WHAT KIND OF GEOMETRIC ANOMALIES ARE THERE, AND WHAT CREATES THEM?
External influences, such as geohazards and accidental third-party actions can change the shape of a pipeline and thus threaten pipeline integrity. Changes to the geometry of a pipeline come in two basic forms: There are local features such as dents, buckles and ovalities, and there is bending (more details on bending can be found here).
Find out more about the different geometric anomalies below.
A dent is a permanent deformation of the circular cross section of the pipe (ASME B31.8). Dents cause changes in the pipeline ID, namely a reduction in diameter, which results in them being concave on the inside. This distortion leads to local stress and strain concentrations which can result in crack initiation and accelerate fatigue crack growth. Dents in pipelines can occur in-service as a result of impact by construction or agriculture equipment. However, the majority of dents are introduced during pipeline construction, typically by the pipe being laid directly on rocks within the pipe trench.
DENT WITH METAL LOSS
DENT WITH METAL LOSS
A pipeline dent that is associated with any kind of metal loss, i.e. a measurable reduction in the wall thickness, is called a dent with metal loss. The severity of this feature depends on the cause of the metal loss. A dent associated with a gouge is one of the most severe forms of pipeline defect due to the combination of stress concentrations caused by the dent and potential for cracking caused by work hardening in the base of the gouge. Dents associated with corrosion are less severe but appropriate assessment must be performed to understand the impact on the burst pressure of the pipe and on its fatigue life.
Wrinkles are localized waveform deformations in the pipeline wall, typically consisting of several alternating inward and outward undulations. The most common cause of pipeline wrinkles is from historic pipe bending techniques that permitted the formation of wrinkles on the inner bend radius. Smaller wrinkles (also often called “Ripples”) may also be introduced in more modern pipe bends, if the process is not adequately controlled. Wrinkles can also form in-service, due to excessive bending strains caused by ground movement for example.
Ripples are less pronounced than wrinkles and are typically associated with pipe bending where the bending process has not been adequately controlled. They are more common in pipelines with a high diameter to wall thickness ratio.
A buckle is a partial collapse of the pipe due to a lateral instability caused by excessive bending or compression. The possibility of abrupt changes in the local pipeline curvature at the buckle location may result in cracking and possible loss of containment. Causes of the excessive loading that can lead to pipeline buckling include soil instability, landslides, washouts, frost heave, earthquakes, or operation at temperatures exceeding design limits.
Roof topping, also referred to as peaking or angular misalignment, is the name given to a non-circular geometric anomaly that can occur in longitudinally welded pipes at the seam weld. It occurs more frequently, but not exclusively, in older pipes, particularly pre-1970s. It occurs during pipe manufacturing when plate edges are incorrectly “crimped” when attempting to form a true circle. This causes the edges to meet as a triangular apex and the seam weld protrudes beyond the circular contour of the pipe.
An ovality is out-of-roundness of the pipeline that can occur because of local concentrated loads or pipeline bends.
SCALE AND WAX DEPOSITS
Scale and Wax Deposits
Whilst not geometric anomalies, debris on the inner pipe wall can result in indications in the geometry data that, if not interpreted correctly, can be misclassified as dents. The dual technology used within ROSEN’s RoGEO XT tool allows differentiation between real geometric anomalies and debris and can also quantify the extent of debris such as wax and scale in order to support pipeline cleaning programs.
You can find information about further pipeline deformations like bending or movement here.
A Holistic Approach
The most effective way to assess changes in shape is to approach deformation management with a “big picture” mindset.
The ROSEN Group believes that best way to do this is by tackling the challenge from all angles; combining the most advanced pipeline geometry inspection solutions, the knowledge of subject-matter experts and industry best practices gives operators the information they need to make the best possible integrity management decisions. Our holistic approach is a systematic, collaborative approach effective for managing even the most challenging pipeline deformations.
