Coating Survey Methodology in an FPSO

Abstract

A coating survey in a Floating Production Storage and Offloading (FPSO) unit is a critical process for assessing the integrity and performance of protective coatings applied to structural components. These coatings serve as the primary defense against corrosion, ensuring the longevity of the asset, minimizing maintenance costs, and maintaining compliance with industry standards. This article provides a comprehensive methodology for conducting a coating survey on an FPSO, covering preparation, inspection techniques, data collection, analysis, and reporting. The methodology adheres to international standards such as ISO 12944, NACE SP 0178, and IACS UR Z17.

1. Introduction

FPSOs operate in harsh offshore environments, facing continuous exposure to seawater, humidity, and harsh weather conditions. Protective coatings play a vital role in mitigating corrosion-related degradation. Conducting a systematic coating survey ensures that coatings remain effective and that necessary repairs are identified before failure occurs. The survey methodology must align with industry regulations, classification society requirements, and best practices in corrosion protection.

2. Objectives of a Coating Survey

The primary objectives of a coating survey in an FPSO include:

• Assessing the condition of protective coatings on key structural areas such as cargo tanks, ballast tanks, topside structures, and subsea components.
• Identifying areas with coating degradation, defects, or failures.
• Evaluating the effectiveness of the coating system and recommending maintenance strategies.
• Ensuring compliance with regulatory and classification society requirements.
• Supporting asset integrity management by providing data for predictive maintenance planning.

3. Coating Survey Methodology

3.1 Pre-Survey Preparation

Proper planning is crucial for a successful coating survey. The following steps are undertaken:

3.1.1 Review of Documentation

• Obtain and review past coating reports, maintenance records, and as-built drawings.
• Check coating specifications, datasheets, and application history.
• Refer to regulatory requirements from organizations such as ABS, DNV, or Lloyd’s Register.

3.1.2 Risk Assessment and Safety Precautions

• Conduct a Job Safety Analysis (JSA) to identify potential hazards such as confined spaces, exposure to hazardous materials, and working at heights.
• Ensure compliance with Permit-to-Work (PTW) requirements.
• Confirm that all personnel involved have the necessary safety training and Personal Protective Equipment (PPE).

3.1.3 Equipment Preparation

The following inspection tools and instruments should be prepared and calibrated:

• Dry Film Thickness (DFT) Gauge (e.g., Elcometer 456)
• Surface Profile Gauge
• Surface Contamination Meters (e.g., salt contamination test kits)
• Adhesion Test Equipment (pull-off tester)
• UV Lamps for fluorescent coatings
• Visual Inspection Tools (magnifying glass, pit gauge)
• Inspection Cameras (borescopes or drones for remote areas)

3.2 Coating Condition Assessment

3.2.1 Visual Inspection

A general visual assessment is performed to identify the following:

• Coating defects such as blistering, cracking, delamination, and peeling.
• Signs of corrosion, rust staining, or pitting underneath coatings.
• Areas with mechanical damage due to operational impact.

Visual inspection follows international standards such as ISO 4628 (Assessment of Degradation of Coatings). Defects are categorized by type, severity, and extent.

3.2.2 Dry Film Thickness (DFT) Measurement

• DFT is measured using a non-destructive coating thickness gauge.
• Readings are compared against specified thickness requirements.
• Areas with low DFT values indicate potential coating degradation.

3.2.3 Adhesion Testing

Adhesion testing determines how well the coating adheres to the substrate. The following methods may be used:

• Pull-off Test (ASTM D4541) – Uses a dolly and pull-off tester to measure adhesion strength.
• Cross-cut Test (ISO 2409) – Involves cutting a grid pattern into the coating to assess adhesion.

3.2.4 Surface Contamination Testing

Surface contamination, particularly chloride and salt contamination, accelerates corrosion beneath coatings. The following tests are conducted:

• Bresle Test (ISO 8502-9) – Measures soluble salt contamination.
• pH and Conductivity Tests – Assess surface cleanliness before coating application.

