Long-term strength of steel and welded joints of pipelines under the influence of hydrogen and stress state

Kazbek D. Basiev NCIMM (STU) Vladikavkaz, Russia  
Alan D. Alborov NCIMM (STU) Vladikavkaz, Russia a_alborov13@mail.ru
Tamerlan M. Dzutsev NCIMM (STU) Vladikavkaz, Russia  
Marat V. Etdzaev NCIMM (STU) Vladikavkaz, Russia  
A big amount of oil and gas pipelines is working in complex loading conditions under the influence of active media, causing irreversible physical and chemical changes due to steel corrosion processes that lead to loss of strength and structural failure. Considered processes are dislocation and associated with an increase in the dislocation density. These processes arem\ accompanied by microplastic deformation (creep) and stress relaxation, which are accompanied by the accumulation of damage, change in plasticity and the subsequent destruction of the structure.
Materials and methods
The amount of plastic material particles loosen deformable material is estimated relative increase in residual volume, which is determined by the convolution of the tensor in elastic deformation ?ii.
In article were obtained creep curves under uniaxial tension cylindrical samples for different duration of exposure tube in hydrogen sulfide environment.
On the basis of long-term strength of thedeveloped model that takes into account the effect of hydrogen, were obtained next conclusions:
• The equation of relative residual elongation for a uniaxial stress state and complex 20 steel and welded joints over time;
• Deformation model 20 steel under uniaxial and complex stress states.
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hydrogen frailty microplastic deformation micro-cracks metal loosening intragranular character