1. Overview & Applications
Tape coating systems provide external corrosion protection for buried pipelines through adhesive-backed tapes applied directly to the pipe surface. Tape coatings are economical, field-repairable, and compatible with cathodic protection systems.
New construction
Mainline coating
Factory or field-applied tape coating for new pipeline installation.
Field joints
Girth weld coating
Tape wrapping over welded joints connecting pipe sections.
Repair coating
Coating rehabilitation
Overcoating damaged or deteriorated existing pipe coatings.
Tie-ins and branches
Hot tap coating
Coating new connections and fittings on operating pipelines.
IMAGE: Two-Layer Tape Coating System Cross-Section
Shows pipe wall, primer layer, inner wrap (PE tape with adhesive), and outer wrap (mechanical protection)
Key Concepts
- Primer: Adhesion-promoting coating applied before tape, typically liquid epoxy or rubber-based
- Inner wrap: Corrosion protection layer, typically PE or PVC tape with adhesive backing
- Outer wrap: Mechanical protection layer, thicker PE tape resists soil abrasion and impact
- Holiday: Coating defect (pinhole, void, thin spot) allowing soil contact with pipe
- Dielectric strength: Coating resistance to electrical breakdown, measured in volts/mil
Why tape coating matters: External corrosion is the leading cause of pipeline failures in buried service. Proper tape coating provides 20-50 year protection when correctly applied with cathodic protection, preventing costly leaks and environmental incidents.
Advantages of Tape Coating
- Field applicability: Can be applied on-site without special equipment or facilities
- Repair simplicity: Damaged areas easily repaired by overwrapping with additional tape
- Cost-effective: Lower material and application costs than FBE, liquid epoxy, or polyethylene
- Low temperature tolerance: Can be applied in cold weather (down to 0°F with special primers)
- Conformability: Wraps around fittings, valves, and irregular shapes
Disadvantages and Limitations
- Labor-intensive: Requires skilled applicators for quality workmanship
- Moisture sensitivity: Adhesion degrades if applied to wet or contaminated surfaces
- Mechanical damage risk: Thinner than fusion-bonded coatings, more susceptible to impact damage
- UV degradation: Prolonged exposure to sunlight before burial degrades tape properties
- Holiday-prone: More defects than plant-applied coatings if application quality poor
Industry Standards
- AWWA C214: Tape Coating Systems for the Exterior of Steel Water Pipelines
- NACE SP0169: Control of External Corrosion on Underground or Submerged Metallic Piping Systems
- CSA Z245.30: External Tape Coating Systems for Steel Pipe (Canadian standard)
- SSPC-SP: Surface Preparation Standards (SSPC-SP 6 commercial blast, SP 10 near-white blast)
- ASTM D1000: Standard Test Methods for Pressure-Sensitive Adhesive Coated Tapes
- 49 CFR 192.461: External corrosion control – buried or submerged pipelines (US regulation)
2. Tape Coating Systems
Tape coating systems consist of multiple layers: surface preparation, primer, inner wrap (corrosion protection), and outer wrap (mechanical protection). System selection depends on pipe diameter, operating temperature, and burial conditions.
Two-Layer Tape System Components
| Layer | Material | Thickness | Purpose |
|---|---|---|---|
| Surface Preparation | Abrasive blast or solvent clean | N/A | Remove mill scale, rust, contaminants for primer adhesion |
| Primer | Liquid epoxy, mastic, or petrolatum | 5-10 mils | Promote adhesion, fill surface irregularities, corrosion inhibitor |
| Inner Wrap | PE/PVC tape with adhesive | 20-30 mils | Primary corrosion barrier, dielectric insulation |
| Outer Wrap | PE tape (non-adhesive or adhesive) | 10-20 mils | Mechanical protection from soil stress, impact, abrasion |
Inner Wrap Tape Types
The corrosion protection layer is the critical component:
| Tape Type | Backing Material | Adhesive | Temp Range | Application |
|---|---|---|---|---|
| Polyethylene (PE) | PE film | Butyl rubber | -40°F to 140°F | Most common, good flexibility, excellent moisture resistance |
| Polyvinyl Chloride (PVC) | PVC film | Rubber resin blend | -20°F to 180°F | Higher temperature service, stiffer than PE |
| Petrolatum | Woven fabric | Petrolatum compound | -50°F to 200°F | Specialty applications, excellent cold weather performance |
| Coal tar | Saturated felt | Coal tar enamel | -20°F to 150°F | Legacy system, less common due to health/environmental concerns |
Primer Selection
Primer must be compatible with tape adhesive and provide corrosion inhibition:
| Primer Type | Composition | Cure Time | Min Apply Temp | Compatibility |
|---|---|---|---|---|
