In previous blogs, we have touched on Phased Array technology, a modern ultrasonic testing technique that is commonly deployed at oil and gas refineries, power plants and in other markets. Today, we’ll discuss Full Matrix Capture (FMC) and the Total Focusing Method (TFM), data acquisition applications of Phased Array Ultrasonic Testing (PAUT), and how using robotics assists and enhances use of these cutting-edge technologies.
What is FMC/TFM?
FMC is a PAUT data acquisition strategy. PAUT involves the use of multiple-element probes synthesized by programmed pulse control, with time delays being dependent on multiple factors, including asset geometry and acoustic properties.
Typically, a single element pulse and subsequent receival by that same element results in an individual A-Scan. During FMC, a single element is pulsed, but all probe elements receive the reflected signal, rather than just that specific individual probe. In essences, this creates as many A-scans as receive elements for just a single pulse. This process repeats until every element in the array has, one-by-one, fired all possible transmission/receiving combinations.
For example, if a 64-element probe is being used, the data achieved will be 64 to the power of 2 (nXn), generating 4,096 A-scans. All A-scans are captured and recorded, enabling the full data matrix to be stored for processing and reviewing. This achieves extremely robust, accurate data collection, and improved defect detection and/or characterization. But of course, all this data itself isn’t particularly useful without a processing program, which brings us to TFM. See figure #1 below for more details.
TFM is one of several post-processing algorithms that, once the FMC is complete, reconstructs the data to generate basic, easy-to-understand high resolution images of the area of interest. TFM enables utilization of all data collected from FMC, producing very large, high-resolution files. Correspondingly, the data collection process takes time and requires significant storage space. (NOTE: a very good computer is required to process the data and perform analysis)
Some common damage mechanisms able to be detected and sized by FMC and TFM include, but are not limited to:
- Early stage cracking/HIC
- Intergranular Corrosion cracking (PASCC)
- Volumetric defects.
- Blister periphery cracking confirmation and sizing.
See Figure #2 below showing detection and sizing of HTHA damage.
In short, FCM is the data collection technique, and TFM is the data management program. FCM/TFM enable max data capture and utilization, further extending the capabilities of PAUT.
Moving on to actual deployment of these technologies, the use of robotics can provide even more value and numerous advantages.
Adding Value, Ease of Application, With Robotics
Gecko’s robotic inspections include a wide range of continually expanding applications, from boiler tanks, pipelines and fuel silos to stacks, pressurized vessels and much more.
There are three main categories of robots:
- Pipeline Pigs
Drones: Drones are increasingly being used at facilities for manual and automated flights, in and around assets. The main benefit of drones is that they can enter places that humans cannot—for example, a boiler. Right now, a potential drawback of drones is the limited amount of NDT readings they can take—spot UT readings—and for the most part, they are used to collect visual imagery.
Pipeline pigs: These specialized robots are frequently used in the oil and gas industry. Originally designed to perform cleaning on insides of pipelines, these robots have been made “smart” by adding sensors to collect NDT data.
Crawlers: hence the name, are designed to crawl, or ascend on assets to collect readings and imagery. They typically require adhesion to the surface of the asset to enable the climb—i.e., magnetic wheels. These require a ferrous surface such as a carbon steel tank or boiler, however, there are new adhesion methods being worked on that will enable them to climb nonferrous surfaces such as stainless steel.
The benefits of crawler utilization include the ability to use on in-service assets—for example, tanks. Crawlers can collect NDT readings without taking the tank offline. For internal inspections the asset must be cleaned of material, however research and development is progressing on submersible robots.For inspections making use of FMC/TFM, use of crawlers and pipeline pigs can add many benefits, especially when compared to manual inspections. See Figure #3 Showing scanner configuration for TFM Raster scan.
Manual inspections take time, often days or weeks to complete with larger assets. Because of that, they are often limited in the scope and amount of data that can be collected (and the time it takes to erect scaffolding, rope access, etc.). While FCM/TFM data processing can take time, use of robots cuts down dramatically on overall inspection time, thus minimizing the challenge of slower data processing speed.
Data collection efficiencies during manual inspections often rely on the skill and knowledge of a human operator. If the operator was trained incorrectly, or is not familiar with the asset, they may not be able to obtain good readings; or readings may not show a trend year-over-year, as they may be collected differently every time. A big factor with robotics is repeatability—the data collection method is the exact same each time, resulting in accurate, trending data. If an operator wants to revisit stored FMC/TFM data, they can view any A-scan for future reference.
Robots can go many places where humans can’t—spaces smaller than inspectors can fit in—and can endure harsh operating conditions, up to 120 degrees Celsius (approx. 250 degrees Fahrenheit). Use of robotics also limits the number of people on-site. The typical outage for a recovery boiler might require 20 to 50 inspectors, on-site, whereas with robotic technology, it tends to be closer to four or six for a project of the exact same scope.
In most cases, robots can access assets while they are online, avoiding shutdown and ramping-up processes.
Of course, there are a few potential disadvantages of robotics, human inspectors having certain capabilities that robots do not. For example, easily moving around asset obstructions such as catwalks. Additionally, the upfront service cost can be much higher than manual inspections, though the price has come down substantially in the past year or so—up to 40%--a trend that is likely to continue as technology advances and becomes even more widely adapted.
Coupling the use of robotics with the advantages offered by comprehensive inspections utilizing PAUT, FMC and TFM allows operators to be proactive with repairs, rather than reactive. The predictive maintenance capabilities and detailed data insights that today’s technology offers reduces equipment failure or unplanned downtime, increases reliability and probability of detection, and maximizes the value of asset inspections.