Rust (streaks?) in steel tanks

[wetb4igetinthewater]

So this is a follow on to Rust in steel tank.

Sorry for the bad image. Best I could do, but I think you can see the rust like streaks. I'm going to follow the advice in the above mentioned thread of phosphoric acid. I have 3 tanks to clean up. This is the worst one. I'll report back later with the results.

BTW, I did clean out best I could with one of these:

 

[happy-diver]

Nice I'm interested, the image is fine for those that look in tanks

 

[Tracy]

If that is your worst tank, you are 100% wasting your time. That is perfectly acceptable.

 

[tomfcrist]

That’s pretty minor. I’d let it ride.

 

[wetb4igetinthewater]

So this is after using the internal brush. Prior to that, it was rejected by the shop doing the VIP (I need to renew my own).

Now it is sparkly clean and the cylinders are upside down in the cylinder drying rack I made (nothing pretty as I made it out of scrap wood, but it works) with a hair dryer blown in air via some PVC pipe to avoid rust forming.

I'll put this as a good learning exercise!

 

[Johnoly]

..Sorry for the bad image. Best I could do,

Below is a picture of one of my tanks after diving in the Fl Key's for a week in July a few years ago. It had been filled at several shops, but very similar to yours. It's from moisture blown down during fills because the auto-drains probably weren't working in the humid weather. It's not a big issue but I also tumbled and cleaned it at the end of that year. I pull the valves on my tanks 4 times a year for a peek inside and take pictures to save. It so easy and it builds a history if problems persist. Like all your dive gear, it's good to know how frequent hard use, changes how often maintenance should be done on it. (ie>buy good gear!)

 

[wetb4igetinthewater]

So this is a pic after drying it. Is this a bit of rust? If so, the hair dryer attached to PVC pipe didn't work as well as i would have liked. Or did I need to rinse more?

It was nice and shiny after using the solution.

 

[L13]

Was it upside down (valve opening down) while drying? If not, maybe try that next time.

 

[wetb4igetinthewater]

Was it upside down (valve opening down) while drying? If not, maybe try that next time.

It was upside down with PVC pipe blowing air to the bottom of the cylinder (so pointing up) via a hair dryer duct taped to the PVC pipe. This ran for a number of hours before I had to leave and the cylinders remained upside down in the drying rack I built.

 

[Eric Sedletzky]

If you’re using metal prep 79 then you’ll get flash rust as it dries. The only way to prevent this is to blow them out with CO2 or dry nitrogen to not have any O2 contact wet steel, then they will dry grey with no staining but you also have to have the tanks warm or very warm to aid drying. Metal prep is perfect for painting but not for something that’s to remain bare steel.
The staining you showed earlier was perfectly acceptable to use as is. The slightly pitted image could have been cleaned up with a bottom brush and blown clean.