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Explain the Importance of Scc and the Influence of Key Controlling Variables

Autor:   •  April 30, 2016  •  Essay  •  1,745 Words (7 Pages)  •  782 Views

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KEY LEARNING OBJECTIVES

Give a short concise explanation for any three of terms in consult task sheet.

  1. Explain the importance of SCC and the influence of key controlling variables.

Stress corrosion cracking (SCC) is the progressive cracking, which is made up by the interaction between tensile stress and corrosive environment. In fact, this is a dangerous form of corrosion because of its insidiously damaged inside the material. This impairment is not an obviously visible inspection and it can bring about the mechanical fast displacement and destructive failure of components and structures.

There are several accidents that are resulted from stress corrosion cracking such as the explosion of boilers, the wrecking of power stations and oil refineries, or the separation of high-pressure gas transmission pipes. Therefore, it is important to understand and minimize the risk of SCC by avoiding mechanical tensile stress concentration or selecting appropriate materials.[pic 1]

It is proven that the occurrence of SCC depends on the simultaneous presence of three conditions including: a susceptible material, a critical environment and some component of tensile stress.

Although SCC is not an unavoidable progress and we can detect the particular situation in which the combinations of metal and environment are subject to the problem, however, as the demand of using materials more efficiently by increasing working stresses and cheaper materials, there is a wide range of such combinations. The table below shows some combinations of metal and environment that SCC is most commonly associated with.

Material

Environment

Concentration

Temperature

Carbon steel

Hydroxides

Nitrates

Carbonate/Bicarbonate

Liquid ammonia

CO/ CO2/ H2O

Aerated water

High

Moderate

Low

-

-

-

High

Moderate

Moderate

Low

Low

Very high

Stainless steel

Thiosulphate or polythionate

Low

Low

Copper alloys (excluding Cu-Ni)

N2O4 high ammoniacal solutions and other nitrogenous

-

Low

Low

Aluminum alloys

Titanium alloys

Chlorides

Chlorides

Low

High

Low

Low

...

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