Repurposing an API 650 Tank

[manj1987]

Hi,

We have and oil tank which client wants to be used for water now. We have to give a scope of work for this job. my understanding is that our scope of work will include following things:

1- complete on site inspection of tank as per API 653(we will sub-contract this work)
2- from inspection report i being a static design guy will check whether actual thickness can bear the water head using api 650 formula.


kindly confirm my understanding

 

[JStephen]

That would be a "change of service" as evaluated per API-653.
Tanks in petroleum service are commonly unlined or just lined in the lower portion. Tanks in water service normally require full interior lining, including the roof and roof structure. P/V vents and other hardware may require evaluation for the change of service as well.
You would also need to evaluate the foundation for increased loading if applicable.
There may be regulatory limitations that would prevent the tank being used for potable water service.

 

[manj1987]

So in the light of ur answer these are the main things:
1-Evaluation as per Api 653
2-Checking for the requirement of internal lining
3-Performing venting calculation as per API 2000
4-Checking of foundation against new loads as water has higher sg, but do we need to check other new foundation loads as per latest API 650?
But what do u mean by regulatory limit? Can give some reference stds

Thanks,
Manj

 

[JStephen]

For example, from the State of Texas rules for public water systems: "No tanks or containers shall be used to store potable water that have previously been used for any nonpotable purpose. Where a used tank is proposed for use, a letter from the previous owner or owners must be submitted to the executive director which states the use of the tank."
I don't know the history or reasoning behind that rule, or specifically what problem it was intended to avoid. It may have been partly motivated by the storage of leaded gasoline in decades past.

 

[bimr]

Tanks in oil service may experience corrosion in the bottom area because of water that may get trapped in the bottom. At the oil water interface, the corrosion is typically more severe.

In addition to the above comments, after rebuilding the tank a hydrostatic test is necessary. Some modifications to the tank connections may also be necessary.

 

[sajk14]

Gents,

With regards to checking if the actual/existing shell thickness can take the higher loading due to the increased product density...

From the inspection report would you use the 'average' thickness reading or the 'minimum' thickness reading found for each course when comparing against the calculated minimum acceptable thickness 'tmin' as per API 653 clause 4.3.3.1.a ?