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

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

4. 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

5. What is Thermal Spray?

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

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

8. 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

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

10. 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

11. 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

12. 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

13. 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

14. 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

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

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

17. 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

18. 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

19. Thermal Spraying onto Blast Cleaned Steel

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

21. Thermal Spray System Requirements

22. 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

23. 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

24. Bend Test

25. 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

26. Hammer and Chisel Cut Test

27. Hammer and Chisel Cut Test
Pass

28. Hammer and Chisel Cut Test
Fail

29. Questions?