Dacor Steel Tank

[FredT]

Tank plastic external coating HAS to be removed to be currently legal for any service. It may be either an early version of powder coated, or vinyl or epoxy. To remove start by screwing a PVC 1/2" threaded pipe plug into it and visiting a pressure wand car wash. Start at the vise marks and see if you can lift the coating. IF so just keep at it til it's off. Be sure the plug you use is plastic, as the NGT thread has a different taper than the NPT so you want to deform the plastic plug, not the tank thread.
The vinyl comes off easiest with a hair dryer and draw knife, the same with powder coat, but it's more of a fracturing process than a slicing process. Be careful not to damage the galvanizing under it any more than absolutely necessary. aircraft paint stripper also works on some outside coatings. Strong Acid strippers should be avoided as it'll eat the galvanizing.

The 1/2" NGT valve thread is a bit more of a PITA to deal with then the 3/4" straight thread, and the post valves are harder to find. OTOH if you want an O2 bottle you have the best of all worlds. Simply have the tank cleaned for O2 and install a CGA540 for CGA870 pattern valve in it. You now have a galvanized emergency bottle that won't deteriorate on the boat.

 

[lonestardiver]

Howdy Lonestar......

I know this is a long drive, but if you can not find a good 1/2" valve locally in North Dallas, Fort Worth Scuba Schools in west Ft Worth might still have one or two........Don Reese owns the shop........and he is vintage.......established his business back in 67 or 66.......anyway, he is crusty but has a wealth of knowledge.....he can tumble and hydro that tank too........he rebuilt one of my USD twin manifolds a few years ago........he knows his stuff.........

But it is a long drive from Plano......his shop is on the benbrook traffic circle........

Oldmossback

Thanks Oldmossback....

Thats not a long drive for a Texan.....

I will contact him after I get that coating off my tank....

 

[halocline]

Regular paint stripper (methylene chloride, I think) works fine to get that paint off, it should bubble right up. Try to avoid getting it on the galvanized surface, but as long as it doesn't stay there too long it will be okay. After you're done give it a good washing with a hose, and dry it off. On mine I then LIGHTLY sanded the galvanizing, I mean just a little with 400 grit silicone carbide paper, to make the surface nice and uniform and then sprayed a few coats of ZRC galvilite cold galvanizing compound. That stuff works very well. If the galvanizing under your paint is in excellent shape you might not need it, but often there are a few dings and spots where the galvanizing has taken a beating.

A while back FredT posted a lengthy discussion of finishes on steel tanks, it's worth looking that up.

 

[lonestardiver]

Regular paint stripper (methylene chloride, I think) works fine to get that paint off, it should bubble right up. Try to avoid getting it on the galvanized surface, but as long as it doesn't stay there too long it will be okay. After you're done give it a good washing with a hose, and dry it off. On mine I then LIGHTLY sanded the galvanizing, I mean just a little with 400 grit silicone carbide paper, to make the surface nice and uniform and then sprayed a few coats of ZRC galvilite cold galvanizing compound. That stuff works very well. If the galvanizing under your paint is in excellent shape you might not need it, but often there are a few dings and spots where the galvanizing has taken a beating.

A while back FredT posted a lengthy discussion of finishes on steel tanks, it's worth looking that up.

Thanks mattboy... I will track down FredT's discussion....

I will also post the picks of my soon to be naked tank.... It may pretty... It may be ugly.... but for sure... It will be naked...... :shocked2:

 

[John C. Ratliff]

I have a couple of observations on this tank. Here they are:

--First, this does not look like a 1/2 inch tapered thread; it appears to be a 3/4 inch straight thread with a place for an O-ring seal.

--There appears to be significant corrosion in the area where the O-ring should provide a seal.

--If there is significant corrosion where the O-ring seals, there is also the possibility of significant corrosion inside the tank. This tank has been standing without pressure for quite some time, which would promote corrosion. Also, because this is in Texas, there is the potential for very humid air to enter the tank, and again increase the likelihood of corrosion.

Because of the above, before I'd do anything about the coating, I would get the tank hydrostatically tested to see whether it is worth any further work.

