Hot Bend Design

[spd60]

Hello all,

Can anyone explain the procedure to be used for hot bend design when designing a pipeline under CSA Z662-03?

 

[GregLamberson]

Not sure I understand your question. If you are asking how to calculate minimum wall thickness for induction bends under CSA, then you will need to look up the CSA wall thickness tolerances (API vary by pipe grade and diameter). You can calculate the minimum wt required by:

t = (PD/2S)-F, where,

t = wall thickness
P = design press
D = pipe dia
S = min yield strength of pipe
F = temp factor

Then you can factor in your allowance by taking t/(1-tolerance%).



Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[acedude]

It is not certain what your question is specifically referring to. The Canadian code appears to be somewhat vague on this subject. The ASME B31.4/31.8 Pipeline codes do have some more specific guidance regarding induction bends ("hot bends").

In general, hot bends are used for cross country pipelines where proximity issues cannot be properly addressed using cold bending of the pipe. Hot bends are almost always used to make the below ground to above ground transition at scraper trap locations, and or at intemediate isolation valve locations (if the valve is above ground), and only otherwise used to accomplish a smaller bend radius that might be required to avoid other facilities along the pipeline routing.

Hot bends are provided by specialized vendors, are usually long lead purchase items, and are therefore only used where necessary. Some above ground pipelines with expansion loops may require larger radius bends to accomodate instrumented pigs, in such case hot bends may be appropriate.

During the hot bending process, straight section of line pipe is heated and mechanically "bent" to the desired configuration. During this process, the wall thickness increases on the compression side of the pipe, and reduces on the tension side of the pipe. Therefore the hot bend specification to the vendor needs to specify that the wall thickness of the hot bends (anywhere along the completed hot bend) shall not be less than the wall thickness required for pressure containment (and this minimum wall thickness needs to be specified in the requisition).

Hot bend vendors have tables which they can provide to you that generally quantify this information for their hot bending process.

 

[GregLamberson]

ISO 15590 is another code source for induction bends.

As mentioned by acedude, induction bend supplier's will have their own process and procedures that they will submit to you for approval.

That being said, you should provide them with the tolerances for bend angle, bend radius, out of roundness, bend plane, linear tolerances and end prep.

You will also want to supply them with mother pipe to avoid other problems with weld procedures later.

Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[spd60]

Thanks Guys,

My question derives from that fact that the CSA code is vague and I am trying to understand how to determine if:

a) The straight pipe we order has enough wall thickness so that if we send some joints for bending it will still have the minimum wall thickness required for the design pressure of the pipeline after bending.

(the client has required the pipe wall to be well above the minimum thickness required by the design pressure/code.

b) If the client requires his minimum wall thickness how to back calculate the required thickness of the pipe before bending to achieve that.

 

[GregLamberson]

spd60

Just a clarification, I noticed an error in my submittal, F above indicates not the temp factor but the class location factor (i.e. .72, .6, etc.). Sorry.

Greg Lamberson
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[acedude]

spd60,

Your comment that, "the client required the pipe wall to be well above the maximum thickness required by design/pressure code", raises some concerns.

However, to address your immediate question at hand, you would need to contact an induction bending supplier/vendor and provide all the details to them as suggested by GeregLamberson above. Once you have provided this information to them, inclusive of the minimum required wall thickness, and details of the line pipie you would supply, they will advise you if their induction bending process can achieve the desired hot bends using the supplied pipe without adverse thinning less than the minimmum wall thicknees you specified (or your client specified). If the supplied line pipe is not sufficient thickness, they will suggest alternatives.

With regard to the minimum wall thickness both you have calcuklated and your client has specified, perhaps it would be usefull if you could provide the the details of your pipeline project, specifically, the pipeline length, nominal diameter, type of service (i.e. oil, gas, sour, etc.), design pressure, max operating temperature, selected steel grade and manufacturing method (i.e. seamless, SAW, etc.), and construction mode (buried or above ground). In addition, please advise the minimum wall thickness specified by your client, and why it is felt that you need hot bends (i.e. specific applications).