Ultrasonic Corrosion Mapping
Ultrasonic corrosion mapping is the preferred method for critical pipelines generally on petrochemical sites or offshore platforms. Ultrasonic mapping provides the owner of a pipe line with a detailed C-Scan image of the inspection surface via the means of a semi- automated scanning system.
Silverwing’s RMS2-450 & RMS2-ARC is high-speed remote access ultrasonic corrosion mapping system designed for the circumferential scanning on diameter pipes of more than 152mm (6 inches).
Ultrasonic data is recorded from a single crystal immersion transducer and displayed within the software as a coloured coded C-Scan map, with differing thicknesses represented as changes in colour.
Each thickness level is colour coded and wall thinning by corrosion or erosion is more readily recognised than by manual inspection.
Ultrasonic Thickness Measurement Inspection
Ultrasonic thickness measurement inspection is performed to determine the internal condition and remaining thickness of the piping components. Thickness measurements may be obtained when the piping system is in or out of operation and should be performed by a qualified inspector. Silverwing's ultrasonic thickness gauges, the T-Scan 100 and T-Scan 300. The T-Scan 100 is designed for non-coated pipe work whereas the T-Scan 300 range is designed for coated pipelines.
With the advances in technology and reporting capabilities more and more engineers recommends equipment such as the R-Scan Lite which continuously records thickness measurements as the scanning head is moved over the inspection surface. Inspection results can be viewed in real time in the field or recalled for post inspection analysis at a later date.
Thickness measurement locations (TMLs) are specific areas along the pipeline where inspections are to be made. The nature of the TML varies according to its location in the piping system. The selection of TMLs shall consider the potential for localised corrosion and service-specific corrosion and fittings, with special attention to the inside and outside radius of elbows and tees where corrosion/erosion could increase corrosion rates. As a minimum, the thinnest reading and its location shall be recorded.
In selecting or adjusting the number and locations of TMLs, the inspector should take into account the patterns of corrosion that would be expected and have been experienced in the process unit. A number of corrosion processes common to refining and petrochemical units are relatively uniform in nature, resulting in a fairly constant rate of pipe wall reduction independent of location within the pipeline, either axially or circumferentially.
In these situations, the number of TMLs required to monitor a pipeline will be fewer than those required to monitor pipelines subject to more localised metal loss. In theory a pipeline subject to perfectly uniform corrosion could be adequately monitored with a single TML In reality, corrosion is never truly uniform, so additional TMLs may be required.
Magnetic Flux Leakage Pipe Screening
Magnetic flux leakage (MFL) is a corrosion screening technique which is not affected by product flowing through the pipe so surveys can be carried out in-service or out of service. MFL is a quick and easy method for detecting corrosion which should then be backed up by ultrasonic for suspect areas. Silverwing’s PipeScan is a cost effective MFL inspection tool which is design to operate on pipes with an outside diameter of 48 mm to 2400 mm.
MFL screening relies on the detection of the magnetic flux, which is 'squeezed' out of the pipe under test by any decrease in the wall thickness.
In order to achieve this, the pipe wall needs to be close to magnetic saturation. The amplitude of the signal obtained from any wall loss is proportional to the volume that is missing from the region interrogated.
External Visual Inspection
An external visual inspection is performed to determine the condition of the outside of the piping, insulation system, painting and coating systems, and associated hardware; and to check for signs of misalignment, vibration, and leakage.
When corrosion product build up is noted at pipe support contact areas, lifting off such supports may be required for inspection. External inspections shall include surveys for the condition of piping hangers and supports. Instances of cracked or broken hangers, bottoming out of spring supports, support shoes displaced from support members, or other improper restraint conditions shall be reported.
Support legs also shall be checked to confirm that they have not filled with water that is causing external corrosion of the pressure piping or internal corrosion of the support leg.