Agitator Paddle Corrosion

edited October 15 in General

In disassembly of our agitator unit, noted some heavy corrosion of the bolts and some blue staining around the welds of the agitator paddle. On bolts, reckon this is down to some poor quality ones from factory that are easily swapped out, but more concerned on corrosion around welds. Any insights?

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Comments

  • The problem is ..... That bolt is not Stainless Steel. It's missing its markings. Remove and replace. Done deal.

  • @richard said: The problem is ..... That bolt is not Stainless Steel. It's missing its markings. Remove and replace. Done deal.

    To be clear the bolt is 304 stainless steel. The issue is that the cut threads on the bolt do not / can not be polished therefore the chromium can not be brought back to the surface.

    Pickle/passivate or replace as mentioned.

    StillDragon North America - Your StillDragon® Distributor for North America

  • edited October 16

    Sorry. Nope, the bolt is of very poor quality though may have some SS properties. I had some bolts like this without manufacturers stamp that I in the past used on a conveyor assy. Cost me a shit house of money to correct later.

    Never again purchase bolts without manufacturer's stamp on it.

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  • Shit house? A replacement is about $2.35 usd.

    StillDragon North America - Your StillDragon® Distributor for North America

  • Not familiar with pickling and passivation but a quick Google suggests not something I want to be messing around with if I can help it. Replacements bought (marked). Will test in salt water before fitting to test for corrosion. Thanks for comments.

  • edited October 16

    Test it like that on purpose? Most typical stainless hardware is 304, and it will corrode in high chloride environments (NaCl - Salt Water), 316 is a more stable grade, but far more expensive.

    Sometimes that kind of surface rust is due to residue from the tooling to cut the threads. However, rusting of stainless hardware is actually very, very common, see:

    Rust on Stainless Steel Nuts - Why are my stainless steel nuts rusting? @ Portland Bolt & Manufacturing Company

    Just replace the bolt, no big deal.

    I don't see any issue at all with the welds.

  • Yep. 304 (or 316) is not rust PROOF.

    This is why we no longer use a threaded coupling on our heat exchangers.

    Passivation wise, drop em in a citric acid solution for a few and hit it with a soft brass wire toothbrush.

    StillDragon North America - Your StillDragon® Distributor for North America

  • edited October 17

    @Smaug said: Shit house? A replacement is about $2.35 usd.

    This was exported to another African country. Yes bolts are cheap, but not airfare, hotel, taxi, time etc.. Africa is unbelievably expensive to travel in.

  • @richard said: This was exported to another African country. Yes bolts are cheap, but not airfare, hotel, taxi, time etc.. Africa is unbelievably expensive to travel in.

    Ah, sure. Sometimes I forget that all supply chains are not equal.

    StillDragon North America - Your StillDragon® Distributor for North America

  • edited October 29

    This week I am in Uganda on one of my keg plant machines. Same old story of these shitty bolts

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