Circumferential Scanning Research Articles

Collapse of Deepwater Pipelines

The paper describes a series of full-scale collapse experiments using X-42 and X-65 grade steel tubes. The initial geometric imperfections of the tubes were measured using a specially designed scanning facility prior to collapsing them under external pressure. Geometric deviations from a circular shape were recorded at 90 points around the circumference. The wall thickness was also recorded at the same points. At least 31 circumferential scans were made over lengths of 9 diameters. The stress-strain characteristics in the axial and circumferential directions were measured for each tube. The measured parameters were used to calculate numerically the collapse pressures of the tubes. The biggest deviation between the experimental and calculated values was less than 8 percent. These are compared with the results obtained from the same analysis using various idealized imperfection measures.

A high-speed ultrasonic testing machine for tubes

An ultrasonic flaw detection equipment has been developed for testing steel tubes at speeds compatible with modern rates of production. The system uses a series of identical probes arranged in a ring encircling the tube. Fast sequential pulsing of the probes, together with slow rotation of the tubes gives effective circumferential scanning speeds several times faster than is obtainable by purely mechanical methods. The probe rings are immersed in a small tank of water through which the tube is passed via specially designed water retaining valves.

An Experimental Study of Elastohydrodynamic Lubrication of Foil Bearings: Part 1—Displacement in the Central Zone

An elastic foil under tension is wrapped partly around a rotating cylinder and is supported on a thin film of air. Capacitance probes, coincident with the surface of the cylinder, scan the air gap along the arc of wrap. The cylinder can be traversed across the width of the stationary foil, so that the topography of the air gap can be determined from a series of circumferential scans. Experimental results are compared quantitatively with theoretical predictions for the perfectly flexible and for the elastic foil bearing of infinite width [8, 12]. A comparison is also made with theory, for the case when the angle of wrap is small and the entrance and exit transition zones merge [9]. The effect of foil and gap width on side leakage is illustrated. The last part of this study deals with elastic foil bearings of finite width and with the characteristic “edge effect” in particular. The influence of various parameters on the nature of the displacement field of foils is demonstrated and related to recent analyses [13].