IRRADIATION ASSISTED STRESS CORROSION CRACKING

Irradiation Assisted Stress Corrosion Cracking

Irradiation Assisted Stress Corrosion Cracking

Introduction

A growing concern for electrc utilities around the world has been the degradation of the basic components of nuclear reactors, which are approximately 17% of global electricity production. Service failures have been the core components of boiling water reactor (BWR) and to a lesser extent, in the pressurized water reactor (PWR) core components consisting of Fe and nickel alloy steel that have achieved significant neutron fluence in environments that include hydrogen peroxide to water of 270 ° C to 340 ° C. The effect of a nuclear reactor has a very aggressive environment composed of water, high temperatures and pressures imposed an intense radiation field that can affect water chemistry and microstructure of basic materials. Cracking vulnerability is part of the radiation stress and the environment, and the unsuccessful system has been called irradiation-assisted stress corrosion cracking (IASCC).

Stress corrosion cracking (CR) is the destruction of the metal due to the emergence and development of cracks under the simultaneous effect of tensile stress and corrosive environment. It is characterized by an almost complete absence of plastic deformation of the metal. CD this is a dangerous form of metal fracture. In the chemical apparatus CD is most frequently observed in structures that are the residual stresses after thermal or mechanical processing, installation and assembly equipment for welding, in operating conditions at elevated temperatures and pressures. The emergence of the Kyrgyz Republic and its intensity have a major impact nature of the aggressive environment, its concentration and composition. CD in a stressed state are subject to almost all metals and alloys. The share of the CD in the chemical, oil and gas industries, thermal power accounts for 20 to 40% of all corrosion damage.

Body: Discussion and Analysis

The stress corrosion cracking (SCC) is a progressive failure mechanism of metals that is created by the combination of a corrosive environment and a sustained tensile stress. Structural failure due to the CBT is often unpredictable and appears both after a few hours after months or years of satisfactory service. It is often in the absence of any other type of corrosive attack. Virtually all alloys are susceptible to SCC in a specific environment and a set of conditions. The tensile stress required for CBT is "static" and may be residual and / or applied (see table below). Progressive cracking due to stress "cyclical" is called "fatigue-corrosion." The boundary between the CBT and fatigue-corrosion is evident every time. However, as the mechanisms underlying each phenomenon are different, separate and are treated as different failure mechanisms. The shot peening controlled by introducing a compressive residual stress of the material surface, acts on the two phenomena and can be prevented or delayed.

We present here below micrographs of specimens of type 304 stainless steel, with and without shot peening sensitized at 650 ° C for one hour, subject to intergranular corrosion in NH03-HF solution and shot peening of ceramic ...