ROSEN guides pipeline operators through the entire process from planning for an inspection through to repair and maintenance, ultimately resulting in a complete threat management plan. Thus, ROSEN supports operators beyond short-term decisions and provides management plans as well as training to enable them to take the right maintenance actions at the right time in order to extend the life, safety and performance of their pipelines.
PIPELINE GEOMETRY TECHNOLOGIES
The ROSEN Group operates the largest fleet of pipeline geometry tools in the industry. Paired with a variety of integrity assessments the following technologies help to manage the risk posed by the above-mentioned threats.
- RoGeo XT
Mechanical Dipper and Eddy Current (XT)
The unique XT technology is a combination of mechanical caliper measurements with eddy current proximity sensors which provides unrivalled industry-renowned data sets of the highest quality for both liquid and gas pipelines. The contour-following dual-sensor technology applied enables exceptionally precise mapping and sizing of ID anomalies by providing full circumferential and axial coverage, even under tough operational conditions. Detailed and accurate 3D representations of any geometric anomaly can be generated for visualization and modelling. In addition, the sensors differentiate between geometric features and debris, scale or wax deposits, as well as caliper arm lift-off, significantly reducing false readings.
Our premium RoGeo XT service is a high-definition pipeline inspection service suitable for integrity management programs addressing pipeline ovalities, dents, buckles, stress-induced geometric features and pipeline bending. It is the state-of-the-art pipeline inspection solution for addressing complex geometric anomalies and even combined threats such as corrosion in pipeline dents.
More about our RoGeo XT Service
- RoGeo MD
Mechanical Dipper (MD)
The MD technology is equipped with numerous calipers, ensuring outstanding detection capabilities and sizing performance. The optimized sensor design enables full circumferential and axial coverage, so that pipeline bends, buckles, dents, wrinkles and other pipeline ID changes can be reliably identified and sized. This helps to ensure the success of subsequent pipeline inspections.
Our advanced pipeline geometry service is the perfect solution for many geometry inspection purposes. The robust RoGeo MD service can be used to inspect the as-built quality of a pipeline, identify third-party damage, or confirm passage for subsequent pipeline cleaning or in-line inspection tools. The robust MD technology with mechanical dippers with high-resolution electronic angle sensors provide a cost-effective way to detect geometric anomalies in any medium and monitor the geometric quality of pipelines. The extremely lightweight tool causes only very low friction and provides reliable data even with low operating pressures.
Pipeline inspection and engineering assessments must go hand in hand. Therefore, a broad range of assessment services complements high-end inspection technologies. The combination of inspection and assessment reduces uncertainty, thereby increasing safety and minimizing cost.
ROSEN applies a levelled approach to geometric anomaly assessment starting with basic screening assessments, if appropriate, through to Level 3 stress analysis based methods which involve application of finite element analysis (FEA). The appropriate level will be selected based on a range of factors including the number of anomalies being assessed, the inspection data, loading conditions and the availability of material property data. Assessments are performed in compliance with latest industry practice, for example API 1183.
- Dent Strain Assessment
Dent Strain Assessment
Plain dents, i.e. dents that are not associated with other forms of damage or welds, rarely impact the burst pressure of a pipeline.
A critical part of the assessment of a pipeline dent therefore involves determining the likelihood that the dent has associated cracking.
It is widely acknowledged that the curvature strain associated with a pipeline dent can be used to provide a good indication of whether cracking may have occurred during initial indentation. ROSEN uses high resolution caliper data to calculate the curvature strain at all locations throughout the dent, as described within ASME B31.8, which can be directly compared against critical strain limits specified within the applicable pipeline code or regulations. Integrity engineering input is provided during the assessment to ensure appropriate levels of smoothing are applied and that other associated threats are considered (e.g. the presence of multi peak dents or weld interaction). Dents with strain levels exceeding the critical limits are then subject to either further engineering assessment or repair, whereas dents with acceptable strains can be considered within a remaining life assessment to investigate their impact on the fatigue life of the pipeline for example.
