Steel Tank Condemned: Cracks in Threads?

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What are your justifiable recommendations taking costs into considerations here

It's complex.

Within industry, inspectors come up through the ranks as it were. You don't just leave school and become an inspector. They will had a broad experience with the components and materials already. It's really important that when inspect you have an appreciation of the type of materials, the manufacturing process and what type of defects apply to each.

Generally in dive shops you don't have that depth of experience, thus sometimes people can't tell the difference between a steel and Ali tank, they may not appreciate fully factors like tooling marks vs natural cracks, or different types of corrosion.

For visual inspection you need to have the right candidates and give them in depth training - 2 days IMO doesn't do this

With regard to NDT, the current equipment and training (for use on one type of Ali cylinder) is substandard (and that's me being polite

I've said that you could use both Eddy Currents (EDD) or Ultrasonics (ULT)to inspect, which is true but over simplified.

EDD is more complex especially with regard to steel tanks, since different alloys and heat treatments during manufacture will cause differences in conductivity to varying degrees. This of course can impact teh test, needing something as simple as a slight setting change, all the way to needing a different procedure. You are reliant on the inspector being correctly able to identify the type of tank and the manufacture in order to apply the correct procedure

ULT's is simpler from a materials standpoint - effectively is it steel or Ali, but the inspection procedure would be technically challenging because of reasons I highlighted earlier

Costs:

For NDT inspections, you need a written procedure applicable to that component. It takes upwards of 200hrs (longer for ULTS) to develop write and validate that procedure - in the case of Steel maybe multiple procedures, which is then circulated to all approved facilities. The procedure dictates what component(s) its valid for, the equipment type, settings to be applied, and inspection method and likely defects and artifacts and actions upon finding them.

I've been out of the business for a while so take the following with a pinch of salt. A suitable Ult tester (not thickness gauge from Ebay) will be approx $5000, For Eddy current including high speed guns for rotary inspection $10,000

Training - in order to both test and make a decision (we call it sentencing) you need to be a Level II inspector

The American Society of NDT (ASNT) requires a minimum of 80hr training for Level II in each discipline $5000 + Travel, hotel , and subsistence costs

Lets just round that up to a $20,000- $30,000 ball park figure for each shop wanting to carry out NDT, Oh and the inspector needs to re certify every 2 years.

This is why visual inspection, despite its pitfalls is the "go to" method. It's cheap.

My question though, is why do divers get so het up over tanks failing inspection? Looking at DGX a new HP 120 with valve is only $400. A home washing machine, TV, Laptop or mobile phone all cost considerably more and yet are considered disposable items to be replaced frequently. A 20-40yr old tank needing replacement and there's a massive outcry. I don't get it.

For dive centres adding a total of $3 per week would cover the purchase cost of an Ali tank - effectively new tanks and valves each year (Obv I understand why they don't)

Anyway just my POV I'm sure many will disagree
 
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My question though, is why do divers get so het up over tanks failing inspection?

I'm not disputing the fact that there is lack of training, money or various other issues.

Tanks that fail inspection due to deserving it -- GREAT. I have major issues paying someone to fail a tank that should not be failed be it lack of ability, mistake, or what have you. If they don't have the skills to do it accurately, when the tank is failed they should at minimum (1) give reasons why (2) provide an option and cost on how to get a second expert opinion. If the tank passes from option #2, then they should least refund you for the shops VIP.

I don't care if a tank cost me $5 or $5000. If I pay you for a job, I expect that job to be done as competently as you possibly can, transparently communicated to me, and then given options forward when possibly outside your competency.

But sadly most things in this world is not logical and reasonable.
 
I'm not disputing the fact that there is lack of training, money or various other issues.

Tanks that fail inspection due to deserving it -- GREAT. I have major issues paying someone to fail a tank that should not be failed be it lack of ability, mistake, or what have you. If they don't have the skills to do it accurately, when the tank is failed they should at minimum (1) give reasons why (2) provide an option and cost on how to get a second expert opinion. If the tank passes from option #2, then they should least refund you for the shops VIP.

I don't care if a tank cost me $5 or $5000. If I pay you for a job, I expect that job to be done as competently as you possibly can, transparently communicated to me, and then given options forward when possibly outside your competency.

But sadly most things in this world is not logical and reasonable.

And at the end of the day...that’s EXACTLY what occurred here. It just took a lot longer to get the PSI inspection guru to look at the tank due to the whole pandemic thing.

From my point of view...this isn’t even really an inconvenience yet, as I haven’t had the time to go diving in months. I’m just hoping to get it back next month, which shouldn’t be an issue.
 
Read the thread. My question (coming from an aviation technician). A post previously stated magnaflux. I am ok with that or an Eddie current inspection. The problem I see is that the crack may be migrating under the threads that are not cracked.

Here’s my question. Can there be a weld repair then the threads be re-tapped? Of course after which you would need non destructive testing done.

All that said you would have to weigh the repair cost against a new tank. My thought process is this. Even if the tank is repairable, you would always have that thought in the back of your mind that the tank has had an issue, I know I would. Your peace of mind is worth more than a repaired tank in my opinion.

If it were me, I think I would donate the tank cut your loss and either rent or buy a replacement. New is good just saying. Wish you well.

Glenn
 
@Glenn Williams Yes, it is possible, but the two issues are that the majority of hydro testers are fire extinguisher companies which do not offer cylinder repair services so they skip the portion during RIN registration/certification for cylinder repair and that the repair cost is uneconomical in many cases for relatively cheap cylinders like scuba tanks.

edit: reading the CFR, weld repair possibly may not be authorized as 3 series are seamless. welding repair seems to be for the 4 series welded/brazed tanks and mentions repairs only on seams. rethreading is allowed, but pointless if you can't repair the cracked neck before doing so.
 
Here’s my question. Can there be a weld repair then the threads be re-tapped? Of course after which you would need non destructive testing done.

Not for 3AA or 3AL cylinders.
 
Read the thread. My question (coming from an aviation technician). A post previously stated magnaflux. I am ok with that or an Eddie current inspection. The problem I see is that the crack may be migrating under the threads that are not cracked.

Here’s my question. Can there be a weld repair then the threads be re-tapped? Of course after which you would need non destructive testing done.

Thread route cracks are not uncommon for sure. but it appears the failure mechanism is always perpendicular to the threads. There of course always need to be an initiation point whether corrosion, mechanical (tooling start stop) or material problem) so i won't say it's impossible, given I've found defects that the stress and structures guy said was impossible to occur (according to the models)

I voted down magnaflux (Mag particle or MPI) as an inspection method, since its only applicable to Fe materials (so Ali would need another different procedure and different equipment. with MPI you drench a carrier fluid over the part, and so you have contamination issues. Generally this fluid is kerosene based but water based is available, but the part would need intense cleaning afterwards. Not a simple water wash.

As for repair given a new steel tank and valve only costs $400 and Ali $200 there will never be a cost effective repair method that is cheaper, I doubt any tank manufacturer would even endorse a repair
 

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