A.O. Smith Corp Nitrogen Storage Tank

Is this ASME or DOT rated, and what does that allow me to do with it?

This vessel was manufactured to Mil-Spec code, not ASME Section VIII or DOT. Military specification vessels were typically built to requirements similar to or exceeding ASME standards for defense applications, but lack the ASME U-stamp or DOT certification markings that would permit jurisdictional operation under those codes. You'll need to verify the specific Mil-Spec standard with the seller and determine whether your jurisdiction and insurance carrier will accept it for stationary storage, or whether you'll need a variance or independent engineering assessment.

What is the MAWP and capacity at service pressure?

The working pressure is listed as 2800 PSIG with a capacity of 52.8 cubic feet (396 gallons). Test pressure is 4,200 PSIG, which suggests a 1.5:1 test-to-working ratio typical of high-pressure gas storage vessels. The listing does not specify whether the 52.8 cubic feet represents water capacity or gas capacity at working pressure—confirm with the seller which measurement convention was used, as this affects actual gas storage calculations.

What is the requalification or inspection status?

The listing does not provide any information on inspection history, hydrostatic test dates, or current certification status. For a vessel manufactured in 1960, you should request documentation of all requalification tests, internal inspections, and any repairs or alterations performed over its service life. Mil-Spec vessels don't follow standard DOT requalification intervals, so the inspection protocol will depend on your operating jurisdiction and any existing maintenance records.

What should I inspect before putting it into service?

At a minimum, conduct a complete external visual inspection for corrosion, dents, arc strikes, and any signs of previous repair or alteration, then perform a hydrostatic test to the vessel's test pressure of 4,200 PSIG. Given the 1960 manufacture date, strongly consider ultrasonic thickness testing to assess any wall thinning and an internal inspection if access permits, particularly to evaluate the condition of welds and look for pitting, stress cracking, or hydrogen embrittlement. Verify that all original nameplates are intact and legible, and have a qualified inspector review any documentation the seller provides against the physical markings on the vessel.