Pipelines are used to transport fluids—such as liquids and gases—between two or more facilities, either underground or aboveground. A flowline is a specific type of pipeline designed to carry fluids from the wellhead to a processing facility or gathering manifold. Because corrosion, erosion, cracking, and other defects can occur on both the internal and external surfaces of the pipe and its coating, routine maintenance and repair must be performed in accordance with applicable standards.
The required frequency of maintenance depends on several factors, including the severity of corrosion and erosion, the type of fluid being transported, the pipeline’s location, population density, and the overall importance of the asset. This article provides an introduction and brief overview of maintenance and repair practices for underground oil and gas metal pipelines. Final proposal and scope of work will be determined based on detail and condition of each specified pipeline.
Maintenance requirements for aboveground pipelines are generally similar to those for underground pipelines, with the primary distinction being that aboveground systems do not require excavation. Relevant standards that govern pipeline maintenance and repair include ASME B31.4, ASME B31.8, ASME B31.8S, ASME PCC‑2, API 570, API 1104, API 1111, API 1160, among others.
Work Breakdown Structure (W.B.S) for maintenance and repair for Underground metal Pipeline:
Note: The list of standards referenced in this article is intended to be general and introductory. The practical and final list of applicable standards must be determined based on the specific pipeline, its operating conditions, and all relevant regulatory requirements.
Note: All phases of the work must be performed in compliance with applicable standards, as well as all safety, security, and regulatory requirements.
| Item | Job Description |
| 1 | Review maintenance scope, drawings, technical document and standards |
| 2 | Depressurization, purging, shutdown, and obtain a work permit. Note: In all steps of maintenance must consider safety regulations. |
| 3 | Identify the pipeline boundaries for maintenance work |
| 4 | Excavate soil to safely expose the pipeline surface Note: Cathodic protection wires, cables, and associated junction boxes must be properly located, marked, and removed or isolated as required prior to any excavation activities. |
| 5 | Shoring a pipeline. This involves using temporary support systems, such as hydraulic braces or timber structures, within trenches to prevent soil collapse, ensuring worker safety and stability during pipe installation or repair. This process stabilizes the excavation walls, protects against dangerous cave-ins, and supports adjacent ground or utilities. Systems are installed from the top down and removed from the bottom up for continuous protection. |
| 6 | Release the pipeline from surrounding soil carefully, ensuring tools and excavators do not contact or damage the pipe. For lifting the pipeline use standard and certified tools, side boom or crawler crane. |
| 7 | Place supports under the pipeline immediately after it is released from the soil to ensure stability |
| 8 | Remove existing pipe coating using appropriate tools and prepare the surface for sandblasting |
| 9 | Sandblast the pipe surface to achieve the required standard finish for inspection |
| 10 | Inspect the pipeline in accordance with ASME B31.4, ASME B31.8, and other applicable standards. |
| 11 | Cut out the pipe section that has been inspected, marked, and rejected. NOTES: Common cutting methods include cold cut and hot cut (depending on conditions). Before cutting, ensure a replacement pipe of the same specification is available. The new pipe must be approved by a technical inspector before welding |
| 12 | Fit up the new pipe section to the existing pipeline. Use standard, compliant pipe to replace any defective or rejected sections. The wall thickness, material composition, pipe manufacturing method, and all other relevant properties must conform to applicable standards. NOTE: Pipe must be beveled before fit-up, and all work must comply with ASME and related standards NOTE: As required, the pipe must be bent prior to fit‑up, in accordance with applicable standards. |
| 13 | Weld the new pipe to the pipeline. NOTES: Welding procedure must be prepared and signed by technical inspector; all activities must comply with standards; preheat if required by material; use demagnetizer during welding; welding must be performed by a certified welder per AWS D1.1 and other standards |
| 14 | Perform Non-Destructive Testing (NDT) as required based on standards: • Visual Inspection (VT) • Ultrasonic Testing (UT) • Radiographic Testing (RT) • Magnetic Particle Inspection (MPI) • Liquid Penetrant Testing (LPT) • Impact test • and more |
| 15 | Sandblast the pipe after welding to prepare for coating. NOTE: Surface roughness must be 50–100 microns or upon the related standards |
| 16 | Carry out coating and painting of the pipe surface in accordance with standards. Depending on conditions, coating types may include epoxy, polyurethane, polyethylene and etc. NOTES: Each coating must be approved by the technical inspector before using. Prior to coating, pipe surface roughness must be inspected and approved according to standards. |
| 17 | Perform coating quality tests, including: • Coating Thickness Measurement • Dry Film Thickness (DFT) Measurement • Adhesion/Peel Test |
| 18 | Construct embankment over the pipeline in accordance with standards and procedures. NOTES: Embankment must follow approved specifications. Channel excavation and pipeline depth must comply with applicable standards. |
Material Requirements for Pipeline Maintenance
Note: This list is general and brief; the final list of applicable standards must be determined based on the specific pipeline.
| Item | Specification |
| 1 | Standard pipe (based on ASME B31.4 or ASME B31.8 and other applicable standards) |
| 2 | Pipe welding tools and electrodes. The grade and type of weld and electrode are specified based on pipe material and operating conditions. |
| 3 | Standard soil for embankment |
| 4 | Standard coating for painting, based on pipe material and conditions |
| 5 | Standard supports for pipe seating after excavation. Provided based on pipe size and wall thickness. |
| 6 | Electrodes used for welding must be selected based on the grade and type specified for the pipe material and the operating conditions. |
| 7 | WD-40 (Lubricant) |
| 8 | Anti-seize compound |
| 9 | Bolt and nut |
| 10 | Flange |
Tools and Machines Requirements for Pipeline Maintenance:
Note: This list is general and brief; the final list of applicable standards must be determined based on the specific pipeline.
| Item | Specification |
| 1 | Excavator machine |
| 2 | Welding machine with accessories |
| 3 | Hand wrenches in various sizes |
| 4 | Hydraulic wrenches |
| 5 | Flange jacks |
| 6 | Crane for lifting heavy pipes and spools such as a side boom or crawler crane |
| 7 | Lifting belts |
| 8 | Hydraulic flange spreader |
| 9 | hammers (Iron, brass, and Teflon) |
| 10 | WD-40 (Lubricant) |
| 11 | Anti-seize compound |
| 12 | Pipe cutter, either hydraulic or pneumatic |
| 13 | Welding machine with accessories Note: The grade and type of weld and electrode are specified based on pipe material and conditions. |
| 14 | Air compressor |
| 15 | Disel generator |
| 16 | Bevel tools |
| 17 | Bend machine and related tools |
| 18 | Sandblasting equipment |
