Question: Sand Blasting Surface Damage

[SMF1964]

Anyone have data regarding the depth of the surface damage induced by sand blasting (using sand/slag/oxide, not the more esoteric materials like soda ash, dry ice, or sponge) carbon steel to remove adherent oxide (magnetite)?

 

[metengr]

SMF1964;
What exactly are you trying to determine? We use grit blasting for boiler prep for NDT, turbine prep for NDT (except glass bead blasting to avoid removing material in blade root locations) and pipe prep for NDT. I have never seen in my 25+ years of evaluating tubes, rotors, blades, buckets, pipe and BOP systems any subsurface related damage, period.

 

[arunmrao]

Many of the parts that I produce are machined,heat treated(oil quench and tempered) and then sand blast. There has been no complaint so far regarding surface damage.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[SJones]

The blasting process can induce a surface profile with peaks from anything up to 100+ microns dependent upon the abrasive and the duration of blasting if that's what you were looking for.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[SMF1964]

I'm looking more for the depth of the cold work, rather than surface profile. A vendor provided us with a sample showing his "proprietary" process and our engineers wanted to know how this compares with what they currently do to prepare boiler tubes for ultrasonic inspection.

 

[swall]

If you really need to know, bite the bullet and pay for some XRD work. I would guess you need not go more than .005" below the surface. Shot peening, by which you intentionally introduce stresses , typically effects metal to a depth of about .010" max on a spring made from .20" diameter Cr-Si wire.

 

[SMF1964]

Thanks, People.

Regarding XRD work - Yeah, sure. I blew my available XRD budget when I bought a pencil last month and since the outage is over budget, I don't think I'll find some more shillings laying around.

The Ultra-Double-Secret method produced a visible cold worked surface layer (visible as plasticly deformed in an etched metallographic sample) that was less than 0.001" (actually, around 7µm and less). I reported this to our engineer (mechanical/project) and he asked the question "How does this compare with 'regular' sandblasting?" which is what generated this thread.

I've got a bead blasting cabinet here in the lab that I would experiment with, but was hoping for an easy answer from someone who'd already done this sort of thing.

 

[metengr]

SMF1964;
Don't waste your time and effort on this. Grit blasting is what it is, and for boiler NDT all you need is to effectively remove scale down to white metal for UT. There is nothing beyond this unless your vendor is using rocks to remove scale