Glossary
Terms used across this site, each defined against the standard that governs it. Short enough to quote, sourced so the quote can be checked.
20 terms
- Cavitation erosion
- Material loss caused by vapour bubbles forming in a low-pressure region of a liquid and collapsing against a surface. The damage is mechanical fatigue from repeated implosions, not chemical attack — which is why a harder coating rarely solves it.
- Coating system
- Primer, intermediate and topcoat specified together with a total dry film thickness, and qualified as a set. Substituting one layer from another manufacturer without a compatibility check is where a specification quietly stops being one.
- Cohesive and adhesive failure
- The two ways a coating can break in an adhesion test. Cohesive failure runs through the film itself, meaning the bond to the substrate was the stronger of the two. Adhesive failure follows the interface with the substrate, which implicates preparation or contamination rather than the coating.
- Composite repair
- A laminate of reinforcement and resin bonded to a pipe so that it carries hoop stress in place of the wall that has been lost. Its thickness is derived from the defect, the design conditions and the qualified laminate properties — which is why the calculation governs and the brand does not.
- Corrosion under insulation (CUI)
- Corrosion of a pipe or vessel beneath its thermal insulation, where water is retained against the metal and the surface is hidden from inspection. The mechanism is ordinary atmospheric corrosion; what makes it expensive is that nothing is visible until the insulation is removed.
- Corrosivity category
- A classification of how aggressive an environment is towards steel, from C1 (heated interiors) to CX (offshore and extreme industrial), defined in ISO 12944-2 from measurable parameters rather than from location. It is the input a coating system is specified against, and it is fixed before any product is chosen.
- Dry film thickness (DFT)
- The thickness of a coating after it has cured, measured in micrometres. It is a property of the specified system rather than a count of coats, and whether a job conforms to it is itself a measurement procedure — SSPC-PA 2 sets out how many readings, taken where, and what counts as conformance.
- Dry sand / rubber wheel abrasion test (ASTM G65)
- A laboratory test in which dry sand is fed between a specimen and a rotating rubber wheel, reporting volume loss. It compares materials fairly within low-stress sliding abrasion, and it is the figure most wear liner data sheets quote.
- Durability range
- The expected time to first major maintenance of a coating system, expressed in ISO 12944-1 as low, medium, high or very high. It is a planning parameter used to select a system against a corrosivity category — explicitly not a warranty and not a guarantee period.
- Flash rust
- The light oxidation that forms on freshly prepared steel before the first coat is applied, driven by ambient moisture. It downgrades a surface that has already been paid for, and it is the reason the interval between blasting and coating belongs in the specification rather than in the schedule.
- Flexural strength of advanced ceramics
- The stress at which a ceramic breaks in bending, measured under ASTM C1161. It is the limiting property of hard, brittle wear materials: they resist being scratched extremely well and tolerate very little bending or shock before fracture.
- Fretting corrosion
- Micro-movement between a bearing outer ring and its housing seat under load, which oxidises and removes material at the contact. ISO 15243:2017 classifies it as a damage mode in its own right, with reddish-brown oxide debris and polished bands on the seat as its characteristic evidence.
- Galvanic series
- An ordered list of metals and alloys by their measured potential in a given electrolyte, used to predict which of two coupled metals will corrode preferentially. ASTM G82 is explicit that a series is specific to its electrolyte and is a guide to ranking, not a prediction of rate.
- High-temperature coating
- A protective coating formulated to stay adherent and intact on a substrate held above the service limit of a conventional system. Evaluated for high-temperature service by the methods of ASTM D2485. It protects the surface and does not meaningfully reduce the substrate's temperature.
- Miller number (slurry abrasivity)
- A measure of how abrasive a slurry is, obtained in ASTM G75 by reciprocating a standard wear block through the slurry and recording mass loss. It characterises the slurry itself rather than any particular material exposed to it.
- Near-white metal blast cleaning (SSPC-SP 10 / NACE No. 2)
- A surface preparation grade requiring that at least 95 % of each unit area be free of visible residues, with only light shadows or streaks permitted. It is the grade most structural and immersion systems name on their data sheet, and it is defined by reference photographs rather than by description.
- Pull-off adhesion test
- A test in which a dolly is bonded to the coating and pulled until something breaks, giving a strength in megapascals and — more usefully — a failure mode. ASTM D4541 and ISO 4624 both require the failure mode to be reported alongside the number.
- Rust grade (A to D)
- The condition of steel before preparation, graded A to D in ISO 8501-1: A still carries intact mill scale, B has rusted with scale flaking, C is rusted with scale gone and D is pitted. The starting grade limits what preparation can achieve and what the finished surface will look like.
- Sour service
- Exposure to hydrogen sulphide in oil and gas production at levels where cracking of susceptible materials becomes possible. ISO 15156-1 sets the conditions that define it and the requirements for materials selected to operate in it.
- Wet abrasion resistance
- The ability of a surface to resist material loss when abrasive particles are carried in a liquid. It is not dry abrasion with water added: particle velocity and angularity weigh more heavily, and corrosion of the substrate frequently runs in parallel with the mechanical loss.