Defects can manifest in a variety of differently shaped structures, such as tanks, piping systems, pressure vessels and pipelines, which all have different fabrication and manufacturing characteristics. Often, defects are common, relatively uncomplex and can therefore be assessed using well-established and simple-to-use methodologies. However, some defects are complex to assess; examples include cracks in the door of a micro scrubber, multiple planar girth weld defects in a complex piping system and subsea pipeline buckles subject to Vortex Induced Vibrations (VIV). All of these require careful and considered analysis before the correct assessment pathway can be established.
Sometimes, defects are deemed unacceptable by assessment methods that are overly conservative because of their simplicity. However, if these defects are expensive to access for repair, or if repair requires the stoppage of operations, it can be far more cost-effective to conduct a more detailed analysis to show they are acceptable.
Whatever the situation, ROSEN has the team of experts that will be able to assess even the most challenging of defects. We have a track record of staff contributing to defect assessment guidance documents such as API 579, BS 7910 and PDAM (pipeline defect assessment manual) and conducting research for organizations such as the European Pipeline Research Group (EPRG) and the Pipeline Research Council International (PRCI) on improving existing assessment methods. Our combined expertise allows us to overcome even the most challenging situations.
Most assets are designed to an allowable stress limit, beyond which the operating conditions are considered unsafe due to the risk of material deformation and ultimately failure. Pipe stress analysis takes into account many different factors – weight, pressure, temperature gradient and flexibility, to name a few – leading to lots of interacting loads to consider and understand. Meanwhile, the stress analysis of a tank may only consider two loads: the weight of product and wind. A deep understanding of stress analysis fundamentals is needed to ensure that the correct assessment methodology is applied when confronted with different scenarios. The impact of defects that can cause stress to increase in structures may also need to be considered; often, a Stress Concentration Factor (SCF) is used in these situations, which can be generated by FEA modelling or by using well-established codes. ROSEN has experience in conducting stress analysis for all types of structures and defects.
Industrial assets are made from materials susceptible to many forms of cracking introduced during the manufacturing stage or due to cyclical loading or environmental mechanisms. Fracture mechanics is used to assess crack defects and can be used to model different failure modes, including plastic collapse and fracture. We have conducted assessments on cracks in complex geometries and interacting with other defects, supported where necessary with finite element analyses. ROSEN also has the expertise to develop or review fracture control plans for pipelines transporting different gas compositions and supporting full-scale fracture arrest testing. Tools used by our internationally recognized experts include in-house software, Signal FFS, TWI Crackwise and MAT8.
Assets are exposed to cyclic loading throughout their operational life, which causes fatigue damage to components and defects. Understanding the amount of fatigue damage accrued over time is critical in identifying when remedial action should be taken. Different techniques can be used to calculate the impact of fatigue. For cracks, a fracture mechanics growth assessment is often completed, but for other components and defects, a S-N approach can be taken, where a stress concentration factor is determined, and a stress range and frequency calculated and compared to applicable remaining life (S-N) curves. ROSEN can use these assessment methods to assess all types of components, either deterministically or using probabilistic methods. For geometric deformations in pipelines (i.e. dents), we can use high-resolution ILI geometry data and our FE-DAT software to generate real feature-specific SCFs and calculate remaining life. This is just one application of our advanced fatigue assessment services.
Finite Element Analysis (FEA)
Finite Element Analysis (FEA) is a powerful tool for understanding and predicting the behavior of complex structures. It is used to model a variety of different geometries, and multiple load scenarios can easily be applied. Strength assessments of assets can be conducted and compared to original design criteria and remaining life estimated with fatigue assessments to support life extension activities. The versatility of FEA in the hands of one of ROSEN’s experienced operators allows for even the most complex defects to be assessed and their criticality to be determined. Our world class team utilizes a wide range of advanced software including ABAQUS, ANSYS, BFLEX, Orcaflex, PLE4Win, CAESAR II, SESAM, USFOS, SACS etc.
Strain is a measure of the relative deformation of a material from its original state, so when assessing deformations like dents and buckles, it is critical to understand it, as cracking can occur in materials when strains are too high. Curvature is regularly used to estimate strain, for example by using XYZ data from an ILI Inertia Measurement Unit (IMU) for bending strain or high-resolution geometry data for local surface strain for pipeline dents. Correct application of strain-based assessments requires a thorough understanding of loading conditions and material properties. Another challenge is establishing strain limits when defects are present, for example by calculating tensile strain limits for a pipeline when girth welds have known circumferential flaws. These challenges are difficult, but ROSEN has experience in overcoming them and making sure assets remain safe.
The greatest benefits are achieved when the results of advanced engineering assessments are used to inform key integrity decisions. For example, the simplest repair can sometimes be underwritten by multiple interlinking assessments. Knowing which methodologies are most appropriate is where we start. This way, unnecessary repair work can be avoided, and the remaining life of assets can be extended. Access to ROSEN’s team of experts will give you a conclusive answer as to whether there is a pathway to conclusively assess the integrity of an asset.