If it passes hydro, then I'd start looking at the coating. But with a zinc coating under the vinyl coating, there would probably not be much corrosion to be worried about on the exterior. I'd be much more worried about the interior. If it passes hydro, then get a valve on it and fill it with good, dehumidified air from a reprutable scuba shop. Keep pressure in it to prevent further corrosion.

If you decide to do something with the coating, I'd stay away from methylene chloride (dichloromethane). It is a "A3--Confirmed Animal Carcinogen with Unknown Relavence to Humans;..."* The MSDS from J.T. Baker is linked below:

METHYLENE CHLORIDE

It is one of those chemicals to stay away from.

SeaRat

*American Conference of Governmental Industrial Hygienists (ACGIH) TLV Booklet, 2009.

 

[lonestardiver]

Hi John,

In regards to the neck, I attempted to put a 3/4" K-valve but it was too large... Im assuming its still 1/2 maybe?

In regards to a Hydro Test... (And forgive me for not menitioning this) This tank passed Hydro in June.

Thank you for the suggestions on the coating....

I have a couple of observations on this tank. Here they are:

--First, this does not look like a 1/2 inch tapered thread; it appears to be a 3/4 inch straight thread with a place for an O-ring seal.

--There appears to be significant corrosion in the area where the O-ring should provide a seal.

--If there is significant corrosion where the O-ring seals, there is also the possibility of significant corrosion inside the tank. This tank has been standing without pressure for quite some time, which would promote corrosion. Also, because this is in Texas, there is the potential for very humid air to enter the tank, and again increase the likelihood of corrosion.

Because of the above, before I'd do anything about the coating, I would get the tank hydrostatically tested to see whether it is worth any further work.

If it passes hydro, then I'd start looking at the coating. But with a zinc coating under the vinyl coating, there would probably not be much corrosion to be worried about on the exterior. I'd be much more worried about the interior. If it passes hydro, then get a valve on it and fill it with good, dehumidified air from a reprutable scuba shop. Keep pressure in it to prevent further corrosion.

If you decide to do something with the coating, I'd stay away from methylene chloride (dichloromethane). It is a "A3--Confirmed Animal Carcinogen with Unknown Relavence to Humans;..."* The MSDS from J.T. Baker is linked below:

METHYLENE CHLORIDE

It is one of those chemicals to stay away from.

SeaRat

*American Conference of Governmental Industrial Hygienists (ACGIH) TLV Booklet, 2009.

 

[FredT]

As a very strident point the way to tell the valve size is to go get a 1/2 and 3/4 PVC threaded plug. Cost for both should be under $3 including sales tax even in NYC. You'll need them eventually so you might as well get them. See which one "fits" into the valve port.

If it screws in and stops before the hex head hits the tank it's a NGT thread. If it stops WHEN the head hits the tank it's a straight thread. Read the size cast into the top of the plug to determine the thread size.

BEFORE USING ANY CHEMICAL ON THE OUTSIDE OF THE TANK BE SURE TO HAVE THE TANK SEALED BY SOMETHING TO KEEP THOSE CHEMICALS OUT OF YOUR TANK!!!

 

[lonestardiver]

What it it looks like under the tank boot1

 

[lonestardiver]

What it looks like under the tank boot2

 

[lonestardiver]

I bought the 1/2" PVC Plug at Home Depot for .75 cents...

Bought my .75 cent 1/2" PVC Plug... It fits the opening and will only go down about halfway.... NPT presume...

I will be taking the tank down to the car wash and put a High Pressure hose on it to see what I can get off...

As a very strident point the way to tell the valve size is to go get a 1/2 and 3/4 PVC threaded plug. Cost for both should be under $3 including sales tax even in NYC. You'll need them eventually so you might as well get them. See which one "fits" into the valve port.

If it screws in and stops before the hex head hits the tank it's a NGT thread. If it stops WHEN the head hits the tank it's a straight thread. Read the size cast into the top of the plug to determine the thread size.

BEFORE USING ANY CHEMICAL ON THE OUTSIDE OF THE TANK BE SURE TO HAVE THE TANK SEALED BY SOMETHING TO KEEP THOSE CHEMICALS OUT OF YOUR TANK!!!