Nemrod 05134 tank question

[FredT]

USD used a light blue epoxy liner in it's tanks for a couple years in the late 60s before Al tanks came out. A light blue liner tank will generally have a vinyl overcoat over a galvanized finish (overcoat HAS to come off!) exterior with a current design 3/4" straight thread valve.

Whenever anyone talks of a tank lining it's an interior coating on a steel tank. I don't know of any polymer based coating applied to an AL tank as the AL forms a protective corrosion resistive aluminum oxide coating inside on it's own during the forming process. I still have 3 old steel tanks with intact liners relegated to air only service. One is an older USD with a white liner, one is an unknown brand (original black HARD thick powder coat was stripped right after I got it) with a light brown liner, and Bertha is a SP 95 with a dark brown liner. All three of these liners will come out with a bit of aggressive abrasive tumbling, but as long as they are intact it's wiser to leave them be.

Exterior polymer coatings of any type on a tank are good only until the first untrained tank monkey slaps it into a pipe vise. After that it's a good bet it has been perforated and separated from the metal underneath allowing water to stand there. Bare galvanized lasts for decades, everything else is "temporary" at best.

FT

 

[fire_diver]

I've never dealt with older steel tanks, so learned something here. Thanks for the info.

FD

 

[pescador775]

Removal of liners is not documented to my knowledge. However, it has been "best practice" rule of many dive shops to "fail" such tanks especially after visual inspections came into use. Even prior to that, some ugly situations involving blisters had been observed during hydro testing. Efforts to tumble out the damage made certain things apparent. The very thin coatings employed by USD and others in the early 1960's could be tumbled and scratch tested with satisfactory results. The thicker coatings used later by USD, Dacor and others were difficult to remove even with 24 hours of tumbling. Some of these coatings would crack during hydro testing and even then were difficult to remove and/or inspect. Due to the danger that pits could be hiding under these damaged coatings many dive shops would refuse to affix an inspection label. IMO, any such tank which has a thick coating and visible blisters should be discarded. However, if the coating can be removed with, say, one of the new ceramic media and subsequently passes inspection, what the hey, hold it for hydro.

 

[fringefan]

The tank turned out to be okay and thankfully was not a European tank. I can honestly say I have been given a crash course in reading tank numbers and what to look out for and stay away from when buying a used tank. I am sure someone has writen about it before but if any of you guys write for a magazine this would be a great topic to write about and would benefit any diver. Biggest lesson I learned is to get the info off the tank before buying it, at least luck was on my side and I can only imagine how many people buy tanks that are no good. Oh and that older steel tanks are not always the same size so the first tank I purchased is 2250 versus 3000. For the small amount I have into the tank this was a good lesson learned and I am thankful to have a scuba source of info as good as this one.

 

[FredT]

Please be aware that almost all 3AA tanks pre 1980 were "72s" rated at 2015 or 2250 psi, generally with a + rating. They actually hold about 66-67 cubic feet at rated pressure. They do however have the best buoyancy characteristics of all tanks, including the newer steels. They just don't hold as much air. Either as singles or Doubled up they are quite comfortable and easy to dive unless you HAVE to have more gas for the dive planned.

I can get in plenty of deco trouble with just a 72 on air at any depth over about 50', but with the proper mixes I like a larger volume to play with. For a fun shallow dive, or single deep bounce hunting or inspection dive a 72 is fine.

FT

 

[SparticleBrane]

My girlfriend and I recently came into possession of some gorgeous steel 72s (from 1973 and 1974) with brand new (May of 2006) hydro's...unfortunately neither the latest, nor any of the other hydros other than the original hydro had the +.
How do you guys feel about bringing a steel 72 up to the + rating of 2475, even if the latest hydro doesn't have the + on it?

 

[Nemrod]

The plus rating is no big deal, it is done at the option of the hydro tester. I have two tanks now that were originally 2250 with the plus. Often upon hydro the plus gets dropped. I got them done recently and I asked the facility to run them for the plus and they did. They now have the plus on them again.

Frankly it does not matter--plus or not--we used to fill them to 3,000 or nearly so for cave fills. If your "new" steel 72 tanks are clean and in good shape then you should have no fear of filling to 2475 which is the plus working pressure. My LDS here, both of them, routinely fill my clean 72s to 2500 psi, plus or not.

I am jealous of your tanks, cherish them and let nobody talk you into junking them. N

 

[fringefan]

So the Nemrod tank I have I can have the hydro done on it to add the plus to get the extra 200lbs air? I am not sure if I am reading this right bu that would be great since I plan on using this tank for spearfishing.

 

[SparticleBrane]

How does the finish on this compare to the average steel 72 that's still out there today? Sorry about the quality of the photo. Not well lit where I shot it and then the flash kicked in.
edit: Yes, I don't have valves for them yet so the opening is duct-taped closed for now.
edit 2: The reason I'm asking is because the only other 72s that I've seen all have a very smooth surface, as if the galvanizing had been worn off.

 

[oxyhacker]

I wouldn't worry to much about the plus. If you can find a shop that can do it next hydro, great, but most shops I find just put the same 2300-2500 psi in all 72s, regardless of the plus.

It may not be easy to find a shop that can do the plus on 72s since unlike the newer 3AA steels, the 72s do not have their REE number stamped on them, and without that number doing the plus is a very complicated and difficult affair. So your time will probably be better spent finding a shop that will give your 72 a good fill, than searching for the elusive "+".

So the Nemrod tank I have I can have the hydro done on it to add the plus to get the extra 200lbs air? I am not sure if I am reading this right bu that would be great since I plan on using this tank for spearfishing.