Stainless Tank per API 650 Questions

[EfficientPuppy]

I'm looking through the design on stainless tank API 650 tanks, and I have a few practical questions for you all.

1. How do you all deal with the requirement for stainless steel course widths being set to 4' (without approval) when the only plate widths available in stainless are 4'. Unless that tank height is always a multiple of 4', then per this requirement you need to ask for approval to do the make up course. So are you just preliminarily requesting approval to use different course sizes on any stainless tank? And if you are getting approval do you have an absolute minimum course width that you use?​

2. How do you work with a manway when the first course has to be 4' wide. This would put the seam of the first vertical weld basically in the middle of the manway. Is this even permitted when you have a repad on the manway? Are you using a thickened insert for the manway when needed?​

3. How are you building repads? I guess my assumption has always been that tank repads should be build from a single sheet of plate, but how is that possible if the only plate available is 4' wide. I can't seem to find in API 650 that my assumption is correct, so maybe I am wrong about that. But I also can't find any welding requirements, such as were the weld seam should be, which direction the seam should go, and how to inspect it.​

4. Austenitic Stainless is allowed to have two courses be shop welded before shipping to the erection site, but I am not seeing this same verbiage in the Duplex section. Am I understanding this correctly, that it is not permitted to shop weld two courses with duplex?​

Thanks everyone for your insights.

 

[JStephen]

I don't deal with stainless much, but wasn't aware of any difficulties buying wider-than-48" plate, either.
So my first thought is really work on plate supply rather than detailing, and, if necessary, switch alloys to something more available.
See 5.7.3.4 for nozzles in shell seams.
I don't see any reference to 2-piece repads in API-650, but I'm pretty sure they're allowed in API-653, and presumably would not be objectionable for an API-650 tank. Generally, seam is horizontal at the center of the nozzle, with a weephole in each section.

 

[EfficientPuppy]

Yeah the challenge is that I wouldn't be using stainless materials that are too out of the ordinary. I am talking 304 or 316 stainless, in duplex it would 2205. My suppliers insist that it is only available in 4' width. I've looked at some online suppliers and they all only list 4' wide plates. One of the guys here thought they came went up to 6' wide, but the best he could actually find was in select thickness. I'm not saying that you can't find them, but it does seam to be rarer than I'd expect with API listing it as a minimum. Maybe its time to call up a mill and see what they actually produce.
Thanks for the direction on the the repads. I didn't think of reviewing API 653 I'll give it look over.