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This paper investigates the accuracy of analytical, empirical, and numerical expressions, i. e. the most favourable methods for calculating the cooling time from 800 to 500?C (t8/5). The degree of accuracy of time t8/5 is very significant, because it determines the cooling rate, and consequently the structural changes in heat affected zone for hard faced layers. Based on the presented results, one can conclude that the finite element method provides the best conformity with the experiment and among analytical and empirical formulas the same goes for the expression of Japanese authors, for the case of hard facing of plane and prismatic parts.

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Various factors of thermo-chemical erosion process in gun steel were analysed. The factors are mainly related to the thermal load of gun barrel inside surface, characteristics of barrel surface and chemical interactions between propellant combustion products and barrel surface. The experimental simulation of conditions in gun barrel was carried out by vented vessel firings in the device based on modification of 37 mm M39 gun. The nozzle mass loss during firing was the measure of gun steel erosion. The main thermal factor of erosion is maximum nozzle inner surface temperature. This temperature was determined experimentally by micro thermocouples measurements at specified distance away from the inner surface and by numerical analysis of the inverse heat conduction problem. Modelling of two-phase flow of propellant combustion products and unburned propellant grains in the vented vessel and heat transfer to the nozzle were conducted using developed 1-D interior ballistic code and CFD simulation in FLUENT. Influence of different propellants, TiO 2 /wax wear reducing liner and tungsten-disulfide nanoparticles layer on nozzle erosion was analysed. Good agreement between experimental and computational results was achieved.

Seam casing pipe used in an oil drilling rig, manufactured by high frequency (HF) contact welding of API J55 steel, is tested. The influence of an initial defect (machined surface crack) is analysed, by performing pressure test of a pipe segment closed at both ends. Besides the damages at the internal surface, casing pipes are exposed to damage at the external surface, which is why such configuration is analysed here. Measurement of strains and crack mouth opening displacement (CMOD) enabled the application of direct method for J integral evaluation. This procedure is based on the path independence of the J integral and can be applied both in laboratory conditions (on specimens) and on structures. However, it requires a demanding experimental - computational procedure, which is accomplished here using the developed routine. Additionally, the behaviour of the pipe under internal pressure, including fracture mechanics parameters determination, is modelled numerically (by finite element method) in software package Abaqus. The pressure is applied as distributed load acting on the inner surface of the three-dimensional model, and axial tension is applied at the end of the pipe to simulate the closed end. J integral values determined numerically and using direct method are used for estimation of the critical pressure corresponding to the crack growth initiation. Additionally, plastic limit load, i.e. pressure which causes yielding of the ligament, is determined. Based on the results, criteria for pipe integrity assessment are discussed