Coating inspection glossary

109 terms in plain words. Follow a link for the full explanation.

Find a term

A

Abrasive

Hard particles thrown at a surface to clean it and cut a profile: metallic (steel grit and shot) or non-metallic (slags, garnet, aluminium oxide). More

Adhesion

How strongly a coating bonds to its substrate or to the coat below. More

Adhesive failure

In an adhesion test, a break between two layers or between the coating and the substrate. More

Airless spray

Spray application in which paint is forced at high pressure through a small tip and atomises without compressed air.

Alkyd

A binder that cures by oxidation with air. It is used for mild environments and maintenance painting. More

Amine blush

A greasy, water-soluble film that forms on amine-cured epoxies in cold, damp conditions. It must be washed off before overcoating. More

Anchor pattern

Another name for surface profile. More

Anode

In a corrosion cell, the electrode that corrodes. More

B

Barrier coating

A coating that protects mainly by keeping water, oxygen and ions away from the steel.

Binder

The film-forming part of a paint, which holds the pigment and bonds to the surface.

Blast cleaning

Surface preparation by abrasive thrown at high speed, graded Sa 1 to Sa 3 in ISO 8501-1. More

Blistering

Raised domes in a coating filled with liquid or gas, often caused by salts or moisture under the film. More

Blotter test

A check for oil and water in compressed air: a white blotter held in the air stream (ASTM D4285). More

Bresle test

A patch method that dissolves the soluble salts on a known area of steel so their amount can be measured (ISO 8502-6). More

Brush-off blast

The lightest blast-cleaning grade: SSPC-SP 7 / NACE No. 4, close to Sa 1. More

C

Calibration

A check of a gauge by its manufacturer or a qualified laboratory, documented with a certificate. More

Cathode

In a corrosion cell, the electrode that does not corrode. More

Cathodic disbondment

Loss of coating adhesion around a defect caused by the reactions of cathodic protection. More

Cathodic protection

Making a structure the cathode of a cell, with sacrificial anodes or impressed current, so it does not corrode. More

Chalking

A loose powder on a coating's surface, left when UV light breaks down the binder. More

Cohesive failure

In an adhesion test, a break within one layer of the coating. More

Comparator

A reference surface used to grade surface profile by sight and touch (ISO 8503-1, ASTM D4417 Method A). More

Condensation

Water that forms on a surface colder than the dew point of the air. More

Corrosion

The deterioration of a metal by reaction with its environment.

Corrosivity category

The class of an environment in ISO 12944-2: C1 to CX in air, Im1 to Im4 in water and soil. More

Cratering

Small round holes where wet paint pulled away from a contaminated spot. They are also called fish eyes. More

Cross-cut test

An adhesion test: a lattice of cuts through the film, then tape (ISO 2409, ASTM D3359 Method B). More

Cure

The process by which a coating film reaches its final properties, by chemical reaction or by drying. More

D

Daily inspection report

The inspector's dated record of readings, conditions, areas inspected and nonconformances. More

Dew point

The temperature at which water vapour in the air condenses on a surface. More

DFT (dry film thickness)

The thickness of a cured coating film. More

Dolly

The test stud glued to a coating in a pull-off adhesion test. More

Dry spray

A rough, porous film made of paint droplets that dried before they reached the surface. More

Dry to touch

A drying stage at which the film no longer feels tacky. It is not yet cured. More

Duplex system

A paint system applied over a metallic coating such as hot-dip galvanizing. More

Durability range

The ISO 12944 planning figure for the time to first major maintenance: low, medium, high or very high. More

E

Eddy-current gauge

A thickness gauge for non-conductive coatings on non-ferrous metals such as aluminium. More

Electrolyte

A medium that conducts ions, such as water or wet soil. Corrosion needs one. More

Epoxy

A two-pack coating that cures by chemical reaction. It is a tough barrier that chalks in sunlight. More

F

Feathering

Tapering the edge of sound coating around a repair so the new coats blend in.

Flash rust

Light rust that forms on wet-cleaned steel as it dries, graded light, medium or heavy. More

G

Galvanic corrosion

Faster corrosion of the less noble of two different metals in electrical contact in an electrolyte. More

Galvanizing (hot-dip)

A zinc coating made by dipping steel into molten zinc (ISO 1461). More

Glossmeter

An instrument that measures specular gloss at 20°, 60° or 85° (ISO 2813). More

H

Hold point

A stage at which work stops until the inspection is done and the work released. More

Holiday

A pinhole, void or missed area that goes through the coating to the substrate. More

Holiday detector

An instrument that finds holidays: low-voltage wet sponge or high-voltage DC spark. More

I

Impressed current

Cathodic protection driven by a power source through inert anodes. More

Induction time

A waiting time after mixing a two-pack paint, before application, where the data sheet asks for one. More

Inorganic zinc (IOZ)

A zinc silicate primer that gives galvanic protection and cures by reacting with moisture in the air. More

Inspection and test plan (ITP)

The list of inspections and tests, their criteria, frequency, responsibility, hold and witness points. More

Intercoat adhesion

The bond between one coat and the next. More

Intermediate coat

A coat between primer and top coat, mainly to build film thickness and barrier.