| Epoxy primer | Two-part epoxy resin | 30-60 min @ 70°F | 40°F | PE, PVC tape |
| Mastic primer | Rubber-based compound | 10-30 min | 32°F | PE tape, petrolatum |
| Bituminous primer | Asphalt/solvent blend | Flash-off: 5-15 min | 50°F | Coal tar tape (legacy) |
| Petrolatum primer | Petrolatum paste | Immediate tack | 0°F | Petrolatum tape only |
System Performance Requirements
AWWA C214 and CSA Z245.30 specify minimum performance criteria:
| Property | Test Method | AWWA C214 Requirement | Significance |
|---|---|---|---|
| Peel adhesion | ASTM D1000 | ≥ 15 lb/in width | Resistance to disbondment from pipe |
| Tensile strength | ASTM D1000 | ≥ 25 lb/in width | Resistance to tearing during handling |
| Elongation | ASTM D1000 | ≥ 200% | Flexibility to conform to pipe surface |
| Dielectric strength | ASTM D149 | ≥ 1,000 V/mil (dry) | Electrical insulation for CP compatibility |
| Water absorption | ASTM D570 | < 0.5% by weight | Moisture resistance, prevents coating degradation |
| Impact resistance | ASTM G14 | No cracking at 2 J impact | Survives rocks, equipment during installation |
| Cathodic disbondment | ASTM G8/G42 | < 10 mm radius @ 28 days | Coating remains bonded under CP current |
Tape Width and Thickness Selection
Tape Width by Pipe Diameter:
Pipe Diameter (NPS) | Typical Tape Width
2 - 4 | 2 inches
6 - 12 | 4 inches
14 - 24 | 6 inches
26 - 36 | 8 - 10 inches
≥ 42 | 12 inches
Wider tape reduces number of wraps, speeds application.
Narrower tape easier to handle, better for small diameter or fittings.
Total System Thickness:
T_total = t_primer + t_inner + t_outer
Typical systems:
- Light duty (low stress soil): 35-40 mils total
- Standard duty: 40-50 mils total
- Heavy duty (rocky soil, impact risk): 50-70 mils total
Example - Standard System:
Primer: 10 mils liquid epoxy
Inner wrap: 20 mils PE tape
Outer wrap: 20 mils PE tape
Total: 50 mils (1.27 mm) minimum thickness
Cold-Applied vs. Heat-Shrink Tape
Two application methods with different characteristics:
- Cold-applied tape: Wrapped at ambient temperature, adhesive provides bond. Most common for field joints. Requires clean, dry surface. Faster application.
- Heat-shrink tape: Wrapped loosely, heat applied (propane torch) causing shrinkage and adhesive activation. Better conformability to irregular shapes. Slower application, requires more skill.
System selection criteria: PE tape with butyl adhesive is the industry standard for most applications: good flexibility, excellent moisture barrier, compatible with CP systems, economical. Use PVC or petrolatum only for specific high-temperature or extreme cold requirements.
3. Application Procedures
Proper surface preparation and wrapping technique are critical for coating performance. Poor application causes premature failure through disbondment, holidays, and inadequate coverage.
Surface Preparation Requirements
SSPC surface preparation standards define cleanliness levels:
| SSPC Standard | Description | Application |
|---|---|---|
| SP 1 - Solvent Clean | Remove oil, grease, dirt with solvent | Pre-cleaning before abrasive blasting |
| SP 2 - Hand Tool Clean | Wire brush, scraper remove loose material | Minimal prep for temporary coating only |
| SP 3 - Power Tool Clean | Power wire brush, grinder, needle gun | Field repair of small areas (not recommended for new work) |
| SP 6 - Commercial Blast | Remove ≥2/3 of surface contaminants by abrasive blast | Minimum for field-applied tape coating |
| SP 10 - Near-White Blast | Remove ≥95% of surface contaminants | Preferred for critical service, plant-applied coating |
| SP 5 - White Metal Blast | Remove 100% of contaminants, visible white metal | Maximum adhesion (rarely specified, very expensive) |
Abrasive Blasting Parameters
Blast Cleaning Specifications:
Abrasive type:
- Steel grit/shot: Most common, angular profile
- Aluminum oxide: Very aggressive, sharp profile
- Garnet: Natural mineral, less dust than sand
- Glass bead: Smooth finish (not for adhesion applications)
Blast pressure: 80-100 psi typical for steel pipe
Surface profile (anchor pattern):
- Minimum: 1.5 mils
- Preferred: 2-3 mils
- Maximum: 4 mils (too rough may trap air, create voids)
Cleanliness verification:
- Visual inspection per SSPC-VIS 1 (reference photos)
- Surface must be dry (no moisture)
- No oil film (water break test)
- Dust removed (compressed air blow-off or vacuum)
- Profile measured with Testex tape or replica tape
Time limit:
Apply primer within 4 hours of blasting (8 hours max if protected from moisture/contamination)
If surface flash-rusts, re-blast before priming
Primer Application
Proper primer technique ensures tape adhesion:
- Mix primer (if two-part): Follow manufacturer's mix ratio precisely. Pot life typically 30-90 minutes. Use within pot life.
