Examination of welded joints with UT/TOFD-PA methods

Kvaliteta zvarnih spojev je pretežno odvisna od kvalitete varjenja. Z neporušnimi preiskavami zvarnih spojev se zagotavlja, da je ta kvaliteta kontrolirana in ustreza izbranim standardom. Med novejši metodi neporušnih ultrazvočnih preiskav spadata Time Of Flight Diffraction (UT/TOFD) in Phased Array (UT/PA), ki sta že postali širše uporabljani za preiskavo zvarov v petrokemični in ostali industriji. Tudi na področju zvarnih spojev cevovodov hidroelektrarn postajata UT/TOFD in UT/PA vedno bolj zanimivi in uporabljani. Prednosti teh metod so predvsem: Velika natančnost pri ugotavljanju velikosti in lege defektov, zaznavanje defektov tudi v primeru njihovega prekrivanja ali neustrezno orientiranih defektov, večja hitrost preizkušanja ter zapisi (skeni) kontrole, ki jih lahko arhiviramo, ponovno ocenjujemo ipd. Na podlagi eksperimentov, ki so vključevali neporušne metode UT/TOFD, UT/PA, UT/PE, VT in MT ter žično elektroerozijo kot porušno metodo, lahko potrdimo, da se z novimi ultrazvočnimi metodami zagotavlja velika natančnost določanja lege, oblike in velikosti napak. Že pri samem skeniranju kalibrirnega komada smo ugotovili, da pri debelini stene 44 mm lahko vidimo tudi zajedo globinske razsežnosti 1 mm. Na razrezanih preizkusnih lističih smo z VT in MT metodo našli napake, ki smo jih odkrili po metodi UT/TOFD ter delno z UT/PE in UT/PA. Ugotovili smo, da globinska razsežnost, velikost napak in lega napak ustreza predvidenemu.The quality of welded joints mostly depends on the quality of welding. With non-destructive testing of welded joints it is assured that this quality is controlled and meets the selected standards. Among newer methods of non-destructive ultrasound methods we find Time Of Flight Diffraction (UT/TOFD) and Phased Array (UT/PA), which have already become widely applicable for the examination of welds in petrochemical and other industry. Also in the field of welded joints of hydropower pipelines, UT/TOFD in UT/PA are becoming more and more interesting and useful. The advantages of these methods are mainly great precision in determining dimension and position of defects, detecting defects also in the case of one defect covering the other or in the case of unsuitably orientated defects, faster examination and written records (scans) of examination, which can be archived, re-estimated etc. Based on experiments which included non-destructive methods UT/TOFD, UT/PA, UT/PE, VT, MT and the destructive method of electrical discharge machining we can confirm that with the new ultrasound methods a great precision of determining the position, shape and the dimension of defects can be achieved. Already after scanning the calibration piece, we established that with the wall thickness of 44 mm we can also see an undercut with the depth dimension of 1 mm. With VT and MT method we found defects on the sliced test pieces of the weld, which we detected with UT/TOFD method and partly also with UT/PE and UT/PA. We established that the depth dimension, size and position of defects suit the expected