Need for solution annealing

[yonglwe]

Hi All
I'm buying some 316L Stainless steelplates to fabricate into pipes barrels then cut to suitable spool length and welded to form the discharge portion ( including tees and mitre bend) of a two large pumps system each pump handling 400000 cubic meter per day of municipal treated effluent( total 8 pumps) , pipe dia. from 1400 to 2200mm and thickness from 10 to 12mm . Fabrication to form pipe spools will be by rolling with stainless steel rollers to avoid contamination followed by either longitudinal weld or spiral weld . My question are as regard to the need for solution annealing
1)Would the rolling process of pipe forming cause sufficiently rigorous work hardening thus required some forms of heat treatment such as Solution annealing
2)Or is it because of the longitudinal Or Spiral weldings to form pipe barrel cause stress and embrittlement in the HAZ which then required solution annealing to dissolve carbon particle/precipitate in the HAZ,
3)If both activities in 1 & 2 are the cause for solution annealing, then which one is the main cause.
Solution annealing above is normally as follows :"heat to and soak for 5 minutes at 1040C, then air quenched in 5 minutes to 450C, then cool to ambient in 25~30 minutes".

Thanks you & look forward to your help.

Jyaces

 

[arunmrao]

316L plates are available in solution annealed condition. you do not need to do separately solution annealing for the fabricated component. also since you have selected L grade(low carbon0.03%max), you have minimised the risk of sensitization after welding. so go ahead and complete your fabrication without being too concerned about solutionizing treatment.

 

[unclesyd]

I would not recommend a QA on your fabrication based on your information. Don’t go on my conclusions as we have the opportunity to get some more advice. This is a very is very good subject for this forum.

You have essentially taken out any material problems (HAZ)with welding by using 316L material. The Stresses imposed by the forming are not going to be that high. The stress formed by welding are going to be locally much higher.

As you know most pipe used in the chemical industry is QA up to point where handling becomes a problem. We never QA or stress relieved shop fabricated S/S pipe above 18". In the same vain we never heat treated fabricated columns or vessels that approximate your pipe dimensions.
All this was for very aggressive chemical contact.

The problems in your case is the environment that the pipe will see. Being treated effluent the sulphur compounds should be at very low levels with the only problem being with Chlorine/Chlorine Compounds(mostly salt) if the sludge is Chlorinated. The free chlorine should be quite low.

The biggest problem with what little pipe I seen from waste treatment piping is from MIC and external Chloride induced SCC. The biggest problem was in large piping that was fabricated as you propose, but welded from the outside only. This left the bugs a nice starting point. MIC bugs could care less if the material is heat treated or not.

Do you have you own heat treating facility?

 

[yonglwe]

Thank you both very much
1) To arunmrao:
a) I know of smaller 316L pipe particularly ERW already solution annealed required whether as a result of ERW's HAZ effect or rolling effect on or from mill supplied 316L. Question is really the HAZ OR rolling for which I got a very good amswer from UNCLEsyd .
b) Of course, to compound the problem of HAZ, there is the welding of different pieces cut from fabricated pipe barrels of different diameters(with PWT such as solution annealing done to the whole pipe barrels )to form pipe spools and/or fittings such as mitre bends or tee pieces, this fittings so fabricated will itself called for additional solution annealing ??. Agreed ??

2) To unclesyd (Materials) Oct 30, 2003
a) Agreed with what you said a very good subject for this forum.
b) Appreciate your help to quantify if possible what you said or quote a reference on "The Stresses imposed by the forming are not going to be that high. The stress formed by welding are going to be locally much higher."
c) My pipe will be welded from both sides
d) WE are thinking of setting up own heat treating facility with gas heating.

Look forward to further interesting discussion.

Jyaces

 

[GRoberts]

If 316L is marginal enough for an application that it would require solution annealing in order to be satisfactory, my opinion would be to start out with a more corrosion resistant material in order to avoid solution annealing. The sizes you are talking about are very large, and I can envision many things going wrong during the solution anneal process, not to mention the additional expense. A different material may perform better and be less expensive in the long run depending on your situation. However, in the few waste water treatment plants that I have seen plans for, I have not seen anything more exotic than 316L, so it must be working for some people without solution annealing.

 

[yonglwe]

TO GRoberts (Materials),
The treatment plant is designed for 100 years and thus the need to specify this material.
( as a side note only, but to avoid side-treking the main purpose of discussion on the said topics, MSCL (mild steel cement-lined pipe) was proposed only to be rejected on the ground that as the treated effluent from these pipe will be further processed by MF/RO/UF which ultimately used as portable water, the concrete pipe will hv slime deposit/growth leading to more maintenance cost/operational problem)

 

[Metalguy]

I am in agreement with the other recommendations--do not attempt to SA this pipe or the attachments. The residual tensile stress from the welding will be close to the YS of the pipe, which should be fairly low ~40ksi.

Your real concern should be just what Unclesyd wrote-Cl pitting and MIC. Both of these very nasty problems can be reduced if you can keep the water flow constant and fairly high-around 7-8 FPS min. Stagnant areas and stagnant times are bad.