Firewall stiffener cracks rv-7

[kevinsrv7.com]

Rv-7 builders, I found cracks in both of my firewall stiffeners F601n LT and RT bottom side where the joggle is manufactured. The crack seen in the attached picture was found just before final riveting and after the alodine and priming process. In addition they follow the grain of the material as well. Both of these cracks can be seen with the naked eye. The fuselage kit was purchased Nov. 2005.
I?m curious to see rv7?s with some time on them if cracks are emanating from this area at all.

 

[Mark Burns]

Relax

Hi Kevin,

From the photo I'd have to guess it's not a crack. You'll have to check it with some "Spot check" http://www.magnaflux.com/spotcheck.stm to be sure.

It's looks more like a sharp dent or deep scratch to me. That is an extruded angle. They don't often crack in the grain like that. IMHO. I'm not sure that really is the "grain" of the metal. I think those lines are just marks from the extrusion process.

I've got some spotcheck and I can't tell you how many times I thought I'd found a crack only to be fooled.

Mark

 

[kevinsrv7.com]

Been there done that

Hi Kevin,

From the photo I'd have to guess it's not a crack. You'll have to check it with some "Spot check" http://www.magnaflux.com/spotcheck.stm to be sure.

It's looks more like a sharp dent or deep scratch to me. That is an extruded angle. They don't often crack in the grain like that. IMHO. I'm not sure that really is the "grain" of the metal. I think those lines are just marks from the extrusion process.

I've got some spotcheck and I can't tell you how many times I thought I'd found a crack only to be fooled.

Mark

Actually I did do an NDT inspection (ZYGLO) using die, developer and a black light, shows up like a sore thumb. In addition evaluated it with a very expensive eddy current machine which showed a very abnormal ~ pattern on the scope. Trust me I dotted all my I?s and T's before starting this thread. To see the pictures of the dye penetrate (zyglo) these are them here:

The extrusion process has its own definitive lines which are no factor cosmetic nothings however a crack will "most certainly" emanate from the grain.

 

[Mark Burns]

I didn't notice you are an A&P!

Kevin,
I didn't notice in your signature that you're an A&P. Sorry if my earlier post came across as condescending.

I can see from your additional photos that the CRACK is right where one part of the tool or die contacts the material. So I think it was caused by the stress of the forming (deforming ) operation.

I just checked mine which are installed and primed and I didn't see anything unusual, but I was just looking down through the access holes in the top skin of the fuselage. The cracks shown are on the "bottom", so I really wouldn't be able to see them now anyway.

Mark

 

[kevinsrv7.com]

I can see from your additional photos that the CRACK is right where one part of the tool or die contacts the material. So I think it was caused by the stress of the forming (deforming ) operation.

Exactly, so people are not confused, the cracks are bottom side of the stiffener where the joggle (aka stress) is manufactured.