Corrosion Protection for Industrial Coating Contractors
Article 03: Evaluating the Structure and Service Environment
What Contractors Need to Know Before Surface Preparation Begins
A successful coating project begins before the first abrasive particle strikes the steel. The structure, existing coating, environment, access, contamination, and service conditions must all be understood before work begins.
Big Idea: The specification describes the expected work. The pre-job evaluation determines whether the actual structure and field conditions match those expectations.
Why the Pre-Job Evaluation Matters
Coating failures are often blamed on the material or applicator, but many problems begin before application. The original scope may underestimate coating deterioration, corrosion, contamination, restricted access, weather exposure, or the difficulty of preparing complex surfaces.
A project may call for abrasive blasting, but the structure may contain areas that cannot be reached by normal blasting equipment. The specification may assume ordinary atmospheric exposure, while the structure is actually exposed to chemicals, immersion, condensation, or frequent washdown. The existing coating may contain hazardous materials or be incompatible with the proposed repair system.
If these conditions are discovered after mobilization, they can create delays, change orders, safety concerns, and disagreements about responsibility.
The contractor's job is not to redesign the asset or independently approve structural repairs. The contractor's responsibility is to examine the work area, compare actual conditions with the project documents, identify concerns, document what is found, and obtain clarification before covering a problem with a new coating.
Start with the Project Documents
The field evaluation should begin with a review of the documents controlling the work. The contractor needs to understand what has been specified before determining whether field conditions support the planned approach.
Review the available:
- Project specifications
- Drawings and equipment schedules
- Coating-system requirements
- Product data sheets
- Safety data sheets
- Surface-preparation requirements
- Environmental limits
- Inspection and testing requirements
- Previous coating and maintenance records
- Known hazardous-material information
- Owner-specific procedures and permit requirements
- Cathodic-protection drawings or component information when applicable
Conflicting requirements should be resolved before work begins. The contractor should not guess which document takes priority or silently choose the easiest requirement.
Identify the Substrate
The substrate is the material that will receive the coating. Industrial projects may involve carbon steel, galvanized steel, stainless steel, aluminum, concrete, masonry, or previously coated surfaces.
The preparation method and coating system must be suitable for the actual substrate. A method appropriate for carbon steel may damage galvanized steel, thin aluminum, delicate equipment, or adjacent nonmetallic components.
During the evaluation, confirm:
- The substrate material
- Whether different metals are connected
- Whether the metal is thin, damaged, or heavily corroded
- Whether galvanizing, metallizing, or another metallic layer is present
- Whether concrete, grout, seals, insulation, or nonmetallic materials contact the steel
- Whether the proposed preparation method could damage the substrate
Field Rule: Never assume every silver-colored surface is bare steel or every gray surface is an ordinary coating. Confirm the substrate before selecting the preparation method.
Evaluate the Existing Coating
An existing coating can provide valuable information about previous surface preparation, application quality, service exposure, and failure patterns.
Before disturbing it, examine the coating's general condition and how it is failing. Determine whether the project requires complete removal, localized repair, spot preparation, or overcoating.
Look for:
- Blistering
- Cracking
- Flaking or peeling
- Chalking
- Rust staining
- Rust creepage from scratches and edges
- Loss of adhesion
- Softening, swelling, or chemical attack
- Mechanical damage
- Previous patch repairs
- Areas with unusually high or low film thickness
- Failure concentrated at welds, edges, bolts, or waterlines
If the existing coating will remain, its adhesion, cleanliness, compatibility, thickness, and overall condition must be evaluated according to the project requirements. A tightly adhered coating in one location does not prove that the entire structure is suitable for overcoating.
If the existing coating is unknown, testing or additional owner information may be required before deciding how it should be cleaned, disturbed, or overcoated.
Consider Hazardous Existing Coatings and Contaminants
Older industrial coatings may contain lead, chromium compounds, or other hazardous materials. Process residues, dust, biological contamination, and chemicals on the structure may also create exposure risks.
The contractor should not assume that an old coating is harmless because it looks ordinary. Available surveys, test reports, safety information, and owner records should be reviewed before the coating is disturbed.
The evaluation should determine whether the work requires:
- Additional material testing
- Special worker-protection procedures
- Containment and ventilation
- Exposure monitoring
- Controlled waste collection
- Special disposal procedures
- Decontamination requirements
- Facility-specific permits or controls
Hazardous-material decisions must be made before blasting, grinding, scraping, sanding, or otherwise disturbing the existing coating.
Examine the Corrosion Condition
Article 02 reviewed the common forms of corrosion a contractor may encounter. During the structure evaluation, identify where corrosion is occurring and whether it appears uniform, localized, hidden, or concentrated at specific details.
