Tank Design Consideration 1

[ThisFireBurns]

Dear tank experts,

I'm designing new tank due to increase of capacity from the existing tank. This tank is for the storage of chemical (acidic product) and to maintain the operating temperature in between 60degC to 120degC, external steam coil is required.

Below are some related info regarding the tank:

1) Existing capacity is 1000m3 (10000dia x 13000H). New tank will be 2000m3 (14000dia x 140000H , bottom slope.

2) Design Internal Pressure = 24.75 mbarg
Design External Pressure = -5.25 mbarg
Design Temperature = 140degC

3) Material = SS304L

Existing tank has been constructed in 2001, we found out leakage due to corrosion attack on the bottom plate since end of last year. We assume the situation appeared due to tank life aging. Existing tank placed directly on the concrete foundation without any Cathodic Protection or Bitumen cushion undertank. As for the new tank, I'm suggesting to have internal bottom lining (glass flake vynil ester) based on recommendation in API652. Also bitumen layer required for the undertank cushion instead of having cathodic protection.
Question is, is there any brand/spec of tank internal lining compatible for acidic product operating at elevated temperature of 120degC max? I couldn't find anything suitable from jotun & IP in complying to high heat resistance spec. Appreciate if anyone can share/advise.

4) We also have process concern on the offgas transfer to Vent Pot due to new location of the new tank will be double the distance. Currently both KO pot and blower are operating at atmospheric pressure. Based on new location of tank, offgas line will double the distance to travel to be released to KO pot in which offgas transfer will have a chance of backpressure. Based on our process calculation, more than 25kPa is required to set the Design Internal Pressure in order to cater the offgas transfer to be released. Based on this situation, if we increase the Design Internal Pressure is there any major impact on the tank design if we change the design code to API 620?

Appreciate any professional advise. Thank you!

 

[JStephen]

Is the bottom corrosion underside or topside? If underside, you don't need the liner. If topside, you don't need the bitumen, etc.
You're paying a lot of extra money for SS, so my thought would be to figure out what grade of SS you can use to avoid the issue in the first place, then use the extra money for that rather than the liner. You might do well to have a corrosion engineer or chemist involved.

For a tank of those dimensions, cost gradually increases as pressure goes up. This will be extra roof cost, compression ring cost, anchorage cost, foundation cost, some additional testing, etc. If the design pressure is within the range of API-650, it would be preferable to use it.