SSPC-SP5 — очистка до белого металла: когда она требуется?

SSPC-SP 5 — White Metal Blast Cleaning — is the most stringent abrasive blast cleaning grade in routine industrial use. It requires removal of all visible contaminants from the steel surface, with no staining permitted. Specifying it correctly is as important as achieving it: over-specifying SP 5 where SP 10 is sufficient adds significant cost and production time with little coating performance benefit, while under-specifying it where SP 5 is genuinely required risks premature coating failure in service.

This guide explains what SSPC-SP 5 requires, which applications genuinely demand it, how to achieve and verify it, and how to decide whether it is the right specification for a given project. For the wider context, see our complete guide to SSPC surface preparation standards.

What is SSPC-SP 5?

SSPC-SP 5 was published by SSPC: The Society for Protective Coatings and NACE International, now merged as AMPP. Its full designation is SSPC-SP 5 / NACE No. 1 — White Metal Blast Cleaning. The corresponding international grade under ISO 8501-1 is Sa 3.

The designations describe the same level of cleanliness and are generally treated as comparable in specifications, but they are separate documents with different wording — SSPC uses written definitions, while ISO 8501-1 combines a written description with reference photographs. Name the one you intend to enforce.

What SSPC-SP 5 requires

In summary of the standard: when viewed without magnification, the steel surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter. No staining is permitted.

This is the defining characteristic of SP 5: it is a zero-tolerance standard for visible residue. The prepared surface should show a uniform bare-metal appearance with no shadows, streaks, or residual discolouration. Like the other blast grades, SP 5 is a cleanliness standard; it does not set a surface profile.

SP 5 vs SP 10: the critical difference

SSPC-SP 10 (near-white metal blast) allows random staining on up to 5% of each unit area. SP 5 allows none. In practice, reaching SP 5 takes noticeably more blasting time, media consumption and quality-control effort than SP 10 — for what is, on most substrates in most environments, a marginal improvement in coating adhesion and longevity.

For a side-by-side of the next two grades down, read SSPC-SP 6 vs SP 10: which standard does your project need?

When is SSPC-SP 5 genuinely required?

SP 5 is not a default "best practice" grade. It is appropriate — and necessary — where the coating system or a specific service condition calls for it. For most industrial and marine applications, SP 10 is what coating manufacturers state on their data sheets.

Thermal spray coatings (TSA / TSZ)

Thermal-sprayed aluminium (TSA) and zinc (TSZ) are the clearest case. The sprayed metal adheres mainly by mechanically locking into the steel profile, so cleanliness and a sharp, angular profile are critical; any residue at the interface undermines adhesion. AMPP guidance on inspecting metallizing states that SSPC-SP 5 (NACE No. 1) is used for immersion service and SSPC-SP 10 (NACE No. 2) for atmospheric service, with a sharp, angular profile of 65–125 µm (2.5–5.0 mil).

Immersion and lining service

Continuously or intermittently submerged structures — internal tank linings, ballast tanks, water systems, splash zones — are among the most aggressive service environments. Residual contamination accelerates underfilm corrosion and osmotic blistering. Many high-performance immersion coatings are specified over SP 10 / Sa 2½; some linings (for example, certain chemical, high-temperature or potable-water tank linings) call for SP 5 / Sa 3. The coating product data sheet decides; soluble salt control matters at least as much as the visual grade.

Inorganic zinc silicate primers

Inorganic zinc silicate primers react with the steel surface as they cure. Residual mill scale, staining or oxides interfere with that reaction and reduce bond strength. Inorganic zinc product data sheets commonly specify SP 10 / Sa 2½ as a minimum, and some specify SP 5 / Sa 3.

Nuclear and highly critical structures

Some defence, nuclear and critical-infrastructure specifications mandate SP 5 as a contractual baseline regardless of service environment, to minimise variables in coating system performance over long service intervals.

New construction in aggressive offshore environments

Some operators in extreme offshore environments — deepwater, tropical, high-salinity — specify SP 5 for primary structure coatings even where immersion service is not anticipated. This is a judgement call by the asset owner based on lifecycle cost modelling, not a universal requirement of the offshore environment.

When SP 5 is overkill

Specifying SP 5 for the following applications adds cost without a proportional return in coating performance:

• Atmospheric service on land-based structures: Bridges, pipelines, structural steel and industrial plant operating above the splash zone are routinely and successfully coated on SP 10-prepared surfaces with high-performance epoxy and polyurethane systems.
• Maintenance repainting over aged coatings: Where the existing coating system is only partially deteriorated, requiring SP 5 on all bare areas is rarely justified. SP 10 or SSPC-SP 11 spot repairs followed by overcoating is the standard maintenance approach.
• Organic zinc-rich primers: Organic zinc primers are typically formulated and tested on SP 10-prepared surfaces. Requiring SP 5 may not improve performance where the product data sheet does not call for it.

How to achieve SSPC-SP 5

SSPC-SP 5 is a blast cleaning standard, and on large areas it is achieved by abrasive blast cleaning. Methods include:

• Dry abrasive blasting — Conventional grit or shot blasting with steel grit, steel shot, or mineral media. The most productive method for large surface areas.
• Wet abrasive blasting — Abrasive blasting with water injection, used where dust control is required. Requires flash rust management immediately after blasting.
• Vacuum abrasive blasting — Blasting with integrated vacuum recovery. Used in confined spaces and environmentally restricted areas.
• Centrifugal wheel blasting — Shop application for fabricated steel sections. Highly productive for new construction.

