Problem Solving Forum
September 5 - September 9, 2022
If an owner is using thermal spray aluminum on a pipe exterior as corrosion protection under insulation, and there is a holiday in the coating, will corrosion be substantially accelerated at the base carbon steel, being that the steel is now anodic to the aluminum?
Selected Answers
From
James Weber of James K Weber Consulting on
September 8, 2022:
I have been working in the thermal spray and TSA s ...read more
I have been working in the thermal spray and TSA specific application field of >35 years don't understand how the steel
in your question has become anodic to the aluminum coating. Regardless of this confusion, no, the are many, many "holidays" when TSA is applied on existing piping systems in a plant (bolt holes and under nuts/boltheads, between flanges, under pipe supports, at packing glands, inaccessible areas on bonnets and such, etc.) and there are no problems here. When first wetted, these uncoated areas are somewhat passivated by the TSA and corrosion of the uncoated steel is slowed to a nearly unmeasurable level. This has been proven thousands of times in actual practice and via years long lab testing.
From
Adan Cabeltes of Mega Paint Corp. on
September 8, 2022:
According to galvanic series of metals, aluminum i ...read more
According to galvanic series of metals, aluminum is anodic to steel. So if steel is exposed in a pinhole of TSA, the aluminum around the pinhole will sacrificially-corrode for the steel, not the other way around.
