SP-6, SP-10 and the standards your coating is asking for

Industrial coating specs reference blast cleanliness standards. They look like alphabet soup and they have real cost implications, so it is worth knowing what you are asking for.

The common ones

• Brush-off blast. Loose material removed, tightly adherent mill scale and coating may remain. Cheapest, used for maintenance coatings over sound existing systems.
• Commercial blast (SP-6). Staining permitted on up to a third of each unit area. The workhorse standard for most structural steel and equipment.
• Near-white (SP-10). Staining on no more than five percent. Used for immersion service, aggressive chemical exposure and high-performance systems.
• White metal (SP-5). No visible residue at all. Expensive, slow, and reserved for the most demanding service.

The cost curve is not linear

Going from commercial to near-white is not a small increment. The last few percent of staining takes disproportionate time, media and cost. Specifying near-white on a job that only needs commercial can add substantially to the price for no service life benefit.

Staining is not rust

A common misunderstanding. The staining these standards allow is discolouration in the pits of previously corroded steel, not active corrosion. It is shadow, not scale.

Anyone tendering work through the City of Medicine Hat, or subbing to a fabricator in Brier Park Industrial or Box Springs Business Park, will see these standards written into the specification rather than described in words.