- Apply uniform coat: Brush, spray, or roller application. Target thickness: 5-10 mils wet. Avoid runs, sags, or dry areas.
- Cure time: Allow minimum flash-off time per manufacturer (10-60 minutes typical). Surface should be tacky but not wet when tape applied.
- Temperature check: Pipe surface temperature must exceed dew point by ≥5°F to prevent moisture condensation.
- Film thickness verification: Use wet film thickness gauge to ensure adequate coverage.
Tape Wrapping Technique
IMAGE: Spiral Tape Wrapping Technique
Illustrates 50% overlap pattern, wrap direction, tension application, and tape advance per wrap
Spiral Wrapping Method (Most Common):
1. Starting point: Begin at "6 o'clock" position (bottom of pipe)
2. Tension control: Maintain consistent moderate tension (hand-tight)
- Too loose: Wrinkles, air pockets, disbondment
- Too tight: Thinning, adhesive squeeze-out, tearing
3. Overlap: 50-55% overlap (half-lapping)
- Ensures minimum double layer coverage
- 4" tape with 50% overlap = 2" advance per wrap
4. Angle: Perpendicular to pipe axis (90°) or slight spiral (80-85°)
5. Air removal: Roll or squeegee each wrap to remove trapped air
6. Finishing: Overlap final wrap by 6 inches minimum, secure end
Wrapping Formula:
N = L / (W × (1 - O))
Where:
N = Number of wraps required
L = Length to be coated (inches)
W = Tape width (inches)
O = Overlap (decimal, e.g., 0.50 for 50%)
Example:
Pipe circumference: 12 feet = 144 inches
Tape width: 4 inches
Overlap: 50% (0.50)
N = 144 / (4 × (1 - 0.50))
N = 144 / (4 × 0.50)
N = 144 / 2 = 72 wraps around circumference
Inner vs. Outer Wrap Application
Two-layer system requires proper sequencing:
| Layer | Overlap | Tension | Notes |
|---|---|---|---|
| Inner wrap | 50-55% | Moderate (hand-tight) | Adhesive side against primer, critical for corrosion protection |
| Outer wrap | 50-55% | High (firm tension) | May be non-adhesive PE, wraps over inner layer for impact protection |
Staggered wrap pattern (optional): Offset outer wrap seam from inner wrap seam by 50% to eliminate continuous weak point through coating thickness.
Field Joint Coating Procedure
Coating girth welds requires special attention:
- Weld completion: Allow weld to cool to <150°F before coating. Verify weld quality (UT, radiography as required).
- Surface prep: Abrasive blast weld and 6 inches onto adjacent factory coating on each side (total 12" + weld width). SSPC-SP 6 minimum.
- Primer application: Coat blasted area including overlap onto factory coating. Feather edge onto factory coating.
- Tape application: Center tape over weld, wrap to extend 6-12 inches onto factory coating each side.
- Edge sealing: Ensure tape firmly adheres to factory coating edges (no lifting or gaps).
- Inspection: Holiday detect entire joint area at specified voltage (typically 67 V/mil coating thickness).
