The design metal temperature for a tank

[zjliang]

As recommended in API 650, the minimum design metal temperature is the lowest one-day temp plus 8 dC. However, does it apply to an electrically heat traced or immersion heater heated tank? Seems too conservative if there is temperature gauge installed to monitor the temperature.

Any comments or experiences?
Thanks.

 

[dtn6770]

I would imagine the intent of the recommendation would be to NOT consider controls or human intervention. Think of a commom cause of failure...You get a serious cold snap that takes out your utilities (electricity) which isn't too much of a stretch. Loosing utilities will give your operators a lot of distractions so there's a good chance that your tank temperature will go un-monitored.

Go with the recommendation.

How the "lowest one-day temp" is determined may offer some latitude.

 

[JStephen]

The point is to avoid using steels in conditions where brittle fracture can be a cause of failure. If the heating or operating conditions are such that it can be shown that a higher temperature will always be maintained, it wouldn't be unreasonable to use the higher temperature. This would be the "experience or special local conditions" phrase in the API-650 requirement.

If it's a small tank, also consider using App. A, which will let you use some materials at colder temperatures than the standard code.

 

[zjliang]

Thanks a lot guys.