Development and Validation Testing of High-Temperature Phased-Array UT Transducers and Wedges for Process Industry Applications

Introduction

The adage “time is money” has never been truer than when discussing the inspection of critical assets in the oil and gas and power generation industries. With many of the assets running at temperatures well over the typical recommendation for standard ultrasonic (UT) transducers and wedges, inspections are often a major financial burden to energy providers. While solutions to this problem do currently exist, they are often cumbersome, expensive, and altogether untenable. It was therefore decided to pursue the development and validation of phased array/time of flight diffraction (TOFD) transducers and corresponding wedges to service these high temperature inspections with the hope to discover reliable, convenient, and, most importantly, cost effective alternatives.

As we moved through the research and development process, we sought to complete two main goals. First and foremost, the goal was to design a line of transducers that could withstand the rigors of testing assets at elevated temperatures. Most standard phased array and TOFD transducers can be operated at a range of 0°F to 135°F (-18°C to 57°C). This limitation creates major challenges when dealing with prolonged exposure to elevated temperatures. Acoustic performance of the probe often degrades and becomes unusable. The duty cycles of these probes are often a major inconvenience to inspectors, causing disruptions and delays in the inspection, with the worst-case scenario being the destruction of the probe after prolonged use.

The second goal was to design and validate a line of phased array and TOFD wedges to help make these inspections less cumbersome, time intensive, and costly to their operators. Material selection was the most important part of the new design. The thermal properties of many traditional materials exclude them from consideration as the melting temperatures are often too low or the material velocity has decreased to the point where it is not viable for shear wave inspections. Extensive testing has been done to make sure that the selected material meets the thermal and acoustic requirements.

As design and testing progressed, two secondary goals were also established: to limit the overall footprint of a wedge and to create two wedge designs made of different materials. Limiting the footprint of a wedge allows for minimal irrigation during testing. In turn, this will decrease setup time and lead to easier completion of critical inspections. Additionally, material costs are a major consideration when establishing final pricing. We strove to provide options in materials dependent on the temperature range requirement for a given inspection.

New Transducer Design and Testing

As stated earlier, the primary goal of the project was to design and then produce phased array and corrosion transducers that could withstand prolonged exposure at elevated temperatures. This is one of the main issues when discussing the feasibility of these inspections. While inspections are currently happening at or above the current specified ranges for the transducer, they are often very cumbersome, requiring very large wedges or complicated irrigation systems. These are required because the typical phased array transducer will only withstand temperatures up to around 135°F, well below the 400°F target set for this study. Performing these inspections often poses a financial risk as well. The costs of these transducers can be extremely high depending on what is necessary, or what is specified, to complete an inspection. Potentially operating these transducers past their specified temperatures can endanger their functionality and present a large financial risk to the inspector(s). With a newer design that can withstand the rigors of these inspections, risk can be mitigated from the operation and the inspections can be performed in the field.

As testing progressed a secondary goal was established, which was to make sure all of the versions of the transducers would have same performance as their standard temperature equivalents. As previously stated, these transducers can represent a very large investment for the consumer. If the performance is equivalent to our standard offering, then we can provide solutions for a much broader range of inspections. The biggest issue [from a performance perspective that we encountered] is the inevitable drop in sensitivity as temperatures increase. Figures 1 and 2 will show before and after photos of identical inspections, the first being taken at room temperature and the second being performed at 400°F Please note that there was a fifteen-minute normalization period before the data was collected in Figure 2. This allowed the wedge and transducer to get up to temperature. These screen shots were gathered using a manufactured defect in a piece of four-inch schedule 40 pipe. Figure 3 shows the full pipe mockup used for the testing.