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Are All Surface Prep Standards Created Equal? Part 2

WEDNESDAY, JANUARY 25, 2017

By Lee Wilson

In last week’s blog post, I discussed ISO 8501-1, specifically Standard Sa2½, and some of the ambiguity that surrounds the surface preparation standard. This week, let’s take a look at SSPC-SP 10/NACE No. 2, Near-White Metal, which is considered to be the equivalent to ISO 8501-1 Standard Sa2½.

How are they different? What more do we get from the joint SSPC/NACE standard?

Abrasive blasting
© iStock.com / Glenj

The joint standard explains what stains are allowed, and it tells the inspector the amount of such staining allowed on the surface after blast cleaning.

Let me start with the definition—that’s where the fun really begins. This is the heart of the standard. and the section for which the standard is remembered.

SSPC-SP 10/NACE No. 2

SSPC-SP 10/NACE No. 2, Near White Metal, states: “A near-white metal blast cleaned surface, when viewed without magnification, shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter. Random staining shall be limited to no more than 5 percent of each unit area of surface (approximately 5,800 mm2 [9.0 in.2] (i.e., a square 76 mm × 76 mm [3.0 in. × 3.0 in.]), and may consist of light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale, or stains of previously applied coating.”

Here is my point: The joint standard tells me what stains are allowed (light shadows and slight streaks or minor discolorations caused by stains of rust, mill scale, or previously applied coating), and it tells me the amount of such staining allowed on the surface after blast cleaning. I now know that I am allowed 5 percent of visible contamination and in what form—much more information than is given in ISO 8501-1.

Abrasive blasting
© iStock.com / kimtaro

The joint standards thus come with copious amounts of information, directions, and a visual supplement from SSPC. So why are specifiers still choosing the ISO 8501-1 standards without stating the SSPC/NACE standards as equivalent standards? The next installment of this series examines just how equivalent they are.

What else does the SSPC/NACE standard tell me?

It gives me clear instructions that no oil, grease, or dirt is allowed on the substrate, and it tells me how to remove the contamination—by following SSPC-SP 1, “Solvent Cleaning.”

However, even SSPC-SP 10/NACE No. 2 isn’t perfect. SSPC-SP 1 advocates solvent cleaning, and cleaning with most solvents is not an environmentally friendly or operator-friendly procedure. SP 1 does give the option of emulsion/alkaline cleaning or steam/hot water/detergent cleaning. These methods can leave residues as potentially harmful as oil, grease, or dirt on a metal surface unless an adequate freshwater cleaning (not an option in a lot of cases) follows.

Requirements

The joint standard also gives a full rundown of the requirements for the written standard, including:

•    General information regarding the standard;

•    Definition or the heart of the standard;

•    Reference documents such as SSPC-SP 1 and SSPC-VIS 1 (pictorial standard, described below) as well as abrasive (AB) standards and SSPC-PA Guide 3, on safety in paint application;

•    Procedure before blasting;

•    Blast cleaning methods;

•    Blast cleaning abrasives

•    Procedure following blast cleaning immediately before coating;

•    Inspection;

•    Safety and environmental conditions; and

•    Comments.

From SSPC-SP 10/NACE No. 2, I get five pages of information telling me what to do and in what order to do it to comply with the requirements of the standard—five pages of information, as opposed to ISO 8501-1’s one sentence, which does little more than confuse me and my fellow inspectors.

Other References

In addition to the five-page written joint standard, I get a reference to SSPC-VIS 1, “Guide and Reference Photographs, Steel Surfaces Prepared by Dry Abrasive Blasting.” Similarly to ISO 8501-1, SSPC-VIS 1 shows the rust grades (five in the SSPC standard) blasted to all the SSPC/ NACE joint standards. It also informs me of acceptable variations in appearance—factors such as the original surface condition or the type of abrasive used that may affect the visual appearance of the standard but not the actual surface cleanliness.

The joint standards thus come with copious amounts of information, directions, and a visual supplement from SSPC, so I ask: Why, when all this information is available to us, are specifiers still choosing the ISO 8501-1 standards for dry abrasive blasting without stating the SSPC/NACE standards as equivalent standards?

Next week, in the final installment of this series, I’ll look at what makes a standard, what makes a good standard, and whether or not the ISO and SPPC/NACE standards that we generally think of as equivalent really are.

ABOUT THE BLOGGER

Lee Wilson

Lee Wilson, CEng, MICorr, is a NACE Level 3-certified CIP Instructor and Senior Corrosion Technologist, as well as an ICorr Level 3 Painting Inspector and Level 2 Insulation Inspector. The author of the best-selling Paint Inspector’s Field Guide, Lee was named one of JPCL Top Thinkers: The Clive Hare Honors in 2012. Contact Lee.

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Tagged categories: Abrasive blasting; Certifications and standards; ISO; SSPC; SSPC-SP 10; Surface preparation

Comment from Paul Buchanan, (1/30/2017, 6:09 AM)

I have had several differences of opinion with coating contractors about what is a slight streak,light shadow or minor discolouration, these descriptions are not helpful. If free of ALL dirt, oil grease etc then what is the streak etc comprised of.


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