First of all, when you ask questions like "is it necessary", we don't have near the information to make that determination. Like what the service temps and medium will be. And even with that there is few in here can make that determination. But I'll attempt at an opinion here which may help a little. Or at least provide info for later questioning and/or dialogue with your customer.
From my own perspective, I wouldn't mess with STT on something 11 feet in diameter. I'd use SAW.
I also wouldn't worry about chill bars on something that big. By the time you get back around on it your gonna be cool enough I would think.
Also, in my opinion, if the customer is insisting on annealing (I'm assuming solution annealing) and quenching (thus solutioning) it tells me (in my opinion again)they are sittin right on the edge of acceptability for this alloy in this service and wish to homogenize the microstructure (or they are playing it conservative to say the least). And if your annealing there ain't no point in worrying about chilling because the carbides, what few there may be with 321, will go back into solution anyhow.
Necessary will be determined by what the service requirements are and can't be determined here, but annealing and quenching 321 is unusual (we could sure use Chuck here to help us out on current industry practice). The primary idea of 321 is to not have to do things like annealing. If your gonna anneal and quench, why not go to a cheaper filler alloy (like 308), unless you need the additional strength (in which case 316 I believe can match, and I believe also cheaper). And you may find a slight loss in strength with solution annealing.
The advantage to 321 is essentially eliminated with the anneal. Unless there is something I'm overlooking.
I notice you said customer is suggesting solution anneal. which tells me they don't have a specific insight on the particular service. If they have a concern for mechanicals or corrosion, do some testing. But keep inmind corrosion services are like finger prints. Very individual. They will only give you a reference.
In addition to JS55's great advise, think about the following when dealing with your customer's suggestion of solution annealing and quenching this 11 ft x 40ft vessel.
I'm sure there may exist an oven big enough to heat a vessel that size up to around 1800-1900F, but I don't know who would have any. And even if you found one (or had to build one), I don't think you would end up with anything resembling a round vessel after you heat treated it. Even if you could actaully build enough supports into a 3/8" thick walled vessel that size so that it did not completely collapse into a pancake about 3/4" thick when heating it up to 1800F or so, what would happen to it when you try to quench it? It is much too big to water quench in a tank (which would give you the best results ,microstructurally, after a solution anneal), so you would have to at least fan cool or water spray cool. This thing would be bannana/pretzel/record in the sun/oil can when you are done.
Your best route is to see what your customer is concerned about and what they are trying to achieve with thier proposed annealing/quench, and see what other ways you can try and achieve the same objective.
When I was reading the original post and js55's response I was wondering "how in the he** do You solution aneal somthing this size?" Now I am a country boy who hasn't seen all of the big wide world, reading GRoberts's reply, now I know.
A couple of the fabricators I've worked for in the past had batch furnaces big enough (railroad car types and cap types) for 11X40 (just barely though-and where do you put the thermocouples to regulate to the cook?-the flame ports are generally on the sides and low, so thats where your heat is gonna concentrate-try maintaining a narrow temp range throughout-critical to minimizing stresses), but Greg is right. If I may use technical language to emphasize his excellent point, in my opinion what you will probably end up with is a 'big'ol chocolate mess' trying to anneal and quench something like that.
If you are forced to do it you might try locals over the welds as opposed to a batch furnace. But even that is gonna be tough (we're still talking about SS that just loves to move around on ya), the dimensional and tolerance issue Greg spoke will still be there just a little more limited.
Oh ya, and in agreement with Greg again, your gonna need so many spiders its gonna look like the production set of the movie Arachniphobia.
You are definitely looking at this from a very practical manner. I agree that this would be not only expensive but impractical and customer has no justification for annealing when his service temperature of 300F is way below sensitizing. Your opinion quite in line with other and with mine.
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