Kirk wrote: You show decent metallurgical knowledge. A pressure vessel is one of those items which needs bleeding edge strength and so which we would want to avoid any processing which could change the steel's temper. Welding always affects the temper. The heat affected zone (HAZ), the weld itself and a small band on either side of the weld, will be back to or nearly back to the annealed condition. Heating to the molten state in the weld and somewhat less warmth in the nearby areas removes or reduced any work hardening or heat treatment previously done to the alloy. Annealed is much weaker than the heat treated or work hardened state. Some alloys can be reheat treated though rarely to the same high strength achievable the first time the alloy is heat treated. And of course work hardening on a finished item like a pressure vessel is impossible, beyond bead blasting the surface. Some alloys will only strengthen via work hardening. Some only via heat treatment. Steels fit into both categories depending on the alloy.
Even so, all that would be required to create the pressure vessel on site via welding is to take this strength reduction into account. Start with pieces sufficiently thicker that the alloy in the annealed condition is strong enough. Shipping problem solved. I'm not sure why this particular pressure vessel could not be done that way. Perhaps the cost of shipping something this ungainly isn't as expensive as using more metal to make the pressure vessel out of an annealed alloy.
Thanks, I'll take that as a high compliment, considering how basic my metallurgic training has been.
Obviously taking the strength reduction into affect would be possible, but for the amount of steel and the high pressure that's probably required, it's likely a high grade of steel that is significantly more expensive. If this was in a high density area that'd probably be cheaper, but Saskatoon is in Saskatchewan, which is prairie country. I don't imagine it'd be too much more expensive to ship as is and have the fabrication in a tightly controlled environment. The oil industry doesn't tend to skimp.
If I remember correctly, when welding a strength critical area, the steel is often preheated before welding, and is insulated or even heated over the cooling period using heating blankets to reduce brittleness and maintain the correct ratios of grain structure in the steel. That's a shipyard practice though, and I don't know if it'd transfer to terrestrial applications. There is no large scale welding in the civilian maritime world that I know of equals the type needed for a pressure vessel.
Aquaman sucks
