[PSUBS-MAILIST] Pressure Test

Tue Jul 11 01:46:40 EDT 2017

Thanks, Hugh.

This is interesting.  I will look into it.  The local hydro static firm tests the tanks for a single fee regardless of whether or not it fails.  The only party benefiting from the failure is my local dive shop who sold me the replacement.  Unfortunately, the tester x-ed out all the marks on the cylinder marking it such that no one will fill it (unless I get my own compressor and fill it myself).  My wife's tank (5 years old) also showed a minor crack, but it was within specs so it passed the hydro.  If during the next hydro that crack has not increased then it will pass again, otherwise it too will be failed.

James, six of your tanks failed!  These things are supposed to last 30 years or more.  I had to decommission three tanks back in 2011 only because they were made during the 1980's and their alloy was no longer acceptable.  Apparently, in California those tanks could have been hydro'ed and accepted.  

Tim

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Hugh Fulton via Personal_Submersibles
Sent: Monday, July 10, 2017 7:27 PM
To: 'Personal Submersibles General Discussion' <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Pressure Test

Tim,

There were some cylinders that developed cracks years ago but there were triple the number that were rejected for false instrument reading on crack detection.  The detector will say that a good neck is cracked if the thread has a line through the threads which is caused by the thread tap where it stops.  You will see 4 lines through the treads caused by the  4 flutes of the thread tap.  I challenged them when they rejected my tank and showed that by burnishing with a rotary wire brush in the threads that eliminated the tap finish marks.  They tried the instrument again and hey presto it passed with flying colours.  These guys are not engineers testing threads and it is in their interest to fail a cylinder. 

Hank,  

It does not matter if it is hydrogen or not but hydrogen is one of the most dangerous gases in that it can cause hydrogen embrittlement in higher tensile steels etc.   Same rules will apply for the same pressure generally speaking as they need to meet DOT or ASME.   

CNG cylinders are too thin for going deep but there is an Argentinian crowd, Kioshi, who make big diameter steel cylinders.  Trouble is to go deep they will not be buoyant.  Rule of thumb Under 12 inches diameter any pipe will tend to sink.  Best flotation devices are likely to be spherical.

Chs,  Hugh

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of T Novak via Personal_Submersibles
Sent: Tuesday, 11 July 2017 12:26 PM
To: 'Personal Submersibles General Discussion'
Subject: Re: [PSUBS-MAILIST] Pressure Test

Hank,

What is the price for those 21x120 composite CNG tanks?  

Unrelated: for the first time in my diving history I have a scuba tank that just failed its hydro.  Apparently a minor crack has appeared at the valve neck.  This 12 year old, hardly used, aluminum 80 that came with my sub is now scrap metal, maybe worth $6.  Darn.

Tim

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] <mailto:[mailto:personal_submersibles-bounces at psubs.org]>  On Behalf Of hank pronk via Personal_Submersibles
Sent: Monday, July 10, 2017 2:26 PM
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> >
Subject: Re: [PSUBS-MAILIST] Pressure Test

Kieth,

What are you up to that you need a cng tank?

Hank

On Monday, July 10, 2017 9:13 AM, k6fee via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hank,

Thanks for the info, I'll check out Evil Bay and see what I can find. 

Keith T 

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Date: 7/10/17 2:48 AM (GMT-08:00) 

To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Subject: Re: [PSUBS-MAILIST] Pressure Test 

Kieth,

There are CNG tanks on Ebay, with some sellers that have lots of tanks that are still in service.  The largest composite CNG tank I have come across is 21 inches OD by 120 inches long.  There is a seller close to Salt Lake City Utah with a pretty big inventory.

Hank

On Sunday, July 9, 2017 9:24 PM, k6fee via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Where are you guy sourcing the CNG tanks? Are larger diameter tanks available?

Keith T 

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Date: 7/9/17 7:49 PM (GMT-08:00) 

To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Subject: Re: [PSUBS-MAILIST] Pressure Test 

Steve,

Greg was referring to steel cng storage tanks that are 48 inch ID spheres 3.25 inches thick. 

I have also been looking at composite cng type 4 tanks as buoyancy modules.  The tanks would be at full pressure (3,600 psi) 

Hank

On Sunday, July 9, 2017 8:44 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hi Hank,

I was under the impression your CNG spheres are composite/fibre-wrapped?  I presume you're aware that using a model based on metal components wouldn't apply well to composite.

I think I posted about it, but I've done a lot of research and some testing on using composite cylinders underwater and it's potentially a bit scary, especially with salt water.  If anyone is interested I can go into more detail.

Cheers,

Steve

On Mon, Jul 10, 2017 at 11:53 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

I use the calculator on Psubs written by Alec, it is fabulous because you change the values for different materials.  

Hank

On Sunday, July 9, 2017 7:17 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> > wrote:

I still think that a CNG sphere will go way deeper. How did you calculate that?

  _____  

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> >
To: Personal Submersibles General Discussion <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> > 
Sent: Sunday, July 9, 2017 4:38 PM
Subject: Re: [PSUBS-MAILIST] Pressure Test

Very true.

I do love the idea, but, weight is a real killer, every pound is super critical.  If I go with a 7500 footer then the buoyancy is cheap because I will use CNG tanks, don't tell Sean ;-)   Then it will be awesome to have it rotate, just think you can rotate so the port is pointing down between your feet.

Hank

On Sunday, July 9, 2017 2:26 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> > wrote:

Yes....BUT...being able to get out on your own is never a bad thing.

  _____  

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> >
To: Personal Submersibles General Discussion <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> > 
Sent: Sunday, July 9, 2017 4:12 PM
Subject: Re: [PSUBS-MAILIST] Pressure Test

Greg,

That was my original plan, I think it is a great idea for a shallow diver.  But if your going real deep then chances are it will be lowered into the water from a boat or barge, so need for the swivel.  If I end up being less ambitious, and build an Elementary 7,500 I will do just that.

Hank

On Sunday, July 9, 2017 1:57 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs. org <mailto:personal_submersibles at psubs.org> > wrote:

Hank,

I was thinking that it might be possible to mount a sphere within a steel frame that allows it to swivel up and down like a gun turret in a bomber. That way, the forward viewport could be incorporated into the hatch and the hatch/ port could be in the "up" position to get in and out and then in the "down" position during the dive for viewing. All internal components could be mounted on an internal frame that hangs from a bearing so that the pilot is always upright. The main ballast system could be a pair of port/ starboard pontoons.

For a shallow diving sub, the hatch/ port could be a large dome for good viewing. A self draining "sail" could also be added around the hatch/ port. If Darth Vader had a sub it would look like that one!

Greg

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