L

Lining

A coating on the inside of a tank, vessel or pipe, often in immersion service. More

M

Magnetic gauge

A DFT gauge for non-magnetic coatings on steel: magnetic pull-off (Type 1) or electronic (Type 2). More

MEK rub test

A cure test for inorganic zinc silicate primers: a cloth soaked in MEK rubbed on the film (ASTM D4752). More

Mill scale

The blue-grey oxide layer formed on steel during hot rolling. Most coating systems need it removed. More

Mist coat

A thin coat over a porous surface, such as inorganic zinc, that lets air escape before the full coat. More

Mixing ratio

The proportion of base to hardener in a two-pack paint, by volume or by weight. More

Mud cracking

A network of cracks in a film applied far too thick, typical of inorganic zinc. More

N

Nonconformance report (NCR)

The record of work that does not meet the specification, closed only after the corrective action is verified. More

Nominal DFT

The specified thickness of a coat. It is the reference value for ISO 19840 acceptance (CIP 2 and FROSIO only). More

O

Orange peel

A dimpled film surface like the skin of an orange, caused by poor flow-out. More

Overspray

Paint droplets that miss the target or land partly dry on nearby surfaces. More

P

Pinholes

Tiny holes through a coating film, often from air or solvent escaping from a porous surface. More

Pinpoint rusting

Many tiny rust spots, often where profile peaks were not covered by the film. More

Plural-component spray

Equipment that meters and mixes two components at the gun, for fast-reacting products such as polyurea. More

Polysiloxane

A durable, UV-stable top coat chemistry. More

Polyurea

A very fast-curing two-pack coating sprayed as a thick membrane with plural-component equipment. More

Polyurethane (aliphatic)

A two-pack top coat that keeps its colour and gloss in sunlight. More

Pot life

The time within which mixed two-pack paint must be used. More

Pre-job conference

The meeting before work starts where owner, contractor and inspector agree the specification, ITP and procedures. More

Primer

The first coat of a system, applied to the prepared surface for adhesion and corrosion protection.

Profile correction value

The value subtracted from DFT readings on blasted steel under ISO 19840: 10, 25 or 40 µm for fine, medium or coarse. More

Psychrometer

An instrument with a dry and a wet bulb thermometer that gives relative humidity and dew point (ASTM E337). More

Pull-off test

An adhesion test in which a glued dolly is pulled off at right angles and the stress recorded (ISO 4624, ASTM D4541). Applies to CIP 2 and FROSIO only. More

R

Recoat window

The minimum and maximum time before the next coat, from the data sheet, at a given temperature. More

Reference area

A small area prepared and coated at the start of a job as the agreed standard for the rest of the work. More

Relative humidity

The water vapour in the air as a percentage of the most the air can hold at that temperature. More

Replica tape

A compressible tape pressed onto blasted steel and read with a spring micrometer. The profile is the micrometer reading less 2.0 mils for the tape's backing. More

Rust grade

The starting condition of uncoated steel in ISO 8501-1, from A (adherent mill scale) to D (pitted). More

Runs and sags

Drips and curtains on vertical surfaces where too thick a wet film flowed down. More

S

Sacrificial anode

A zinc, aluminium or magnesium anode that corrodes in place of the protected steel. More

Safety data sheet (SDS)

The supplier's document on a product's hazards, safe handling and emergency measures.

Shop primer

A thin primer applied to blasted steel in the shop to protect it during fabrication.

Soluble salts

Invisible chlorides and sulfates on steel that cause blistering and corrosion under a coating. More

Solvent

The volatile liquid in a paint that dissolves the binder and evaporates as the film dries. More

Solvent entrapment

Solvent trapped in a film under a skinned surface, causing bubbles, popping or a soft film. More

Spot (SSPC-PA 2)

The average of three or more DFT readings within a 4 cm circle. More

Spreading rate

The area a litre of paint covers at a given DFT: theoretically 10 × volume solids % ÷ DFT in µm, in m²/L. More

Stripe coat

An extra coat brushed onto edges, welds, corners and bolts, where spray leaves less film. More

Substrate

The surface a coating is applied to.

Surface profile

The peak-to-valley height of the roughness that blast cleaning leaves on steel. More

Sweep blasting

A light blast that cleans and roughens galvanized or coated surfaces without removing them (SSPC-SP 16). More

T

Technical data sheet

The manufacturer's document with a coating's properties and limits: solids, DFT, mixing, recoat times and temperatures. More

Thermal spray

Molten zinc or aluminium sprayed onto blasted steel as a metallic coating (TSZ, TSA), usually sealed. More

Thinner

Solvent added to adjust viscosity. It adds volume but no solids. It changes the wet film needed. More

Top coat

The final coat of a system, chosen for appearance, weathering and UV resistance.

U

Ultrasonic gauge

A thickness gauge that uses sound pulses, for coatings on concrete and other non-metallic substrates. More

Undercutting

Corrosion that spreads under a coating from damage or an edge, lifting the film. More

V

Verification of accuracy

The user's check of a gauge against reference standards, at least at the start and end of each shift. More

Viscosity

A liquid's resistance to flow. It changes with temperature and thinner.

VOC

Volatile organic compounds: the solvent part of a paint that air-quality rules limit.

Volume solids

The share of a paint's volume that remains as dry film. More

W

Waterjetting

Cleaning with high-pressure water, graded WJ-1 to WJ-4. It exposes the existing profile but does not create one. More

Wet film thickness (WFT)

The thickness of a coating as applied, measured with a notch gauge straight after application. More

Wet sponge test

A low-voltage holiday test for thinner films, up to about 500 µm (20 mils). More

Witness point

A stage the inspector is notified of and may attend; work can continue if the inspector does not come. More

Z

Zinc-rich primer

A primer with enough zinc dust to protect steel galvanically: inorganic (silicate) or organic (epoxy). More

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