Pipeline integrity is essential to ensure the safety of critical pipelines.
Ultrasonic Corrosion Mapping
This is the preferred inspection method for critical pipelines, generally on petrochemical sites and offshore platforms. Ultrasonic corrosion mapping offers pipeline owners detailed C-scan images of inspection surfaces generated by semi-automated scanning systems.
RMS2-450 and RMS2-ARC are high-speed, remote-access ultrasonic corrosion mapping systems designed to scan the circumference of pipes 152 mm (6 in) or more. The ultrasonic data is recorded from a single crystal immersion transducer and displayed by the software as a color-coded C-scan, where different thicknesses are represented with different colors. Each thickness level is color-coded making wall thinning by corrosion and erosion easier to recognize than with manual inspection.
Ultrasonic Thickness Measurement Locations
Ultrasonic thickness measurement location (TML) inspection is used to determine the internal condition and remaining thickness of piping components. The method can be used in or out of service, but must be performed by a qualified inspector.
With advances in technology and reporting capabilities, more and more engineers recommend equipment such as R-Scan Lite, which records thickness continuously as the scanning head moves over the surface under test. Inspection results can be viewed in real time and reviewed post-inspection for analysis. TMLs are specific areas along the pipeline where inspections are made. The nature of a TML varies according to its location in the piping system. The selection of TMLs considers the potential for localized corrosion, service-specific corrosion, and fittings, with special care given to the inside and outside radii of elbows and tees where corrosion/erosion can increase corrosion rates. Minimally, the thinnest reading and its location is recorded.
Inspector should account for expected and actual corrosion patterns in the process unit when selecting or adjusting the number and locations of TMLs. A number of common corrosion processes in refining and petrochemical units are relatively uniform in nature, resulting in fairly constant pipe wall reduction rates, independent of location, axially or circumferentially. In these situations, the number of necessary TMLs to monitor pipelines are fewer than those necessary to monitor pipelines subject to more localized metal loss. In theory, pipelines subject to perfectly uniform corrosion can be adequately monitored with a single TML. In reality, corrosion is never truly uniform, so additional TMLs are almost always necessary.
Magnetic-Flux Leakage (MFL) Pipe Screening
This corrosion screening technique is unaffected by product flowing through a pipe, therefore surveys can be performed in or out of service. MFL is a quick and easy method of detecting corrosion, verified by ultrasonic testing on suspect areas. Pipescan is a cost-effective MFL inspection system designed to operate on pipes with outside diameters 48–2400 mm (1.9–94.5 in).
MFL screening relies on the detection of the magnetic flux “squeezed” out of the pipe under test by decreases in wall thickness. To do this, pipe walls must be close to magnetic saturation. The amplitude of the signal obtained from any wall loss is proportional to the missing volume in the tested region.
External Visual Inspection
This is used to determine the outer condition of piping, insulation systems, paint, and coatings to check for signs of misalignment, vibrations, and leaks. When corrosion by-product build-ups are observed at pipe support contact areas, lifting them may be necessary for inspection. External inspections include surveying the condition of piping hangers and supports. Instances of cracked and broken hangers, bottoming out of spring supports, displaced support shoes from supports, and any other improper restraint conditions must be reported.
Support legs must also be checked to make sure they have not filled with water causing external corrosion of the pressure piping or internal corrosion of the support leg.