Various inspection techniques are available that allow operators to gather valuable information on their piping assets that may have been damaged over time by Corrosion Under Pipe Supports (CUPS). The first step is to evaluate the extent of the damage at the pipe touchpoint, however limited access around the contact area between the pipe and the support makes this a challenge.
Some inspection techniques allow you to collect qualitative measurements without direct access to the damage location but quantitative readings require the line be lifted using some form of pipe rack jack for direct access inspection.
Different inspection methods require different clearances between the pipe and the support meaning the line must be lifted to an appropriate height to provide sufficient room for the inspection to take place.
Engineered line lifting enables this by providing safe access for crews to carry out a wide range of inspection and repair methods by considering the required lift heights and the effects they have on pipe stresses and reaction loads on lifting equipment.
All the methods described below are forms of Non-Destructive Testing (NDT).
3.1 Visual Inspection
Visual inspections are often performed as a first pass to identify problem areas. While visual inspection alone can't detect internal flaws or quantify the extent of external damage, it is an inexpensive technique that is essential for identifying external issues that may require further inspection using other quantifiable methods.
Inspectors thoroughly examine the piping exterior, looking for visible signs of damage like cracks, bulges, corrosion or leaks. This includes inspecting welds, joints, flanges, and most critically the areas around the pipe-to-support interface.
Discoloration, deformation, or pitting can all indicate potential problems.
3.2 Pit Gauge Measurement
Pit gauge measurements offer a quick and easy method for assessing corrosion depth on the surface of process piping. These portable gauges have a pointed tip that fits into corrosion pits. The gauge's scale then indicates the pit's depth, allowing inspectors to determine the severity of corrosion and its impact on pipe wall thickness.
While not suitable for deep flaws or internal corrosion, pit gauges are a cost-effective way to identify areas requiring further evaluation with techniques like ultrasonic thickness measurement. Their simplicity makes them ideal for routine inspections, helping to prioritize maintenance needs and ensure process piping safety.
This method of inspection requires at least 2" (50mm) gap clearance between the pipe and the support so the line must be lifted to create this room.
3.3 Ultrasonic Testing (UT)
Ultrasonic Testing (UT) is a widely used non-destructive inspection method that employs high-frequency sound waves to detect corrosion, measure material thickness, and locate defects in pipes. Three common types of ultrasonic testing techniques are Conventional UT, Phased Array UT (PAUT), and Guided Wave UT (GWUT). These methods vary in their applications and the level of detail they provide but share the same underlying principle of using ultrasonic waves to assess the integrity of materials.
3.3.1 Conventional Ultrasonic Testing
Conventional UT works by sending a pulse of high-frequency sound waves into the material using a transducer. These waves travel through the material and are reflected back when they encounter a boundary, such as a defect or corrosion. The time taken for the waves to return is measured to determine the thickness or locate defects.
This method is commonly used for thickness measurements at touchpoints and is highly effective for detecting localized corrosion at a single location. UT's portability and size enables inspection at the pipe touchpoints with as little as 1-½” lift height, and can be used with the line still in-service.
3.3.2 Phased Array Ultrasonic Testing (PAUT):
Phased Array Ultrasonic Testing (PAUT) is an advanced NDE technique that allows precise control of ultrasonic beam angles, offering dynamic depth focusing and improved coverage. PAUT uses an array of transducers that can be electronically controlled to send and receive sound waves at various angles, creating a detailed, high-resolution image of the material being inspected.
This allows for the detection of complex corrosion patterns or defects in hard-to-reach areas, such as pipe supports. By adjusting the angle of the wave emission, inspectors can scan larger areas and get more precise data than with conventional UT.
3.3.3 Guided Wave Ultrasonic Testing (GWUT):
Guided wave NDT is used for the inspection of elongated materials like piping and is frequently used during routine NDT in the oil and gas industry. It propagates ultrasonic waves in an elongated structure using the boundaries of the structure itself to guide the waves.
These waves can detect corrosion or wall thinning at supports and along the pipe's length. The sound waves propagate along the pipe, and any changes in material thickness or defects reflect the waves back, revealing the location of potential corrosion.
This method is ideal when direct access to the pipe touchpoint is obstructed by the supporting beam, pipe shoes or insulation.
3.4 Smart Pigging
Smart pigging is an advanced inspection method used to measure remaining wall thickness hence it can also detect corrosion under pipe supports (CUPS) in pipelines. A "smart pig" is a device equipped with sensors, such as ultrasonic or magnetic flux leakage (MFL), that travels inside the pipeline, gathering real-time data on wall thickness, corrosion, and metal loss. For touchpoint corrosion, smart pigs can detect changes in wall thickness at points of contact between the pipe and its supports, where external visual inspections are limited. The data collected helps pinpoint areas of concern without requiring the pipeline to be lifted or shut down.
Smart pigging offers the advantage of covering long pipeline distances, providing a detailed assessment of corrosion and other defects in areas that would otherwise be difficult to inspect using traditional methods. It also helps assess the overall pipeline integrity, making it a crucial tool in corrosion management and predictive maintenance.
3.5 Conclusions
When selecting inspection methods for Corrosion Under Pipe Supports (CUPS), feasibility and cost are critical considerations. Techniques like visual inspection and ultrasonic testing are inexpensive but often require lifting the pipe or accessing hard-to-reach areas.
Smart pigging provides very accurate measurements but it is very costly due to the specialized equipment that’s required and not all pipelines can be pigged. Pigging is typically done on long pipelines to capture data across long sections of piping in one pass.
Phased Array UT and Guided Wave offer qualitative data and are costly but they are the least invasive since they can be used without needing to lift the pipe away from the support. Ultimately, the choice of method depends on the pipeline's complexity, location, and the resources available. A balanced approach, often combining methods, can offer thorough corrosion detection while optimizing costs and minimizing operational disruptions.
For more information on Ovolifts capabilities and services, please reach out:
Comentarios