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UG-101(l) Brittle-Coating Test
- Thread starter Vladeng
- Start date
In my early years as a valve R&D lab. engineer, I used a product called Stresscoat from the Magnaflux Corp. I don't know if it's still around. You might try talking to some testing lab.
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We used to use StressCoat & Tenslac to determine where to locate strain gages for further testing of pressure vessels & components.
I think Measurements Group [Vishay] made Tenslac. It was in spray cans & was easier to use - but they stopped making it. Stress Coat came in quarts & you had to put it in a special sprayer - a wicked pain in the ......
I don't know if either are made any more.
The stuff was very difficult to use reliably - especially due to thermal cracking.
You'd have to maintain the temperature within 10degF,while drying over a couple of days, otherwise the whole coat would crack. not to easy to do in a shop winter/summer environment.
We also had trouble hydrotesting when the tap water temp was 10F colder than the room temp. [solved that by mixing hot/cold on feed line into hydrotest cart] Also you have to "dye check" with their penetrant - regular welding PT stuff dissolved the lacquer & made a big mess. [maybe that's why FEA is so popular - it keeps your hands clean ;-)]
The Japanese JIS Pressure Vessel Code had a recipe for limestone coating, but that only showed gross deformations.
Probably the best way nowadays is to use FEA to locate the high-stress areas, then put on rosette strain gages so you can get the max. stress & direction.
I think Measurements Group [Vishay] made Tenslac. It was in spray cans & was easier to use - but they stopped making it. Stress Coat came in quarts & you had to put it in a special sprayer - a wicked pain in the ......
I don't know if either are made any more.
The stuff was very difficult to use reliably - especially due to thermal cracking.
You'd have to maintain the temperature within 10degF,while drying over a couple of days, otherwise the whole coat would crack. not to easy to do in a shop winter/summer environment.
We also had trouble hydrotesting when the tap water temp was 10F colder than the room temp. [solved that by mixing hot/cold on feed line into hydrotest cart] Also you have to "dye check" with their penetrant - regular welding PT stuff dissolved the lacquer & made a big mess. [maybe that's why FEA is so popular - it keeps your hands clean ;-)]
The Japanese JIS Pressure Vessel Code had a recipe for limestone coating, but that only showed gross deformations.
Probably the best way nowadays is to use FEA to locate the high-stress areas, then put on rosette strain gages so you can get the max. stress & direction.
Stresscoat is still available from Stresscoat, Inc Upland, California. 909/981-6990
The stuff is not easy to work with and requires experience to apply. It seems the consistency of batch to batch is spoty. For best results, it requires tightly controlled temperatures to cure and crack. Humidity might be a problem, too. Our sister organizations have applied, cured and cracked "in the field" on small parts with good success. If you have an active/efficient/effective Environmental/Chemical Management group they won't like the stuff. You need self contained breathing apparatus or external supplied air respirator and other protective equipment if you spray it inside.
The stuff is not easy to work with and requires experience to apply. It seems the consistency of batch to batch is spoty. For best results, it requires tightly controlled temperatures to cure and crack. Humidity might be a problem, too. Our sister organizations have applied, cured and cracked "in the field" on small parts with good success. If you have an active/efficient/effective Environmental/Chemical Management group they won't like the stuff. You need self contained breathing apparatus or external supplied air respirator and other protective equipment if you spray it inside.
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