3.2.5 Holiday Testing (High-Voltage & Low-Voltage Inspection)

Holiday testing detects pinholes or discontinuities in coatings:

• High voltage (spark testing) for thick coatings (>500 µm).
• Low voltage (wet sponge test) for thin coatings (<500 µm).

This is critical for coatings applied to tank linings, piping, and submerged surfaces.

3.3 Advanced Inspection Techniques

For a more detailed assessment, advanced non-destructive testing (NDT) methods may be used:

3.3.1 Infrared Thermography

• Identifies delaminations and voids in coatings.
• Useful for large-area scanning.

3.3.2 Ultrasonic Coating Thickness Measurement

• Used for multilayer coatings and measuring coatings on non-metallic substrates.

3.3.3 Drone-Based Inspection

• Enables access to high-risk areas without scaffolding or rope access.
• Provides high-resolution images for analysis.

3.4 Data Collection and Analysis

• All observations, measurements, and photographic evidence are recorded.
• Coating conditions are categorized using rating systems such as the IACS UI SC 223 standard.
• Data is compared against past surveys to identify trends.

4. Reporting and Recommendations

A detailed coating survey report is prepared, including:

• Executive Summary – Overview of findings and critical issues.
• Inspection Scope – Areas surveyed, and methods used.
• Findings – Defects, coating condition, and quantitative data.
• Recommendations – Immediate repairs, long-term maintenance strategies, and future inspection schedules.
• Compliance Statement – Confirmation of regulatory compliance.

Reports should be submitted to asset integrity teams, classification societies, and regulatory authorities as required.

5. Conclusion

A systematic coating survey in an FPSO ensures asset integrity, extends service life, and reduces corrosion-related maintenance costs. By following standardized methodologies and utilizing modern inspection techniques, operators can proactively manage coating performance and prevent premature failures. The integration of data analytics and predictive maintenance strategies further enhances coating management in FPSOs.

References

1. International Organization for Standardization (ISO) 12944-1:2017 – "Paints and Varnishes – Corrosion Protection of Steel Structures by Protective Paint Systems."
2. ISO 8501-1:2007 – "Preparation of Steel Substrates before Application of Paints and Related Products."
3. NACE SP0178-2016 – "Design, Fabrication, and Surface Finish Practices for Tanks and Vessels."
4. ASTM D4541-17 – "Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers."
5. IACS UR Z17 – "Procedural Requirements for Service Suppliers Engaged in Coating Condition Evaluation of Hull Structures."
6. Lloyd’s Register – "Coating Condition Assessment Guidelines for Offshore Structures."
7. Det Norske Veritas (DNV) RP-B401 – "Cathodic Protection Design for Subsea Structures and Pipelines."
8. ABS Guide for Hull Inspection and Maintenance Program, 2020.

This methodology provides a structured approach to conducting coating surveys in an FPSO, ensuring compliance with industry best practices and enhancing long-term asset integrity.

Summary of ISO 12944: Corrosion Protection of Steel Structures by Protective Paint Systems

ISO 12944 is an international standard that provides comprehensive guidelines for the protection of steel structures from corrosion using protective paint systems. It is widely used in industries such as oil and gas, marine, infrastructure, and offshore structures, including FPSOs.

Key Sections of ISO 12944

1. Scope and Purpose

• Defines the requirements for designing, selecting, applying, and maintaining protective coatings for steel structures exposed to various environments.
• Aims to extend the service life of coated structures by preventing corrosion.

2. Environmental Corrosivity Categories (ISO 12944-2)

ISO 12944 classifies environments based on their corrosivity levels:

FPSOs typically fall under C5 or CX due to constant exposure to seawater, humidity, and harsh weather.

3. Design Considerations (ISO 12944-3)

• Emphasizes designing structures to minimize corrosion risks (e.g., avoiding crevices, sharp edges, and water traps).
• Recommends proper weld preparation and smooth transitions to improve coating adhesion.

