Inspection of Thermal Spray Coatings Presented by: Dean Hooks, Thermion

Scope This webinar defines thermal spray coating (TSC) and provides an overview of its inspection

Introduction This webinar will review the procedures for the inspection of metallic thermal spray coatings (TSCs) of aluminum, zinc, and their alloys and composites for the corrosion protection of steel Inspection requirements in accordance with SSPC-CS 23.00/AWS C2.23/NACE No.12

What is Thermal Spray?

Thermal Spray Coating (TSC) Materials Aluminum, zinc, and their alloys in the form of powder or wire heated to a plastic or molten state

How does TSCs Protect Steel? Sealed: Good barrier protection Unsealed: Galvanic (sacrificial) protection

Special Properties Very good resistance to high temperatures, sunlight, and weathering Good application properties: adhesion to metals, film build, edge retention, and transfer efficiency Good impact and abrasion resistance Attacked by acids or alkalis unless topcoated

Environmental Advantages No volatile organic compounds (VOCs) to cause air pollution (100% solids) No hazardous air pollutants (HAPs) Limited overspray into surrounding areas

Economic Advantages Long-term protection (40+ years) of steel structures resulting in low life-cycle costs (costs per year) Reduced rework for original coating defects Reduced maintenance over coating life

SSPC-CS 23.00/AWS C2.23/NACE No.12 Revised May 2016 A procedure for the application of metallic thermal spray coating (TSCs) of aluminum, zinc, and their alloys and composites for the corrosion protection of steel Required equipment, application procedures, and in-process quality control (QC) checkpoints are specified

Pre-Surface Preparation Requirements The steel surface temperature shall be at least 3°C (5°F) above the dew point temperature Verify compressed air cleanliness in accordance with ASTM D4285 Verify cleanliness of abrasive in accordance with SSPC-AB 1, 2, or 3

Surface Cleanliness Before TSC application, steel substrate shall be prepared in accordance with: SSPC-SP 5/NACE No. 1 for immersion service; or Minimum of SSPC-SP 10/NACE No. 2 for other service applications; and Level of nonvisible contamination specified

Surface Profile Unless otherwise specified: Minimum angular profile depth of 65μm(2.5 mil) Maximum angular profile depth of 125μm(5.0 mil) Measured in accordance with SSPC-PA 17 using ASTM D4417: Method B – Depth Micrometer Method C – Replica Tape

ASTM D4417 Method B Depth micrometer Profile measured using a fine pointed probe

ASTM D4417 Method C Replica Tape A composite tape is impressed into the blast cleaned surface forming a reverse image of the profile

Job Reference Standard (JRS) A JRS shall be prepared for each TSC application or product Intended to be used as a “comparator” to evaluate the application process TSC thickness and adhesion measurements shall be performed on the JRS

Inspection of TSC Thickness TSC thickness measured in accordance with SSPC-PA 2 Coating Thickness Restriction Level 4 Spot readings can be between 80% of the specified minimum and 150% of the specified maximum thickness Area average must be within specified thickness

Thermal Spraying onto Blast Cleaned Steel

Inspection of TSC Adhesion TSC adhesion measured in accordance with ASTM D4541 Methods C, D, E, or F

Thermal Spray System Requirements

Nonmandatory Adhesion Testing Bend Test 180 degree bend on a Mandrel Qualitative, testing proper surface preparation, equipment setup, and spray parameters Mandrel diameter for threshold of cracking depends on substrate and coating thickness

Bend Test Passes On the bend radius, there is no cracking or spalling, or only minor cracking that cannot be lifted from the substrate with a knife blade Fails Coating cracks with lifting from the substrate

Bend Test

Nonmandatory Adhesion Testing Hammer and Chisel Cut Test A procedure to identify areas of metallized coating that are poorly adhering Involves impacting the coating with blow from a hammer to a masonry chisel Any disbonding or peel of the coating is considered a failure

Hammer and Chisel Cut Test

Hammer and Chisel Cut Test Pass

Hammer and Chisel Cut Test Fail

Questions?