Pay particular attention to:
- Deep pits
- Holes and perforations
- Cracks
- Severe section loss
- Corrosion at welds and heat-affected areas
- Attack around bolts and connections
- Corrosion beneath deposits or insulation
- Damage concentrated at waterlines
- Corrosion around dissimilar metals
- Recurring failure in previously repaired areas
Photograph these conditions before surface preparation removes the evidence. Include overview photographs that establish location and close-up photographs that show the condition clearly.
Structural damage should be evaluated by qualified and authorized personnel. The coating contractor should not hide severe deterioration beneath filler or coating without approved repair instructions.
Understand the Service Environment
The service environment is one of the most important factors in coating-system performance. A system that performs well in a dry interior may fail quickly under immersion, chemical exposure, condensation, abrasion, or coastal conditions.
Atmospheric Exposure
Determine whether the structure is indoors or outdoors and whether it is exposed to rain, sunlight, windborne salts, industrial fallout, temperature changes, humidity, or condensation.
Immersion and Submersion
Identify the liquid, operating temperature, water chemistry, contaminants, cleaning procedures, and whether immersion is continuous or intermittent.
Buried Service
Buried structures may be exposed to soil moisture, salts, bacteria, rocks, backfill pressure, ground movement, and cathodic-protection current. The coating must also withstand handling and installation damage.
Chemical Exposure
Identify the chemicals involved, their concentrations, operating temperatures, frequency of exposure, and whether mixtures or cleaning chemicals may be present.
Abrasion and Impact
Consider traffic, moving solids, slurry, loading operations, cleaning equipment, maintenance activity, and other conditions that may physically damage the coating.
Thermal Exposure
Review normal operating temperature, temperature cycling, shutdown conditions, hot spots, insulation, and whether the coating will be applied while the equipment is warm.
Field Rule: Select and apply the coating for the actual service environment - not simply for the conditions present on the day it is painted.
Identify Surface Contamination
Visible rust is not the only contamination that can interfere with coating performance. Industrial structures may carry contaminants that are difficult or impossible to identify by appearance alone.
Possible contaminants include:
- Oil and grease
- Soluble salts
- Dust and abrasive residue
- Process chemicals
- Fuel and hydraulic fluid
- Soap and cleaning residue
- Weld spatter and fabrication residue
- Biological growth
- Condensation and trapped moisture
- Old marking materials or adhesive
Abrasive blasting does not reliably remove every contaminant. Oil and grease can be spread across the surface or driven into the profile. Soluble salts can remain in pits and crevices after the surface looks visually clean.
The project should define the required inspection and testing. Article 06 will examine surface cleanliness and contaminant testing in greater detail.
Evaluate Surface Geometry
Complex geometry affects surface preparation, coating application, inspection, and long-term performance. Sharp edges and difficult recesses often receive less coating than broad flat surfaces.
Identify:
- Sharp edges
- Welds and weld spatter
- Bolts, nuts, and fasteners
- Lap joints and crevices
- Pits and rough corrosion
- Back-to-back angles
- Stiffeners and attachments
- Restricted spaces behind piping or equipment
- Drainage problems and water traps
- Areas that cannot be reached with normal spray equipment
These areas may require grinding, edge treatment, stripe coating, brush application, smaller equipment, special access, or approved changes to the work plan.
Review Access and Workability
A coating system cannot be applied correctly if workers cannot safely reach the surface, position their equipment, control the spray pattern, inspect the work, or perform repairs.
The access evaluation should consider:
- Scaffolding and work-platform requirements
- Fall-protection needs
- Confined-space requirements
- Lighting
- Ventilation
- Equipment placement
- Abrasive and waste removal
- Hose routing
- Material-delivery distance
- Emergency access and rescue planning
- Access for inspectors and testing instruments
Do not evaluate access only from the applicator's perspective. The inspector must also be able to see, reach, measure, and verify the completed work.
Identify Adjacent Equipment and Sensitive Components
Abrasive, dust, water, solvents, overspray, and coating materials can damage equipment that is not part of the coating scope.
Identify and protect:
- Instruments and control panels
- Valves and valve stems
- Nameplates and warning labels
- Grounding and bonding points
- Electrical connections
- Machined surfaces
- Gaskets and seals
- Moving parts
- Fire-protection equipment
- Nearby vehicles, buildings, and occupied areas
The protection plan should identify what will be masked, covered, isolated, temporarily removed, or inspected after completion.
Locate Cathodic-Protection Components
Structures protected by cathodic protection may include cables, anodes, test stations, reference electrodes, rectifier connections, isolation joints, bonds, and other electrically important components.
