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Interfaces in bonded structures influence the mechanical behavior of components significantly, and often limit their load capacity. This requires nondestructive testing techniques allowing one to investigate the interaction forces in adhesive joints and to evaluate the quality of bonds. To this end the nonlinear stress-strain relationships of adhesives and adhesive interfaces, which cause a nonlinear modulation of ultrasonic waves in reflection as well as in transmission, may be exploited. Bonded interfaces which are much thinner than the ultrasonic wavelength can be approximately described only by the binding forces, without explicitly taking into account the material properties of the adhesive layers. These may be measured by the amplitudes and phases of ultrasonic waves transmitted through the interface. Measurements are presented on aluminum plates joined together by thin epoxy adhesive layers. A threshold behavior of the harmonics generated in the adhesive layer has been observed. Their amplitudes depend on the excitation following the power series expansion of a quasi-static interaction force curve, and their phases vary little for low-amplitude excitation. Exceeding the threshold causes a change in the response of the interface. The input and output ultrasonic amplitudes in the interface are calibrated interferometrically to obtain the absolute interaction force. The ultrasonic transmission data are related to destructive tensile tests of the adhesive bonds. IntroductionThe interfaces in bonded structures influence the mechanical behavior of components significantly. Therefore, an important task in nondestructive testing (NDT) is the investigation of the interaction forces in adhesive joints and the development of techniques to evaluate the bond quality. The load capacity of such joints is often limited by regions of weak bonding. As in all materials, the 403 Adhesion -Current Research and Application. Wulff Possart

The general trend in oil and gas industry gives a clear direction towards the need for high strength grades up to X100. The exploration in extreme regions and under severe conditions, e.g. in ultra deep water regions also considering High Temperature/High Pressure Fields or arctic areas, becomes more and more important with respect to the still growing demand of the world for natural resources. Further, the application of high strength materials enables the possibility of structure weight reduction which benefits to materials and cost reduction and increase of efficiency in the pipe line installation process. To address these topics, the development of such high strength steel grades with optimum combination of high tensile properties, excellent toughness properties and sour service resistivity for seamless quenched and tempered pipes are in the focus of the materials development and improvement of Vallourec. This paper will present the efforts put into the materials development for line pipe applications up to grade X100 for seamless pipes manufactured by Pilger Mill. The steel concept developed by Vallourec over the last years [1,2] was modified and adapted according to the technical requirements of the Pilger rolling process. Pipes with OD≥20″ and wall thickness up to 30 mm were rolled and subsequent quenched and tempered. The supportive application of thermodynamic and kinetic simulation techniques as additional tool for the material development was used. Results of mechanical characterization by tensile and toughness testing, as well as microstructure examination by light-optical microscopy will be shown. Advanced investigation techniques as scanning electron microcopy and electron backscatter diffraction are applied to characterize the pipe material up to the crystallographic level. The presented results will demonstrate not only the effect of a well-balanced alloying concept appointing micro-alloying, but also the high sophisticated and precise thermal treatment of these pipe products. The presented alloying concept enables the production grade X90 to X100 with wall thickness up to 30 mm and is further extending the product portfolio of Vallourec for riser systems for deepwater and ultra-deep water application [1, 3, 4].