Benefits of Laser Measurement Supported JCOC Process for Improvement of Clad Pipe Quality

Metallurgically bonded CLAD pipes consist of a thick carbon steel bulk and a thin layer of a corrosive resistant alloy (CRA). In order to perform a girth weld of such pipes, the clad layers of both parts must geometrically fit to each other. Thus, the field weldability of CLAD pipes are to a large extent determined by dimensional tolerances of pipe ends, which have to be smaller than CRA thickness, typically 3mm. To ensure such tight tolerances, EBK has developed and installed a new calibration machine called Impander and corresponding cold sizing technology, in which the pipes are compressed (impanded) from outside. Thus, the traditional JCO manufacturing process is supplemented by a Compression step, which leads to the abbreviation JCOC. In contrast to an expander, the Impader tools operate from the pipe outside and produce tight dimensional tolerances without contacting the sensitive CRA layer. Controlled adjustment and final inspection of pipe dimensions demand an accurate measurement of pipe shape. For this, a laser tracker which allows precise measurements of complete pipe circumference with an accuracy of 0.1 mm both from inside and outside was installed and a corresponding evaluation software was developed. The paper gives a comparison of different pipe production technologies pointing out the advantages of the JCOC process using the Impander for manufacturing of CLAD pipes. An analysis of the influence of dimensional tolerances on edge misalignment of two pipe ends during girth welding is given. The precise laser measurements allow to mark exactly the largest and smallest diameter on pipe ends, that helps to reduce time for pipe adjustment during field welding. In addition, using numerical and experimental investigations, the pipe impansion was shown to significantly reduce residual stresses in the pipe. Thus, when cutting the pipe, a change of pipe shape due to springback effect is considerably reduced. Additionally, the compressive strengthening in hoop direction due to cold work by impansion in combination with a low ovality along the whole pipe length considerably increases the external collapse pressure, which makes the pipes particularly suitable for deep water applications. So far, this has been experimentally proven with a full-scale-collapse-test on a conventional pipe, but is suggested to be applicable for the CLAD pipes too.