HDG Defects; Nonferrous and Concrete Coating Inspection

HDG Defects; Nonferrous and Concrete Coating Inspection

Quick Answer: CIP Level 2 must identify defects in hot-dip galvanizing—bare spots/uncoated areas, dross, ash, flux inclusions, wet storage stain, and excessive (or insufficient) thickness issues—and apply inspection procedures for nonferrous and concrete coating systems that respect substrate-specific prep, moisture, profile, and test methods.

HDG process knowledge (Domain 6) explained how zinc bonds. This section is the defect recognition and multi-substrate inspection half of that story.

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Part A — Defects in Hot-Dip Galvanizing

HDG is judged against product standards such as ASTM A123-type requirements (thickness/weight, finish, continuity) and job specifications. Zinc coatings are not organic paint; defect names and dispositions differ.

1. Bare spots / uncoated areas

Appearance: Patches of bare steel (or only oxide-stained steel) with no continuous zinc coating; edges of surrounding zinc may be abrupt.

Typical causes:

• Residual mill scale, paint, oil, grease, welding slag, labels, or markers that prevented wetting
• Inadequate pickling or fluxing
• Touching/overlapping surfaces that trapped acid or excluded zinc
• Design features that prevent drainage/venting (related process issues)

Inspector logic (exam favorite): On newly galvanized steel, bare spots where adjacent zinc already meets thickness mean local failure of zinc to metallurgically bond/wet, not “patina,” not decades of sacrificial consumption, and not normal spangle variation.

Disposition awareness: Bare spots are generally rejectable or must be repaired per ASTM A780-type repair practice and owner acceptance—not hidden under paint without addressing the HDG product requirement.

2. Dross inclusions

Appearance: Hard, dark, gritty inclusions of zinc-iron dross particles trapped in or on the coating; rough spots that may snag or show as raised inclusions.

What dross is: Intermetallic zinc-iron particles that form in the kettle and settle as bottom dross; if stirred up or dragged out on the work, they can embed in the coating.

Inspector concerns:

• Local roughness and appearance
• Possible weak spots or points that affect fit-up of mating parts
• Confusion with other inclusions—dross is metallic/intermetallic kettle debris, not organic dirt alone

Heavy dross that compromises coating quality or dimensional fit is a process/quality finding for the galvanizer disposition.

3. Ash

Appearance: Powdery or flaky zinc oxide ash deposits on the surface after withdrawal; dull, dirty-looking patches that may wipe or brush differently than sound free zinc.

Origin: Oxidation products and bath-surface skimmings that deposit on the article during withdrawal.

Inspector concerns:

• Appearance and cleanliness before duplex painting (ash interferes with paint adhesion if not removed)
• Differentiation from wet storage stain (different chemistry and morphology—see below)
• Excessive ash may require cleaning per galvanizer/finishing practice before acceptance or painting

4. Flux inclusions / flux residues

Appearance: Blackish, glassy, or crystalline residues; sometimes associated with bare or poorly coated spots; residues in crevices, lap joints, and undrained pockets.

Origin: Flux (e.g., zinc ammonium chloride chemistry) trapped or incompletely displaced, especially in overlapping surfaces, tubulars with poor drain holes, or complex fabrications.

Inspector concerns:

• Flux residues are corrosive hygroscopic contaminants if left
• Often co-located with bare spots or weak coating in traps
• Design for galvanizing (vent/drain) reduces flux traps—field inspectors still document residues when present

5. Wet storage stain (white rust)

Appearance: White, bulky zinc corrosion product (basic zinc compounds) on galvanized surfaces stored wet, stacked tightly, or shipped with moisture trapped between contacting surfaces—especially before a stable zinc patina forms.

Conditions that promote it:

• Nested or bundled galvanized parts with poor air circulation
• Condensation, rain water trapped between flats
• Fresh zinc more susceptible than fully weathered patina

Inspector concerns:

• Light wet storage stain may be primarily cosmetic and removable; heavy staining with zinc consumption can be more serious
• Do not confuse white rust on zinc with osmotic blistering of organic coatings—or with bare steel
• Storage and packing practices are preventive controls; field receipt inspection should note severe staining

6. Excessive thickness issues (and related thickness problems)

Excessive thickness / roughness can cause:

• Poor fit of bolts, sleeves, and machined interfaces
• Runs, drips, and heavy edges that chip or interfere with assembly
• On high-silicon steels, thick brittle alloy layers that may flake or crack under impact or bending (chemistry-related growth—still a coating condition to document)
• Difficulties for subsequent painting if surface is extremely rough or flaky

Insufficient thickness (below ASTM A123 material category minimums or job requirements):

• Reduced service life of sacrificial zinc
• Rejectable under product standard sampling rules

Inspector tools: Magnetic thickness gauges on steel, coating weight records from the plant, visual assessment of runs/drips/spikes. Thickness must be interpreted against the correct material category and steel thickness class in the governing HDG standard—not against an organic coating DFT table from an unrelated epoxy PDS.

