Home tumbling-old steel 72

[Aigtbootbp]

As noted in another thread I have an old (1959) steel 72. It has passed hydro but failed vis. The consensus is the vis guy didn't want to deal with tumbling a 1/2 neck tank until the factory internal coating is removed so I am going to do this myself. I will be picking up the first free treadmill I find on craigslist but what should I use for media? I have heard filling it half full with stainless steel sheet metal screws but is that the best choice? What else would work? Any ideas how long I should tumble it?
The coating (IIRC) is a white epoxy type used by US Divers in 1959.
Thanks!
Gary

 

[Gilldiver]

Paul Blanchette developed the use of the screws to act as a cutting media to cut into the epoxy resin which is what standard medias will not do, they have to try to wear through it and that takes time. Once the resin is cut up, standard media can be used to clean up whatever is left.

Paul used stainless steel, but I know of no reason why standard steel screws can't be used.

If you plan to use only air in the tank, there is no need to remove the resin as the white coating will show any corrosion easily. The red resin can be much more difficult to see through.

 

[oxyhacker]

It's not really necessary to remove the lining unless you have an inspector who is obsessive on the subject. Global has recommended for years just tumbling long enough to remove any loose coating. I don't really buy the argument about the liner hiding corrosion since any corrosion bad enough to be a problem will bubble and loosen the coating enough that it will be visible under the coating to a competent inspection, and so that tumbling or whipping will reveal the spot (Global also suggest drilling a couple extra holes in the dip tube just in case it does flake).

Oh, one reason for using SS screws is that they will stay sharp longer, but you got to balance that against higher cost. If you aren't in a hurry, any fine stone like peastone works fine - I get mine from my driveway, screening it through hardware cloth wire screen. Tests done by Bill High/PSI many years ago showed that such stones are about 1/2 as fast as abrasive chips.

 

[rjack321]

I tumbled one for 8-12 hours with sheet rock screws for media and its still not coming out. Its blue and blistered in places from the blasting the hydro place did when they tried to get it out. There's some pitting in places although I don't know if it extends under/near the blisters. Honestly this tank was wearing out the idler pulley on my tumbler so I gave up, since the tank ceased being worth the tumbler repairs if I kept going for days.

Media is bad enough, I would hate to have try to get actual screws out a 1/2" neck.

 

[Scared Silly]

Before going to all the extra effort you might want to take it to another shop and have someone there who knows what they are doing give it a peak and their opinion on the coating. They might be able do a quick tumble and have you on your way for a lot less cost and hassle.

 

[TropicRat]

back in the day....... I used cutnails. tough hard steel and not costly.