Advances in operating capacity and life time of centrifugal cast pipes for high-temperature pyrolysis of NRC “Kurchatov Institute” – CRISM “Prometey”

On the basis of expert examinations of spent pipes metal operated as coil-pipes at pyrolysis furnaces, heat-resistant alloys and technologies for manufacturing standard products from them have been developed. The service characteristics of the developed alloy 45Kh32N43SB and its welded joints at temperatures of 1100 and 1150°C have been investigated. It is shown that the alloy has structural stability and the ability to resist high-temperature creep at operating temperatures up to 1150°C. A method has been developed for assessing the resource of pipe elements, taking into account the peculiarities of its operation, as well as crack-like defects in the pipe material. The reasons for the significant deformation and damage of the crossover piping, leading to the premature failure of the coils, have been found. The most significant operational factor of damage to the heat exchangers at pyrolysis plants has been identified.

Solid Solution Strengthening of Mo, Re, Ta and W in Ni during High-Temperature Creep

Solid solution strengthening of the unordered γ matrix phase by alloying elements is of great importance during creep of Ni-based superalloys, particularly at high temperatures above 1000 °C. To study the role of different potent solutes, we have conducted creep experiments on binary Ni-2X alloys (X = Mo, Re, Ta, W) at 1000 °C, 1050 °C, and 1100 °C at a constant stress of 20 MPa. Compared to mechanical tests below 800 °C, where the size of the elements mostly determines the solid solution hardening contribution, the strengthening contribution of the different alloying elements above 1000 °C directly correlates with their diffusivity. Therefore, elements such as Ta that lead to strong solid solution hardening at low temperatures become less effective at higher temperatures and are exceeded by slower diffusing elements, such as Re.

Simulation of crystal plasticity of P92 heat resistant steel considering martensitic lath structure

Based on the theory of crystal plasticity, coupled with dislocation and lath hardening models, this paper establishes a crystal plasticity finite element model describing the high temperature creep of P92 steel. Open source software was used to generate lath models with an average size of 350nm, 650nm and 950nm to explore the effect of lath coarsening on the high-temperature creep behavior of P92 steel. The results show that the roughening of the slats increases the rate of creep deformation, resulting in a decrease in the service life of the material. Observing the slat model, it can be seen that the roughening of the slats enlarges the numerical gradient of stress and strain, and aggravates the overall plastic strain of the model. The coarsening of the slats accelerates the movement of dislocations, causing the density of movable dislocations to increase, and at the same time the shear strain amplitude of the slip system increases, thereby reducing the hardening behavior of the material.

Ultra-High Temperature Creep of Ni-Based SX Superalloys at 1250 °C

Very high temperature creep properties of twelve different Ni-based single crystal superalloys have been investigated at 1250 °C and under different initial applied stresses. The creep strength at this temperature is mainly controlled by the remaining γ′ volume fraction. Other parameters such as the γ′ precipitate after microstructure evolution and the γ/γ′ lattice parameter mismatch seem to affect the creep strength to a lesser degree in these conditions. The Norton Law creep exponent lies in the range 6–9 for most of the alloys studied, suggesting that dislocation glide and climb are the rate limiting deformation mechanisms. Damage mechanisms in these extreme conditions comprise creep strain accumulation leading to pronounced necking and to recrystallization in the most severely deformed sections of the specimens.