I am not aware of any piping code requirement addressing distance between welds.

There are several engineering specifications that limit the distance. They are usually expressed in rule of thumb terms (like 5 times diameter). I can only assume the basis for the is accumulative residual stress and effects of shrinkage. Although I have never seen that addressed in the text of the specifications. I know when I worked to such a specification in nuclear plant construction (early 70s) where the rule was 5 x diameter. The eccentric reducers used in the system failed to meet this rule. When I asked the Senior Piping Engineer why we in the field could use fittings to do this but not pipe. He insisted I needed a haircut and that I should leave his office immediately and go get one. This lead me to believe that this rule is engineering folklore and not based on solid principle.

In my business of power plant repairs we often weld right next to an existing weld. Our practice is to assure the adjacent weld weld is sound using either surface or volumetric NDE prior to completing the weld and then include it in the final examination of the new weld.

I hope you get more posts on this subject.

There are many questions related to this topic. It often seems if an individual (me included) can't find the requirement in the applicable code or standard or project specification, they look for some other source with that requirement. Why is that ? If this were an important issue during all welding, It would be in the code (I am onlyexperiences with ANSI,ASME)! I am not saying that there are not times when it should be controlled. Thats why designers use engineers. Engineers could then either lookup the results from having overlapping/adjacent heat affected zones or perform the study on their own. Then the requirement would be in the applicable specification


Here is some text from a spec at http://docstream.no/ppcon/4980/4980%20rev.02%20Welding%20Piping.pdf

4.1 General
Distance between welds:
Normally the minimum distance between welds shall be 1x diameter of the pipe. If this for
practical reasons is not possible the minimum distance between the welds may be reduced to
2xWT or 50mm (between the weld caps) whichever is greatest.

Here is a shipbuilding spec with some design requirements for distances between welds that may help you. http://www.dimar.mil.co/curso/Archivos/Documentaci%F3n%20Relacionada/Art%EDculos%20de%20inter%E9s/repair%20qua.pdf

There is WRC bulletin referenced at http://www.forengineers.org/cgi-bin/wrcbulletin/bulletin.pl?action=view;id=464

In some cases the distance could be restricted to prevent interference with NDT and I'm sure there are sometimes GOOD engineering reasons for this but it seems to be a very widespread wivestale as related to being a code requirement. I often wonder when I see this in an owner prepared spec for a carbon steel pipe with hot water in it, if it is there for a good enginnering reason or just a reinforcement of the wivestale.

Also



Here are some related topics discussing this same issue

http://www.eng-tips.com/viewthread.cfm?qid=53925
http://www.eng-tips.com/viewthread.cfm?qid=45263
http://www.eng-tips.com/viewthread.cfm?qid=25912
http://www.eng-tips.com/viewthread.cfm?qid=34893
http://www.eng-tips.com/viewthread.cfm?qid=77845

If anyone comes across some weld related failures related to this subject, let us know. I'm sure there are some special alloys/service conditions that would not like to have multiple heating cycles and those would be interesting to know about as this may apply there.

I wonder if I told the welding foreman that he must maintain an inter toe distance inversely proportional to the number of words in the applicable code paragraph, he would think "Boy he really knows that code". Or look it up and ask me to show him? :)

Have a good day