Cold Weather Application
Low temperatures challenge tape adhesion and handling:
Cold Weather Precautions:
Minimum application temperatures:
- Standard PE tape with butyl adhesive: 32°F
- Cold-applied PE tape (special adhesive): 0°F
- Heat-shrink tape (with heating): 0°F
- Petrolatum tape: -20°F
Cold weather best practices:
1. Pre-warm tape rolls to 70-90°F (storage in heated space)
2. Pipe surface temp must exceed dew point + 5°F (prevent condensation)
3. Use low-temperature primer formulations
4. Protect work area from wind, precipitation (tent enclosure)
5. Apply heating pads or radiant heaters to maintain pipe warmth
6. Allow extended primer cure time at low temps (2× normal)
7. Increase wrap tension slightly (cold tape less conformable)
Do not coat if:
- Pipe surface below minimum temp for tape/primer
- Precipitation occurring (rain, snow)
- High humidity (>85% RH) without surface heating
- Visible moisture or frost on pipe surface
Coating Fittings and Irregularities
Valves, tees, and elbows require special techniques:
- Elbows: Apply tape in short sections, cutting and overlapping to conform to curvature. Avoid bridging or wrinkles.
- Tees/branches: Coat main pipe first, then branch, overlapping onto main. Use "shingles" method (cut tape into patches, overlap like roof shingles).
- Flanges: Wrap up to bolt circle, seal edges carefully. Leave bolts accessible for assembly.
- Valves: Coat body, bonnet, operator as accessible. Use mastic or petrolatum putty to fill recesses before taping.
Critical success factors: Surface must be clean, dry, and within temperature limits. Tape must be applied with consistent tension, proper overlap, and no bridging or wrinkles. Quality control inspection (holiday detection) verifies workmanship before burial.
4. Quality Control & Inspection
Rigorous inspection detects coating defects before burial. Holidays (pinholes, voids, thin spots) must be found and repaired to prevent corrosion.
IMAGE: Holiday Detection Equipment and Procedure
Shows high-voltage spark tester with rolling spring electrode, ground connection to pipe, and scanning technique
Holiday Detection Methods
| Method | Principle | Voltage Range | Application |
|---|---|---|---|
| Low-voltage wet sponge | Conductive sponge + low DC voltage detects electrical path to pipe | 9-90 VDC | Thin coatings (<20 mils), small areas, requires contact |
| High-voltage spark tester | High voltage probe, spark jumps through defects to grounded pipe | 1,500-15,000 VDC | Standard method for tape coatings, 100% coverage |
| Pulse DC (Tinker & Rasor) | Pulsed DC reduces arcing, safer for thin coatings | 500-15,000 V | Field joints, thin coatings |
| AC holiday detector | AC voltage creates current flow through holidays | 500-30,000 VAC | Thick coatings, less common for tape |
Holiday Detection Voltage Calculation
NACE SP0188 High-Voltage Spark Test Formula:
V = k × √T
Where:
V = Test voltage (volts DC)
T = Total coating thickness (mils)
k = Coating constant (V/mil^0.5)
k-Factor Values (NACE SP0188-2006):
Standard coatings (PE tape, FBE, liquid epoxy): k = 525
Thin coatings (<20 mils): k up to 1,250
Calculation Examples:
45 mil tape coating (2-layer):
V = 525 × √45 = 525 × 6.71 = 3,523 V ≈ 3,500 V
60 mil coating (heavy duty):
V = 525 × √60 = 525 × 7.75 = 4,069 V ≈ 4,100 V
90 mil coating (3-layer FBE):
V = 525 × √90 = 525 × 9.49 = 4,982 V ≈ 5,000 V
Acceptable Range: ±10% of calculated voltage
Minimum Practical Voltages:
High-voltage spark tester: 1,500 V minimum
Maximum safe voltage: 15,000 V
Safety Requirements:
• Ground pipe to detector before energizing
• Use insulated probe handles and safety gloves
• Never touch probe tip or pipe during test
• Trained operators only per NACE certification
Holiday Detection Procedure
- Equipment setup: Set voltage per coating thickness. Ground detector to pipe. Verify tester operation on known holiday (test piece).
- Scanning: Move probe or spring electrode over coating at walking speed (2-3 ft/s). Maintain contact or near-contact (spring electrode).
- 100% coverage: Overlap passes to ensure entire surface scanned. No skip areas.
- Holiday indication: Audible alarm and/or light signals holiday. Mark location immediately with paint or marker.
- Repair: After scanning complete, repair all holidays before burial.
- Re-test: Re-test repaired areas at same voltage to verify repair quality.
