Identify, Evaluate, Measure - Hidden Risk and Chronic Conditions of Components

Although engineering structures and components are designed to last for a specified period, premature failure does take place for a variety of reasons viz., design deficiencies (lack of knowledge), material selection deficiencies, processing deficiencies, assembly and installation error, operational and maintenance error, and environmental impact.

Therefore, Remaining life assessment (RLA) becomes crucial in securing the operational safety of aged equipment and structures in plants.

RLA when combined with RBI (Risk Based Inspection) can essentially prevent unanticipated breakdown and failures that can have disastrous and expensive consequences.

Remaining life assessment technique would depend on the nature of damage or defects that may have accumulated during service. Careful non-destructive evaluation is always the first step in any integrity evaluation activity. Modem non-destructive tools can not only detect fine defects / cracks but also provide an estimate of material properties.

With our extensive experience in remaining life assessment of mechanical components, EILAB can assist you with RLA or related structural integrity issues.

TECHNIQUES FOR REMAINING LIFE ASSESSMENT

The defect size determines the approach which would be most applicable, e.g. for steel, if it is less than 1 mm (i.e. microscopic), damage mechanism approach will be suitable; whereas if it is greater than 1 mm, fracture mechanics based method would be more appropriate.

DAMAGE MECHANISM

Service exposure often leaves permanent marks on components being investigated. These may be in the form of micro-structural / dimensional changes, accumulated strain, nucleated defects or cracks etc. Many of these can be detected by nondestructive means. However, there are certain other characteristics (e.g. mechanical properties, extent of embrittlement etc) which can be estimated only by conducting tests in the laboratory on service exposed materials.

The most common damage mechanisms include:

• Creep: Occurs when components are subject prolonged loading under high temperature.
• Fatigue: Occurs when components are subject to prolonged cyclic loading or vibrations.
• Corrosion: An electrolytic reaction between material and environment. Several forms of corrosion exist which can lead to thinning, crack, erosion.
• Erosion: Occurs when particles impact on the surface resulting in loss of material.