HDG defect summary table

HDG inspection procedure outline (receipt / shop)

1. Verify product standard and thickness class on PO/submittal.
2. Visual 100% accessible surfaces for bare spots, inclusions, ash, flux, damage.
3. Thickness survey per standard sampling rules.
4. Note wet storage stain from shipping/storage.
5. Document; require repair per A780-type methods only where allowed; escalate systemic bare-spot lots to galvanizer/owner.
6. If duplex system (paint over HDG) follows, confirm cleaning/sweep blast/profile requirements separately—ash and smooth free zinc are paint-adhesion risks.

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Part B — Inspection Procedures for Nonferrous Coating Systems

Nonferrous substrates (aluminum, copper alloys, stainless steel, galvanized steel as a substrate for paint, titanium, etc.) break ferrous-only habits.

Key inspection differences

Nonferrous coating inspection procedure elements

1. Identify substrate and alloy family from drawings/tags—do not assume “steel.”
2. Confirm specified prep standard for that substrate (special substrates standards from Domain 5).
3. Contamination control — iron contamination on stainless (rust blooming later), chlorides on aluminum, oil on all metals.
4. Profile and cleanliness verification with methods allowed for that substrate.
5. Environmental controls same discipline as ferrous (dew point, temperature) unless PDS differs.
6. DFT with correct instrument technology for non-magnetic substrates.
7. Adhesion sampling when specified (pull-off on aluminum/concrete-coated assemblies needs proper dollies and limits).
8. Holiday testing for linings on nonferrous tanks when dielectric criteria apply.
9. Document substrate ID, prep method, instrument type, and results.

Inspector traps: Using only a magnetic DFT gauge on aluminum and recording nonsense; blasting aluminum with dirty steel grit; applying IOZ systems meant for carbon steel indiscriminately on stainless without engineering basis.

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Part C — Inspection Procedures for Concrete Coating Systems

Concrete is porous, alkaline, and often moist. Coatings and linings on concrete (secondary containment, tank pads, walls, floors, pipeline weight-coat interfaces when coated) need a concrete-specific inspection package.

Substrate readiness checkpoints

Concrete coating inspection procedure (field outline)

1. Verify concrete prep method completed (shotblast, scarify, grind, acid etch only if still specified and controlled—modern practice often mechanical).
2. Confirm cleanliness and profile against CSP or standard invoked.
3. Moisture testing per specification (plastic sheet, electrical impedance, RH probes—as required by method).
4. Detail work — crack chase, joint sealant compatibility, cove bases, penetrations.
5. Primer/sealer application — coverage, holidays in primer if specified, recoat windows.
6. Body coats / lining — WFT/DFT or mil checks, mix ratio for plural systems, pot life.
7. Holiday detection on dielectric linings over concrete when specified (grounding path considerations differ from steel—follow equipment guidance for conductive underlays or wet sponge methods as applicable).
8. Adhesion tests (pull-off common on concrete) with failure mode: coating vs concrete cohesive failure (sometimes concrete breaks first—interpret carefully).
9. Cure before traffic, chemical exposure, or water immersion.
10. Documentation of moisture numbers, CSP, DFT, holidays, and repairs.

Concrete vs steel coating inspection (exam contrast)

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Integrating HDG, Nonferrous, and Concrete on One Project

A single facility may have galvanized grating, aluminum handrails, carbon-steel pipe, and concrete secondary containment. CIP Level 2 switches defect vocabulary and procedure by substrate:

• Grating: HDG bare spots, wet storage stain, thickness
• Aluminum rail: nonferrous prep and eddy-current DFT
• Containment: concrete moisture, CSP, lining holidays

Using only carbon-steel blast-and-epoxy mental models on all three is a classic Level 2 exam and field failure mode.

Exam Focus

Expect items that:

• Name HDG defects (bare spots, dross, ash, flux, wet storage stain, thickness issues)
• Attribute new bare spots to bonding/wetting failure
• Contrast nonferrous instrument/prep needs with carbon steel
• List concrete readiness checks (moisture, CSP, laitance, cure)

Bottom line: The HDG-defect blueprint line demands fluent recognition of galvanizing defects and thickness problems. The nonferrous/concrete blueprint line demands substrate-correct inspection procedures for nonferrous metals and concrete—prep, moisture, profile, instruments, adhesion, and holidays aligned to each material. Master the defect table for HDG and the procedure checklists for nonferrous and concrete to close Domain 7’s assessing skills.