API 620 or API 650?

[uncletank]

We are currently designing a number of tanks in Asia which store chemicals that require to be kept at temperatures equal to or below 15°C (60°F) to prevent polymerization of the stored products. Note that the average ambient temperature at this site is around 30°C (85°F).

To maintain product temperatures of 15°C (60°F) the tanks will be cooled via jet mixing systems that route the cycling product through shell and tube type heat exchanger, refridgeration system before it is returned to the tank. Note that Cooling bands will not be installed around the tank.

The minimum design temperatures of the cooled product is - 15°C (5°F). The tanks will be insulated. Please note that these tanks will not be subject to thermal shock or significant variations in temperature


My question is - can these tanks be designed to API 650 or do I need to design to API 620 (Appendix R)- bearing in mind that you can design a tank to API 650 in Canada with a much lower design temperature than what we are using.

Thanks in advance
Sam

 

[rneill]

We routinely design storage tanks in Western Canada to API 650 with design temperatures far lower than this. The last project I had some involvement with was an API 650 tank with a design minimum temperature of -32 C.

Typically, we would select materials with inherent toughness (fully killed, fine grain practice, etc) to avoid the cost of impact testing. However, make sure that the material you select is rated by API 650 to the design temperature you require.

 

[JStephen]

Assuming the tanks are not pressurized beyond the App. F limits, I would go with API-650, making allowances for the temperature.

 

[uncletank]

Thanks very much for your replies, I will design to 650 taking into account design metal temp during steel selection.

These tanks will be fitted with Nitrogen blanketing systems, but the design pressure will not exceed the limiys in App F.

Regards
Sam