AMPP Marine Coatings cheat sheet

Inspection verifies three things: surface preparation conformance, coating application conformance, and final film integrity against the specification.

Standard inspection sequence: pre-job meeting, surface preparation check, primer application check, intermediate and finish coats, final inspection and report.

A specification defines required surface standard, coating system, DFT ranges, cure intervals, and acceptance criteria; inspection measures against that document only.

Hold points are stages where work cannot proceed until the inspector signs off; witness points require notification but not mandatory attendance.

Coating systems are typically multi-coat: primer for adhesion/corrosion inhibition, intermediate for barrier thickness, topcoat for environment and color.

Inspector authority is limited to acceptance and rejection against the spec; changes to the spec require the owner or coating manufacturer in writing.

Nonconformance reports record the deviation, location, measured value, spec limit, and disposition (rework, repair, or accept by concession).

Environmental conditions (ambient and steel temperature, relative humidity, dew point) must be recorded at each application and inspection stage.

ISO 8501-1 rust/cleanliness grades: A, B, C, D for initial rust condition; preparation grades Sa 1, Sa 2, Sa 2½, Sa 3, plus St and Fl grades.

Sa 2½ (near-white blast) is the most common marine requirement: only slight staining permitted, no visible oil, grease, dirt, mill scale, or rust.

Sa 3 (white metal) allows no staining at all; used for aggressive immersion or specialized systems where the spec demands it.

Surface profile: ISO 8503 comparators grade fine, medium, or coarse; typical marine blast profile is roughly 50–100 µm depending on system.

Abrasive cleanliness matters: ISO 11124/11126 cover metallic and non-metallic abrasives; contaminated abrasive can embed salts and cause premature failure.

Soluble salt testing (ISO 8502 series, Bresle method) measures conductivity; many marine specs limit chloride to low levels (commonly ≤ 2–5 µg/cm²).

Dew point rule: steel temperature must be at least 3 °C above dew point to prevent condensation during preparation and application.

Edge, weld, and corner preparation (stripe coating, grinding, weld spatter removal) is required because sharp geometry causes thin films and early failure.

Common marine binders: epoxy (barrier/immersion), polyurethane (topcoat/UV), zinc-rich primers (cathodic protection), and polysiloxane or silicone for weather resistance.

Mixing ratio and induction time are product-specific; incorrect ratio causes incomplete cure, soft films, or amine blush.

Pot life is the usable time after mixing; exceeding it causes viscosity rise and application defects, so batches must be tracked.

Stripe coating applies a brush coat to edges, welds, and corners before full spray to ensure minimum film on difficult geometry.

Recoat window: applying outside the manufacturer's minimum/maximum interval can cause intercoat adhesion failure; max interval may require abrading.

Wet film thickness (WFT) is measured with a comb gauge; DFT = WFT × volume solids fraction (as a decimal).

Airless spray parameters (tip size, pressure, fan) and environmental conditions (temperature, humidity, ventilation) strongly influence film build and finish.

Ambient cure is temperature- and humidity-dependent; low temperature slows cure and can extend recoat intervals beyond the nominal data sheet value.

DFT is measured with magnetic/electromagnetic gauges (ISO 19840 or SSPC-PA 2) using the average of multiple readings per area and checking against spec min/max.

ISO 19840 applies a roughness correction to DFT readings taken on blasted steel; ignoring it overstates the true film thickness.

Holiday/pinhole detection uses low-voltage wet sponge for thin films and high-voltage spark testing for thicker or immersion coatings per spec.

Adhesion testing methods: cross-cut (ISO 2409), pull-off (ISO 4624), and knife/impact tests; destructive tests require repair of the test area.

Visual standards for defects (ISO 4628 series) classify blistering, rusting, cracking, and flaking by quantity and size.

Environmental monitoring records ambient temperature, steel temperature, RH, and dew point; instruments should be calibrated and traceable.

Acceptance criteria are numeric and product-specific (DFT range, adhesion value, holiday count); results are documented in the inspection report.

Calibration records for gauges and verification of test equipment are part of QC documentation and are commonly audited.