Ultrasonic inspection, pipeline

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

Ultrasonics has been utilised in several versions of pipeline inspection vehicle see section below). The use of ultrasonics for detection of hydrogen damage in steels has been reported"". ... 

Intelligent vehicles have been developed with arrays of ultrasonic probes for pipeline inspection — one commercial version contains 512 ultrasonic sensors. 

In areas where general corrosion is the expected form, a simple ultrasonic thickness gage can be utilized to determine the extent of corrosion, based on baseline readings made at installation or previous inspections. The entire unit need not be examined. Attention can be focused on those areas most likely to corrode, such as liquid levels, mixing zones, or areas of high turbulence. Corrosion probes, which can be placed in process equipment or pipelines, can monitor corrosion conditions by measuring an actual corrosion current, or other process parameters known to be related to general corrosion rates. These data can be constantly monitored and recorded to predict equipment wear, or as an alert to upset conditions. 

Improved Performance of Guided Wave Ultrasonic Testing for Long Range Inspection of Pipelines using Multi-Channel Systems... 

Electromagnetic acoustic tools are particularly adapted to the detection of cracks in dry gas pipelines. This tool generates ultrasonic signals without requiring liquid couplant to transfer the ultrasound into the steel. These tools are new to the pipeline inspection industry, so their effectiveness has not yet been determined. 

There are two principle types of inspection vehicle used to survey the internal and/or external condition of steel transmission pipelines. The first involves the direct measurement of wall thickness by ultrasonics. The second uses an induced magnetic flux in the pipe wall to assess the defect size from the perturbation caused by defects. Both techniques require the pipe internals to be thoronghly cleaned and free of deposits for them to function successfiiUy. 

Proper field monitoring and inspection techniques can be used to measure the real corrosion rate, to find safety risks on time and to avoid corrosion accidents. The field monitoring and inspection techniques normally include weight-loss coupons, electrical resistance probes, ultrasonic wall thickness measurements, infrared thermal imaging systems, etc. Ultrasonic wall thickness measurement is widely used to monitor the general and erosion corrosion rates of the equipment and pipelines in crude oil processing plants. 

---