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Finite Element Analysis (FEA)

AFAA have considerable experience in the field of finite element analysis (FEA) using ABAQUS and ANSYS software. We are frequently involved with determining the acceptability of piping components that have exceeded piping stress code allowable stress limits by creating accurate 3-dimensional geometries using CAD and analysing them using FEA.

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Elastic Analysis (Linear)

A static stress analysis assumes the relationship between the applied load and its structural response remains in the elastic region of the stress-strain curve.

 

AFAA have extensive experience in performing assessments to the requirements of codes such as ASME VIII Division 2 and PD 5500.

Elastic-Plastic Analysis (Non-linear)

In a non-linear analysis the structure's stiffness changes as it deforms. Whilst in reality all structural problems are non-linear, considering them as linear is a convenient way of approximating the solution. However there are instances where a linear analysis yields non-favourable results or material non-linearity must be considered.

 

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Explicit (Dynamic) Analysis

Whilst a static analysis is sufficient for long term response of a structure, a dynamic (explicit) analysis is required for considering short term duration and response. 

AFAA have used explicit dynamic analysis for developing a model to predict instantaneous failure of a pipeline due to third party interference.  AFAA have experience in modelling the impact on the pipeline to simulate the damage (dent and gouge) profile and to establish the strain and stress fields from the resulting analysis to determine the acceptability of the damage.

Case Studies

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To maintain the supply of gas to a Power Station whilst the modifications were implemented, a temporary by-pass arrangement was to be constructed including 2 split-tees. Due to the non-standard geometry of the tees, a detailed FEA analysis of the fittings was undertaken. Design changes were recommended to satisfy the code assessment.

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Several CO2 storage vessels were exposed to bullets and explosion projectiles resulting in a combination of dent and metal loss type features. FEA analyses were undertaken and the features were assessed to the requirements of API 579. Recommendations were made to repair the damage and put the vessels back into service.

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AFAA were awarded a research project to determine the feasibility of replacing steel pipework supports with GRP type supports. Through FEA it was possible to demonstrate the GRP supports could be included without causing deleterious effects to stress in the pipework.

AFAA were commissioned to investigate the conditions that cause instantaneous failure of a pipeline. A failure model was developed based on the failure assessment diagram, which is an alternative means of expressing the ratio of elastic J-integral to plastic J-integral. The model incorporated the effects of pressure induced stresses, residual stresses due to denting, a stress concentration factor due to the presence of a gouge, dent and crack.

 

A high level of agreement between an extensive range of tests was obtained. The model is considered to represent a significant step forward towards understanding of the behaviour of mechanical damage in pipelines, and provides a sound basis for integrity management strategies.

Pipe stress analysis

An in-line inspection identified numerous dent anomalies along a section of newly installed offshore pipeline, caused by a single dragged anchor incident. AFAA were contracted to perform non-linear FEA analyses and assessments to determine if the pipeline section remained fit-for-purpose. Of the 15 dents 3 were recommended for repair, 12 were found to be acceptable.