Before surface preparation begins:
- Ask whether a cathodic-protection system is present
- Locate visible cables, test points, anodes, and connections
- Confirm which components must remain uncoated
- Protect components from abrasive blasting and mechanical damage
- Do not disconnect, relocate, or alter components without authorization
- Document damaged or questionable components before work begins
- Coordinate with the responsible cathodic-protection specialist
Accidentally coating, blasting, cutting, or disconnecting one of these components can interfere with the corrosion-control system even when the coating work itself appears satisfactory.
Evaluate Environmental Control Requirements
The coating may have strict limits for air temperature, surface temperature, relative humidity, dew-point separation, wind, moisture, and cure conditions.
The pre-job evaluation should determine:
- Whether weather conditions can be expected to remain acceptable
- Whether the steel is affected by process heat or cold contents
- Whether condensation occurs during daily temperature changes
- Whether dehumidification, heating, cooling, or ventilation is required
- Whether wind can carry abrasive, dust, or overspray beyond the work area
- Whether the coating can cure before weather or service conditions change
- How environmental conditions will be measured and recorded
Article 09 will examine environmental conditions and dew point in greater detail.
Define Hold Points and Authority
A hold point is a stage of the work that cannot proceed until the required inspection or approval has been completed.
Common hold points may include:
- Initial condition assessment
- Hazardous-material review
- Cleaning before abrasive blasting
- Surface preparation and profile acceptance
- Environmental-condition verification
- Primer application
- Stripe-coat inspection
- Dry-film-thickness inspection
- Holiday testing
- Repair acceptance
- Final project closeout
Before work starts, everyone should understand who can accept the work, reject the work, authorize repairs, approve substitutions, and resolve unexpected conditions.
Unclear authority creates delays and encourages field decisions that may not comply with the specification.
Document the Existing Condition
Good documentation establishes what the contractor found before beginning work. It also creates a record of questions, decisions, approvals, and changes.
A useful pre-job record may include:
- Project name and location
- Date and time of inspection
- Names of participants
- Areas included in the coating scope
- Substrate and existing coating condition
- Observed corrosion and damage
- Known or suspected contamination
- Access limitations
- Sensitive equipment and cathodic-protection components
- Environmental conditions
- Overview and close-up photographs
- Questions requiring clarification
- Approved changes or repair instructions
Photographs should be identifiable. A close-up of rust with no location reference may be difficult to use later. Pair close-up images with wider photographs that show where the condition is located.
Pre-Job Evaluation Checklist
- Have the project documents been reviewed?
- Has the actual substrate been identified?
- Has the existing coating been evaluated?
- Has hazardous-material information been reviewed?
- Has corrosion damage been photographed and reported?
- Is the actual service environment understood?
- Have possible surface contaminants been identified?
- Can all surfaces be safely reached, prepared, coated, and inspected?
- Have sensitive components been identified and protected?
- Have cathodic-protection components been located?
- Can environmental requirements be maintained?
- Are hold points and approval authority clearly defined?
- Have questions and changed conditions been resolved in writing?
Bottom Line: Do not begin by asking, "How fast can we blast it?" Begin by asking, "What are we protecting, what has it been exposed to, and what conditions must be corrected before we coat it?"
Key Takeaways
- The pre-job evaluation compares actual field conditions with the project documents.
- The substrate must be confirmed before selecting a preparation method.
- The existing coating can reveal important failure patterns and service conditions.
- Hazardous coatings and contamination must be addressed before the surface is disturbed.
- Unexpected corrosion damage should be documented before blasting removes the evidence.
- The coating system must match the actual service environment.
- Access must support preparation, application, inspection, and repair.
- Sensitive equipment and cathodic-protection components must be identified and protected.
- Hold points and approval authority should be established before work begins.
- Clear documentation protects the asset owner, inspector, and contractor.
Knowledge Check
- Why should the structure be evaluated before surface preparation begins?
- Why is it important to confirm the actual substrate?
- What information can an existing coating provide?
- Why should corrosion damage be photographed before abrasive blasting?
- What service conditions should be considered when reviewing a coating system?
- Why must cathodic-protection components be identified before work begins?
View Knowledge Check Answers
1. The evaluation determines whether the actual structure, coating condition, contamination, access, and environment match the project documents and planned work.
2. Preparation methods and coating systems that are suitable for one substrate may damage or perform poorly on another.
3. It can provide information about previous surface preparation, application quality, service exposure, compatibility, and failure patterns.
4. Blasting can remove the coating and corrosion patterns that show the original location, type, and severity of the condition.
5. Consider atmospheric exposure, immersion, buried service, chemicals, abrasion, impact, temperature, condensation, cleaning, and other actual operating conditions.
6. Blasting, coating, cutting, disconnecting, or damaging these components can interfere with the operation of the corrosion-control system.
Coming Next
Article 04: Protective Coatings as the Primary Barrier
The next article explains how protective coatings isolate steel from corrosive environments, how different coating layers work together, and why surface preparation and film continuity determine the strength of the barrier.
