Inspecting Steel and Concrete Before Lining Work Begins

Inspection Comes Before Preparation

Surface preparation does not begin with the blast nozzle, grinder, or pressure washer. It begins with understanding what is present, what is damaged, what is contaminated, and what must be corrected before the lining can perform.

A pre-work inspection establishes the condition of the substrate before the contractor changes it. Once an old lining has been removed or steel has been blasted, it can be difficult to prove which defects were pre-existing and which were created during the work.

What the Pre-Work Inspection Must Accomplish

The inspection should answer five basic questions:

1. Is the substrate structurally sound enough to receive the lining?
2. What contamination or previous material must be removed?
3. What repairs must be completed before surface preparation?
4. Can the specified preparation method reach every area?
5. Are the proposed lining and details appropriate for the actual condition?

The contractor is not expected to perform structural engineering unless that service is specifically included in the contract. The contractor is expected to recognize and report visible conditions that could interfere with the work.

Review the Project Information

Before entering the work area, review the information that defines the project:

• Project specification and approved lining system
• Drawings, repair details, and lining limits
• Previous inspection and maintenance records
• History of the stored material or process exposure
• Previous lining type and known failure areas
• Required surface cleanliness and profile
• Specified tests and acceptance criteria
• Manufacturer's current application instructions
• Access, ventilation, lighting, and confined-space requirements

When the written documents conflict with the actual field condition, stop and request clarification. The contractor should not silently redesign the work.

Begin With a Safe Initial Survey

Tanks, pits, vaults, pipelines, and process vessels may be permit-required confined spaces. Before entry, the responsible employer must address isolation, atmospheric testing, ventilation, entry authorization, communication, rescue, and other applicable safety requirements.

Residues from the previous service may be toxic, corrosive, flammable, reactive, or oxygen-displacing. A surface that looks dry and empty can still present serious hazards.

Inspecting Steel Before Lining Work

Corrosion and section loss

Look for general corrosion, deep pitting, grooving, undercutting, perforation, and visibly thin areas. Heavy corrosion may require ultrasonic thickness measurements or evaluation by the owner or qualified engineer.

Filling deep pits with lining material does not restore lost structural thickness. The repair may require welding, plate replacement, pit filling, or another approved procedure.

Welds

Welds are common lining failure locations because they may contain sharp ridges, spatter, undercut, porosity, pinholes, slag, rough starts and stops, or irregular contours. These defects can prevent complete coverage and create thin film over sharp projections.

Inspect longitudinal welds, circumferential welds, attachments, nozzles, brackets, supports, reinforcement pads, and repaired areas. The required weld finish should be defined by the project specification.

Edges and corners

Sharp edges tend to pull liquid coating away as the material cures, leaving reduced film thickness. Identify cut edges, plate corners, bolt heads, nuts, stiffeners, supports, and other projections requiring rounding, grinding, or stripe coating.

Laminations and fabrication defects

Plate laminations, rolled-in defects, gouges, arc strikes, temporary welds, and fabrication damage may become visible before or after blasting. Mark and document questionable areas so the owner can determine the required repair.

Connections and inaccessible areas

Check lap joints, skip welds, bolted connections, back-to-back angles, crevices, and areas behind attachments. If the surface cannot be properly prepared, inspected, coated, or holiday tested, the design may require modification.

Steel Inspection Checklist

Existing Coatings and Linings

Determine what coating or lining is currently present, if possible. Record its approximate thickness, condition, adhesion, failure pattern, and areas of corrosion beneath it.

Look for:

• Blistering, peeling, cracking, and delamination
• Rusting at holidays, welds, edges, and damaged areas
• Softening, swelling, discoloration, or chemical attack
• Previous patches and incompatible repair materials
• Moisture or liquid trapped behind the lining
• Failure concentrated at the vapor-liquid interface
• Abrasion or erosion in flow and impact areas

The failure pattern can help identify whether the problem involved chemical attack, poor surface preparation, contamination, movement, excessive temperature, abrasion, incorrect material selection, or incomplete cure.

Existing coatings may contain lead, chromium, or other hazardous constituents. Testing, containment, worker protection, waste handling, and disposal requirements must be established before removal begins.

Oil, Grease, and Chemical Contamination

Oil and grease must generally be removed before abrasive blasting. Blasting an oily surface can drive contamination into the profile or spread it across a larger area.

Chemical tanks and process equipment may retain contamination inside pits, cracks, seams, pores, and welds. Heat generated during preparation can draw residues back to the surface.

Cleaning may require repeated cycles followed by inspection or testing. The cleaning method must be compatible with the substrate and must not leave its own harmful residue.

Soluble Salt Contamination

Chlorides, sulfates, nitrates, and other soluble salts can remain on steel or within corrosion pits even after visible rust is removed. When moisture reaches these salts through the lining, osmotic blistering and underfilm corrosion may develop.

