Hazardous liquid and natural gas pipelines have been used for decades to transport crude oil, refined petroleum products, and natural gas from their respective gathering systems to facilities where they are refined, processed, or stored. As with any aging infrastructure after a certain period of time, preventative and ongoing maintenance is required to ensure the continued performance of the asset and to prevent issues from arising which could potentially have a detrimental effect or even lead to failure. Pipelines are no different in this respect. In order to align with federal regulations and ensure continued reliability of their pipeline assets, operators are required to develop and implement an integrity management plan for each pipeline they operate.
All manufacturing processes have the potential introduce imperfections into the pipe. Inspections during manufacturing and construction along with methods of pre-service testing prove that the pipe is fit-for-service at the proposed operating pressure. However, history has shown that some flaws can degrade over time to the point where a failure could occur. Additionally, certain conditions such as corrosion can initiate after a pipeline has gone into service. Therefore it is imperative that the integrity of the pipe is appropriately managed throughout the service life of the pipeline. While there are many processes, systems, and technologies dedicated to mitigating the causes of degradation of flaws in pipe, eventually the severity may require that the pipe be repaired.
What are the options for pipeline repair?
While federal regulations establish the criteria used to define injurious defects, damage, or anomalies, they do not specify acceptable repair methods or under what circumstances different repair methods are applicable. For this type of guidance, one must refer to industry codes and standards which contain industry best practices. Below is a list of the most common repair methods recognized and discussed by industry standards.
- Replace as Cylinder
- Removal by Grinding
- Deposition of Weld Metal
- Reinforcing Full Encirclement Sleeve (Type A)
- Pressure-Containing Full Encirclement Sleeve (Type B)
- Composite Sleeve
- Mechanical Bolt-on Clamps
- Hot Tap
It is important to understand that while the above repairs are specifically mentioned and discussed by common industry standards, an operating company may choose to complete a more rigorous analysis to justify a different repair approach. In other words, while industry standards recommend the above repairs under certain circumstances based on industry best practices, those industry standards do not prevent an operator from using another type or method of repair so long as such alternative practices can be demonstrated to be consistent with the objectives of industry codes, standards and best practices. When an operating company decides to take this approach, it is recommended that the operating company provide details and calculations demonstrating that such alternative practices are consistent with industry codes, standards and best practice objectives. This is generally the practice for alternative methods as prescribed in the industry documents.
Considerations for Determining the Most Appropriate Method of Repair
After it has been determined that a repair is required, the next question that must be answered is: “How are we going to repair it?” The answer to this question varies and is based on many different elements. There are many acceptable repair methods recognized by the industry, however not all repair methods are applicable in all situations and some repair methods require special procedures to be in place in order to ensure they are properly completed. Timing, material availability, or the additional procedures that may have to be in place, all can have an impact on the method selected to repair a pipeline. Some repair methods just may not be practical, while others just may not be applicable or appropriate. Therefore, first it is important to consider the limitations of each repair method in order to determine whether the repair method is valid, per industry codes, standards and best practices, and second whether it is feasible with respect to the specific situation. That being said, there are three repair methods recognized by industry standards which are acceptable for repairing any type of potentially injurious condition. Those repair methods are Replace as Cylinder, Type B Sleeve, and Mechanical Bolt-on Clamps. Below are some examples of items that must be considered prior to implementing other repair methods and why.
- Does the defect, damage, or anomaly affect a seam or girth weld? If so, the repair methods available may be limited depending on whether the weld is ductile or brittle. For example, the only methods applicable for repairing a 3% dent with 5% strain affecting a brittle weld in a gas pipeline are Replace as Cylinder, Type B Sleeve, or Mechanical Bolt-on Clamp. Whereas for the same dent affecting a ductile weld, there are additional repair options which are acceptable: Composite Sleeve, Type A Sleeve, or Hot Tap.
- Is the defect, damage, or anomaly leaking? If so, the only repair methods allowed are Replace as Cylinder, Type B Sleeve, Mechanical Bolt-on Clamps, and, depending on the specific scenario, removal by Hot Tap.
- Can the pipeline be shut down or diverted? If not, then this eliminates the option to Replace as Cylinder.
- What is the size of the targeted repair? Defects which cannot be contained entirely within an NPS 3 fitting cannot be repaired using a fitting type repair method. Additionally, defects which exceed the largest possible coupon of material that can be removed through a hot-tap fitting cannot be repaired by using a hot tap to remove the defect, damage or anomaly from the pipeline.
- Schedule/availability of materials: How soon is the repair required to be completed? Some repair methods such as using mechanical bolt-on clamps are designed for a single specific application and may have long lead times to obtain the repair clamp which eliminates it as a repair option depending on the repair schedule.
- Are all required procedures and qualified personnel available to perform the repair? Regulations require that some repairs, such as deposition of weld metal, be performed by a qualified welder using an approved welding procedure. If these required items are not already in place they can cause delays to the repair schedule.
The Engineering Team at Kiefner, an Applus+ company, has extensive experience in supporting and providing guidance to pipeline operators for making individual pipeline repairs as well as experience in writing complete pipeline repair manuals for both liquid and gas pipelines which cover all types of pipeline repair methods and aid the operator in selecting the most appropriate repair for each defect type they encounter on their pipeline.