Holiday Repair Methods
Small defects can be patched; large defects may require overwrapping:
| Defect Size | Repair Method | Procedure |
|---|---|---|
| < ¼" diameter | Spot patch | Apply 2"×2" tape patch over holiday, roll firmly |
| ¼" - 1" diameter | Patch and overwrap | Patch, then apply tape strip 6" wider than defect |
| > 1" diameter | Complete overwrap | Wrap additional tape layer over 6 ft section containing defect |
| Large area (multiple) | Strip and re-coat | Remove tape, re-blast if needed, re-prime, re-wrap entire section |
Acceptable Holiday Density
Industry standards define acceptable defect rates:
AWWA C214 Acceptance Criteria:
Field joints:
- Maximum 5 holidays per joint
- No holiday > ¼ inch diameter after repair
- All repaired areas must pass re-test
Mainline coating:
- Maximum 3 holidays per 100 feet
- No clustered defects (>3 within 1 foot)
- All holidays repaired and re-tested
CSA Z245.30:
- Holiday density < 1 per 100 m² coating area
- Repairs verified by re-testing
Rejection criteria (excessive holidays indicate poor application):
- > 10 holidays per joint or 100 ft → Reject, re-coat section
- Holidays indicating tape not adhered → Reject, remove/re-apply
- Bare pipe exposed → Reject, immediate re-coating required
Adhesion Testing
Verify tape bond strength through pull-off testing:
| Test | Method | Acceptance Criteria |
|---|---|---|
| Peel adhesion | Cut tape strip, pull at 180° angle | ≥ 15 lb/inch width per AWWA C214 |
| Knife test | Attempt to pry tape edge with knife blade | Tape tears before lifting (qualitative) |
| Foremat test | Cut X through coating, apply/remove tape, visual inspection | < 15% area removed per ASTM D3359 |
Visual Inspection Checklist
Before holiday detection, visually inspect for obvious defects:
- ☐ Surface preparation adequate: No visible rust, oil, moisture on pipe
- ☐ Primer properly applied: Uniform coating, no bare spots or excessive thickness
- ☐ Tape wraps uniform: Consistent overlap, no gaps or bridging
- ☐ No wrinkles or air pockets: Tape conforms to pipe surface
- ☐ Edges sealed: Tape ends firmly adhered, not lifting
- ☐ No physical damage: Gouges, cuts, tears repaired before inspection
- ☐ Adequate thickness: Coating meets minimum specified mils
- ☐ Field joints properly overlapped: Tape extends onto factory coating minimum 6"
100% holiday detection required: All buried tape-coated pipe must be holiday detected before backfilling. Undetected holidays lead to concentrated corrosion at defect sites, causing pitting failure within 5-15 years despite cathodic protection.
5. Cathodic Protection Compatibility
Tape coatings must be compatible with impressed current or sacrificial anode cathodic protection (CP) systems. Coating acts as high-resistance barrier between pipe and soil, allowing CP current to protect pipe at coating holidays.
Coating Requirements for CP
NACE SP0169 specifies coating properties for effective CP:
| Property | Requirement | Reason |
|---|---|---|
| Electrical resistivity | > 10^6 ohm·cm² | High resistance limits current wastage through coating |
| Dielectric strength | > 1,000 V/mil | Withstands CP voltages without breakdown |
| Water absorption | < 0.5% by weight | Prevents moisture penetration that lowers resistivity |
| Cathodic disbondment | < 10 mm radius @ 28 days | Coating remains bonded under CP polarization |
| Soil stress resistance | No cracking or failure under load | Maintains integrity despite soil movement |
IMAGE: Cathodic Protection System Schematic
Shows impressed current CP system with rectifier, ground bed, pipe coating, and current flow at holidays
Cathodic Protection Principles
CP Protection Criterion (NACE SP0169):
Pipe-to-soil potential must be:
E ≤ -850 mV vs. Cu/CuSO₄ reference electrode
OR
Polarization shift ≥ 100 mV from native potential
Current requirement:
I = A × i_d
Where:
I = Total CP current required (amperes)
A = Bare pipe area (ft² or m²)
i_d = Current density (typically 0.5-5 mA/ft² depending on soil)
With good coating:
Bare area = Total area × Holiday fraction
Holiday fraction = (Number of holidays × Average holiday size) / Total area
Typical: 0.1-1% of pipe area is bare (holidays + coating damage)
Example:
10,000 ft of 12" pipe = 31,416 ft² total area
Coating has 0.5% bare area = 157 ft² exposed
Soil resistivity 5,000 ohm·cm (moderate) → i_d = 1 mA/ft²
I = 157 × 0.001 = 0.157 amperes (157 mA total current)
Good coating dramatically reduces CP current requirement and cost.
Coating Disbondment Mechanism
CP current can cause coating failure if coating not properly designed:
- Cathodic reaction at holidays: Oxygen reduction at bare pipe creates hydroxide ions (OH⁻), raising pH to 10-12.
