Fitness for Service & Intergrity Assessment.
Experts at Rave Limited have extensive experience applying Fitness-for-service (FFS) assessments methods to evaluate
the structural integrity of components containing flaws and their suitability for continuous service.
Fitness for Service & Intergrity Assessment.
Hazardous liquid and gas pipelines are relatively safe compared to other forms of energy transportations systems. However, they do fail, and failure could cause fatalities, environmental damage and business losses. Pipeline could fail as a leak or a rupture. Causes of pipeline failures vary around the world, and from country to country. In order to prevent pipeline failure it is important that operators conduct studies to assess the condition of their pipeline assets, including those with identified or known flaws or defects to ascertain their continued fitness for service (FFS).
The fitness-for-service of a pipeline containing a defect or threat condition may be determined by a variety of methods ranging from previous relevant experience, to model testing, to ‘engineering critical assessments’ (ECAs), where a defect is appraised analytically, taking into account applied loadings and its environment.
Procedures in standards such as BS 7910, API 579/ASME FFS-1, ASME B31G, DNV-OS-F10, and integrity management standards such as API 1176, API 1160, can be used to evaluate the integrity of critical pressure components and welded structures against different failure modes, using proven engineering approaches. Industry documents such the Pipeline Defect Assessment Manual (PDAM) also provide guidance on best practices available in the industry for assessing the wide variety of defects or threat conditions that may be identified in pipelines.
ASME B31.8S identified Nine (9) categories of threats conditions that could potentially cause pipeline failure, namely:
Services We Offer
- Defect Assessment;
- Corrosion Rate Assessment
- Remaining Life and Reassessment Interval
Assessment - Crack-growth Analysis;
- Fatigue Analysis;
- MAOP Validation, Uprate and Restoration Studies;
- Hydrostatic Test Planning
- Review Effectiveness of Hydrostatic Tests in Assuring fitness for Service
- Assessment of Free Spans or Unsupported Pipeline Segments;
- Girth Weld Engineering Critical Assessment (ECA).
- Establish Interim Pressure Reduction Requirements to Support Safe Working Conditions
or Assure Pipeline Safety Pending Implementation of Repairs or
Condition Assessment;
Defect Assessment
Rave Limited staff have the requisite engineering expertise and experience in performing defect assessments, and have applied industry
best practices to conduct FFS evaluations of a variety of pipeline defects including:
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- Corrosion defects;
- Cracks and crack-like indications;
- Deformation anomalies including dents,
wrinkles and buckles; - Selective seam weld corrosion;
- Pipe diameter expansions;
- Girth weld anomalies;
- Mechanical damage features such as gouges, scrapes.
- Interacting threat conditions;
Remaining Life Assessment
The condition of time-dependent threats such as corrosion and cracks may deteriorate over time. Predictions of the remaining life of such defects are necessary to enable re-assessment or remediation to be implemented in a timely manner to prevent them from deteriorating to a critical point that could cause pipeline failure in service.
Remaining life assessment may involve the following
- Corrosion rate assessments;
- Assessment of remaining life of corrosion features;
- Apply fracture mechanics principles to evaluate crack growth and pressure-cycle induced fatigue of crack anomalies;
- Determination of reassessment intervals;
Assessment of Interacting Threat Conditions
Two forms of interactions are generally recognized in pipeline integrity evaluations. One form of interaction occurs at the feature level, while the other at the integrity threat level.
Interacting Defects
Two or more features are considered to “interact” if the presence of the features together results in a larger reduction of failure pressure than would be expected for any of the features alone.
Interacting Threat
Where two or more threats or damage mechanisms are considered to interact where they act together on a pipeline segment leading to an increase in the likelihood of failure to a greater level than the effects of the individual threats acting alone. Some examples of threat interaction include:
- Selective seam weld corrosion (SSWC)
- External corrosion and previously damaged pipe;
- Pressure-cycle-induced fatigue or construction defects;
- Stress corrosion cracking (SCC) and defective pipe;
- External/internal corrosion subjected to severe compressive longitudinal or axial tensile loading;
- Dents with external corrosion;
- Among others
Other examples of interacting threats can be found in API RP 1160, ASME B31.8S, CSA Z662, DNVRP F116, PDMA and other relevant industry publications.