Silicone acrylic coating blistering issue 2

[nyfi]

Dear Experts,

Kindly help me out to figure out the reason of below query.

I had inspected Inorganic Zinc silicate (IOZ) and Silicone acrylic coating inspection applied to stacks of inline heater.
just after three hours in service , only silicone acrylic blistering started. Due to mechanical works, stacks are now offline. they only commissioned equipment for three hours only.
IOZ primer was Hempel Galvosil 15700 and Hempel Silicone Acrylic 56940.
IOZ was moisture cured by placing wet sacks and MEK was also acceptable. Final DFT after Silicon acrylic application was in range of 89-130 micron.

Stacks connected to firetube have operating temperature 550Degree Celsius.
Stacks temperature between 150-250 degree Celsius.

I did lots of search. I got to know lots of things but need specific info.

 

[SJones]

Take a look at the 56940 datasheet and note the maximum service temperature of 200 deg C, the need for a mist coat, and the prevention of excessive thickness.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[nyfi]

Dear SJones,

Thank you for your reply.
Let me clear that mist coat was also applied.
thickness was in range of 89-130 micron as required is 125 micron.

this defects occurred when stack placed in service. I also joined coating inspector while stack inspection. there were no defects nor popping that usually occurs overcoating IOZ.

I look forward to your reply

Thank you.

 

[david339933]

Many things could go wrong, but this stands out in the data sheet.

HEMPEL'S SILICONE ACRYLIC 56940
Weathering/service temperatures:

On first exposure to heat the temperature increase from ambient temperature to the required service
temperature must run over a period of 24 hours.

 

[SJones]

@david - good catch; I missed it when scanning.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.