Salt soluble test for un-coated surface

[Syahar1975]

Good morning Gents,

We have hydrotested our tanks with ground water where high Chloride concentrate (more than 10000 ppm) is in the water.

The interior of our tanks would be coated only bottom plate + 1 M of shell from the bottom. The rest would be no blasting nor coating.

After washing down the interior surface of the tank with a good quality water our painting subcontractor only check the salt soluble on the area that would be coated. They did not check the other area. Yes they did use high pressure pump during washing. But I am not sure the cleanliness on the top side. They did not use a scaffolding during washing.

The salt content on area that would be coated are within tolerance. So they assume it would be the same for other area. They don't want to build a scaffolding to check the area above 1 M.

Do you think this is acceptable ?

Your comments and advise is highly appreciated.

 

[cloa]

What is the material of construction?

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[SJones]

Normally, the testing for soluble salts for the purposes of surface preparation acceptance prior to coating is performed on the blast cleaned surface. In this manner, the area of the tank that requires such testing is readily apparent.

Steve Jones
Corrosion Management Consultant

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[Syahar1975]

Good morning Gents,

Cloa, Do you mean the material of the tank ? It is carbon steel.

 

[CoCoE]

Basically the salt test is carried out because of its' hygroscopic nature, which will be detrimental to the coating. For a carbon steel vessel this is not an issue. If there is cl- ions present in aqueous phase, yes, it may cause increased corrosion. But in this scenario, it is not a significant concern.

 

[Syahar1975]

Good morning Cococa,

The water that we use for hydrotesting of this tank has more than 10000 ppm Cl. The exposure time (water filling to draining) about 3 weeks.

Yes we did wash the tank with clean and fresh water but we did not check the chemical content of this water.

After washing down, we check the salt soluble on bottom and 1 M shell and found an acceptable reading. But we did not check the shell area above 1 M.

The subcontractor said (I am still arguing) since bottom and 1 M shell is acceptable after washing so it would be the same for the rest of the shell.

My concern if there is a possibility that corrosion above 1 M on shell will effect to the coated area.