achieving a joint in seamless pipes 1

[trish129]

The very thought of having a joint in seamless pipes seems absurd but what if the required length of seamless pipe is not available and the only option is to join two pipe pieces such that the joint sustains a particular operating pressure.?is welding recommended in this case?

 

[CoryPad]

Welding is an option: friction, arc, laser beam, etc.

 

[trish129]

thank you Corypad..is welding an established method to obtain this joint?

 

[EdStainless]

What are the operating conditions? Very high temp? Is this application creep limited? What is the pipe material?

If it is not creep limited then there is no issue whatsoever (in fact you could use welded pipe). Just develop a weld procedure and do a but weld, they do it all of the time.
If creep performance is critical the process is more involved, but still done often. The boiler tubes in a power plant are only 40' long and the boiler is 120' tall, there are a lot of welds.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Circumferential butt welds in seamless or even seam welded pipes and seamless or seam welded boiler tubes are done routinely with proper selection of filler metal and a qualified welding procedure. For heat exchanger tubes, tube to tube butt welds are avoided from a good engineering design.

 

[EdStainless]

And Trish, please don't post in multiple forums.
Most of us read a large number of these so we will see your questions.

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P.E. Metallurgy, Plymouth Tube

 

[DeleteriousPhases]

not absurd at all. pressure piping codes address this in-depth, and welded pipe is more than established - else the challenges faced in refineries and powerplants would be much larger.

welds can distort a part - especially thin wall. ensuring you're able to reach your tolerance/alignment after the weld is completed should also be a consideration.

 

[Guest102023]

It can't be both. But it's not even clear from your question what you are trying to do.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[trish129]

thank you all for your replies..

let me lay down the specifics of my problem...

Operating conditions: water for jetwashing at normal temperature and a operation duration of 14 hours subjected to a working pressure of 260 bar
Seamless pipe material: ASTM A 106 Grade B
Pipe schedule: 160
¾” (the nominal pipe size)

Important consideration:1) this pipe travels horizontally between circular supports/guides.so the weld beads should be flush with the outer surface of the pipe so as to avoid interference/jamming with the circular guides.

2)alignment..the tolerances and alignment issues are of paramount importance because any mis-alignment would inhibit smooth travel through the circular supports

circumferential butt welding of seamless pipes must be somewhat different from butt welding of welded pipes .what weld procedure should be adopted? What are the considerations for butt weld specific for seamless pipes like proper selection of filler metal

DeleteriousPhases "welds can distort a part - especially thin wall. ensuring you're able to reach your tolerance/alignment after the weld is completed should also be a consideratio"n.------->> you said it ALL...

what would be the testing plan for the welded joint to ensure integrity at such operating pressures?what should be the possible configuration of test samples?

 

[metengr]

1. How much length do you need to avoid butt welds for the lance???
2. If you need to butt weld pipe segments to form a lance, hire a mechanical contractor that is experienced in welding to accomplish this for you. It will be far cheaper and less risk of failure.

 

[moltenmetal]

Jig tack the pieces to ensure proper alignment, weld in a rotator with proper guiding, grind the weld OD flush, then do the required radiography. 3/4" sch 160 has a huge wall to ID ratio- it's almost like hollow bar. As long as the cap passes aren't put in too heavy and hot, it should work out fine. Plenty of piping requires either ID or od welds to be ground flush- happens every day.

 

[trish129]

metengr:How much length do you need to avoid butt welds for the lance??? --> the length of travel is such that the joint travels thru the guide..

moltenmetal ->Jig tack the pieces to ensure proper alignment, weld in a rotator with proper guiding, grind the weld OD flush, then do the required radiography. 3/4" sch 160 has a huge wall to ID ratio- it's almost like hollow bar. As long as the cap passes aren't put in too heavy and hot, it should work out fine. Plenty of piping requires either ID or od welds to be ground flush- happens every day. ------> 1.how do i jig tack the pieces? any videos/images demonstrating this? 2.what do i look in the radiography results? 3.what filler material to use? 4.there must be well laid down procedures and codes written down for welding of seamless pipes...where do i find them?

5.what actually determines the joint integrity? how can one declare a given joint fit for service.?

 

[moltenmetal]

There are piping jigs which hold two pieces in precise alignment while they are being tacked. Any piping fabricator will have something to do the job.

Pipe is generally welded in accordance with ASME IX qualified procedures by qualified welders. The procedures control all variables including welding process and conditions, filler metal etc. The procedure is qualified for a thickness range, a material class (for instance, austenitic stainless steels are P8)

Radiography is usually required to assure the quality of piping butt welds. A company specializing in radiography and other non-destructive examination shoots the X-ray, develops the film and interprets the results. They are looking for flaws such as lack of fusion, porosity, cracks etc. There are criteria for the acceptance of welds for code piping in a piping code such as ASME B31.3.

If a qualified welder welds to the correct procedure, the required NDE is done and passed and a hydrotest is completed, the weld is assigned a joint efficiency of 1, meaning that it can be taken for design purposes as at least as strong as the unwelded material.

If you are jetwashing with a fluid not more hazardous than water, per B31.3 the service might be considered Category D- nonhazardous. One thing that this would imply is that you would not need to cap the end of the lance and hydrotest it prior to putting it in service, if the owner agrees. It is difficult to overpressure a pipe which is open at one end. Is it fitted with a spray nozzle of some sort, or some other flow restriction device? If so, you should probably hydrotest it to ensure joint integrity.