Shot Blast Profile Deterioration: Humidity v Time

[deco0404]

Hi guys,

need a little advice here. We are having a little difficulty with owners reps at the moment over the time taken from blasting sections of steel to the application of primer coat.

The steel is bog standard - nothing special. Surface finish is SA2.5

The general rule of thumb (as I understand it) is that at 85%RH, you have 4 hours before the blast finish deteriorates. We are currently working on averages of 50-60%RH.

I am assuming that the relationship between the two is exponential, the question is, does anyone have anything concise on this please? Or can anyone tell me how long I have at, say 60%RH

We are using big de-humidifiers, but we are working on a dock, so almost impossible to reduce the RH% any further.

Declan

 

[eyec]

my understanding is that you need to watch for rust back. the blast profile will only change with the appearance of contamination (rust). SA2.5 is the same as SSPC-10 NACE 2(I think). the other requirement to watch is the dew point. u need to be at least 5degF above the surface being blasted.