- Alkaline attack: High pH degrades adhesive bond, causing coating to disbond (lift off) from pipe.
- Disbondment propagation: Once started, disbondment spreads outward from holiday, exposing more pipe area.
- Shielding: Disbonded coating traps electrolyte, shields pipe from CP current, allowing corrosion under coating.
ASTM G8 Cathodic Disbondment Test:
1. Apply coating to steel panel
2. Scribe 1/8" wide holiday through coating to bare metal
3. Immerse panel in 3% NaCl solution at 77°F (or elevated temp)
4. Apply CP current: -1.5 V vs. Cu/CuSO₄ for 28 days
5. Remove panel, strip coating radially from holiday
6. Measure disbondment radius
Pass criteria:
Disbondment radius < 10 mm (0.4 inches) from holiday edge
Good tape coatings typically show 3-8 mm disbondment.
Poor coatings or incompatible adhesives can disbond 25+ mm.
CP System Design Considerations
Coating quality affects CP system sizing and cost:
| Coating Condition | Estimated Bare Area | Current Density (mA/ft²) | Relative CP Cost |
|---|---|---|---|
| Excellent (new, well-applied) | 0.1-0.5% | 0.5-1.0 | 1× (baseline) |
| Good (typical field-applied tape) | 0.5-1.0% | 1.0-2.0 | 2× |
| Fair (older coating, some damage) | 1-5% | 2.0-5.0 | 5× |
| Poor (deteriorated coating) | 5-20% | 5.0-20 | 20× |
| Bare pipe (no coating) | 100% | 20-100 | 100× |
Holiday Detection Voltage vs. CP Voltage
Holiday detector voltage is much higher than CP voltage:
Voltage Comparison:
Holiday detection: 500-15,000 VDC
Duration: Milliseconds per location
Purpose: Break down thin coating at holidays, arc to pipe
Cathodic protection: 0.5-3.0 VDC (pipe-to-soil)
Duration: Continuous, 24/7/365
Purpose: Polarize pipe cathodically, prevent corrosion
Why holiday detection doesn't damage coating:
- Very brief exposure (ms)
- Energy dissipated at holidays, not through intact coating
- Voltage below breakdown threshold for properly applied tape (1,000+ V/mil)
CP voltage too low to damage coating:
- Maximum CP voltage ~ 5 V across coating
- Intact coating dielectric strength > 1,000 V/mil × 40 mils = 40,000 V
- 5 V vs. 40,000 V → No electrical stress on coating
Tape Coating vs. Other Coatings for CP
Comparison of coating types for CP effectiveness:
| Coating Type | Resistivity | Disbondment Resistance | CP Compatibility |
|---|---|---|---|
| Tape (PE/PVC) | Excellent | Good to Excellent | Excellent |
| Fusion-bonded epoxy (FBE) | Excellent | Excellent | Excellent (industry standard) |
| Coal tar enamel | Good | Poor (alkaline susceptible) | Fair (historical, less common now) |
| Polyethylene (3-layer) | Excellent | Excellent | Excellent (mainline transmission) |
| Liquid epoxy | Excellent | Good | Good (field joints, repairs) |
CP Testing and Monitoring
After coating application and CP system activation:
- Pipe-to-soil potential surveys: Measure voltage at test stations, verify -850 mV criterion met along entire pipeline
- Close interval surveys (CIS): Measure potentials every 2.5-5 ft to locate coating holidays (areas requiring more current)
- Current requirement monitoring: Track rectifier output current over time, increasing current indicates coating deterioration
- Holiday surveys (DCVG, ACVG): Above-ground coating defect surveys locate holidays without excavation
- Coating resistance measurement: Pearson surveys estimate coating quality based on current distribution
Coating + CP synergy: Tape coating provides passive protection (barrier), CP provides active protection at holidays. Together, they provide >50 year corrosion protection for buried pipelines. Good coating reduces CP cost 10-100×.
Standards for CP-Compatible Coatings
- NACE SP0169: Control of External Corrosion on Underground or Submerged Metallic Piping Systems
- NACE SP0189: On-Line Monitoring of Cathodic Protection Systems
- ASTM G8: Standard Test Method for Cathodic Disbonding of Pipeline Coatings
- ASTM G42: Standard Test Method for Cathodic Disbonding of Pipeline Coatings Subjected to Elevated Temperatures
- ISO 15589-1: Petroleum and Natural Gas Industries – Cathodic Protection for Pipeline Systems – Part 1: On-land Pipelines
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