joint design for pipe welding

Date 03-16-2010 20:47

I think that's a lot of tribal knowledge. A good place to start would be to snag a copy of a D1.1 and take a look at the prequalified joint conifgurations that would give you a good starting point for allowable sizes of configurations in relation to material thickness.

I could be wrong but I've never seen a formulas or ratios for bevels and angles and the likes, too many variables like material, process, heat input etc.

By fatehy88 (*)

Date 03-16-2010 20:59

thank u very much for your reply
really i want to know what is selection criteria which directly affect in choosing the joint design may be another parameters ( not thickness only )
but ( from the real work ) how can the welding engineer say ( for example ) i will use single v or double v to be joint design for this pipe thickness ??!!
i hope u get my inquiry and thanks a lot for your time
regards

By Metarinka (****)

Date 03-16-2010 21:09

When designing a joint the things I take into consideration are

Time and ease of fabricating and fitting joint profile and time to weld
Ease of welding joint profile
amount of filler used
likelihood that it will meet quality requirements

For example J-grooves are harder to machine than a single bevel, but require less filler material. Which might mean less welding time and cost if doing thick or expensive material. Over 1" J-grooves become very economical in my experience.

Double bevels are preferred if both sides are accessible and the back can be gouged. Otherwise I would specify a single sided bevel.
using a backing strip is preferred unless one isn't allowed. An Open root is my least desired configuration because it takes more skill.

Of course this is a all a function of thickness and process. On thin gauge tig for example, fusing with open root and no preparation is preferred.
On a process like Submerged arc penetration is expected to be deep, so a large landing and narrower bevel angle is used.

A could and easy starting point is to find the volume of the joint if more than one are possible (single bevel vs double bevels) so you know which one theoretically takes either longer to weld or more filler. Thats $$ right there.

By fatehy88 (*)

Date 03-16-2010 22:06

again thank you very much for your kind reply,
but how can i find relations to make selection for pipe joint design,
i am working on ASME IX but i don't see anything related to the previous .
actually i am making theoretical working on codes related to my graduation project,
so i will not take the cost parameter in my consideration .
i will look ( for example ) for constraints like thickness, process and position ( if the position is constraint ) but till now i can't find any tables or data related to that .
thank you very much for your time and help .
hope you can help me ....

By G.S.Crisi (****)

Date 03-18-2010 21:05

All of the replies to fatehy's question are correct, but they don't answer what he's actually looking for.
Fatehy wants a standard, or table, or graph, or etc, saying that for a given pipe thickness the selected pipe end is this one.
Fatehy, I'm sorry to tell you that there's no official standard or whatever official publication that says what's the correct pipe end shape for a given thickness.
By "official" I mean a professional organization like AWS, ASME. API or others that have published standards, Codes or any printed material sold to the public, where their (the organizations') experience is condensed and made available to the interested persons.
What exist are General Specifications for Piping Systems issued by project engineering firms that are handed to their clients as part of their (the firms') services. In fact, when a client appoints a project engineering firm to undertake the design of a new plant or the revamp of an existing one, the project engineering firm hands to the client a whole set of documents, including, if it is the case, piping documents: General Piping Specification, Piping Detailed Specifications, List of Lines, Piping Layout, Isometrics and so on. These documents are confidential and are given to the client as part of the project engineering services. When receiving them, the client promises (usually in writing) not to disclose any document to unauthorized third parties. Back in my days of erector and project engineer dozens of General Piping Specs passed under my eyes.
Well, fatehy, it's on these General Piping Specs that you will find what you're looking for; it's these documents that, in most cases (but not always) state the type of welding end to be selected for a given thickness. Unfortunately for you, these documents are not sold to the public, for they're confidential information that belongs to the project engineering firm and makes part of its knowledge and experience.

I'll give you a couple of clues, based on my personal experience of the many years I spent erecting and designing industrial plants. K and X joints are unfeasible for piping, because you won't be able to weld them by the inside, unless the piping diameter is large enough to allow a welder to get into it (the pipe). J joints must be machined, they can't be cut with the torch. So they're feasible for thicknesses of, say, one inch and above in piping prefabricating shops, where there's a lathe available at hand. J joints don't compensate their cost for lower thicknesses. If the pipes are to be cut to length at the job site, where there's not a lathe easily available, then the best solution is to cut a V bevel with the torch, no matter the thickness.
Giovanni S. Crisi
Sao Paulo - Brazil