Heat treatment of U-bend in Heat exchangers 1

[starrproe]

Hi All,
Does anybody know of some reference material for guidance on requirements of heat treatment for U-bent tubes of U-tube heat exchangers?

I am particularly interested in knowing the conditions under which heat treatment of tubes after bending becomes mandatory.

Also, can somebody please let me know whether UCS-79 is applicable to tubes also or does it apply to plates only.

Regards,
Starrproe

 

[metengr]

What is the tube material? This will drive the decision regarding post bend thermal treatment.

 

[starrproe]

The tubes are seamless CS, SA 179- 19.05mm OD x 2.11mm thick.

 

[metengr]

For a CS tubing heat exchanger in steam service, post bend thermal treatment is not required nor prohibited. For a CS heat exchanger in more corrosive service conditions where residual tensile stress can drive a failure mechanism, a post bend thermal treatment may be warranted. In other words, it is up to the Designer to decide on this.

Re;UCS-79, this does not apply to tubing, only to shells and heads that are formed.

 

[ijzer]

You could have a look in the TEMA.

 

[DG72]

TEMA does not specify.

 

[EdStainless]

Remember that a standard u-bend heat treatment does not reduce the stresses, it only randomizes them. If you want them reduced have someone prove with testing that their process will do that.

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Plymouth Tube

 

[bernoullies123]

The requirements of heat treatment post cold tube forming is covered in Australian Standard AS 4458:1997 Section 6.4.

It states that cold formed bends in tubes required heat treatment (excluding for boiler, superheater, reheater and economizer tubes) is required for (a) CS material with a center-line radius < 3.5*OD (b) bends with strain > 5% (where: 100*OD/2R) c) when SCC (stress corrosion cracking) is an issue.

For boiler, superheater, reheater and economizer tubes, it is also covered.