Completion Is More Than the Last Coat

The spray equipment may be clean and the crew may be ready to leave, but the lining is not complete simply because the last coat has been applied. It must satisfy the specification, complete its required cure, pass the required inspections, and receive authorization for service.

Final project closeout should answer these questions:

• Has the entire specified area been lined?
• Does the lining meet the visual requirements?
• Does the installed thickness comply with the specification?
• Has required holiday testing been completed?
• Have specified adhesion or cure tests been completed?
• Have all defects and punch-list items been repaired and retested?
• Has the system received its required cure?
• Are the project records complete?
• Has the authorized party released the system for service?

The Final Acceptance Inspection

Final inspection should be conducted under suitable lighting after the lining has reached the condition required for inspection. Difficult areas, repairs, welds, edges, penetrations, nozzles, floors, sumps, and termination points deserve close attention.

Final inspection may include:

• Visual inspection for workmanship and defects
• Verification of total dry-film thickness
• Holiday or discontinuity testing
• Adhesion testing when specified
• Hardness, solvent-rub, or other cure testing when specified
• Review of repaired areas and retest results
• Confirmation that drains, nozzles, threads, and openings are clear
• Confirmation that masking, abrasive, debris, and temporary protection have been removed

Acceptance must be based on the project specification, approved product information, and written project procedures. The inspector should not reject acceptable work because of personal preference or accept nonconforming work because it appears close enough.

Developing the Punch List

A punch list identifies work that must be corrected before final acceptance. Each item should identify the location, observed condition, applicable requirement, corrective action, and required retesting.

Understand the Defect Before Repairing It

A repair that addresses only the visible symptom may fail again. Before choosing the repair procedure, determine why the defect occurred and how far it extends.

Planning and Performing the Repair

The lining manufacturer should provide or approve the repair procedure. The correct method depends on the substrate, service environment, lining chemistry, age of the system, size of the defect, and remaining recoat options.

A repair procedure should establish:

• How the repair boundary will be located and marked
• How unsound material will be removed
• How far the work must extend into sound lining
• How exposed steel or concrete will be prepared
• How the existing lining edge will be tapered or feathered
• How contamination will be removed
• Which compatible repair material will be used
• Whether a primer or tie coat is required
• The required overlap, coat sequence, and thickness
• The required curing conditions
• The inspection and testing required after repair

Defective material should be removed back to firmly bonded lining. The repair perimeter must be examined because failure can extend beyond the visible defect.

Exposed steel or concrete must receive the preparation required by the approved repair procedure. Existing sound lining normally must be cleaned and mechanically abraded to provide a suitable bonding surface.

Reinspect and Retest Every Repair

A repair is not complete when the repair material has been applied. It is complete when it has cured, passed the required inspection, and been documented as accepted.

Repair verification may include:

• Visual examination of the repair and transition edges
• Wet- or dry-film-thickness measurement
• Holiday testing after the required cure
• Hardness or other cure verification
• Adhesion testing when specifically required
• Confirmation that the repair is clean and undamaged

Final Cure and Return to Service

Dry-to-touch time is not the same as full chemical cure. A lining may be firm enough to walk on while still being vulnerable to immersion, solvents, elevated temperature, cleaning, pressure, or abrasion.

Before return to service, verify:

• The time of the last application and final repair
• The actual temperatures maintained during cure
• The minimum cure required for the intended service
• Whether low temperatures require additional curing time
• Whether post-curing, heating, ventilation, or testing is required
• Whether the first fill has special restrictions
• Whether washdown or decontamination is required
• Who has authority to release the equipment

The Project Closeout Package

The closeout package documents what was installed and establishes the baseline for future inspection and maintenance.

• Approved specification and lining schedule
• Product data and safety data sheets
• Product names, batch numbers, and material records
• Surface-preparation and substrate-repair records
• Environmental readings
• Mixing, application, pot-life, and recoat records
• Thickness, holiday, adhesion, and cure-test reports
• Defect and repair log
• Photographs and location drawings
• Nonconformance reports and corrective actions
• Final acceptance and return-to-service authorization

Maintenance Begins With a Baseline

The final inspection report becomes the baseline for future condition assessments. Without it, an owner may not know whether a rough area, thickness variation, mark, or repair existed when the lining was installed or developed later in service.

Baseline photographs should identify the vessel, location, direction of view, and approximate scale. A vessel drawing divided into repeatable inspection zones helps future inspectors compare findings with earlier records.

Establishing an Inspection Schedule

There is no single inspection interval suitable for every lining. Inspection frequency should reflect risk, service severity, operating history, manufacturer recommendations, regulatory requirements, and available shutdown opportunities.

More frequent inspection may be appropriate when there is:

• Severe or changing chemical exposure
• High temperature or thermal cycling
• Abrasion, erosion, vibration, or impact
• Frequent cleaning or steam-out cycles
• Known moisture or permeation risk
• A history of repairs or recurring defects
• A high consequence of containment failure
• Evidence of corrosion, leakage, or product contamination

What Maintenance Inspections Should Look For

• Blistering, bubbling, swelling, or softening
• Cracking, checking, crazing, or splitting
• Rust staining, corrosion, or exposed substrate
• Delamination, peeling, flaking, or lifting edges
• Erosion, abrasion, scratches, gouges, or impact damage
• Discoloration, chemical attack, or surface deposits
• Failure around welds, nozzles, drains, joints, and penetrations
• Damage around mixers, baffles, ladders, and flow paths
• Deterioration of previous repairs

The location and pattern of a defect often reveal more than the defect alone. Repeated damage near an inlet may indicate erosion. Failure near a liquid line may point to changing chemical or vapor exposure. Cracking around a joint may indicate structural movement.

Repair, Overcoat, or Replace?

Applying a new lining over a failing system does not remove the weak layer underneath. An overcoat is only as reliable as the existing material to which it is bonded.

Changes in Service Must Be Reviewed

A lining selected for one service is not automatically suitable for another. Suitability should be reviewed whenever there are changes in:

• Chemicals or chemical mixtures
• Concentration or contamination
• Service temperature
• Immersion duration
• Cleaning chemicals or procedures
• Steam or hot-water exposure
• Abrasion or solids content
• Pressure, vacuum, agitation, or flow

Changed service should be reviewed with the lining manufacturer, owner, project specifier, or qualified corrosion professional before exposure.

Safety During Maintenance Inspection

Used tanks and vessels may contain hazards that were not present during the original application. Residues, oxygen deficiency, toxic gases, flammable vapors, cleaning chemicals, and process contamination must be evaluated.

• Isolate, drain, clean, ventilate, and lock out the equipment.
• Follow the applicable permit-required confined-space program.
• Test and monitor the atmosphere as required.
• Identify the previous contents and related hazards.
• Provide trained attendants, communication, and rescue capability.
• Select protective equipment for the actual exposure.
• Control electrical and ignition hazards during holiday testing.
• Do not disturb an unknown lining until hazardous-material risks are evaluated.