Water storage tank - repair or repalce?

[eieio]

I have to project to either replace or repair two water storage tanks: (1) a 25,000 gallon tank used to store post-filtered and pre-chlorinated water and (2) a 5,000 gallon tank post-chlorination hydro-pneumatic tank for distribution into a potable water system.

The tanks, believed to have been installed in 1957, appear to be in good condition with only a few visible signs of corrosion at the concrete saddles.

There have been reports of some small leaks that appear to have corrected themselves over time.

There is some speculation that the corrosion and/or leeching seen at the concrete pedestals may be due to the the material between the tanks and may not be the tanks at all.

Are there any concerns that I need to address due to the (a) age of the tanks that might not be of concern with newer carbon steel tanks, (b) presence or source of lead (perhaps in the welds?) or (c) the continued use of the tanks for another 20-30 years?

The repair approach being looked into is as follows:
1. lift tanks off saddles
2. remove all paint and coating off tanks
3. inspect conditions
4. weld new plate as needed to repair any areas where there might be corrosion
5. recoat tanks
6. provide new saddle/tank interface material (not sure what type of material at this point)
7. reconnect and place back into service

I hate to arbitrarily throw away the existing tanks, but do not want to overlook potential problems incurred by keeping them in service in years to come.

 

[JedClampett]

I would consider replacing the hydropneumatic tank. Any welding on will have to be designed to ASME pressure vessel standards and done by ASME qualified welders. It would be cheaper and better to get anew tank.
As far as the water tank, I would remove the old coating, repair and recoat. Without the pressure vessel complication, this is routine.

 

[eieio]

Just one more question:

If you repair a tank that has a interior coating for potable water, how do you restore that if it is disturbed in the welding process?

 

[hokie66]

Your repair operation provides a good opportunity to recoat the tank. I would look at recoating the whole thing, not just where welding occurs. Preparation of the existing surface and using a coating which is compatible with the original are the key concerns. First you need to determine if the original coating can be overcoated. If it is an organic epoxy, perhaps not. Suggest involving a coatings expert, perhaps from one of the industrial coatings manufacturers.