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History of Automated Ultrasonic Testing

Abstract :Automated Ultrasonic Testing (AUT), as defined in this paper, is the process of acquiring a digitized signal from amoving probe. AUT has been used for industrial inspection since the 1980s. Since that time the technology has

advanced significantly, and today there are many elaborate systems that capture, process and display data for avariety of applications.

This paper will track the advancement of AUT through the last two decades. It begins with the old AUT systemsthat ran on 8086 CPU technology, used 5.25 floppy drives as the primary boot and storage media, and required alarge truck to be transported. It advances through the multi channel and downsizing phases of the bulky old

systems and looks at many innovative ideas on analyzing and displaying the enormous amounts of data. It endswith phased array technology running on notebook systems with 32 channels, a 100Mhz A/D rate and a vector B-scan sweep display.

An email survey of todays AUT manufacturers, users, vendors and researchers will be conducted; generalinformation regarding AUT history, vendors, capabilities and applications will be summarized and presented.


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History of Automated Ultrasonic Testing

Ken L. HeapsK2 Technologies

4109 Lynn Dr. #213Anchorage, AK 99508Tel: 907-333-1666

Em: [email protected]

Danny KeckBP Exploration, Alaska

CIC-Mechanical Integrity Specialist564-4413 (ph)564-4450 (fax)

Background

Automated Ultrasonic Testing (AUT), as defined in this paper, is the process of acquiring a digitized signal from amoving probe. An (AUT) system may be either semi automated or fully automated. In a semi automated systemprobe scanning is done manually. A computer is used to monitor position and to analyze and present the

ultrasonic data. In a fully automated system, the probe scanning is performed by an automated scanning systemunder the control of the computer. Today all AUT systems provide a C-scan display.

Displaying one sample point from each digitized signal in a grid produces a C-scan display. It is a plan view ofall the grid readings (digitized signals) acquired on a two dimensional grid by a moving probe usually mounted on

a mechanized scanning device. The computer generally displays each grid point as a color related to either theTime of Flight (thickness) or Amplitude value of the digitized signal. A corrosion-monitoring scan performed at a.050 by .050 grid pattern accounts for 400 readings per square inch, or 57,600 per square foot. That translatesinto an enormous amount of data that without the support of current high-speed computers would be virtually

impossible to record and analyze!

The digitized signal is acquired by selecting a timeline and assigning digitized sample points to it (see Fig. 1).The number of points assigned is controlled by the The Analogue to Digital (A/D) Conversion Rate, and is usually

assigned in millions per second. Each point generally saves two pieces of information to the disk drive; theAmplitude and the Time. Once the digitized sample points are assigned they can re-position themselves to thecorrect amplitude value of the analogue signal at their respective points in time (see Fig. 2). The digitized signal

can be stored to disk and later retrieved and displayed as a dot-to-dot replica of the analogue signal.

Figure 1. Sample points assigned to time line Figure 2. Analogue signal with sample points

The entire analogue signal, known as RF data, may be digitized and stored, or one single sample point, known asPeak data, may be captured. Many of the first AUT systems captured only Peak data. Most of todays systemshave the processing and storage capabilities to digitize and store the entire analogue signal from multiple

transducers.


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History of Industrial ApplicationsThe claim to the first ultrasonic C-scan image was inCalifornia in 1956 (see Fig. 3). These Ultrasonic C-

Scan images are the VERY FIRST ever created byanyone anywhere. These early images wererecorded using storage tube technology originally

designed for radar applications. The image created onthe CRT was photographed to document the results ofunbonds within brazed honeycomb material and was

later used in the aviation industry. The system used ahigh frequency pulse echo immersion technique.(http://www.uxr.com/webpg9.htm, UXR Ultrasonic C-

Scan History)

In the 1980s the use of immersion tanks increased significantly with the development of automated scanning

systems. These bridge and carriage scanning systems enabled immersion tank systems to generate grid type C-scan images.

The earliest claims to development of contact based digital automated ultrasonic imaging technology in the USA

were both in California and within two years of each other. 1979 is the earliest known claim to development of theIntraspect Imaging technology that is now represented by Amdata NDE Products.

