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Thread: DPT - TUBE to TUBESHEET JOINT

  1. #1

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    DPT - TUBE to TUBESHEET JOINT

    Dear Friends,
    I have a question about what is the need for DPT test on Tube-Tubesheet Welding. what is the effect of using DPT and what type of defect it can detect and whether it result is reliable or not.

    If there is any other method for testing the Tube-Tubesheet Welding of cost effective, please inform me and also give a guidance to do.

    My higher management people feel DPT is a waste of money and time, it result will not reliable and does not show anything. Previously i had a experience on one of our equipment passed the DPT but failed in the Pressure Testing and we had to repair it, later we found we had used wrong electrode ( instead for stainless steel we used Carbon steel). My manager refer to this incident and telling it is a waste of doing. I tried to explain him it is not because of DPT but due to the wrong electrode but he is not ready to accept that and he tell, choosing electrode is depend on production and only i want the answer why it passed DPT and failed Hydrostatic test, so DPT is waste

    I feel to do DPT is better to asses defect opened to surrounding and also the finish of the welding.

    Please help me in this topic and also suggest some other method to test the welding .

    Thanks a Lot for all

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  3. #2

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    Dye Penetration Test is a quick way of finding surface weld defects. If the weld leaves even a micoscopic ----- on the surface you are sure to catch it with DPT.

    As for the use of wrong electrodes, you must have failed in inforcing welding schedule for the perticular joint. Generally agencies dont care about the welding schedule. if the target is tight they will use large electrodes with higher current just to finish the job in time. but in my experience anything done in hurry is compromises the quality and to set things right you have to expend double the effort than originally enivsaged.

    you should read about the limitations of DPT. if the weld is critical dpt is not sufficient. DPT is a quick way of finding if the wled is really bad, but it will not catch all the defects.

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  5. #3

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    DPT is used for detection of surface flaws. Even i had faced problems in tube to tubesheet welds whic passed DPT but failed in pressure test. I didint get any satisfactory reasoning for this. But if the joint is vey critical process wise orsafety wise then there is radiography technique called Microfocal Radiography. Though I have not tried it yet.

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    • #4

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      Helium Leak test can detect any defect in the weld. Hekium is the smallest atom in the world. So it can detect defect easily.

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