4. Surface Preparation (ISO 12944-4)

• Specifies surface preparation standards, including abrasive blasting to achieve cleanliness levels like:

Sa 2½ (Near-white metal) – Common for marine and offshore structures.

Sa 3 (White metal) – Used in highly aggressive environments.

• Discusses methods such as hand tool cleaning, power tool cleaning, and water jetting.

5. Protective Paint Systems (ISO 12944-5)

• Defines coating types, including epoxy, polyurethane, zinc-rich primers, and multi-coat systems.
• Specifies coating thickness requirements based on environmental category.
• Recommends multi-layer systems (e.g., primer, intermediate, and topcoat) for long-term durability.

6. Laboratory Testing for Coating Performance (ISO 12944-6)

• Defines accelerated testing methods such as: Salt spray testing (ASTM B117). Cyclic corrosion testing. Humidity resistance testing.

7. Durability Categories (ISO 12944-1 & 12944-9)

Coatings are classified based on expected durability before major maintenance:

For FPSOs, coatings must meet Very High Durability requirements to withstand harsh offshore conditions.

8. Application and Quality Control (ISO 12944-7 & 12944-8)

• Provides guidelines for proper coating application, including temperature, humidity, and curing conditions.
• Emphasizes quality control through Dry Film Thickness (DFT) measurement, adhesion testing, and visual inspections.

ISO 12944 is a critical standard for corrosion protection in steel structures, especially in offshore environments. It ensures coatings are selected, applied, and maintained correctly to maximize the service life of FPSOs and other marine structures. Following ISO 12944 helps prevent premature coating failures, reducing maintenance costs and ensuring long-term asset integrity.

Summary of NACE SP0178-2016

"Design, Fabrication, and Surface Finish Practices for Tanks and Vessels"

NACE SP0178-2016 provides guidelines for the design, fabrication, and surface finish practices of tanks and vessels to ensure proper coating performance and corrosion control. The document is widely used in industries such as oil and gas, petrochemicals, and marine applications.

Key Areas Covered in NACE SP0178

1. Scope and Purpose

• Establishes best practices for preparing metal surfaces before applying protective coatings or linings.
• Aims to reduce coating failures caused by poor design, fabrication defects, and inadequate surface preparation.

2. Design Considerations for Corrosion Control

• Emphasizes the importance of designing tanks and vessels to minimize corrosion risks.
• Recommends avoiding sharp edges, crevices, and complex geometries that can lead to coating failures.
• Specifies requirements for weld preparation, structural reinforcements, and drainage considerations.

3. Surface Preparation Standards

• Defines surface preparation levels based on service conditions.
• Provides classifications for surface finish conditions, including welds, edges, and attachment points.
• Refers to standards such as ISO 8501, SSPC-SP 10 (Near-White Blast Cleaning), and NACE No. 2 for cleanliness requirements.

4. Weld and Surface Finishing Requirements

• Classifies weld surface conditions into four categories:

Category A: Best condition, smooth, fully ground, and free from defects.

Category B: Moderate condition with minor surface irregularities.

Category C: Rougher condition with allowable imperfections, but suitable for less critical applications.

Category D: Poorest condition, often unsuitable for protective coatings.

• Provides guidance on grinding welds, removing sharp edges, and minimizing undercuts and porosity.

5. Coating and Lining Application Considerations

• Discusses the impact of surface cleanliness on coating adhesion and durability.
• Provides best practices for applying coatings to prepared surfaces.
• Covers thickness requirements, inspection procedures, and curing conditions.

6. Inspection and Quality Control

• Recommends non-destructive testing (NDT) techniques to detect surface defects before coating application.
• Specifies criteria for visual inspection, adhesion testing, and holiday detection.
• Encourages the use of quality control checklists to ensure compliance with coating specifications.

NACE SP0178 is an essential guideline for industries relying on protective coatings for corrosion control. By implementing its recommendations, asset owners can enhance coating performance, extend equipment lifespan, and reduce maintenance costs. The document is particularly valuable for FPSO operators, as it ensures that coatings in tanks and vessels withstand harsh offshore environments.