Advanced ultrasonic technologies offer diverse uses for in-service assets and are applicable to many industries including power generation, oil and gas, petrochemical, and pulp and paper manufacturing.
Ultrasonic testing (UT) instruments have a long history dating back to World War I, when the technology was first used to detect hidden objects under water, such as icebergs or submarines. The first instruments needed large, heavy vacuum tubes, required AC power and were not portable.
Technology evolved to smaller, battery-powered instruments, making UT more practical for field applications, but since earlier instruments utilized analog signal processing, they were more susceptible to calibration drift inaccuracies. Since the mid-1990's, digital instruments have become the standard, providing repeatable and accurate measurements, along with onboard data logging. The ability to share screens and test records, as well as integrate with computers, has greatly evolved the industry.
The Basics of Ultrasonics
In the simplest definition, UT is the conversion of electrical energy into sound energy to look for flaws in materials such as near welds, or to obtain general thickness measurements. In most industrial applications, a pulse echo configuration is used. Sounds are sent at one angle and reflected off a surface to discover discontinuities such as cracks, lack of fusion, or general corrosion.
With the advancements in digital, handheld ultrasonic meters, manual thickness gauging has become prevalent in the industry. This technique has been readily adopted for the reasons, along with caveats, below.
Can we do better? Recent advances in robotic control, high-speed interfaces and signal processing are allowing engineers to once again re-think the state of the art.
In a previous blog article we covered Automated Ultrasonic Testing, or AUT, which integrates all of these advances to make ultrasonic inspections faster, provide more coverage, and give more accurate measurements.
Automated Ultrasonic Testing (AUT), equipment, techniques and nomenclature have become synonymous with one another making it difficult to differentiate between systems. What is commonly called AUT, today, involves the use of simple robots that ride along the surface of the inspection material with magnetic wheels. The material is scanned automatically, generally in a circumferential direction, using a single, or dual, element probe that raster scans, or sweeps, along the material in the Y-axis.
Conventional AUT is advantageous due to its much higher data density over manual methods, and unlike manual UT, AUT allows the recording of raw A-scans for post-review. However, because of the use of a single probe and circumferential scanning, production rate is very low. Additionally, since it’s a non-drivable system, it must be placed exactly where the scan is wanted, and then be manually moved to the next location. Direct access to the asset is required, which may pose exposure risks to technicians.
Seeing the limitations of conventional AUT, Gecko Robotics has invested significantly in applying robotics and cloud processing to enhance the production rate of ultrasonic inspections, from large asset screening down to fine damage mechanism detection. An automated UT inspection technique “for any season," let’s dive into RUG, Rapid AUT, and Phased Array UT (PAUT).
RUG: Cover More Ground in Less Time
RUG is best applied to assets with large surface areas — as a replacement to manual UT or conventional AUT where more coverage is needed. For piping systems, RUG is a game-changer. Because the robots drives quickly in a longitudinal axis, two technicians can cover hundreds of linear feet a day, which is not possible with conventional AUT.
A quantitative tool, RUG captures all raw A-scans for post-analysis. Once the validated data is uploaded to the customer portal for review, it can be displayed in a 2-D C-scan, or 3-D C-scan view, manipulated with interactive tools to drive predictive insights.
The following are excellent applications to employ RUG.
RUG provides for quick screening at larger grid sizes, but, also, can approach the grid resolution traditionally seen with conventional AUT. The main advantage is significantly more area can be covered in much less time. For example, an overhead line or 24-inch process line, a RUG robot can cover 500-600 feet per day, in comparison to about 40 linear feet per day with conventional AUT.
Another example of an effective RUG application is a large, vertical vessel. In a scenario where conventional AUT is used without building scaffolding, it may take technicians around five or six weeks to complete the inspection, as scanners must be placed in every location to cover the large area. Using RUG, the same task can be accomplished in 4 days or less, depending on the size of the asset. Typically, the time on-site is reduced by about 90%.
RUG can screen the entire asset and find damage mechanisms very quickly—a 40-foot diameter tank floor can be done in one (12-hour) shift; without technicians entering the confined space.
