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PTFE failure of Cross Joint

  • 1.  PTFE failure of Cross Joint

    Posted 06-15-2020 03:38 AM
      |   view attached

    Does anyone have experience such PTFE failure with in one year service period.
       It contains 60- 70%H2SO4 and has about  temperature cycles from 15 to 30c. with moisture and some traces of cl2 from chlorine dryer column.


  • 2.  RE: PTFE failure of Cross Joint

    Posted 06-16-2020 09:36 AM
    ​Aamir, is the PTFE reinforced by fiber glass or pure PTFE? I didn't see the vent hole on the cross, is there any vent hole? it looks like there was air trapped between PTFE and steel surface caused the PTFE damage.

    Youyu Lu

  • 3.  RE: PTFE failure of Cross Joint

    Posted 06-16-2020 09:52 AM
    ​Wow!  I have seen brittle fracture of polypropylene lined pipe in low temperature and oxidative degradation leading to severe embrittlement in polyethylene.  I have never seen PTFE do that.  Are you sure it is PTFE?  PP would not have a weep hole in the fitting.


    Ben McCurry
    Materials & Inspection Engineer
    BASF Corporation
    Geismar LA

  • 4.  RE: PTFE failure of Cross Joint

    Posted 06-16-2020 10:11 AM
    Are you sure this is PTFE? From what looks like sever chemical degradation, presumably caused by the chlorine, I would expect that this is not PTFE.

    Best regards

    Karin Jacobson

    Karin Jacobson
    PDS Consulting - Expertise in Long Term Properties of Polymers

  • 5.  RE: PTFE failure of Cross Joint

    Posted 06-16-2020 10:57 AM

    Hello, Mr. Saddiq,


    I have worked quite a bit on PTFE lined equipment though mainly for HCL service.  Is the PTFE liner as "yellowed" as it appears to be in the photo?  Also, do you know the age of the fitting?  Typically, I expect the liner to be whiter than the image shows.  The color gives me the impression of either permeation or the liner perhaps being made of a fluorocarbon different than PTFE (PFA?) Typically, for these failures, the following examinations give a great deal of information:


    1. Profile radiography.  I can't tell from the images, but if the fitting diameter is less than NPS 8, the radiographs (computed radiography and digital detector array radiography) are easy to obtain and very informative.  They could show that a great deal of steel corrosion products have accumulated behind the liner.  I have seen the tearing along the flange face develop after extensive annular rust develops that pushes the fluorocarbon inward.  The inward protrusion further cracks the fluorocarbon, which results in yet more steel corrosion.
    2. Fourier-transform infrared spectroscopy (FTIR) will let you know if the liner is PTFE or a different fluorocarbon.  Alternatively (or as well), you can do density tests for verification.
    3. Cross-sections similar to those prepared for metallographic examinations are also very useful since they let you see gradients of permeation.


    I would also discuss the large temperature fluctuations with the supplier.  Most liners do not like thermal shocks.


    Ana Benz, P.Eng.

    Chief Engineer, Director


    Direct Line: 780-577-4481

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  • 6.  RE: PTFE failure of Cross Joint

    Posted 06-16-2020 12:15 PM

    The sharp edge of the liner inside diameter indicates that the liner is injection molded and PTFE does not flow.
    This liner looks to be polypropylene, a melt flow rate analysis can provide data to help determine if the material is polypro.

    Ahmed Altaher
    Ingleside TX

  • 7.  RE: PTFE failure of Cross Joint

    Posted 06-17-2020 03:37 AM
    You can also just quickly check if the material floats. If it does it is most probably a polyolefin; PP or PE.

    Karin Jacobson
    PDS Consulting

  • 8.  RE: PTFE failure of Cross Joint

    Posted 06-17-2020 08:44 AM
    Hi Aamir,
    It will certainly not be PTFE. One-piece crosses can not be made with PTFE, but are normally offerered with transfer moulded PFA. The PTFE lined crosses are two-piece items.
    But apart from that, also PFA should not show this behavior in your conditions. We use PTFE and PFA lined parts in exactly the same conditions to support this.

    My first impression was also that this might be made of PP lined steel, an option offered by most PTFE lined pipe suppliers. PP would show a more brittle behavior and also more interaction with the chlorine in the sulfuric acid.

    Bernhard Rijpkema

    Manager Materials Technology

  • 9.  RE: PTFE failure of Cross Joint

    Posted 06-17-2020 10:48 AM
    If it is PTFE (this can be confirmed by analytical tests) then one possibility is an extremely poor sintering.  I did come across a case of poorly sintered lined pipe spool which looked like this. Also the lining thickness looks to be too high. I can't be sure from the picture.

    Pradip Khaladkar
    Fellow and Associate Director
    302 245 8426

  • 10.  RE: PTFE failure of Cross Joint

    Posted 06-18-2020 08:48 AM
    appears that previous posts have addressed the situation well - check to verify material as it does not appear to be PTFE - I have seen brittle fractures similar to this in PVDF lined pipe and fittings - PP lined components I suspect would be similar - PFA or PTFE fractures such as this I have not seen.

    easy check is what Karin has recommended, put in water if it floats chances it is PP are good - if it sinks I would suspect it to be PVDF.

    do you have data on the original manufacturer of the fitting (unfortunately many are supplied by a distributor and not well traceable to the original mfg...).

    the pictures sent are not all that clear for determination of liner material - traditionally the liner color indicates the material; black = PVDF, orange = PP, white or translucent = PTFE/PFA - I have seen instances where the natural color of PVDF was supplied ​

    Dale Keeler
    Non Metals TSTL
    lake jackson TX

  • 11.  RE: PTFE failure of Cross Joint

    Posted 06-19-2020 02:01 AM
    If it is PTFE lined cross, it would have been iso-statically molded. If the pressure of molding was less, it can generate porosity. Also for thicker PTFE lining, sintering is critical and there are chances that it can remain un-sintered. In case of porosity, the acid vapours permeates through the wall of PTFE and if there is inadequate venting on the metal body, the entrapped vapours pushes the PTFE to inner side causing it to bulge and crack. This is just a possibility.