What is SSPC-PA 2 and why does it matter for DFT measurement?

SSPC-PA 2 (Measurement of Dry Film Coating Thickness with Magnetic Gauges) is the standard procedure for measuring coating thickness on steel. It requires: taking minimum 3 readings per 1.5m² area, calculating the average, ensuring no reading is below 80% of specified DFT, and no more than 10% below 80%. DFT gauges used must be calibrated to certified standards (Type 2 gauges per SSPC-PA 2). BLAST APEX DFT gauges are calibrated and traceable to NIST standards.

What surface profile should be specified for different coating environments?

C3 (low): 30-45µm Ra — covered structures, mild industrial. C4 (medium): 45-75µm Ra — industrial areas, coastal — Sa2.5 standard. C5-I/C5-M (high/very high): 75-100µm Ra — heavy industrial, offshore, tidal zones — Sa2.5 with metallizing often required. Profile is measured with replica tape (Testex) or stylus profilometer per ISO 8503 and ASTM D4417.

What is a holiday test and when is it required?

A holiday test detects pinholes and discontinuities in coating films using low-voltage (67.5V) or high-voltage (up to 30kV) spark testing. Required for: tank linings (API 651 for petroleum storage), marine ballast tanks (IMO PSPC), pipeline coatings (ISO 21809), and any coating where film continuity is critical for corrosion protection. Low-voltage testers (up to 90V) for coatings up to 500µm; high-voltage (above 900V) for thick films above 500µm.

Quality Control & Verification

Inspection
Instruments

BLAST APEX supplies precision industrial inspection and testing instruments designed for comprehensive coating quality verification. Our instruments are essential for maintaining compliance with NACE, SSPC, and ISO standards, ensuring every surface preparation and coating application meets the highest technical specifications for long-term corrosion protection.

Digital DFT Gauge

Precision digital meter for non-destructive measurement of dry film thickness on ferrous and non-ferrous substrates.

Verification: SSPC-PA 2 Compliance | Real-time Data Logging

Industrial Role:

Final quality check to ensure coating thickness meets engineering specs.

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Holiday Detector

High-voltage porosity detection unit used to identify pinholes, cracks, and flaws in protective industrial coatings.

Focus: Pipeline Integrity | Tank Lining Verification

Industrial Role:

Critical safety tool for detecting microscopic gaps in anti-corrosion shields.

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Surface Profile Gauge

Precision gauge for measuring the peak-to-valley height of abrasive-blasted surfaces to ensure mechanical bond strength.

Standard: NACE / ASTM Compliance | Anchor Profile Verification

Industrial Role:

Ensures surface roughness is ideal for maximum coating adhesion.

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Coating Inspection Toolkit

Instrument	Measures	Standard	Required For
Digital DFT Gauge	Dry film thickness	SSPC-PA 2, ISO 19840	Every coating project with DFT specification
Surface Profile Gauge	Surface profile depth	ISO 8503, ASTM D4417	SSPC-SP10/NACE 2, ISO 8501-1 Sa2.5 verification
Holiday Detector	Film discontinuities	ASTM D5162, ISO 29601	Tank linings, pipelines, marine ballast tanks

Frequently Asked Questions

What instrument measures surface profile?

Surface profile is measured with: (1) Testex replica tape — most common, compresses into profile valleys, measures with spring gauge. (2) Digital profile gauge — stylus instrument, direct reading in µm. (3) ISO 8503-2 visual comparators — reference cards for field assessment. Profile depth (Rz) is the primary specification — typically 30-75µm for industrial coatings per ISO 8503. BLAST APEX stocks all three instruments.

What DFT gauge do I need for thick coatings?

For thick-film coatings (250µm+ DFT): use mechanical dial gauge (magnetic pull-off) or high-range eddy current gauge. For thin-film coatings (25-150µm): use low-range eddy current gauge. For non-conductive coatings on steel: use ultrasonic gauge. DFT is measured per SSPC-PA 2: minimum 3 readings per 10 sqm, average must meet specification. DFT gauges need calibration annually.

What is holiday detection and when is it required?

Holiday detection (spark testing) finds porosity in coating films — pinholes, voids, or thin spots where substrate is exposed. Required for: tank linings, pipeline coatings, marine coatings, immersion service coatings. Method: low-voltage (67.5V sponge) for films <500µm, high-voltage (up to 30kV) for thick films. Every holiday must be repaired and re-tested. ASTM D5162 is the standard test method.

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