Vessel integrity solutions depend greatly on the type of vessel, defect type, and regulations. The following are some of the more common inspection solutions for vessel integrity.
Ultrasonic Corrosion Mapping
This is the preferred method of inspecting critical vessels, generally in the petrochemical sector. Ultrasonic corrosion mapping provides owners detailed C-scan images of the surface under test using semi-automated scanning systems. RMS2-450 is a high-speed, remote-access ultrasonic corrosion mapping system designed for circumferential scanning of diameters 152 mm (6 in) or more.
Ultrasonic data is recorded from a single-crystal immersion transducer and displayed by the software as a color-coded C-scan with differing thicknesses represented as different colors. Each thickness level is color coded and walls thinned by corrosion and erosion are easier to recognize than by manual inspection.
To accompany the RMS2-450 is Thetascan, which is designed for corrosion mapping of areas inaccessible to the RMS2 such as saddles and dome ends. Thetascan is a dry-coupled, manual, ultrasonic C-scan imaging system that can be used on flat plates and curved surfaces with a diameter larger than 300 mm (12 in). The system continuously records thicknesses as the scanning head moves over the inspection surface. During a scan, thickness information is presented as an A-scan trace, a digital thickness measurement and a C-Scan.
Ultrasonic Thickness Measurement Locations (TML)
Ultrasonic thickness measurement inspection is used to determine the internal condition and remaining thickness of a vessel. Thickness measurements are collected in or out of service and by a qualified inspector. With advances in technology and reporting capabilities, more and more engineers recommend equipment such as dry-coupled R-Scan Lite, which continuously records thicknesses as the scanning head moves over the inspection surface. Inspection results can be viewed in real time in the field or recalled for post-inspection analysis.
Magnetic-Flux Leakage (MFL) Pipe Screening
This is a corrosion screening technique un affected by product in the vessel, so surveys can be carried out in or out of service. MFL is a quick and easy method used to detect corrosion, and then validated with ultrasonic testing (UT) for suspect areas. Pipescan is a cost-effective MFL inspection tool designed to operate on curved surfaces with an outer diameter 48–2400 mm (1.9–94.5 in). Larger vessels and tank shells can also be screened with Handscan.
MFL screening relies on the detection of the magnetic flux, which is squeezed out of the pipe under test by any decrease in wall thickness. To do this, the pipe wall must be close to magnetic saturation. The amplitude of the signal obtained from wall loss is proportional to the volume of missing material in the inspected region.
External Visual Inspection
This inspection is used to determine the condition of the exterior insulation, the supports, the allowance for expansion, and the general alignment of a vessel on its supports. Any sign of leakage is investigated to identify its source. Inspection for corrosion under insulation (CUI) is considered for externally insulated vessels subject to moisture ingress.