Another type of AUT Gecko offers is Rapid AUT, which is appropriate to use on assets that are identified as having corrosion or thinning issues, or in cases where there are isolated issues of interest discovered with another screening method, like RUG.
Rapid AUT: (Much) More Data, Quicker
Rapid AUT has dense coverage like RUG, but at much higher resolution. This is a perfect tool for mapping out corrosion or when more data is needed for a fitness-for-service determination or finite element analysis post-inspection.
Broadly speaking, Rapid AUT uses a phased-array probe that can house 128+ elements. A combination of hardware movements and software-controlled pulses permit a much faster AUT system. One-axis of the scan is along the phased array, controlled in software. The other-axis is controlled by mechanical movement. Opposed to conventional AUT which mechanically rasters both axes, Rapid AUT results in a much faster scan.
[Note: since this process is enabled by a phased-array, these same techniques can be used to quickly scan at angles looking for specific damage mechanisms. But that is a story for another day.]
A potential disadvantage of Phased Array is that the probe is large and can lift off, resulting in loss of data. This can be prevented careful with process setup, and ensuring a sufficient surface to accommodate the probe.
So, how does Rapid AUT stand up to conventional AUT?
For every move that the Rapid AUT system makes, the same thing must be done multiple times with a conventional AUT unit. Therefore, a lot of ground can be gained with Rapid AUT corrosion mapping over conventional AUT, all while gaining significantly more data.
For example, to cover a five-by-two foot surface will take approximately three minutes with Rapid AUT, whereas with conventional AUT, it will take 14 minutes. In addition to being faster, the data has significantly higher resolution, as millimeter by millimeter coverage is achieved.
For some applications, it makes sense to combine RUG with Rapid AUT for a very thorough, fast inspection.
RUG + Rapid AUT + Phased Array = A Turnkey Solution
(1) RUG is a very good tool to use for accomplishing a general thickness inspection. It can be followed with (2) a Rapid AUT inspection to further explore areas of corrosion, and (3) a Phased-Array inspection of suspected areas of damage and welds. Pairing these tools together results in a turnkey solution to for the highest fidelity non-intrusive inspection.
While planning an inspection, Gecko Robotics works with clients to evaluate each asset and review previous inspection reports. Our goal is to measure all susceptible areas prone to known damage mechanisms, such as hydrogen-induced cracking or stress-oriented cracking in the welds or any of the base materials. By combining these three technologies, we can target an asset and satisfy the NDE/NDT data needed for an API inspection, Risk-Based Inspection (RBI) or Fitness-For-Service (FFS) determination.
When RUG is deployed alongside Rapid AUT and Phased Array UT, every part of the asset can be inspected. The comprehensive information gathered can be used to plan future maintenance activities, upcoming shutdowns, future turnarounds, and even monitoring slow corrosion growth to maximize service life.
Real-World Examples & Applications
Case Study: Bullet Tank (On-Stream)
Summary: Full shell and head thickness evaluation via RUG, Rapid AUT inspection of the Heat-Affected-Zones (HAZ), and Phased Array UT for fatigue cracking inspection of each weld.
Coverage: 1,105 square feet / 714,000 A-Scans
Inspection time: 1.5 (12-hour) shifts
Manpower: 3 technicians and two crawlers—(one Rapid AUT + Phased-Array UT system, one RUG system.
Result: A non-intrusive, on-stream inspection. Eliminated costs of de-inventory, cleaning and scaffolding.
Case Study: Flare Line
Summary: Two limited days with RUG, followed with 50% percent Phased Array UT in areas for weld inspection
Coverage: 1,300 linear feet / 1.54M A-Scans
Inspection time: 7 (12-hour) shifts
Manpower: Five operators, 2 robots
Result: Used RUG instead of conventional AUT; achieved a 70% reduction in man hours.
In summary, advances in ultrasonic probes, robots and processing are continually improving the production rate of AUT inspections. These result in faster, more complete, and more data-rich inspections. With Gecko Robotics full-complement of AUT systems, we will work with your team to ensure the right dose of technologies are applied to achieve your inspection outcomes, balancing time, coverage and data quality.