buffing out the scratches

[Ted R.]

I am considering purchasing a used brite tank that has some green scrubby scratches on the interior. What should be used to polish the scratches out and give it that shinny new look and clean-ability?

Thanks.

[Woolsocks]

All I can think of is to get a welding-type-person to buff it as if they had just freshly welded it. Someone else may have a better idea.

[NESTAFL]

I have used a polishing wheel on the end of drill to polish out some rust specs. It worked well but there was an obvious patch that had been polished. I followed with a passivation.

Jordan

[gabewilson50]

A hand grinder fitted with a polishing wheel (120 grit) works quite nicely, or you can get some acid and some of the red scotch brite pads (specifically designed for cleaning stainless steel) and hand do it, or a combo of both. That's what my stainless welder did for anything that needed cleaning or polishing. Acid should be a nice strong inorganic acid (HCl aka muriatic acid or HF in gel form).

[gitchegumee]

Unless your tank interior is mirror finish--and I haven't seen many of these--chances are that your scratches are NOT from a green 3M "Scotch-Brite" pad. Tank manufacturers use these pads as a first choice when buffing and are WAY less abrasive than 120 grit. I've said it before, and I'll say it again: Scotch-Brite is safe for tank interiors. I would suggest using 180-220 grit to get the scratches out, then buffing with "Scotch-Brite". Follow that with passivation using 50% nitric acid at around 30C for 45 minutes. Open the tank and let it air dry. Good luck!

[Moonlight]

Try to only use the scrubbies in the same direction instead of circles or random actions. Ideally use a repeatable pattern- like around the tank, not up and down. This alone will solve your problem. If you have ever sanded wood, it is just like sanding with the grain.

[gabewilson50]

Follow that with passivation using 50% nitric acid at around 30C for 45 minutes. Open the tank and let it air dry. Good luck!
I also had always heard (from other brewers) that we want the tank to air dry after acid treatment to passivate. I have a crapload of SS surfaces that I'm going to want to passivate before I start them into service, so I started looking up how to passivate, and all of the metalworking sites I visited were adamant about rinsing the acid off immediately following treatment with cold water and not letting any of the acid dry before the rinse. I haven't sprung for the ASTM A 380 document that spells it out, but everything else mentions rinsing. Are we incorrectly passivating (or worse, not really passivating) our steel? Does anyone have any input on this? Any help would be great.

Thanks,

--Gabe

[NESTAFL]

I used to hear the theory of air dry after acid passivation and even did it a couple of times. About year and half ago, I was setting up a new place so I talked a lot with the chemical supplier. He kinda chuckled at the air dry thing and said with confidence "rinse". So i did. All I can say is everything has been good and I feel he would know best.

[Kevin O'Connell]

The guys that recomended scotchbrite are on the right track. Scotchbrite makes various grit abrasive pads and backing plates that will mount on die grinders or drills. Die grinders are optimum due to the higher RPMs they turn. Be sure not to over rev them in accordance with RPM limits listed on them.
For mirror polishing, use a buffing wheel and Jeweller's rouge. It also comes in various grits to make it cut faster. As stated in other post, acidizing after using the rouge will ensure the residues are out of the tank.
You can call me at 620-875-1083 to discuss further. Kevin.