(http://www.amdatande.com/history.htm ) Shortly following is a 1981 claim to development of the first UltrasonicData Recording and Processing System that eventually grew into AIS Automated Inspection Systems.(http://www.ais4ndt.com/about.hml ) By 1985 an International firm called the Danish Welding Institute (now known

as FORCE Technologies) were well on their way to producing an Automated Ultrasonic Imaging system nowknow as the P-Scan. (http://www.force.dk/p-scan/ )

The nuclear industry, beginning with the discovery of service-induced intergranular stress corrosion cracking(IGSCC) in reactors in the early 1970s, has driven much of the development for AUT systems for all industrialapplications. Automated scanning systems allow AUT operators to be outside hazardous (radioactive) areas

while gathering ultrasonic data. The Electric Power Research Institute (EPRI) has funded a vast amount ofrelated research. In the mid 1980s EPRI qualified AUT operators in the detection and sizing of cracking inaustenitic materials. Since the mid 90s they have qualified AUT operators to the Performance Demonstration

Initiative (PDI) in over 50 materials and product forms used in the nuclear industry. Today an AUT operator mayhave over twenty different PDI certifications.

In 1988 AUT served as a tool to augment recertification of pressure vessels on the oilfields of Alaskas NorthSlope

2. External AUT examinations of in-service process vessels provided a cost effective means to ensure safe

operation and vessel integrity until a plant shutdown and internal visual testing could be performed at a later date.

AUT examinations continue still today to provide valuable data for the Fitness for Service evaluations of pressurevessels and tanks across the North Slope.

AUT Inspection of floor plates in Above Ground StorageTanks was introduced at the 1990 ASNT SpringConference in Seattle (Macroscan Inc). This technology

was developed to perform high-speed inspection over

large areas of tank floor plates for soil side corrosion. Thescanner was semi automated and multiplexed fifteen dual

element transducers on independent suspension andwater supply systems (see Fig. 4). The prototype wasqualified, but later outbid by a then little known technology

called Magnetic Flux Exclusion. Figure 4. 15-channel tank floor scanner, 1990

Figure 3. First C-scan images, 1956


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In the mid 1990s AUT corrosion monitoring was introduced on cross-country flow lines on Alaskas North Slope todetect and quantify the increased corrosion and erosion rates caused by new extraction techniques, which used a

mixture of seawater and gas to artificially pressurize the reservoirs. Part of the aggressive preventivemaintenance program included high resolution AUT corrosion monitoring. These scans were performed at a.050 grid pattern, covered two square feet and were monitored on a monthly frequency. Third party software was

developed to manage the enormous numbers of thickness readings being acquired and compared. It displayedthe original C-scan on the same page as the current and allowed the operator to select specific areas of corrosionwithin a C-scan for monitoring purposes. Algorithms were hard coded in the program, filtered the thousands of

thickness readings and replaced nonrelevant readings (noise spikes) with an average of adjacent readings3

.Neural networking and filtering software has taken advantage of the digitized signal. Ultrasonic waveforms from agood reflector can be stored and compared to ultrasonic signals acquired during scanning. If the acquired signal

exhibits different characteristics from the good signal it can be further evaluated by then comparing it to a libraryof known flaw signals. Development of deconvolution and wiener filters has allowed the segregation of one backwall echo into an echo from a steel/paint interface followed by the echo from the paint/air interface. This

technology targeted in-service coating integrity examinations in the petrochemical industry and was demonstratedat Alaska ASNT Section meetings in the early 1990s.

Present and Future State of AUTTodays AUT technology is very diverse in its applications. The most recent and recognized advancement is inphased array technology. Many small elements are housed in a single transducer and pulsed in phase. Software

utilizes beam profiles from all elements to direct or steer the beam. This creates situations where the first pulse

can be displayed as a 45o

angle and the next pulse at a 46o

angle and so on and so forth without ever changingor stopping the automated scanner. It is likely that C-scan displays will be replaced by 2 and 4 dimensional

sonograms in the not to distant future, even on manual flaw detectors.

Odds and Ends

The picture shown in Fig. 5 is titled Dotmatrix Landscape. It is apicture of a field generated C-scan of non-relevant indicationsacquired during a troubleshooting session. It has been reproduced

and has sold over six copies J (photo provided by M. Engblom).

An email survey of todays AUT manufacturers, users, vendors and

researchers is being conducted; general information regarding AUThistory, vendors, capabilities and applications will be summarized

and presented at the ASNT Fall 2004 Conference.

The American Petroleum Institutes Qualified Ultrasonic Testing

Examiner (QUTE) certification is currently considering qualification ofAUT operators.

References:

1. Mike Engblom, Consideration for AUT Inspection of In-service Pressure Vessels in the Petrochemical Industry,

Material Evaluation, December 19892. K. Heaps / J. Degner, Enhanced Corrosion Monitoring Techniques, ASNT ICPIIT IV Topical Conference, June

1995

Figure 5. Dotmatrix Landscape, 1989

history of automated ultrasonic testing01

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