The project specification should identify the test method, locations, frequency, and maximum acceptable contamination. Testing is especially important in marine, wastewater, chemical, deicing-salt, fertilizer, and immersion environments.

Inspecting Concrete Before Lining Work

Soundness and strength

Concrete must be strong enough to support the lining. Look for scaling, spalling, delamination, honeycombing, laitance, soft surfaces, exposed aggregate, and deteriorated repairs.

Sounding with an appropriate tool may help identify hollow or delaminated areas. Pull-off testing may be required to evaluate surface tensile strength or the bond of an existing system.

Cracks

Record the location, width, length, and apparent condition of cracks. Determine, as far as the project requires, whether they are dormant, active, leaking, or structural.

Active cracks and moving joints require a different treatment from stable shrinkage cracks. The lining contractor should not decide that a crack is harmless simply because it is narrow.

Joints and penetrations

Inspect expansion joints, control joints, wall-to-floor transitions, pipe penetrations, drains, embedded steel, and terminations. These areas require details that accommodate movement and prevent liquid from traveling behind the lining.

Bugholes and surface voids

Bugholes, honeycombing, and open pores can trap air. During coating application, expanding air may create pinholes or bubbles. Voids should be opened, cleaned, and filled with a compatible repair material as required.

Concrete Moisture and Vapor

Concrete can contain moisture even when the surface appears dry. Moisture may come from incomplete curing, groundwater, cleaning, leaks, process exposure, or vapor moving through the slab.

Excess moisture can interfere with adhesion and cure or create blistering after the lining is placed in service. A plastic-sheet test may indicate moisture at the surface, but it does not provide every piece of information needed for every resin-floor or lining system.

The specification and manufacturer should identify the required test method, acceptance limit, test locations, and number of tests. Follow the complete test procedure rather than relying on touch, appearance, or an unapproved handheld reading.

Concrete Contamination

Oils, fats, chemicals, sewage, salts, previous sealers, curing compounds, and cleaning residues can penetrate below the visible surface. Removing only the surface discoloration may not remove the contamination.

During inspection, identify:

• Dark or oily areas
• Unusual odors
• Softened or discolored concrete
• White salt deposits or efflorescence
• Low or high surface pH
• Previous sealers and curing compounds
• Biological growth and wastewater residue
• Areas where water beads instead of wetting the surface

Heavily contaminated concrete may require removal to sound material. The owner or designer should approve the depth and method of removal.

Document Existing Repairs

Old repairs can behave differently from the surrounding substrate. They may have different strength, moisture content, porosity, thermal movement, or compatibility with the proposed lining.

Mark patches, crack injections, grout, sealants, resurfacing materials, and previously replaced steel. Loose or incompatible repairs should be removed. Sound repairs may still require special preparation or a transition detail.

Confirm Access and Constructability

The inspection must also determine whether the specified work can actually be performed. Confirm that workers and equipment can reach every surface requiring preparation and lining.

• Are openings large enough for workers and equipment?
• Can abrasive, debris, and wastewater be removed?
• Can ventilation reach dead-air areas?
• Is lighting sufficient for preparation and inspection?
• Can spray equipment maintain the required material conditions?
• Can inspectors reach all test locations?
• Can holidays and repairs be completed before access is removed?

Establish Hold Points

A hold point is a stage at which work stops until the required inspection or approval is complete. Useful hold points may include:

1. Initial substrate inspection
2. Completion of structural and fabrication repairs
3. Removal of contamination and existing lining
4. Completion of surface preparation
5. Acceptance of cleanliness and surface profile
6. Completion of concrete repairs and moisture testing
7. Acceptance before primer or lining application

Hold points prevent important conditions from being covered before they can be verified.

Photographs and Written Records

Photographs should show the overall structure as well as close views of defects. Include a scale, location marker, or identifiable reference when practical.

The written report should record:

• Date, time, location, and inspector
• Structure identification and previous service
• Areas inspected and areas that could not be accessed
• Observed defects and contamination
• Test methods, instruments, locations, and results
• Photograph numbers tied to specific locations
• Required repairs or unresolved questions
• Owner, manufacturer, or engineer direction
• Final acceptance or release to begin preparation

Conditions That Require Work to Stop

• Suspected structural failure or unsafe access
• Unexpected perforation or severe steel section loss
• Unidentified hazardous residue or coating
• Active water infiltration that prevents proper preparation
• Concrete that continues to break apart during preparation
• Cracks or movement not addressed by the specification
• Inaccessible areas that cannot be prepared or lined
• Contamination exceeding the specified acceptance limit
• Field conditions that conflict with the approved lining design

Stopping work is not a failure of production. It prevents the contractor from burying a problem beneath an expensive lining.

Contractor Pre-Work Checklist

Knowledge Check

Key Takeaway