Optimizing the service life of drill-collar joints on the basis of fracture mechanics criteria

A method of calculation of the lifetime of fish-mouth collar joints has been proposed that is based on selecting a model and using the criteria of fracture mechanics. By this method it is possible to optimize the design parameters of collar joints as a function of the cyclic crack resistance of steels. It is shown that the lifetime of a collar joint with a fatigue crack can be predicted, and the size of the crack can be estimated for a certain operating time of the collar joint. The critical values of the length of a fatigue crack were calculated for various types and dimensions of collar joints, which is important in fixing the periodicity of crack detection operations.     

Development of heat-and impact-resistant coatings for main pipelines

We have developed composite layered temperature-resistant silicon-organic sandwich-type coatings with thin polyurethane silicon-organic interlayers. We used the following materials as binding components: KO 921 silicon-organic lacquer with addition of éD-20 epoxy resin for prime coat, the same lacquer with addition of PZ 1040 S polyurethane elastomer for thin soft interlayers, and only KO 921 lacquer for thick hard layers. The mineral filler represented a mixture of coal ash and omiacarb in proportion 70 / 30 mass %. We have manufactured and tested laboratory specimens with two hard layers and two interlayers as well as with three hard layers and two thin interlayers. We have established that the developed composite layered coatings exceed, in their basic characteristics, the requirements of the State Standard Committee of Ukraine and foreign normative documents for the rust protection of steel main pipelines. Our coatings possess high impact strength, heightened elasticity and adhesion strength and, as to their electrical insulating characteristics, exceed these requirements by an order of magnitude. We note the complexity of the technology of applying layered composite coatings and the necessity of its improvement. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 59–65, July–August, 2006.     

Electrode for measuring ohmic and impedance characteristics of protective coatings of pipelines

We propose a mobile electrode of original design for measuring the ohmic and impedance characteristics of protective coatings on pipes of diameter 57 to 1420 mm under laboratory and field conditions. The electrode was calibrated on plane specimens with respect to measurements of the transient ohmic resistance by the method of “hollow cylinders.” We present the results of measurements of the transient ohmic resistance of identical coatings on plane specimens and pipes of different diameters as well as the values of relative errors. A good agreement between the results of investigations is shown. Owing to the original design of the working chamber and magnetospring hold-down device, the electrode can be used for the survey of inclined, wall, and ceiling surfaces of steel structures. As a result, we conclude that it is expedient to introduce this electrode into the State Standard. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 98–102, September–October, 2006.     

Methodical aspects of determining the elasticity of electrical insulating coatings

We have studied the elasticity of 12 different types of polymeric protective coatings. In the course of pure-bending deformation of rectangular plates—specimens, we controlled their dielectric continuity using an electric-spark flaw detector, measured the direct-current resistance, and looked for the appearance of indications of the fracture of the coating surface under a microscope with a ×30 magnification. We have established that highly elastic coatings lose their dielectric continuity under relative strains an order of magnitude lower than those corresponding to the appearance of cracks on the surface. We have concluded that evaluation of the elasticity of coatings by the criterion of loss of their dielectric continuity is the most correct and reliable approach. We also describe the procedure of tests of specimens. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 65–69, November–December, 2005.