The tank that went BOOM!

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Are there any reports of steel bursting without corrosion evident? Understand that a little salt water and a good oxygen rich mixture can eat up the inside of a steel tank. Just wondered outside of that, if there was any corrolation between materials and their stregnths.
 
Firstly, I agree with Roakeys comments about the frequency of hydro testing here in NZ. I've long argued that hydro testing must substabtially shorten a tanks life.
As far as tank testing goes I don't know that we can blame the scuba industry. Dive tanks are treated mo differently to any other pressure vessel and are subject to the same regulations. I've only dealt with 2 testing stations, one is a specialized cylinder tester and the other a dive store. Both are fussy almost to a fault. If they have the slightest doubt then the tank gets sent away for an x-ray. The incident in Tairua scared a lot people an prabably saw quite a few acts cleaned up. Today I wouldn't even waste my time trying to get a bottle filled that was even a day out of test. It just wouldn't happen.

As far as my comments about Luxfer goes, I have read of several incidents here in NZ and they ALL inovlved Luxfer tanks so as soon as I read the title of the original post I had to say to myself "I bet I know the make of that tank..."
OK, I know that's not very scientific. I admit I have absolutely no idea about what percentages of tanks in NZ are made by Luxfer, they're certainly very common.
Also, I beleive that our tanks are made in Australia so they could be slightly different to the US or UK versions.

Down here Luxfer is the Ford Pinto of dive tanks and you certainly won't find one strapped to my back.
 
The oxidation, deformation and grain structure visible in the #8 photo tells the story better than anything else if it's "read" correctly.

The thread is deformed significantly. The direction and extent of deformation of the top 8 threads would indicate an overtorque condition on the valve somewhere in the tank's history. Proof of an overtorque would be to examine the valve too. That dats is not available on the link. While it is possible the deformation happend during the failure other items indicate that it is probable it happened earlier.

It appears the cracking started adjacent to the thread near the base of the valve. Fracture initiation lines are visible on the right photo at the upper root of the 6th and 8th thread up from the bottom. Fracture surface corrosion and crystal flowline tracking indicates the propagration of the initial defect over time to a point where the wall suddenly failed in a tensile failure and the tank simply "unzipped" The tensile failure is indicated by the small grain size relatively planar fracture of the wall and outer skin of the neck.

The darker grey "butterfly wings" indicates a fairly consistant growth rate from the seed defects with resultant discoloration to the inside of the butterfly and a clean "new metal" break outside the butterfly.

This fracture looks like a VERY preventable event with proper visual inspection techniques. This tank should have been pulled from service by either a good visual with neck crack inspection or Vis+ inspection months or years before it failed.

Mr Erickson is one lucky camper to have been out of the fill room when it let go!
 

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