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Surface Preparation Standards

From Draftsperson.net

This information applies to the American Steel Industry

A basic description of the different standards is as follows:

SSPC-SP1 - Solvent Cleaning. Oils used in various cutting and drilling machines are deposited on the steel. These must be cleaned off prior to applying any coatings. The solvent cleaning process uses an organic solvent that is either wiped or sprayed on the steel to remove dirt, oil, grease, and other contaminants from the surface of the steel. This can be followed with detergents or steam cleaning. This step is integral because it is the only surface preparation process that removes oil and grease from the steel. Other processes will roughen the steel but not remove oil and grease.

SSPC-SP2 - Hand Tool Cleaning. Hand tool cleaning is usually done with a wire brush or sandpaper. This process will remove loose surface rust and mill scale but is not intended to remove strongly adherent rust. This preparation is generally not adequate for structural steel that will remain exposed. This method is often used to spot clean areas of a structure that might have rusted, at regularly scheduled maintenance times. It does not require a large working area or produce as much dust or noise as power tool cleaning. As a result, it can be performedin higher profile areas without disturbing the surroundings. Oil-based alkyd paints and epoxies work well with hand tooled preparation.

SSPC-SP3 - Power Tool Cleaning. This level of preparation will produce the same results as SSPC-SP2, but uses power tools such as grinders or sanders instead of wire brushes or sandpaper. The cleaning removes all loose mill scale, weld spatter, rust, paint, and other surface contaminants. This level of preparation is usually a minimum for most AESS steel. The main advantage of this method over hand tool cleaning is time savings when working with larger quantities of material.

SSPC-SP5 - White Metal Blast Cleaning. Blasting to white metal is the most rigorous preparation that can be specified. The surface shall be completely free of all contaminants; no surface contaminants may be visible. These include oil, grease, dirt, rust, paint, mill scale, and oxides. In a 9-sq.-in. area, no rust staining can be present. Blasting is done in a rotary blaster or with compressed air through hand-held nozzles. Small abrasives of metal shot or mineral grit are used.

SSPC-SP6 - Commercial Blast Cleaning. This process is common for AESS steel that will receive a high-end finish. It is more intense than brush-off blast cleaning but not as rigorous as near-white or white metal blast cleaning. No surface contaminants may be visible. In a 9-sq.-in. area, no more than 33% of the area can be stained due to rust. It is required for most epoxy primers and polyurethane finish coats.

SSPC-SP7 - Brush-Off Blast Cleaning. This is the least intensive type of blast cleaning. Its main advantages are speed and economy. Tightly adherent contaminants may remain on the surface of the steel.

SSPC-SP8 - Pickling. This process is most commonly seen as one in a series of baths used in preparation for hotdip galvanizing. The steel is dipped in a series of tanks to cleanse, pickle, and flux the material. The pickling material can be sulfuric or hydrochloric acid. It will provide a chemically clean surface for galvanizing.

SSPC-SP10 - Near-White Metal Blast Cleaning. This category is more rigorous than commercial blast cleaning but not as rigorous as white metal blast cleaning. It will add significantly to the cost of the preparation, but when done correctly and with a compatible paint system, will provide a longer service life than other systems. No surface contaminants may be visible. In a 9-sq.-in. area, 5% rust staining can be present.

SSPC-SP11 - Power Tool Cleaning to Bare Metal. This method utilizes power tools to remove all adherent contaminants on the surface of the steel. It also has a required surface profile that must be produced. It usually requires impact-based tools rather than rotary-based tools. It is more rigorous than power tool cleaning. It is generally specified if the preparation is to be performed on spot areas in the field where there is no blasting equipment available.


AISC Recommendation

Section 6 of the AISC Code of Standard Practice (COSP) states that steel that is to remain unpainted "shall be cleaned of oil and grease with solvent cleaners, and of dirt and other foreign material by sweeping with a fiber brush or other suitable means." Steel that is to be painted must be prepared to a minimum of SSPC-SP2 (Hand Tool Cleaning).

The COSP addresses AESS in Section 10. This section notes that weathering steel must be prepared to category SSPC-SP6 (Commercial Blast Cleaning). This is done to remove scale that prevents the material from generating the even patina it is chosen for. However, nowhere in this section are guidelines given for general surface preparation of AESS members. Levels of preparation beyond SSPC-SP2 must be specified by the designer.


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