Hydrotest in a freshly welded water tank

[pbc825]

We've been retained to provide repair recommendations for an elevated water tank. The tank froze as a result of a water recirculation system failure in the dead of a cold Canadian winter. Large crack. I'm a structural engineer and I've done a number of water tower repairs, assessments and certifications. We will be issuing drawings soon with repair recommendations for welding and coating. I'm going to specify a hydrotest between welding and coating to ensure we don't miss any cracks prior to the costly recoat.

I'm wondering about good practices for the hydrotest as it relates to the water distribution system for the town. My sense is telling me the town doesn't want to drink welding slag or blast media, so I suspect disposing of the water is a reasonable practice. There will be ~65,000 US gallons to dispose of. My questions are as follows:

1) Is it a good practice to dispose of the water? If so, do we put it in a ditch or are there other disposal measures to be taken?
2) Are there distribution system protection measures that should be taken during the hydrotest (i.e. a condom over the water system inlet pipe, or something of the like)?
3) Does the distribution system require a flush after the painting is finished and the water system is refilled with potable water?
4) What sort of water quality testing measures are appropriate following completion of repairs?

We typically work for a multi-disciplinary firm as a sub-contractor to provide the repair recommendations. The larger firm typically has water experts who deal with this. In this instance we've been retained directly by the owner. I'm going to refer the owner for this scope; however, the specifications are going out shortly and I wouldn't mind some advice in the interim.

 

[fel3]

Why not hire the multi-discipline firm as a sub-contractor? That way you would have water experts you are familiar with to handle a task you are not familiar with.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[pbc825]

Thank you Fel3. That is the plan. Looks like they will be retained directly for this scope. Any advice in the interim would be appreciated.

 

[LittleInch]

The bit I'm worried about is using a hydro test to find cracks in the existing metal.

Are you really sure repair is the right way to go?

Can you use some investigation techniques instead? U/T or similar crack detection systems.

Then you have the confidence to repair and then coat before hydro.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pbc825]

Thank you for your comments LittleInch. We're planning to do a thorough inspection using magnetic particle techniques from both the interior and exterior. We're simply planning to compliment the inspection with a hydrotest so as to reduce the risk of leaking following a $100K+ coating application. A second check if you will.

I'm not sure I understand your question about repair. Are you asking if replacement is a preferred alternative to repair? I've done a thorough investigation of the repairs, and I'm confident repairs are reasonable, suitable, and economic for the damage observed.

Any water system protection measure comments are still welcome.

 

[amlinerrichard]

Disconnect the tower from the existing water mains. Chlorinate the tower and dump that water before reconnecting. Retest the water main system for proper chlorination.

 

[mk3223]

To minimize the impact to the local community, the disposal of the testing water can be a critical task to your project if the proper procedure is yet defined.
Suggest to contact the local environmental specialty company, such as Clean Harbors, for a proper treatment solution.

https://www.cleanharbors.com/services/technical-services/waste-disposal-services

 

[pbc825]

Thank you for your comments.

I’ll report back when I know the project outcomes to wrap up the thread.

 

[bimr]

1) Is it a good practice to dispose of the water? If so, do we put it in a ditch or are there other disposal measures to be taken?
The only issue is that the used water must be dechlorinated.

2) Are there distribution system protection measures that should be taken during the hydrotest (i.e. a condom over the water system inlet pipe, or something of the like)?
Yes, should have a blind flange in the connection line.

3) Does the distribution system require a flush after the painting is finished and the water system is refilled with potable water?
If the distribution system has been out of service, you will need to chlorinate and then flush the distribution system.

4) What sort of water quality testing measures are appropriate following completion of repairs?
Bac-T is our shorthand term for the total coliform bacteria presence/absence test.