4000 Series steel, MAWT=40 deg C, Un-welded, monobloc pressure vessel

[dengmech]

I am trying to justify the use of 4000 series steels in the hot rolled Quenched and Tempered, either 4140 or 4340, in our high pressure (P>40 ksi) product. The product does not have to meet ASME div 3, although we often refer to the code for best practice. I know the the 4000 series is problematic when welding, high temperature service, corrosion cracking in some environments, graphitization at high temperature, although none of these issues are a concern for our product. Our product is not welded, it operates at 40 deg C max, the pressure vessel is machined from solid hot rolled quenched and tempered seamless tubing. From the perspective of looking at yield, ultimate, area reduction, elongation, and charpy, the 4000 series seams like it can work, although I have never seen it mentioned in any pressure vessel hand book, or other reference for that matter. I do notice there are companies that make ammonia reactor vessels with 100 ksi MAWP, and 250 deg F MAWT, from 4340 steel. I would think these steels could be used in the conditions I have described. Was wondering if anybody had insight or experience in this issue.