AMPP Marine Coatings common mistakes
AMPP Marine Coatings · Understand the traps and how to avoid them.
Treating a surface-preparation standard's visual comparator photographs as a pass/fail specification and approving a surface that merely resembles the photo, rather than measuring the specified surface profile and verifying soluble salt and cleanliness levels.
Candidates memorize the look of abrasive-blasted steel from the standard's comparator images and assume visual similarity equals compliance, forgetting that profile depth, salt contamination, and dust are separate measurable requirements.
What to do instead
For each job spec, list every independently verifiable attribute (profile depth, salt level, dust, oil/grease, ambient conditions) and state the test method and acceptance value for each; treat visual standards as only one line item.
Recording environmental readings once at the start of the shift and applying them to the whole coating operation, instead of measuring steel temperature, dew point, and relative humidity at the point and time of application.
Candidates conflate ambient air temperature with steel surface temperature and underestimate how fast steel temperature can fall toward or below dew point, especially on cool or shaded substrates.
What to do instead
Practice computing dew point margin (steel temperature minus dew point) and require on-substrate readings immediately before and periodically during application; know the typical minimum margin and the prohibition on applying to steel at or near dew point.
Confusing dry film thickness (DFT) with wet film thickness (WFT) and reporting a single spot reading as the coating thickness, rather than a statistically valid set of gauge readings per specified area.
Candidates learn the WFT-to-DFT conversion concept but forget that DFT gauges have measurement uncertainty, require calibration checks on the substrate and on foils, and that specifications call for a defined number of readings per area.
What to do instead
Memorize the relationship WFT = DFT / volume solids, and drill the reading-count and averaging rules the specification requires; always verify gauge calibration against a known foil and the uncoated substrate before accepting DFT data.
Assuming a coating that looks uniform and defect-free is acceptable, skipping holiday (pinhole) detection and adhesion testing on the finished film.
Candidates rely on visual inspection because it is quick and intuitive, and they underestimate how thin spots, pinholes, and poor adhesion are invisible to the eye but critical in immersion service.
What to do instead
Build a checklist that pairs visual inspection with the specified non-destructive tests (holiday detection, DFT) and destructive tests (adhesion, where permitted), and know which tests are required for immersion versus atmospheric service.
Mixing up the roles of the coating manufacturer's product data sheet, the project specification, and industry standards, and defaulting to the data sheet when they conflict.
Candidates treat the product data sheet as the governing document because it is the most detailed source they have studied, forgetting that the project specification and contract documents control acceptance.
What to do instead
Establish and memorize the hierarchy of documents (contract/specification governs; manufacturer data sheet informs application parameters; standards define test methods) and answer conflict questions by citing the governing document first.
Failing to identify the substrate condition or prior coating system before specifying surface preparation, then applying a preparation method incompatible with the existing coating or contamination.
Candidates jump to 'abrasive blast to Sa 2½' as a universal answer without first assessing whether the substrate is new steel, previously coated, or contaminated, and whether the existing system tolerates the proposed preparation.
What to do instead
Practice a decision sequence: identify substrate and existing coating, test for contamination and adhesion, then select preparation consistent with the coating's stated surface tolerance and the specification.
Misapplying the surface preparation grades (e.g., treating a commercial-blast grade as equivalent to near-white blast, or confusing hand/power tool grades with abrasive blast grades) when answering cleanliness questions.
The grade designations and their visual descriptions are similar and easy to conflate under exam pressure, and candidates memorize labels rather than the defining characteristics of each grade.
What to do instead
Build a comparison table of the blast and hand/power tool grades with their defining features (amount of tightly adhering residue permitted) and test yourself by describing each grade without the label.
Overlooking stripe coating and edge/ weld preparation requirements, and evaluating those areas only as part of the general coating thickness survey.
Candidates focus on large flat areas and forget that edges, welds, cutouts, and back-to-back steel require stripe coats and often have different acceptance criteria for profile and DFT.
What to do instead
Add stripe coating and edge/weld treatment to every inspection plan and practice identifying which areas require stripe coats, what DFT criteria apply there, and how weld spatter and sharp edges must be corrected before coating.
Ignoring or misjudging pot life, induction time, and recoat windows for multi-component coatings, and treating a coating that has exceeded its recoat interval as directly overcoatable.
Candidates memorize mixing ratios but not the time-based parameters, and they underestimate how exceeding pot life or recoat windows changes adhesion and requires surface preparation before recoating.
What to do instead
Memorize the definitions of pot life, induction time, and recoat window, and practice the decision logic: discard coating past pot life; if the recoat window is exceeded, follow the manufacturer's surface preparation requirement before applying the next coat.
Reporting inspection results without documenting the measurement method, instrument, calibration status, and conditions, so the record cannot support an accept/reject decision.
Candidates treat inspection as a measurement exercise rather than a documentation exercise and do not appreciate that undocumented or uncalibrated data is not defensible quality control.
What to do instead
Use a standard inspection report template that captures instrument identity and calibration, environmental conditions, test locations, and acceptance criteria, and practice writing a report that a third party could audit.