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Pickling of stainless steel piping

  • 30-06-2010 5:15am
    #1
    minnow
    Registered Users, Registered Users 2 Posts: 202 ✭✭


    A question for any of you with experience in doing this.

    We recently pickled some new welded stainless steel lines internally with nitric/hydrofluoric acid. A boroscope inspection revealed that the welds themselves are completely clean of oxides, however the areas either side of the weld (approx 30 cm each side) which were heat-treated still have a strong dark discolouration, which we believe means that it has not been effectively pickled.

    Can anybody offer an opinion on this ? Will re-pickling the line help ?

    Note, there is no access to the welds for mechanical removal.


Comments

  • #2
    rowa
    Closed Accounts Posts: 2,296 ✭✭✭rowa


    could you not flush through the pipes with dilute pickling paste or fill them and leave it in there for a few hours ? it is unusual to get discolouration if the pipes were back purged with argon , were the welds made with tig , mig or stick ?


  • #3
    Philistine
    Registered Users, Registered Users 2 Posts: 159 ✭✭Philistine


    rowa wrote: »
    could you not flush through the pipes with dilute pickling paste or fill them and leave it in there for a few hours ? it is unusual to get discolouration if the pipes were back purged with argon , were the welds made with tig , mig or stick ?

    I'd be shocked if they weren't Orbital Welded? Is it in a pharmaceutical plant OP?


  • #4
    goonup
    Registered Users, Registered Users 2 Posts: 49 ✭goonup


    rowa wrote: »
    could you not flush through the pipes with dilute pickling paste or fill them and leave it in there for a few hours ? it is unusual to get discolouration if the pipes were back purged with argon , were the welds made with tig , mig or stick ?


    Wat type of stainless pipe is it. Is it biobore or normal shed 10 or 12. If the pipework had been properly purged ( all the oxygen in the pipe replaced with Nitrogen or argon ) there would be no discolouration inside the pipe. Its the oxygen in the pipe which causes this discolouration. Depending on wat the spec of the project is & if its Pharmasuitical or food, if its coming into contact with the product, it would probably have to be ripped out & replaced.

    Pickling paste cam only be used on the outside of the pipework to clean off the oxide residude from the welding process


  • #5
    hi5
    Registered Users, Registered Users 2 Posts: 3,107 ✭✭✭hi5


    Sounds like 'heat scale' a common enough problem in the jewellery trade.

    http://en.allexperts.com/q/Jewelry-Making-3236/2009/9/Removing-heat-scaling-soldering-1.htm


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