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  1. #21

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    The requalification process required every 5 years includes both the hydro test and a visual inspection. For a 6351-T6 alloy aluminum tank requalification also requires a visual eddy inspection.

    Most RINs will do the VIP first rather than waste time hydro testing a tank that won't pass a VIP.

    Someone commented above that if you have a tank with one or more pits that possibly exceed the allowable limits in the side wall or the base, you should send it in for hydro test and see if it passes. Well, that's just passing the liability buck on to someone else. It can be really hard to accurately determine the depth of a pit so if it's close to the limit and there's any doubt at all on which side of the limit it is on, or if there are a large number of pits, where line corrosion becomes an issue, just put your big boy pants on and refuse to pass it. If the customer wants to send it out for hydro for a second opinion that's fine, but I'm not inclined to give it a shop VIP and seal of approval even if it passes - because quite frankly some RINs are really poor at their jobs.

    As noted above some RINs don't do a good job drying tanks after the hydro test portion of the requalification. I've had some of mine come back with rust stains in the bottom or on the side walls where you can see the water sat while the water slowly evaporated. Some have had more than just flash rust by the time they got back to the dive shop.

    I'm picky and I'll tumble my tanks if they have even flash rust, particularly if I plan to use them for any type of O2 service. Rust is fuel, if you doubt that, degrease a piece of steel wool, leave it out in the rain and humidity for a week or two to rust, and then dry it out and take a match to it. It makes great kindling.

    Blue Gold is a good O2 cleaning agent works well as a rust inhibitor. It's expensive in dive shops (about $30 per pint) but it's also used to clean turbine blades in jet aircraft and you can find it in aviation supply houses for about $150 in 5 gallon buckets.

    Rinsing a steel tank in cold water than then immediately blowing it dry with cool, dry air, works really well to prevent rust as also, even without a rust inhibitor.

    Back in the day it was also common to use a weak solution (5%) of phosphoric acid as a rust inhibitor. In more concentrated form (10% to 15%) it was also used as a rust remover. In essence it creates a lightly parkerized surface on the tank which inhibits rust just like it does on a military firearm. It has fallen out of use since the advent of nitrox and the related potential for partial pressure blending.

    NACD Cave DPV Cert # 666: Cave DPV Anti-christ

  2. #22
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    Quote Originally Posted by DA Aquamaster View Post
    Someone commented above that if you have a tank with one or more pits that possibly exceed the allowable limits in the side wall or the base, you should send it in for hydro test and see if it passes. Well, that's just passing the liability buck on to someone else. It can be really hard to accurately determine the depth of a pit so if it's close to the limit and there's any doubt at all on which side of the limit it is on, or if there are a large number of pits, where line corrosion becomes an issue, just put your big boy pants on and refuse to pass it. If the customer wants to send it out for hydro for a second opinion that's fine, but I'm not inclined to give it a shop VIP and seal of approval even if it passes - because quite frankly some RINs are really poor at their jobs.



    I was the one that said it, and totally agree that it's passing the buck. It's what I was taught in the course and was in the written paperwork as well. Basically the way I was explained it is that if you're unsure if it totally qualifies as a fail, you will be passing it onto the hydroer, who should see the pits as well and will help make a qualification of pass or fail based on visual, or will be unsure as well and rely on a hydro as the answer. Unfortunately a lot of pit inspection is subjective, and can lead to two different opinions, though that rarely happens. I was also told if I ever had a questionable tank, to make sure I discuss the concerns with the person hydroing or put notes on a piece of tape on the bottle asking for a second opinion. At places like fire extinguisher hydro facilities, those guys typically suck and are no help in the vip process. Luckily, I only do tanks for myself or friends, so if there's a question it goes to Dave. I had a set of PST 104s that had splatter pitting pretty badly but I didn't think they were failable. I sent them to Dave (eventhough they were a year till hydro) and he used that fancy camera with pit measurer and was able to confirm they were close to the fail point, but not fully there.


    So yes, it's passing the buck, but I was taught to think of it more as "getting a second opinion" or sending it to a "specialist".



 

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