Welding Tips and Tricks

Was wondering if anyone had any tips for using dye penetrant to inspect cracks in steel.

More particularly I'm curious about paint removal prior to checking and anything that would help flush the crack beforehand of oil/diesel fuel.

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Remove paint. A good / standard die pen kit comes with cleaner, penetrant, and developer. Use the cleaner to final clean the surface after you degrease. Then spray the die into a cup and just brush it on where you want to check. Check the specs on the can you usually need to let it set for about 20 minutes for the stuff I use. Then you spray the cleaner on a rag and wipe down the excess die.

(If you spray the surface of the metal with the cleaner at this point instead of the rag you risk washing it out of the cracks that it has penetrated)

Then spray it with the developer.

Back when I was an aviation inspector, we used MEK and air to degrease prior to DP. Sometimes a heat gun would be used to help pull oil out of cracks.
Carefully follow the instructions with the kit. The DP kit we used the most, was very specific about spraying the dye on, and not brushing it. I do agree with being careful to not wet the surface with cleaner when removing the dye. Spray the cleaner on the rag and wipe carefully. Proper waiting time may be tied to temperature, again check the instructions for your kit. Last suggestion, the developer is like a dry power that serves as a wick to draw out the dye left in the crack. On more critical stuff we did 2 tests. The first one got a fairly light coat of developer. The second time got a heavier coat of developer.

Makes sense to me. My kit has three cans. I believe cantesco is the brand.


I'm just trying to figure out if I glazed over the surface of the crack during wire brushing the 3 or 4 layers of paint off this tank or if the crack just was not thoroughly flushed of diesel before I did my check.

I know there was 5 cracks since I could see the fuel coming out of them, yet when I due checked to see how far/where they went I got very poor results.




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Power wire brushing is a bad idea. Chemical paint removal is preferred method prior to inspection. You can actually plasticize the paint, and pack it in the cracks with a power brush.
At this point I would try MEK and hand scrub with Maroon Scotchbrite in a circular motion. Clean with high pressure shop air, then repeat the process a few more times. The MEK can break down the packed paint, and the air helps to blast it out of the cracks.

If the problem is glazed over metal, the Scotchbrite MAY help with that too.

VA-Sawyer wrote:Power wire brushing is a bad idea. Chemical paint removal is preferred method prior to inspection. You can actually plasticize the paint, and pack it in the cracks with a power brush.
At this point I would try MEK and hand scrub with Maroon Scotchbrite in a circular motion. Clean with high pressure shop air, then repeat the process a few more times. The MEK can break down the packed paint, and the air helps to blast it out of the cracks.

If the problem is glazed over metal, the Scotchbrite MAY help with that too.

Yup!

Pretty sure I got mek in the shop. Will try that next time. Might have to see if I can soften with mek and get under the bulk of the paint with a scraper etc cause I have a feeling like it might take a while due to many many layers of paint on these old tanks but definitely worth trying if I get better results in determining just where the crack is and how long it goes for.


Thanks for the tips. Gives me something to try for the next time this job comes into the shop

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I'm suggesting the MEK for where you used the power wire brush. For areas with intact paint, use actual paint remover. When using the shop air, get the nozzle real close to the part. Less than an inch will clean it better.

https://www.amazon.com/Citristrip-QCSG8 ... 1394&psc=1

Love this stuff!

I always forgot about chemical strippers since usually our go to in the shop is sandblasting of it fits in the cabinet. (These tanks we're about the size of the cabinet)

Will dig up the can of aircraft stripper we have for the next time and see how it does.


Thanks for the tips!

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