One of the concerns of a fitness for purpose analysis is the quantification of the relevant material properties. It is known from experiments that the mechanical properties of a material can change due to a monotonic plastic deformation or a cyclic plastic deformation. For a fitness for purpose analysis to be accurate in these cases, it has to take into account the current mechanical properties of the material. The problem is that the current properties may not always be known and retrieving material from the component or structure for testing is often not practical or possible. It is therefore desirable that the mechanical properties of the material after deformation can be estimated from the mechanical properties of the undeformed material. For welded structures or components, a further complicating factor for the fitness for purpose analysis is the residual stress distribution that is caused by the welding. In order to be able to account for these residual stresses, they have to be known. As these stresses are difficult to measure on-site, a numerical tool may provide a suitable means to predict these residual stresses. A practical example of where cyclic plastic deformations are applied to welded structures is the reeling and unreeling of pipelines as used in the oil and gas industry. In order to be able to tackle the subject of reeling welded pipelines, the cyclic plastic deformation and the simulation of welding were investigated separately. The investigation into cyclic plastic deformation was performed on Grade X-80 pipeline steel. However, the welding simulations used AISI 316LN stainless steel in order to reduce the complexity. This is because AISI 316LN is an austenitic stainless steel and therefore no solid-state phase transformations occur during welding. Unfortunately, there was no time to incorporate phase transformations into the welding model and therefore the cyclic plastic part and the welding simulation part of this research could not be combined at this time.

Applied Sciences