Corroded bare steel pump columns filtered/chlorinated water

[kmer]

We have new vertical turbine pump columns (installed a year ago, and finally put into service about two months ago) that are badly corroded.

The columns are bare steel (no lining). They were installed in a new water treatment facility about 14 months ago, before the building was finished. The plant is only now becoming fully operational. During their time on site, the reservoirs were coated internally with a highly-corrosive cement based waterproofing agent that was wet cured. Exhaust fans were used to bring fresh air into the reservoirs during this process. Humid air escaped throught the overflows and the column shafts.

Shortly after the waterproofing was completed, the reservoirs were filled and emptied several times for leak testing.

Once hydrostatic testing passed, the reservoirs were super chlorinated and rinsed.

Obviously there were many occasions for rust to form on the interior surface of the columns. The rust now has a firm grip and was evident by the turbidity spikes observed after switching to an idle pump.

We disassembled one column and revealed the culprit, as suspected. Failure to adequately protect the bare steel finish has resulted in an amazing buildup of scale and pitting.

We've settled on removing the columns and having them sandblasted and epoxy lined by a reputable industrial firm.

The question is... suppose we elected instead to simply go through the sandblasting process and leave the columns untreated, would we expect to see more/less/same amount of rust develop over the life of the column with the mechanically altered finish as opposed to the mill finish?

 

[EdStainless]

I would expect less corrosion in regular service than you saw during construction. The alternate wet/dry (with chemicals and Cl thrown in) will make the problem worse.

Epoxy lining is a good step. Since the surfaces are damaged now just cleaning them will not put you back to where you started. They need a bit more help than that.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[kmer]

Thanks for your reply EdStainless.

So you've touched on the concept that I'm trying to explain to the conrractor. I'm still at a bit of a loss for the right words. The best way I can put it is that the original surface was 'compromised'.

In my mind, it's like the tight-grain steel surface is disrupted leaving the lower density structure exposed. Do I have it right?

 

[EdStainless]

No, not really.
A better way to look at it that the original surface was smooth with no crevices or pits to trap material. Now after the corrosion issues the surface has been roughened. This will result in the trapping of more debris and the rough surface will be more easily corroded than the original smooth surface.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[kmer]

I didn't think of that aspect. Thanks.

Kmer