Conventional power tools — wire brushes, grinders, flap discs — do not reach a white-metal appearance with a profile across a production area; the power tool bare-metal grade is SSPC-SP 11. The Bristle Blaster® is the exception worth knowing: in documented tests it produces cleanliness comparable to ISO 8501-1 Sa 3 / SSPC-SP 5 (and Sa 2½ / SP 10) with a 65–85 µm Rz anchor profile on standard steel, without loose abrasive. Results vary with steel grade, rust grade, belt and technique, and its production rate (around 1.1 m² per hour on rust grade B pipe steel) suits spot repairs, welds, field joints and areas where blasting is impractical rather than large new-build areas. Because SP 5 is written for blast cleaning, a bristle-blasted result is described as comparable to SP 5 and should be accepted in writing by the specifier or inspector. The background is in our summary of defining surface preparation standards with power tools.

How to verify SSPC-SP 5 compliance

Visual assessment

Compare the prepared surface with the ISO 8501-1 Sa 3 reference photographs or SSPC-VIS 1 for the appropriate original rust grade (A, B, C or D). The surface must show a uniform metallic appearance with no staining, shadows or discolouration. Inspect under good diffuse daylight or equivalent artificial light; many project specifications set a minimum illuminance, often 500 lux.

Anchor profile

SP 5 does not specify a minimum anchor profile — that is set by the coating system product data sheet. Measure and record per ASTM D4417 (Method C replica tape or Method B depth micrometer), with frequency per SSPC-PA 17, and confirm the result falls within the coating manufacturer's range. Our anchor profile measurement field guide covers the methods.

Soluble salt contamination

For immersion service and other critical applications, verify soluble salt levels per the project specification — typically by Bresle patch extraction (ISO 8502-6) and conductivity measurement (ISO 8502-9), reported in mg/m² or µg/cm². SP 5 cleanliness does not guarantee freedom from soluble salts — chlorides and sulphates must be assessed separately.

SP 5 and recontamination

White-metal surfaces are highly reactive and recontaminate quickly; in humid conditions flash rust can appear soon after blasting. Typical project practice includes:

• Priming within a short interval after blast cleaning — often specified as around 4 hours in normal conditions, shorter in high humidity or marine environments, and always before visible rust bloom
• Monitoring relative humidity and steel temperature — final blast cleaning and coating commonly require the steel to be at least 3 °C above the dew point, and many specifications set an RH limit such as 85%
• Protection of blasted areas from contamination by spent media, dust, rain, or direct contact
• Inspection and re-blasting of any areas that develop flash rust or visible contamination before priming

Key takeaways

• SSPC-SP 5 / NACE No. 1 / Sa 3 is white metal blast cleaning — no staining permitted, uniform bare metal across the entire surface.
• It is required where the coating system calls for it: thermal spray for immersion, some tank linings and inorganic zinc systems, and owner specifications for critical assets.
• For most atmospheric industrial and marine applications, SSPC-SP 10 delivers comparable coating performance at significantly lower cost and production time.
• SP 5 is a blast cleaning standard; on production areas it is achieved by abrasive blasting. Bristle blasting can produce comparable cleanliness on spot repairs and difficult areas, subject to the specifier's acceptance.
• SP 5-prepared surfaces recontaminate quickly and must be primed within a tightly controlled window.

Frequently asked questions

What is the difference between SSPC-SP 5 and Sa 3?

Both describe white metal blast cleaning with no visible mill scale, rust, coating or staining. SSPC-SP 5 / NACE No. 1 is the North American written standard; ISO 8501-1 Sa 3 is the international grade defined by a description and reference photographs. They are generally treated as comparable, but specifications should name the one being enforced.

Is SSPC-SP 5 required for immersion service?

Not automatically. Many immersion coatings are specified over SSPC-SP 10 / Sa 2½. SP 5 is required where the data sheet or owner specification calls for it, for example thermal-sprayed metal in immersion and some tank linings. Soluble salt limits are as important as the visual grade.

Does SSPC-SP 5 specify an anchor profile?

No. SSPC-SP 5 defines cleanliness only. The required anchor profile comes from the coating product data sheet or project specification and is measured with ASTM D4417 methods, such as replica tape or a depth micrometer, at the frequency set by SSPC-PA 17.

Can a power tool achieve SSPC-SP 5?

Conventional power tools reach SSPC-SP 3 or SP 11, not white metal. The Bristle Blaster® produces cleanliness comparable to Sa 3 / SP 5 in documented tests on standard steel. Because SP 5 is written for blasting, the result is described as comparable and must be accepted by the specifier.

How quickly must an SP 5 surface be primed?

Before any visible rust bloom or recontamination appears. Many specifications set a maximum of around 4 hours, shorter in humid or marine conditions, and require the steel to be at least 3 °C above the dew point during blasting and coating.

Related articles

• SSPC-SP 10 Near-White Metal Blast: Complete Technical Guide
• Bristle Blaster® vs. Sandblasting: Which Method Achieves SSPC-SP 10-Comparable Results?