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October 21, 2024A World of Acronyms and Standards
When I first saw a real coating specification I was overwhelmed by the amount of information and references to different industry standards – AWWA, NACE, SSPC, MPI, ASTM, ISO, and so forth. While each of these acronyms reference important associations, this article will be focused on SSPC.
By providing a brief summary of the SSPC standards that you may encounter in coating specifications, you will develop a working knowledge for when you are speaking with your customers, engineers, designers, architects, project managers etc.
Before we begin
If you are going to reference standards when incorporating standards for jobs, we strongly recommend purchasing the complete standard directly from SSPC. Referencing this article or other summaries found online will not provide sufficient information. SSPC can be found online at http://www.sspc.org. These standards provide a universal reference point when addressing any questions or issues on a project and should be kept at hand.
In addition to written standards, SSPC also provides visual standards to use a reference point when determining what the acceptable blasted surfaces look like.
If your customer does not have their own reference standard, I would strongly advice becoming familiar with SSPC-VIS1: Reference Photographs for Steel Surfaces Prepared by Dry Abrasive Blast Cleaning and SSPC-VIS3: Reference Photographs for Steel Surfaces prepared by Hand and Power Tool Cleaning.
An overview of applicable standards
SSPC-SP1: Solvent Cleaning
SSPC-SP2: Hand Tool Cleaning
SSPC-SP3: Power Tool Cleaning
SSPC-SP5/NACE No.1: White Metal Blast
SSPC-SP6/NACE No.3: Commercial Blast
SSPC-SP7/NACE No. 4: Brush Blast
SSPC-SP10/NACE No.2: Near-White Metal Blast
SSPC-SP16: Brush-off Blast cleaning of Non-Ferrous Metals
The above lists the standards that will be covered in this article. In the cases where NACE appears, this indicates that SSPC and NACE have agreed on joint standards in regards to the abrasive blasting.
SSPC-SP1: Solvent Cleaning
This surface preparation standard is used for the purpose of removing oils, soils, grease, salts and other contaminants by wiping with solvent, degreasing, steam cleaning, etc. For a full list of suitable methods the standard should be referenced. The sole intention is to clean the substrate prior to coating or blasting to avoid entrapping any contaminants that would lead to premature failure. In the case of a part requiring blasting, it is always referenced as a requisite before blasting or tool cleaning. Failure to do so may contribute to premature coating failure.
In most job shop environments the way that this standard will be followed is by use of solvent and a rag. When doing so, a continuous wipe in one direction on the substrate is required. Once the wipe is completed, observe the rag and turn it to a new area that is clean. Failing to do so will simply result in the smearing of oil across the substrate. The entire purpose is to remove “visible deposits of oil, grease, and other contaminants…”[1].
[1] Surface Preparation Specification No.1: Solvent Cleaning, SSPC: The Society for Protective Coating, November 1, 2004.
SSPC-SP2: Hand Tool Cleaning
While not an ideal method of preparing a surface to receive a powder coated finish, if your customer requires the part to be cleaned to this degree of cleanliness be aware that to conform to SSPC-SP2 the part is to be free of all loose material. This means that if there is left over paint, rust, mill scale that cannot be removed by “lifting with a dull putty knife”[1] then you’ve achieved SSPC-SP2.
As a powder coater, I cannot think of a time when this would ever be satisfactory. The only time that I would reference SSPS-SP2 is when removing weld splatter and slag with a chisel hammer for the purpose of prepping for blasting.
SSPC-SP3: Power Tool Cleaning
The requirements to achieve a surface free of contaminants that cannot be lifted with a dull putty knife applies to SSPC-SP3 as well. The key difference is that this standard is based on the use of power tools. It is worth mentioning, however, that when employing power tools to prepare a surface, the operator should not remove any more material then what is intended. On certain projects, removal of material could lead to visual defects that result in costly rework.
Moving into Blasting Standards - a word...
What the following blast cleaning standards are not:
Before diving into the particulars of the SSPC standards which apply to dry abrasive blast cleaning, it is worth mentioning what is applicable to SP5, SP10, SP6, SP7, and SP16.
- Abrasive blast media is not specified
- Blast profile depth is not specified
- All standards expect that the substrate conforms to SP1 prior to blasting.
- It is mandatory that the blast system be using clean, dry, air.
- If between the time of blasting and coating the part no longer conforms to the required standard, it must be blasted again. (eg. Customer has pipe spooling that is to be blasted to SP5. It flash rusts in the oven during prebake. You must blast it again to SP5 before applying your coating).
- The condition of the steel prior to coating will have an impact on the appearance of the steel after blasting – deeply pitted and corroded steel will still look pitted after blasting.
- Sharp edges, burrs, weld splatter, and slag should be removed prior to cleaning as abrasive blasting is not an effective means of removing these.
SSPC-SP5: White Metal Blast Cleaning
This is the cleanest degree of blasting that you will encounter. Typically SP5 is referenced when substrates are going to be exposed in a hostile environment such a chemical treatment facilities, oil and gas, marine environments, etc.
SP5 requires that “when viewed without magnification [the part], shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter.” Simply put – it has to be white metal clean. Even the staining that mill scale and rust can leave behind must be cleaned from the substrate.
SSPC-SP10: Near-White Metal Blast Cleaning
At my company we typically end up blasting to an SP10 even when an SP6 is required. This is the case when working with tightly adherent mill scale that must be removed. According to SSPC-VIS1 the effort required to remove tightly adherent mill scale typically results in an appearance that is closer to an SP10 than an SP6.
This is our go-to degree of cleanliness any time we are preparing product for long term use outdoors. The key differentiator between an SP5 and SP10 is that on any surface of the part, there can be no more than 5% random staining in each unit area of surface measuring 9 in² as per the standard. Staining from rust and/or mill scale would show up as discoloration on the surface.
SSPC-SP6: Commercial Blast Cleaning
Most of what would apply to SP6 has been covered in the above discussion. In the case of SP6, we will use this degree of cleanliness when a single coat indoor application is required, or a low cost outdoor two coat system is requested. The key difference is that it allows for up to 33% random staining instead of 0% (SP5) or 5% (SP10).
SSPC-SP7: Brush-Off Blast Cleaning & SSPC-SP16: Brush-off Blast Cleaning
of Coated and Uncoated Galvanized Steel, Stainless Steel, and Non-Ferrous Metals.
The SP7 degree of cleanliness on steel should result in the removal of all previous coating, mill scale, and rust that cannot be removed with a dull putty knife. Anything that is tightly adherent is considered acceptable by this standard.
It should be noted that in the case of blasting aluminum, stainless steel, or galvanized steel, the same technique would be used by the operator as is used in SP7, however the technical differences to be considered are contained in SSPC-SP16. Of particular importance here is the use of blast media. To prevent the potential for creating a corrosion cell by impinging steel into aluminum or stainless steel – new media should be used when changing over to blasting non-ferrous substrates.
Conclusion
For a comprehensive overview of the standards and detailed information, SSPC has a document called Surface Preparation Commentary for Steel and Concrete Substrates available on their website. This should be used in conjunction with the standards produced by SSPC.
At the end of the day – the important thing is being able to provide your customer with the basic understanding of how these degrees of cleanliness differ and how to tell the difference. These standards do not define future success of a coating system, but they do have an impact on the total coating systems performance.
Consultation with the end user and coating supplier should always take place to determine that the cost/benefit be weighed out based on the end goal of the project.
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