee must determine exactly what paragraph of the Code the question is asking about, so it is convenient to rephrase the question in a way that it can be answered by a "yes" or "no" - the Committee may expand upon the short answer if they think it is needed.  Minimum distances between components is not addressed by B31.3, and I think that since the Code is not a design text book, it should not be addressed by the Code.

Actually, I think that there are some really good discussions on this board - Mike can recommend other good boards.  There are some very good ferrets out there who find good references on the Internet and who share those finds on discussion boards (Do we all know about the Standards of the "Pipe Fabrication Institute"?

Best regards, John.