- Dent Fatigue Life Assessment
DENT FATIGUE LIFE ASSESSMENT
Dents introduce localized stress concentrations within pipelines that can result in crack initiation and fatigue growth, if the pipeline is subject to cyclic loading. Dent fatigue life assessments address the question of whether dents are susceptible to fatigue crack growth and whether this could impact the integrity of the pipeline during its operational life. Screening level assessments can be performed based on the reported dent depths in order to quickly prioritize pipeline dents for more detailed assessment. However, most of ROSEN’s dent fatigue assessments make maximum use of the high resolution data that can be gathered using the RoGeo XT geometry service and consider the shape of the dent in order to investigate the restraint condition of the dent and to quantify the associated stress concentrations and, where appropriate, residual stresses. Consideration will also be given to the possibility of interacting anomalies through detailed review of the available inspection data, typically comprising of multiple technologies.
- Interacting Damage Assessment
INTERACTING DAMAGE ASSESSMENT
The most severe dents are those that are associated with other forms of damage such as cracks, gouges and other forms of metal loss.
An understanding of the potential damage mechanisms combined with a deep understanding of the capabilities of available in-line inspection technologies allows to perform detailed, reliable assessments of pipeline dents that are combined with other anomalies.
The assessments consider the impact of the combined damage on both the burst pressure of the pipeline and its remaining fatigue life.
Where required, the combined effects of multiple damage mechanisms (e.g. fatigue and corrosion growth) can be considered.
- Pipeline Wrinkle, Ripple and Buckle Assessment
PIPELINE WRINKLE, RIPPLE AND BUCKLE ASSESSMENT
High-resolution geometry tools can detect, classify and size deformations that have been introduced by excessive or uncontrolled bending and/or compressive loads. The severity of such anomalies depends on their shape and size, the pipeline operating conditions and whether the loading that led to the formation of the damage is present and if it is stable. ROSEN’s geometry assessment approaches review the impact of damage such as wrinkles and ripples on the immediate and future integrity of the pipeline and provide recommendations for ongoing monitoring or further inspection.
In addition to localized geometric damage like dents, pipelines can also be affected by out-of-roundness issues such as ovality and roof topping.
In many cases, such damage does not significantly impact the integrity of the pipeline but the stresses associated with such damage can lead to crack initiation and accelerate fatigue crack growth. ROSEN’s holistic approach to integrity assessment is of particular benefit with regards to out-of-roundness due to its influence on cracks that may be detected as part of a crack detection inspection.
- Depth-of-Cover Mapping
ROSEN provides a depth-of-cover assessment to ensure pipeline safety and compliance with local, state, and federal regulations.
- Geometric Anomaly Management
Geometric Anomaly Management
Once the deformations detected by in-line inspections have been classified, sized and assessed, pipeline operators are able to make short-term decisions relating to further investigations, repairs and whether additional mitigation is required to manage the associated threats. Even after these short-term decisions, ROSEN supports the operators with a proactive and forward-looking approach.
A customized Geometric Anomaly Plan should pull together all relevant pieces including ILI data, verification findings, operational pressure history and mitigation strategies to develop a flexible, targeted plan to ensure geometric anomalies do not compromise safety during the intended life of the pipeline.
All elements of the management plan should be adequately documented and key integrity data should be aligned to support quick and reliable assessments in the future. Additionally, some regulations now require that pipeline records be traceable, verifiable and complete. With the amounts of collected data steadily growing, the establishment of a data management system where all available data is readily accessible is becoming an increasingly critical issue for pipeline operators. ROSEN provides an Asset Integrity Management platform to support operators with data management as well as a range of integrity based assessment activities.
Competence is a key consideration in managing pipeline assets. The risks they present – and the safety of people and the environment – are becoming more imminent. Plus, standards and regulations explicitly require all personnel to be competent and qualified in their respective fields of responsibility. Understanding this need, ROSEN has developed training courses, education programs and qualifications specific to addressing threats.
Find out more about Competence Training