ASME B31/3 pipe spool adjustment

Date 11-22-2007 19:56

Mickey,
I didn't understand what kind of adjustment are you talking about nor to which temperature you intend to heat the spools. Usually, prefabricated spools have one joint that is only tack welded, one flange that is loose and one straight piece of pipe that is a couple of inches (50 mm) too long, so it can be adjusted during erection.

This comment has nothing to see with your question.
Back in 1970/71, I was one of the engineers who took part in the erection of a new oil refinery in Argentina. The client was YPF (the name has now changed to Repsol), and the designer of the plant was The Lummus Company. I worked for the erection contractor.
The process turbocompressors were Peter Brotherhood brand. I'm happy to see that it's still in business and they havn't changed its name. And now I'm going to ask you a favor: would you please have the company send me by air mail a set of catalogues published by the company? They (the catalogues) will be very useful to me, for I'm a college professor now, and the subject I teach includes turbocompressors.
If you agree, I'll let you know my postal address. Thank you.
Giovanni S. Crisi
Sao Paulo - Brazil

By mick dale Date 11-22-2007 20:13 Edited 11-22-2007 20:21

hello Giovanni S. Crisi
will contact the marketing department with your request. hopefully all will be ok - send your address

the spools in question are quite complicated consisting of pipe with butt weld flanged ends and various fittings in between e.g. 90 degree elbows and reducing tees. The pipefitters are building up the spools for the welders using bridging tacks and we are experiencing distortion once the spools have cooled so the flanges no longer fit exactly (anything up to 15mm out max). Dont want to keep cutting the spools, then reassembling with new weld preps etc.
was thinking of heating the pipe on the spool to allow the pipe to slightly move on cooling bringing it back into realignment but not sure if it is allowed in ASME B31/3 (pretty sure its a no no on stainless anyway)
thanks
mick

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

Date 11-22-2007 23:24

Mick,
Personal address:

Giovanni S. Crisi
R. Marques de Itu 181 - Apt. 81
01223-001 Sao Paulo
Brazil

I thank you for your kindness. Catalogues from reputable manufacturers are always very useful for an engineering professor as an aid to prepare his lessons.

And now let's go to your question: Taking into account what Gerald quoted and said, and considering that A-106 Gr. B is a low carbon steel (C max. 0.30%, if I remember well), I see no problem for its ductility in heating it up and cooling it slowly after corrections has been carried out.
As for 316 SS, I don't recommend to do the same, as you yourself have stated.

Giovanni S. Crisi

By CWI555

Date 11-22-2007 22:28

301.9 Reduced Ductility Effects
The harmful effects of reduced ductility shall be taken
into account in the design of piping. The effects may, for
example, result from welding, heat treatment, forming,
bending, or low operating temperatures, including the
chilling effect of sudden loss of pressure on highly volatile
fluids. Low ambient temperatures expected during
operation shall be considered.

332.3 Forming
The temperature range for forming shall be consistent
with material, intended service, and specified heat
treatment.

332.1 General
Pipe may be bent and components may be formed by
any hot or cold method which is suitable for the material,
the fluid service, and the severity of the bending or
forming process. The finished surface shall be free of
cracks and substantially free from buckling. Thickness
after bending or forming shall be not less than that
required by the design.

In light of these paragraphs, My advice to you would be to pass it off to the engineer. If you are the engineer, and are not intimately familiar with the material at hand, I would suggest passing to someone who is.

Regards,
Gerald

By ZCat

Date 11-22-2007 22:59

we always dry washed stainless back into shape.

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

Date 11-22-2007 23:28

What does "dry washed" mean, Zcat? I've always thought that for washing, a liquid (water, kerosene, dilute caustic soda etc.) is involved.
Giovanni S. Crisi

By ZCat

Date 11-23-2007 01:24

it means to run over it with a TIG torch without adding wire, using the heat to draw it where you need it to go.

By 803056

Date 11-23-2007 13:24

You can cause permanent deflection by heating the pipe with a torch to about 600 to 650 degrees F and allowing it to cool back to ambient. The trick is to maximize the delta T from one area to another, so you can use wet rags to wet and cool the areas not heated to keep the heat confined to one specific area. You want to concentrate the heat to only the areas you want heated and you want to heat it quickly. If you want the pipe to bow up when completed, heat the top half. If you want the bow to be downward, heat the bottom half. Note that the pipe will deflect in the wrong direction as you heat it. The heating should be pie shaped with the wide area toward the direction of the final deflection and progressing from the center line of the pipe. Start heating at a point at the center line (both sides) and work the heat toward the outer edge. Hopefully, the attached sketch will help with my explanation.

You can repeat the heating several times, but you have to let the pipe cool to ambient between heating cycles. It may be slow, but the temperature is low enough that there should be no changes in the microstructure of the carbon steel pipe.

Best regards - Al

Attachment: HeatBending24-Nov-07.wmf (9k)

By mick dale Date 11-23-2007 17:50

many, many thanks for all your replys.

(catalogues should be on their way soon Giovanni)

By js55

Date 11-26-2007 14:33

Keep in mind a few things when heating 316;
It doesn't take much to get it to move. In fact, if you start using heat to align it you may find the problem getting worse.
If you are going to use the GTAW autogenous for moving assemblies be sure you have an autogenous WPS in place.
And keep in mind that Mo will continue to segregate in 316 the more heat you add to it,
And, if you heat it too much you will precipitate sigma as well.
To my memory there is no prohibition for 'diamond' heating of SS (or variants thereof), but having someone available that understands the material, as Gerald suggested, is a must, and using proper procedures even more so.
If its orange, its way too hot.

By scrappywelds (***)

Date 11-27-2007 22:37

In the field nobody really cares what it took to fit up the pipe to the pump, as long as there is no stress on the pump for alignment. We always dry wash and use water if needed to make a flange move. If it wouldn't we would cut it out and weld in place.

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

Date 11-27-2007 22:45

Attention though!
Heating the pipe up and then cool it with water is acceptable for low carbon steels, such as A-53 and A-106, because little martensite will form and the material will keep its ductility. The method is unacceptable for hardenable steels such as chrome moly, because they will harden up, and thus become fragile, due to martensite formation.
Giovanni S. Crisi

By 803056

Date 11-28-2007 09:34

I agree Dr. Crisi, that's why I limit the temperature to stay well below the lower temperature of transformation for carbon and alloy steels and below the temperatures where embrittlement or the temperature range where the formation of Sigma phase is an issue with the austenitic stainless steels. My experience and a few experiments shows that permanent deflections can occur with temperatures as low as 250 to 300 degrees F above room temperature.

The use of water soaked rags is to limit the heating (delta T) to a specific area, not to cool the heated area. The idea is to maximize the temperature differential between the area heated and the surrounding base metal (that is kept cool). Once the area is heated and plastic deformation (yielding) has occurred, water cooling has no adverse affects on the metal because the temperature of the area heated is well below the transformation temperature. Subsequent water cooling will not cause the formation of martensite because the temperatures involved are well below the temperatures required to start the transformation to austenite.

All bets are off if the parts are heated above the lower transformation temperature. If the lower transformation temperature is exceeded, the final microstructure is dependent on the alloy constituents present and the cooling rates. As you suggest, martensite can result and the final properties of the metal are a toss of the dice.

Best regards - Al

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

Date 11-28-2007 19:37

Don't call me Doctor, Al, I'm just a Bachelor of Science in Chemical Engineering.
Giovanni S. Crisi

By 803056

Date 11-28-2007 20:06

Sorry, however I do think of you in that capacity.

Best regards - Al