Operational Temperature vs. Pressure

Can a carbon-steel tank take the high temperatures of superheated-steam cleaning?

Superheated-steam cleaning of alkali-metal tanks has long been a concern because of the high temperatures in the liquid pool. Tanks are normally designed for a pressure-and-temperature limit that does not anticipate temperatures as high as 1200°F.

CEI has been cleaning tanks with large quantities of alkali metals for many years and never experienced a problem, principally because the process is run at essentially zero pressure. To help potential customers understand that the process can be done safely, CEI commissioned a Licensed Professional Mechanical Engineer with pressure-vessel design experience to tell it what the ASME-code calculations would predict for an allowable operating pressure under various scenarios.

In all cases, it was determined that the allowable pressure was higher than the 0–1 psig that CEI’s system would place on the tank. Remember that the advantage of the superheated-steam process is that the large “excursions” that happen with WVN do not happen with superheated steam.

Here are a couple of examples to help illustrate the point.

Case 1
50,000-gallon vessel rated at 50 psig at 300°F constructed at SA 516 Gr 70 Carbon Steel, FD head, 0.25-inch-thick plate, 12′ dia. by 56′ straight side.
Allowable pressure at 300°F = 59 psig
Allowable pressure at 750°F = 44 psig
Allowable pressure at 1000°F = 7 psig
This shows that CEI can implement the superheated-steam process on a carbon steel tank up to 1000°F without exceeding the pressure capability of the tank, even using the conservative calculations of the ASME Pressure Vessel Code.
Case 2
50,000-gallon vessel rated at 45 psig at 300°F constructed at SA 240 (316 SS), FD head, 0.25 inch thick plate, 12′ dia. by 56′ straight side.
Allowable pressure at 300°F = 46 psig
Allowable pressure at 750°F = 35 psig
Allowable pressure at 1000°F = 33 psig
Allowable pressure at 1400°F = 7 psig
This shows that with a SS tank, CEI can safely implement the superheated-steam process up to our typical 1100°F with no concerns about exceeding the pressure capability of the tank.

 
Note: We realize these calculations are for a given tank configuration. The design of your tank can be easily reviewed in the same manner to set the upper bounds of the superheated-steam process for your tank.