Internal rust & flash rust in steel tanks

[VTernovski]

My OMS tank has also flash rust inside, but the shop instructor passed the visual saying it's normal and wasn't severe. Usually these types of rust occurs due to filling the tank right after a dive, without "blowing some air out"... so, when you have droplets of water in the valve, and you start filling the tank, it shoots it right inside.

 

[mcrae]

Hi all, while it may be stating the obvious, PST tanks and probably most others are uncoated carbon steel on the inside.

OK it probably has some alloys such and chromium and molybendeum for additional strenght.

Bare carbon steel will flash rust with just the tinest bit of moisture and if you are diving Nitrox then it will obviuosly be worse.

Basically even though I am very careful where I get fills I find that I need to redo the O2 cleaning every year, as generally there is some rust present. This light coating should in no way affect the life of the tank. As I see it anyway.

Have fun and I am very jealous of the Gentleman who dives the Channel Islands most weekends. Did it once and loved it.

Gary

 

[drbill]

My goodness, I think mcrae just referred to me as a "gentleman." My reputation will never recover from that.

Dan the Man, thanks for adding the details on the four tanks. I will be interested to hear how your experiment goes. The HP120 was my "clean" tank... only filled by the two LDS'es here on the island. My HP100 (still going strong after more than 15 years) is the tank I take on boat trips if they don't have their own on board. I may get an aluminium tank to dive with on boat trips.

Dr. Bill

 

[FredT]

Dan The Man once bubbled...
I had 2 relatively new tanks (PST HP100, manufactured 1 year ago, bought 4 months ago) fail visual due to rust.

A tank that fails visual in the US is condemed and destroyed, period. DOT and OSHA rules apply here so there is really not much wiggle room.

A tank that needs to be cleaned does not technically "fail" a visual, it's just that the visual can't be completed until the tank is cleaned since the metal under the contamination can't be inspected. It does happen where a tank is cleaned, and THEN fails visual. Generally the cleaning charges apply either way.

A good dive shop with an experienced inspector should at least give you odds on if the cleaning is likely to result in a useable tank before they do it.

FT

 

[VTernovski]

right... I was gonna say.... last thing I want my LDS is to charhe me for cleaning, and then tell me that the tank is "shot".

 

[Dan The Man]

What I meant by "failed visual" is that they said "There is rust, you need to get it tumbled". The probability of passing after the tumble was calculated to be approximately 99.999%

On my brother's tanks they said it was "flash rust" and it was "relatively normal" but that we might want to tumble it just to be safe. For $20, what the heck, might as well get rid of that yucky stuff.

--Dan

 

[NAM001]

I just took my tanks in to have a manifold installed. The tanks are 8 months old and are now being tumbled due to rust inside.

They have never been below 500 psi. I guess the moisture came from a compressor somewhere.

Any other thoughts on what could have caused it.

Thanks

Chad

dont know if this will help but i have a pair of faber lp95's they were perfect when new. one year later at the vip they had some flash rust. i have accredited it to being open to the local area high humidity with out a valve in it. now every opening of the tank i preasure it to 500 psi and vent 2-3 times to purge the remaining moisture out. i have had no more rust issues since. either it worked or it is just a coincidense. it certainly did not cost anything to doit.

 

[NAM001]

A tank that fails visual in the US is condemed and destroyed, period. DOT and OSHA rules apply here so there is really not much wiggle room.

A tank that needs to be cleaned does not technically "fail" a visual, it's just that the visual can't be completed until the tank is cleaned since the metal under the contamination can't be inspected. It does happen where a tank is cleaned, and THEN fails visual. Generally the cleaning charges apply either way.

A good dive shop with an experienced inspector should at least give you odds on if the cleaning is likely to result in a useable tank before they do it.

FT

i have never heard of this as far as vips go . it is true for hydros but not for vips. hydros have definate limits for pass fail. ie no rehydro's allowed if failing results occure of first hydro. a visual i am not sure is regulated. a failure of a visual is not always from incorrectable reasons. a failed vis ie too much rust can be fixed by tumbling and re vised with a passing result.

if i am wrong someone please correct me. hope i did not missunderstand your post.

 

[scubafanatic]

i have never heard of this as far as vips go . it is true for hydros but not for vips. hydros have definate limits for pass fail. ie no rehydro's allowed if failing results occure of first hydro. a visual i am not sure is regulated. a failure of a visual is not always from incorrectable reasons. a failed vis ie too much rust can be fixed by tumbling and re vised with a passing result.

if i am wrong someone please correct me. hope i did not missunderstand your post.

um, this thread is over 8 years old....

 

[captain]

i have never heard of this as far as vips go . it is true for hydros but not for vips. hydros have definate limits for pass fail. ie no rehydro's allowed if failing results occure of first hydro. a visual i am not sure is regulated. a failure of a visual is not always from incorrectable reasons. a failed vis ie too much rust can be fixed by tumbling and re vised with a passing result.

if i am wrong someone please correct me. hope i did not missunderstand your post.

1- Don't confuse the yearly dive shop visual with the DOT mandated visual at the time of hydro.

2- Yes, a DOT authorized hydro tester can fail a tank on visual inspection alone.