The evaluation of protective coatings on lifting equipment in an extreme CX environment

Francois Strydom
Apr 2
3 min read

Updated: Apr 21

Purpose of this report

To summarize the performance of sherardizing in a CX environment both as a single protective layer and in a duplex coating consisting of sherardizing and powder coating. Standard powder coated links were also included for

comparison purposes.

( Orytech Report 2368 )

Sample testing size

The following Grade 8 Master Link size was selected for testing and evaluation:

Verdict from a previous paper

"The sherardizing process is well suited for Grade 8 alloy steel safety critical lifting equipment and brings with it several advantages."

Previous Paper Title

"The use of corrosion protection measures to extend the service life of lifting equipment in a marine environment. F Strydom & B Burgess"

As a follow up to the above paper, an evaluation was carried out within the guidelines provided in ISO 12944-9 Protective paint systems and laboratory performance test methods for offshore and related structures.

Sample categories

Test Methods

ISO 12944-9 specifies the following test methods for (CX) extreme environments:

Artificial seawater testing

as per ISO 2812-2 procedures (4200 hours)

Full immersion testing where samples are removed at intervals and inspected for signs of corrosion or coating defects.

The tests are carried out at 38 +- 2°C.

Cyclic ageing resistance testing

as per ISO 12944-6 procedures (4200 hours)

72 hours exposure that varied between intense ultraviolet and light radiation exposure as per ISO 12944-6 procedures.
72 hours exposure to neutral salt spray as per ISO 9227.
24 hours exposure to low temperature (-20± 2 °C).

25 of these combined cycles = 4200 hours.

Neutral salt spray testing

also performed as per ISO 9227 procedures for comparison and reference purposes, although not a requirement of ISO 12944-9. (4000 hours)

This method uses a 5% sodium chloride solution with a pH range of 6.5-7.2. The solution is atomized in a controlled environment at a temperature of 35 ± 2 °C.

Environmental Classification

The corrosion tests conducted in accordance with ISO 12944-9 relates to extreme conditions which simulate, amongst others, the splash zone in a marine environment (The area on a structure that is intermittently wet and dry due to wave action, tides and spray).

Coating Thickness Measurements

The following average coating thicknesses were measured before testing commenced:

Summary of Artificial Seawater Immersion Test Results | After 4200 Hours

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

Summary of Cyclic Ageing Resistant Test Results | After 4200 Hours

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

Summary of Neutral Salt Spray Test Results | After 4200 Hours

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

Real time examples of products used in the industry

These photos are examples of sherardized slings for offshore container lifting still in excellent condition after use in an extreme environment.

Weight loss

Conclusion

The laboratory tests which were carried out in accordance with ISO 12944-9 indicated that the duplex coated zinc thermal diffused- and powder coated product and the zinc thermal diffused product can be used successfully in an offshore CX environment.

The appearance of the zinc thermal diffused products that has been in service, indicated that the products were still in an excellent condition with no obvious evidence of base metal corrosion.

Conclusion

The standard powder coated samples in terms of surface protection and meaningful long-term durability are deemed not suitable for environments C4 and above.

When the relatively low weight loss of the zinc thermal diffused and powder coated samples is compared, to the 3 to 10 times higher weight loss of the standard powder coated samples, one can conclude that the corrosion rate of the standard samples was significantly higher compared to those of the other two sample categories.

McKinnon Chain has developed and successfully launched the Zinc Tough™ range of sherardized products for the offshore industry in 2018.

Available Product Range

The evaluation of protective coatings on lifting equipment in an extreme CX environment

To summarize the performance of sherardizing in a CX environment both as a single protective layer and in a duplex coating consisting of sherardizing and powder coating. Standard powder coated links were also included for

comparison purposes.

( Orytech Report 2368 )

The following Grade 8 Master Link size was selected for testing and evaluation:

"The sherardizing process is well suited for Grade 8 alloy steel safety critical lifting equipment and brings with it several advantages."

"The use of corrosion protection measures to extend the service life of lifting equipment in a marine environment. F Strydom & B Burgess"

As a follow up to the above paper, an evaluation was carried out within the guidelines provided in ISO 12944-9 Protective paint systems and laboratory performance test methods for offshore and related structures.

ISO 12944-9 specifies the following test methods for (CX) extreme environments:

Artificial seawater testing

as per ISO 2812-2 procedures (4200 hours)

Full immersion testing where samples are removed at intervals and inspected for signs of corrosion or coating defects.

The tests are carried out at 38 +- 2°C.

Cyclic ageing resistance testing

as per ISO 12944-6 procedures (4200 hours)

72 hours exposure that varied between intense ultraviolet and light radiation exposure as per ISO 12944-6 procedures.

72 hours exposure to neutral salt spray as per ISO 9227.

24 hours exposure to low temperature (-20± 2 °C).

25 of these combined cycles = 4200 hours.

Neutral salt spray testing

also performed as per ISO 9227 procedures for comparison and reference purposes, although not a requirement of ISO 12944-9. (4000 hours)

This method uses a 5% sodium chloride solution with a pH range of 6.5-7.2. The solution is atomized in a controlled environment at a temperature of 35 ± 2 °C.

The corrosion tests conducted in accordance with ISO 12944-9 relates to extreme conditions which simulate, amongst others, the splash zone in a marine environment (The area on a structure that is intermittently wet and dry due to wave action, tides and spray).

The following average coating thicknesses were measured before testing commenced:

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

* The formation of white and red rust is to be expected due to the Iron and Zinc in the coating, and this does not necessarily indicate corrosion of the underlying steel substrate. On all three sample types medium blistering was observed.

These photos are examples of sherardized slings for offshore container lifting still in excellent condition after use in an extreme environment.

The laboratory tests which were carried out in accordance with ISO 12944-9 indicated that the duplex coated zinc thermal diffused- and powder coated product and the zinc thermal diffused product can be used successfully in an offshore CX environment.

The appearance of the zinc thermal diffused products that has been in service, indicated that the products were still in an excellent condition with no obvious evidence of base metal corrosion.

The standard powder coated samples in terms of surface protection and meaningful long-term durability are deemed not suitable for environments C4 and above.

McKinnon Chain has developed and successfully launched the Zinc Tough™ range of sherardized products for the offshore industry in 2018.

A minimum sherardized coating thickness of 45 microns average is guaranteed.

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