Pipeline repair: how to determine the most appropriate method

Pipelines are no different in this respect.  In order to align with global standards and ensure continued reliability of their pipeline assets, operators are required to develop and implement a pipeline integrity management plan for each pipeline they operate.

All manufacturing processes have the potential to 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 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.

1. Replace as Cylinder
2. Removal by Grinding
3. Deposition of Weld Metal
4. Reinforcing Full Encirclement Sleeve (Type A)
5. Pressure-Containing Full Encirclement Sleeve (Type B)
6. Composite Sleeve
7. Mechanical Bolt-on Clamps
8. Hot Tap
9. Fittings

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 they 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 pipeline repair

Once a repair has been deemed necessary, the next step is determining the most appropriate repair method. The selection depends on several factors, including the nature of the condition, material availability, timing, operational constraints, and any special procedures required for implementation. While industry standards recognize numerous acceptable repair methods, not all are applicable or practical in every situation. Therefore, each option should be evaluated for both code compliance and feasibility within the specific operating environment.

Industry standards identify three repair methods that are acceptable for any potentially injurious condition: Replace as Cylinder, Type B Sleeve, and Mechanical Bolt-on Clamps. The following examples highlight key considerations that should be evaluated before selecting alternative repair methods.

1. 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.
    
2. 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.
    
3. Can the pipeline be shut down or diverted? If not, then this eliminates the option to Replace as Cylinder.
    
4. 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.
    
5. 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.
    
6. 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.

Applus+ experts have 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.