Evaluation of External Pipeline Coatings

Evaluation of External Pipeline Coatings

Protective coatings are a key component in corrosion control of the exterior of oil and gas transmission pipelines. New regulatory requirements include protective coatings as a specific item within the engineering assessment required for new construction, rehabilitation, and repair. Laboratory test programs are routinely carried out by pipeline owners and coating manufacturers to qualify coatings for pipelines. Selection of an appropriate coating significantly reduces the probability of external corrosion over the life of the pipeline.

Benefits of Laboratory Evaluation of Pipe Coatings

  • Compare competing coating products and select the best for a specific pipeline environment.
  • Qualify coatings for use on pipelines based on the owners qualification test program.
  • Evaluate new coatings.
  • Assess coating performance for a change in service, eg. increased line temperature.
  • Determine coating performance for specific pipeline environments, eg. aggressive soil, high temperature.
  • Ensure that the coating is compatible with CP (Cathodic Protection).
  • Confirm coating application quality.
  • Assess the effect of a formulation change in a coating.
  • Determine the tolerance of coatings to challenging application conditions, eg. cold-wet surfaces, hot surfaces.
  • Failure analysis to determine the cause of failures.

Examples of Common Laboratory Tests:

  • Cathodic Disbondment: Coating resistance to disbondment at a holiday in the presence of cathodic protection. Evaluated at temperatures from 0 to 150°C (32 to 200°F) (CSA Z245.20/21 ASTM G8, G42, G95).
  • Adhesion: Wet adhesion (ie. immersion) at temperatures from 0 to 95°C (32 to 200°F) (CSA Z245.20, ASTM D870). Adhesion is determined by knife test or pull-off adhesion (ASTM D4541).
  • Impact: Resistance to cracking and disbondment when struck at temperatures from -60°C to 95°C (-40°F to 200°F) (CSA Z245, ASTM D2794).
  • Flexibility: Resistance to cracking and disbondment at bends from 0.5° to 3°/PD at temperatures from -60°C to 95°C (-40°F to 75°F) (CSA Z245.20-02).
  • EIS (Electrochemical Impedance Spectroscopy): The stability of barrier properties (permeability to water) are determined during immersion at temperatures up to 95°C (200°F) (ASTM and ISO Standard under development).
  • Hardness: Resistance to softening at temperatures up to 95°C (200°F) under immersion. (ASTM D2240 (Shore Durometer), ASTM D3363 (Pencil).
  • Peel adhesion: Adhesion of tape coatings by peel after immersion in water. (CSA Z245.21).
  • Abrasion Resistance: Resistance to abrasion. (ASTM D4060 (Taber), ASTM G6 (slurry erosion), ASTM D968 (falling sand).
  • Penetration test: Penetration resistance of pipeline coatings (ASTM G17).
  • Cure: Extent of cure by differential scanning calorimetry (CSA Z245.20).
  • QUV Resistance: Resistance to deterioration during outdoor storage (ASTM G53 QUV/Condensation).
  • Gouge Test: Resistance to directional drill type gouging. (CSA Z245.20)
  • Others: Many other test methods of evaluation as applicable.

Coatings that can be evaluated:

  • Main line coatings such as fusion bond epoxy (FBE), multi-layer coatings (polyolefin/FBE).
  • Field-applied girth weld coatings, repair coatings, ancillary component coatings, such as liquid epoxy, polyurethane, tape coatings, sleeves.
  • Coating compatibility (adhesion) between mainline coatings and repair or joint coatings.

EIS (Electrochemical Impedance Spectroscopy):

Coating impedance, a measure of coating barrier properties, is measured as a function of time during immersion at ambient or elevated temperature. The loss of impedance is related to an increase in coating permeability and physical / chemical deterioration. EIS is particularly useful in evaluating competing products that show little difference in results from standard test methods. See our EIS Information section for more details.

Evaluation of Pipeline Coatings During Excavation:

EIS measurements can be made on mainline coatings and joint coatings on operating pipelines, with the objective of assessing barrier properties, extent of deterioration, and remaining life. EIS is used in combination with visual inpsection and DFT determination.

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