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Old 09-21-2011
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Corrosion dye test

I did a corrosion dye test on some backstay hardware. First, you clean the hardware with "cleaner/remover" (seems like acetone). Second, you spray the dye on (see picture), and leave it on for "one to thirty minutes" (what happens if I leave it on for 31 minutes?). Third, you clean off the dye with the cleaner/remover, then apply "developer" which brings back the dye in any corroded areas. The test indicated corrosion in two places where it was apparent without the test. However, it also illuminated about an eighth of the surface of the the hardware in the picture. This was not a crack or line, but an entire section which appeared as perfectly sound stainless without the test. I wish I took a picture, but I didn't. Picture the top left section of the hardware (next to the hole) red, and the rest of the piece, shiny stainless steel. Anyone have any idea what this might indicate?
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Last edited by L124C; 09-21-2011 at 04:07 PM.
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Old 09-21-2011
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I can only guess, but it's sort of an educated one. I think what you're seeing is metal fatigue. I have never used the dye. I just clean the metal with a scotch bright pad and use a magnifying glass to inspect things. But I have often seen toggles, tangs, chainplates and eyes of all sorts fatigued in the same area. Under a big enough load, holes will even get oblong. Add some corrosion and you have a crack.

Seriously, I urge you to just replace all those t-bolts. If your turnbuckle bodies are bronze and in good shape, you can just replace the t-bolts.
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Old 09-21-2011
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Dye Penetrant inspections are *not* for corrosion. Such testing it to visualize micro-cracks as evidence of the beginnings of FATIGUE or 'brittle failure' of metals.
If stainless materials are 'fatigued' and with the accompanying micro-cracks, then for sure, crevice corrosion will simultaneously begin inside the micro-cracks if the cracks are subject to 'constant wetting'.

example: WeldingDepot -- Magnaflux® Spotcheck Dye Penetrant Inspection 16oz can

To perform the dye penetrant test correctly you have to thoroughly wipe the red dye from the surface of the part being examined, the dye that penetrates into cracks and pin holes and therefore is not 'wiped away' will later be a reservoir for the 'developer' and will show a 'red line' (crack) or 'spot' (pin hole) in the developer.

Here's an example of the procedure for using 'dye penetrant':
How to Use Magnaflux Dye Penetrant | eHow.com

Last edited by RichH; 09-21-2011 at 06:31 PM.
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Old 09-21-2011
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Quote:
Originally Posted by L124C View Post
I did a corrosion dye test on some backstay hardware. First, you clean the hardware with "cleaner/remover" (seems like acetone). Second, you spray the dye on (see picture), and leave it on for "one to thirty minutes" (what happens if I leave it on for 31 minutes?). Third, you clean off the dye with the cleaner/remover, then apply "developer" which brings back the dye in any corroded areas. The test indicated corrosion in two places where it was apparent without the test. However, it also illuminated about an eighth of the surface of the the hardware in the picture. This was not a crack or line, but an entire section which appeared as perfectly sound stainless without the test. I wish I took a picture, but I didn't. Picture the top left section of the hardware (next to the hole) red, and the rest of the piece, shiny stainless steel. Anyone have any idea what this might indicate?
My guess is porosity, perhaps factory original. Those dyes are penetrants and to colour an area, rather than a line there would have to be some kind of porosity to the metal - this is not a form of cumulative failure mode AFAIK.

Those T-bolt turnbuckles are nasty things IMHO - replace them with proper jaw to eye ends.
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Old 09-21-2011
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Quote:
Originally Posted by L124C View Post
Picture the top left section of the hardware (next to the hole) red, and the rest of the piece, shiny stainless steel. Anyone have any idea what this might indicate?
I find the description of the red portion a bit unclear, but if you mean the bend area of the toggle, next to the hole, it is almost certainly fatigue. My last boat would reliably fracture that piece every 5-8 years. it would start as a great number of micro-cracks, resembling surface roughness, and then it would start to open up.

Good that you caught it.

Yes, penatrant testing can show up porosity, but it is very rare. It is sometimes seen in carbon steel fuel tanks that have seen salt, sulfur, and bacteria. It is possible for a tank to ooze oil without any identifiable pinhole.
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Old 09-22-2011
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Originally Posted by knothead View Post
Seriously, I urge you to just replace all those t-bolts. If your turnbuckle bodies are bronze and in good shape, you can just replace the t-bolts.
As I indicated in the other thread Backstay hardware, threaded or not? , I fully intend to replace the parts. This thread was posted strictly out of curiosity. Just trying to learn.
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Originally Posted by RichH View Post
To perform the dye penetrant test correctly you have to thoroughly wipe the red dye from the surface of the part being examined, the dye that penetrates into cracks and pin holes and therefore is not 'wiped away' will later be a reservoir for the 'developer' and will show a 'red line' (crack) or 'spot' (pin hole) in the developer.
I did clean off the dye using the cleaner/remover, before applying the developer. I left that out because I thought it was obvious. Guess I was wrong.
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Quote:
Originally Posted by pdqaltair View Post
I find the description of the red portion a bit unclear, but if you mean the bend area of the toggle, next to the hole, it is almost certainly fatigue. My last boat would reliably fracture that piece every 5-8 years. it would start as a great number of micro-cracks, resembling surface roughness, and then it would start to open up.
Yes, penatrant testing can show up porosity, but it is very rare. It is sometimes seen in carbon steel fuel tanks that have seen salt, sulfur, and bacteria. It is possible for a tank to ooze oil without any identifiable pinhole.
I could kick my self for not taking a picture of the dye resurfacing! I used "paint" to mark the surface yellow where the dye resurfaced in this picture. There is no roughness to the surface, and it appears normal to my eye. Think I'll get a magnifying glass and have a look.
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