Vonmet’s Asset Integrity management services

Remaining Life and Condition assessment

Through remaining Life and Condition assessment of high energy components – using replication and other inspection techniques, Vonmet is able to accurately predict the condition and life of high temperature and high-pressure components. This gives the end user an inspection and replacement philosophy to prevent catastrohpic and unpredicted failures.

High energy components are subject to a creep failure mechanism as it operated at temperatures above approximately 400-450°C. The consumption of creep life is assessed using replication and other non-destructive inspection techniques. Creep strain is used to estimate the creep life prediction and inspection intervals.  Creep void formation has a direct correlation to creep strain accumulation and therefore quantitative creep evaluation is used to predict a component’s life. Understanding that material is unique, with unique degradation and mechanical properties, Vonmet can assist customers with developing a scope of work (including inspection locations and techniques to be used) in order to manage the components operating in the creep range.

Creep failure in weld –leak before break.

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Creep rupture of main steam piping

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Carbon steel piping showing graphitisation which leads to creep crack initiation

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Severe graphitisation in carbon steel piping after exposure to above design temperatures for extended periods

We have experience with the following materials

Carbon steels

These include material specifications like SA106 and SA105, which can lead to graphitisation and creep failure. Leading components include welds, forgings and bends

High alloy steels

These include material specifications like X20CrMoV121, P91, 321H and 347H, which can lead to creep and stress relaxation failures. Leading components include welds and bends.  Heat treatment of these materials has a significant impact on how they behave in the creep range.

Low alloy steels

These include material specifications like 10CrMo910 (P22), 13CrMo44 (P11) and 14MoV63, which can lead to creep failures. Leading components include welds, and bends

Component Failure Examination

Assets can experience unexpected failures that can lead to high costs due to repair and replacement, but also due to unplanned downtime. Thirty percent of failures of components have a repetitive nature, and failures can typically lead to unsafe situations for people, plants and the environment. The cause of the failure might be clear enough to take adequate preventive measures.

However, in many cases, a failure examination and its subsequent analysis are needed to determine the primary cause of the failure. Based on the analyses, corrective action can be implemented which may prevent similar failures in the future.

Vonmet utilises two labs, located in Johannesburg and Middelburg, to assist customers with failure examinations. A failure examination typically includes: detailed on-site examination, design consideration and operating conditions, visual examination, macro and microscopic investigation, hardness testing and chemical analysis. The importance of a detailed visual examination, both on-site as well as in the laboratory, as well as the collection of all design and operating conditions cannot be over-emphasised. These, along with an assessment of the contributory causes are necessary for the final analysis as well as the conclusions drawn from the laboratory work. Failed components examined within Vonmet’s experience includes steam lines, boiler tubes, heat exchangers, impellers, lifting equipment, other rotating equipment like turbine components, gears and more.

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Fatique crack initiation and growth through the thickness of a gas cylinder wall

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SEM photo of a ductile fracture

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Intergranular fracture feature known as rock candy fracture associated with Aluminium Nitride embrittlement

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Fracture features showing ductile hairlines, yawning grain boundaries and pores which are indicative of hydrogen embrittlement

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Hydrogen cracking due to incorrect weld procedure

In-situ hardness testing

In-situ hardness testing – with experienced technicians and with procedures that align with internationally recognized standards.
All technicians are trained and authorised by an experienced and professional Metallurgical engineer. Technicians are taught to understand the importance of the two different in-situ hardness techniques (UCI and rebound) and the influence that surface preparation, material thickness, material grade, temperature etc. has on the outcome of the hardness results.

Metallographic Surface Replication and Evaluation

Metallographic Surface Replication and Evaluation – with experienced technicians and procedures that align with internationally recognised standards we can deliver the highest quality work in a short time span.

To reveal creep voids requires careful in-situ preparation which follows the basic laboratory preparation procedures.  Mechanical preparation is the preferred preparation method.  When comparing microstructures the same etching solution and preparation procedure should be applied.  During preparation of weldments, the replica film should be of an appropriate size to include the weld material, heat affected zone (HAZ) and the parent material (PM) on both sides.  During replication, the temperature of the material is important and typically should be between 20 to 30 ºC.  Below is an illustration showing the basic principles of replication.

All replicas are evaluated using an optical light microscope at 50, 200- and 500-times magnification.  The 50 times magnification is used to scan the replica for any macro defects in the PM, HAZ, and weld. The 200 times magnification is used to look for any evidence of graphitisation and creep. The 500 times magnification is used to detect and quantify creep damage and graphitisation.  Results are reported for each weldment zone. Creep damage is reported quantitively in voids/mm2 and also noted if orientation and linking can be observed.   In order to relate the creep damage to a known internationally accepted standard, the creep damage is classified according to the VGB-S-517 damage classes.

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