rreplacement of buttweld ellbows by heat bend pipe 1

[lganga]

Is the first time that i am involved in an specification that replace standard ellbows by induction heate bend pipe.
The enginneering company propose that alternative as a way of saving welds during construction.

 

[stanweld]

It is more economical, even in smaller bores and has been done for a number of decades. In short, using bends in place of fittings has a long history. What you need to do is define the heat treatments after bending and specific mechanical properties required and whether the company performing the bends has adequate data insuring those properties.

 

[stanweld]

And you need to define the permitted geometry (wall thickness variation, out of roundness, etc.) and any added NDE (MT) examination, hardness requirements.

 

[lganga]

Thanks stanweky
Does ANSI B31.1 and B31.3 accepts this type of spool construction.?
Luis

 

[europipe]

Never saw in petrochemical heat bending.
Why should You do that, heating pipe is to my knowledge more expesive then a few welds more, what does it do to the material?
up to 4" saw a lot of cold bending.

 

[C2it]

Riser and pipeline bends able to pass a pig are commonly made by induction bending and are used worldwide in petrochem and offshore facilities.

Fabricom used to offer spools consisting of several induction bends and straight elements, to reduce welds. The service was and maybe still is available in UK and Belgium. From memory I am pretty sure the work complied with B31.3.

 

[LittleInch]

You just need to check the wall thickness that remains after the bending. 5D bends are commonly 8-10% less than normal pipe, but if your pipe bend radius is tighter than that then you can get some significnat thinning.

Watch for heat treatment and cooling as the material proeprties can be seriously affected. Post bending hardness tests and wall thickness checks are required on all bends.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[europipe]

Thought the OP means bending instead of elbows, no conveying bends 5D-10D.

 

[stanweld]

lganga,
Both B31.1 and B31.3 permit bending. Suggest that you review Section 129 of B31.1.

 

[davefitz]

If the pipe material is P91, remember to execute a final N+T alter all hot bends are completed, or else there will be multiple over-termpered zones developed immediately outside of the heated zones.

"Nobody expects the Spanish Inquisition! "

 

[stanweld]

europipe,
Induction bends were used extensively on the Prudhoe Bay, Alaska gas/oil processing facilities beginning in the late 1970's after extensive testing to confirm the ability of the bends to meet required low temperture toughness properties as well as the tensile properties. They have also been used in many other USA petrochemical facilities.

 

[BigInch]

More popular than hot bread.
Seems people think they can eliminate a pipeline cold bending machine.

Independent events are seldomly independent.

 

[lganga]

during my years as a mechanical engineer I have been involved in two Petrochemical projects, and working in maintenance for this plants .
have never seen prefabrication and installation of bend pipes instead of ellbows in the proposal of the engineering companies.

I will have to think about this process for the piping construction, As many of you said a procedure for heat bending should be approved for every P number, diameter and schedule,also traceablity must be stablished for every pipe bend.
By the way, ANSI B31.1 has a more detailed description that 31.3 in the scope of this pipe bending. I have not read any limit in the diameter of the pipe to bend

 

[europipe]

Iganga, you are absolutely right, contractors without bending machine are in disadvantage.
So the price goes up.
Also, there is a limit in designing, because of the greater radius.

 

[lganga]

Sure then one of my last questions should be;
Is the induction pipe bending able to copy the standard ellbow radio (1.5D).?
The plant during service can erosion and corrosion and sometimees and sometimes a bend mut be replaced, in the middle of nothing you can have and standrad ellbow but not a bending computarized machine. How can that be replaced in the case that radio is not thesame than a LR ellbow.
i repeat, is my first time with this and is reason for my many and long question
I have appreciate a lot your answers.

 

[SNORGY]

The ASME Code B31.3 does permit bends made from pipe in lieu of elbows, but if you do that, you must derate the design pressure in accordance with the application of the so-called Lorenz factors. The Code also sets limits on permissible bend radius in cold bends and imposes requirements for post-bend heat treatment, notably for impact tested materials.

Refer to ASME B31.3 304.2.1 and 304.7.2, as well as 332.2 thru 332.4 (based on the 2006 edition).

 

[europipe]

Never saw a machine bends 1.5D, I suggest the deformation is then too much.

 

[SNORGY]

Lganga...

But if you take a piece of pipe and bend it, you still have two ends...unless the bend has really long tangents on either end, where are the savings in welding costs?

 

[europipe]

Snorgy,
You can make spools with more bends in it.
But practically there are little savings.

 

[racookpe1978]

In a pipe rack, the extra length of the bends (5x dia mentioned above) greatly increases "rack space" and interferes with adjacent pipes and smaller lines.

In a large, on-ground, single plane situation - where the pipe fab group already has the portable hot bending machines and heat treatment method and the trained operators and the access to the bends ... It can work.

But if your are in limited spaces, consider how you are going to work in three-D bends? Multiple bends in the same plane? You end up with needing 2x welds for each elbow that is replaced by a "long tangent length + bend + long tangent length" . And all of those "long tangent lengths + bend + long tangent lengths" need to be lifted into position and held there in position by heavier cranes as you weld up each section of pipe to its predecessor and successor.