Technical Tips

Some thoughts on welding and related microstructure

Part 1 Welding is arguably the most common, popular and successful method of joining metal components, and has virtually completely replaced older methods, such as riveting.  However, the welding process does affect the microstructure of the welded and adjacent material, which may have effects on local properties and physical performance, particularly as far as fatigue […]

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Unintended Load Paths Leading To Fatigue

This month’s Technical Tip considers an interesting failure arising effectively from a misunderstood load path. The failure in question involved a 1000 tonne 600mm diameter hydraulic cylinder after approximately 3 months in service. Owing to the large size of the cylinder, the piston had been threaded onto the rod and was screwed down against a […]

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Measurement of the true in service stresses

This Tech Tip follows closely from the previous one in which the importance of accurate evaluation of the stresses in engineering design was highlighted. The sentiments expressed in this previous Tech Tip, focussed on the importance of the reliable estimation of loads and theoretical analysis of stresses during design and comparison of these estimates, to […]

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What is the true stress in a structure

A great deal of the work with which Origen is involved, is concerned with failure analysis and fracture mechanics. Both of which require realistic and accurate assessment of loads and hence stresses to which the component or system is subjected. These loads/stresses may be obtained in various ways, and a good starting point is often […]

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Ladders – be careful how you use them

A significant number of injuries and deaths have been attributed to the improper use/failure of ladders and Origen has been involved in a number of investigations/ legal cases related to their failure. These failures occur in both the work and home environments and in some cases involve relatively new ladders. In order to mitigate, there […]

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Strengthening and Plasticity of Metals (The role played by dislocations)

From the perspective of atomic and molecular models of metals, the strength of a material is reached when there is separation of two surfaces within a crystal. This simple assumption and some analysis leads to predicted theoretical ‘strengths’ in the order of E/8 (where E is Young’s modulus). When more rigorous assumptions and the effect […]

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Non Destructive Testing Part 2 Common Techniques

Following from our previous tech tip which addressed some of the key elements associated with NDT, this Tech Tip discusses some of the more commonly used NDT techniques. For External (Surface) Flaw Detection, the NDT process typically starts with Visual Inspection, which can be enhanced by Dye Penetrant. Crack like defects can be readily manifest […]

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Non Destructive Testing Part 1: A practical perspective

In this modern age of design and manufacture, an essential complementary corollary to fabrication is the assessment of the component or structure, to ensure that it is ‘fit for purpose’. It is one thing to design the engineering system, and quite another to ensure it is made to the specifications envisaged, and, critically, that it […]

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Micro-void Coalescence

In many failure investigations, interpretation of the features on the fracture surface (or surfaces) can be extremely useful in determining the mode of failure. One of the most interesting and revealing features is that of micro-void coalescence (MVC). Micro-void coalescence is a high energy fracture mechanism in metals, which is very common and readily interpreted. […]

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Flow accelerated corrosion

Flow Accelerated Corrosion (FAC) refers to a wear mechanism which results in severe wall thinning (up to 3mm/year) and metal loss of carbon steel piping and vessels exposed to flowing water and wet steam. FAC is often occurs in power generation units, including both conventional plants as well as nuclear facilities worldwide, but also occurs […]

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