I too am interested in this response. I have heard many rules similar to this with no backing in the code or specifications. Some with good reasons and others with out.

This subject has (and still does) lead to endless (and most of the times fruitless) discussions between contractors and clients' inspectors in erection jobs. I know of no substantial reasons why two welds in a pipe should be separed by any specific distance. Back in my days of erector engineer in South America (always as a contractor, never as a client) it was usual practice to leave three pipe diameters as a minimum between two welds in a pipe. This left the clients' inspector satisfied. Why 3 diameters and not 2,5 or 3,5 I've never known. Nobody I asked why was able to give a technically sound reason.
Now, sometimes it's impossible to leave 3 diameters for the simple reason that there's no sufficient pipe lenght for them. In these cases there's no other chance but leaving a lesser distance. In the majority of cases clients' inspectors agree. Sometimes, however, they are insensible and keep on arguing. What I used to do in these cases was to tell the inspector that on the isometric it was shown like that and that I was just the erector, not the project engineer, and thus I wasn't going to change what the isometric showed. "If you don't like it" I said, "complain to the project engineer, not me". This worked.
Giovanni S. Crisi
Sao Paulo - Brazil

There shall no more than two girth welds in any 10 ft interval of pipe and Two girth welds shall no be located closer than one pipe diameter or 3 ft whichever is less.
Miguel P.

What about miter bends, gentlemen? Their welds are spaced much less than one pipe diameter. Miter bends are accepted by highly respected standards and codes, such as AWWA (American Water Works Association), ASME/ANSI B31.3 for certain services and diameters above 24 inches and B31.1 for low pressure exhaust steam and diameters also above 24 inches.
Giovanni S. Crisi
Sao Paulo - Brazil

I just don't want anybody welding next to my welds cause they usually make mine look a little rough :)

Limitations on spacing of adjacent girth welds are based on project specifications rather than the ASME B31 piping codes, which do not contain that level of detail. In fact, for piping with a high density of fittings (headers or manifolds), it may be necessary for girth welds to be spaced rather closely to accomodate the design.

I believe that the limitations of girth weld spacing of 1D, 2D or 3D found in some project specification have their origins in workmanship standards rather than a specific technical issue. Welds are generally considered to have a higher risk of leaking than pipe, so most operators would prefer to have the fewest number of welds possible.

The history of arbitrary specification requirements such as this one can be an interesting study. For example, many years ago there might have been a situation in which a fabricator chose to weld together a string of short drops rather than cutting into a "fresh" joint of pipe and ultimately scrapping the short drops. Another possibility is that a fabricator faced with cutting out a weld, elected to insert a 3 inch pup with a girth weld at each end rather than a longer pup that might have been more desirable from a constructability or reliability standpoint.

What ever the specific reason, it is likely that an operator somewhere felt abused by a fabricator inserting short pups where it was not necessary and added a limitation on distance between girth welds in the next project specification. The person or persons involved in the original lilmitation probably took that requirements with them to other projects and other employers for the remainder of their career. This type of restriction has been in piping specification for at least 30 years that I am aware of, so it is unlikely that anyone remembers the initial justification for the limitation on girth welds spacing.

Specification requirements tend to take on a life of their own when a specification is used as a guide or "go-by" by someone not involved in its original preparation (a very common practice for specification preparation). The next specification author may not appreciate the basis of the requirements and thus be afraid to delete any of them. For thsi reason, it is not uncommon to find specification requirements that are completely out of the context where they might have reasonable application.

I don't know the initial cause of the limitation on girth weld spacing, but I am comfortable with requiring in project specifications that a pipe pup in plant piping should be at least 1D in length, unless it is welded to a fitting or flange on each end that requires a closer spacing. For pipeline construction, I am more inclined to consider good workmanship as requiring pipe pups to be at least 3D in length unless both ends are welded to a fitting or flange.

An owner rep is not obligated to provide a rational explanation for a specification / contract requirement that limits minimum spacing of girth welds to 1D, 2D or 3D. If there is a good reason to have closer spacing of girth welds than the specification / contract requires, it is reasonable to ask the owner rep to consider a waiver of the requirement. In the case of shorter spacing between fittings and flanges, the owner rep will have to agree to a waiver or change the design.

Don't expect to find a technical answer to your question in terms of HAZ spacing, etc.

Jim

Well-stated Professor Crisi! It’s easy to forget there were 2 thru 6-weld mitered 90’s successfully used when elbows (especially nickel alloys) and “sweeps” weren’t available at the job site! Depending on the NPS and radius used, the throat welds could very, very close together.

There were two distinct problems that I’ve encountered over the years arising from welding girth welds that are in a very close proximity to each other. I’m certain there are others such as the “un-zipping” previously mentioned and others more specific to a particular service condition outside my experiences.

One has to do with SCC and accelerated, internal corrosion stemming from lack of interpass temperature control when welding the nickel base alloys. It’s a common problem made worse with close welds.

The other stems from trying to simultaneously weld, two welds in a very close proximity to each other and developing cracking problems in one or both when the piping system was restrained. Several times I’ve been called out to investigate why a welder was having cracking problems while welding in a pup piece. The welder would either see the centerline crack develop or would find out one or both welds failed radiograph. Each time I found or determined that the welder was trying to weld both welds at the same time by jumping back and forth at each quarter. A couple of these occurrences involved small diameter piping under 2” NPS with a 2d pup.

The same cracking scenario can often occur while welding small diameter flush patches in vessels. Care has to be taken and the welder made aware of the cooling forces counteracting themselves across the patch especially during the root bead application.

I’m sorry for taking so long to reply to this post and many others but I’m having a heck of a time getting my replies to post. I’ve worn my “clicking finger” to a stub and have about given up replying at all!