Removal of Surface Radiation from Steel- Dry Blasting compared to Ultra-High Pressure Water
John S. Oechsle Jr., who is now retired, worked with S.G. Pinney & Assoc. in Florida and prior to that in the 1950’s worked with Metalweld and DuPont in the nuclear industry. IN 1999, he talked to me about what happened to the surface, removal of Corrosion, and surface radiation. The exterior surface of any metal starts to change as soon as it comes out of the mill. The change is at the outer boundary and as you go into the material, you reach the bulk property region.
Metalweld and DuPont in the 1950’s showed that corrosion invades the surface by about 2.5 mils at the grain boundary. To remove all contamination by dry blasting, it required 5 consecutive blasts consuming 47.5 lb. of abrasive/ft.2 to remove enough steel to eliminate the surface corrosion contamination. NACE No. 1/ SSPC-SP 5 was the standard.
Ultrahigh-pressure water at 36000 to 55000 psi removed the surface contamination in one full pass. On a project in Japan, 28 tons of structural steel had been in immersion in a nuclear plant for 19 years. The steel was corroded and radioactive. The customer wanted to clean the steel to less than detectable radiation for removal from the site. All steel was ultrahigh-pressure blasted at 55000 psi. 27.5 tons were moved off site at less than detectable radiation so only one-half ton of steel was removed in total.