Adaptive Data Compression of Ultrasound Data for Long-term Data Acquisition and Trend Evaluation

Data compression technologies such as MP3 are extensively used for audio technologies.
There are two objectives: to maintain the quality of the original sound and two compress the data as much as possible. The degree of compression depends strongly from the signal character. The information of pure harmonic signals can be much better compressed than by considering noisy signals.
The ultrasound produced by processes in industry is used for maintenance purposes since some decades. On the one hand there are many signals with noisy character. Examples are leakage noise, jet noise, the noise of friction in bearings and gears. On the other hand there are signals with dominantly repeating impulses such as bearing faults (cracks or spalled areas) or arcing during electrical discharge. For both types of data different compressing rates has to be found.
Traditionally, ultrasound data for maintenance are evaluated by means of narrow band techniques such as heterodyning the ultrasound signal in the audible range, thereby a data reduction can be achieved.
In order to avoid the loss of real physical information, an ultrasound broadband technology has been introduced in order to consider the complete frequency range leading to a considerably increased data rate. Long-term recordings of service data would generate a huge amount of data on short time scales. Furthermore, the broadband technologies requires new approaches to make the signal audible. A vocoder technique has been modified in this contribution in order to compress the ultrasound data in real-time to a bandwidth which is compatible to the listening capabilities of testing persons. The spectra of compressed data can be used for the interpretation of measuring data. The degree of loss with respect to the information content has been estimated in comparison to the original uncompressed signal. Furthermore, ultrasound data – original and the compressed audible data – has been taken by applying pattern recognition techniques based on Cellular Neural Networks which will be exemplified by means of maintenance related data.

Peter Holstein, Andreas Tharandt, Christian Probst
(SONOTEC Ultraschallsensorik Halle GmbH)

Ronald Tetzlaff, Steffen Seitz, Jens Müller
(Institute of Circuits and Systems, TU Dresden

Leakage detection in hydraulic and pneumatic systems through infrared thermography and CO2 as tracer gas

Every aircraft is plenty of fluid systems, both hydraulic and pneumatic. These systems are necessary for tasks such as fuel distribution and storage, mechanical actuators and carrying air to cabin interior between others. Manufacturing and assembly of these systems require the performance of leak testing for quality assurance. Traditionally, leakage detection testing is performed through system pressure decay monitoring once the system is filled with an inert gas or working fluid. If a pressure decrease is detected, leakages must be located usually by the application of soapy liquid in each junction point of system, which is a time-consuming task.
In this work, new advances in leakage detection are presented by active infrared thermography and using carbon dioxide (CO2) as tracer gas. The application of post-processing algorithms, developed within this work, allows the automatic detection of the leakages, as well as a qualitative approach for its sizing. These algorithms have been tested on different scenarios that simulate aircraft systems in an industrial environment.

Acoustic signals for fuel tank leak detection

Plastic and composite fuel tanks are widely used in the automotive industry. Quality control systems normally require a non-destructive testing method to ensure they are leak-free during the production stage in the factory before delivery to market. In this paper an acoustic method to inspect the tanks non-destructively and efficiently is proposed. To initiate possible acoustic signals due to leaks, a compressor is connected to the tank which is then sealed and immersed in water. Air is pumped into the tank at a pressure of 1.3bar. If there is a leak, the pressurised air will squeeze out through the leak and bubbles will appear in the water. Four hydrophones are placed in the water surrounding the tank to detect the acoustic signal generated by the bubbles, revealing the presence of leaks in the tanks. The technique is proposed for application in the factory environment where environmental noise may be very high. The bubble signal is found to be very weak and immersed in the noise floor. To improve the signal to noise ratio, a band-pass filter is used where the signal is band-pass filtered around 4100Hz. A number of parameters, such as root-mean-square (rms), standard deviation, etc are extracted after filtering. These parameters are used for automatic inspection of fuel tanks.

Tool design and construction for leak testing of gas electrofusion polyethylene coupler by internal injection system

Nowadays, in many gas projects polyethylene pipes are great replacement for steel pipes due to the ease of implantation. However, applicable and economical nondestructive tests for control the electofusion welding processes in polyethylene pipes is one of the essential aspect to consider. In this paper, we introduce an efficient equipment for test of electrofusion polyethylene coupler in the implementation condition of gas network projects to detect the leakage by internal pressure method. Results of laboratory experiment on artificial defect samples and site work procedure are described and computer simulation by finite element and CFD software are also shown.
The history of high density polyethylene pipes (HDPE) utilization came back to 1950 in American gas industry. In this regards, inspection, maintenance and repair of these pipes are vital for constructors. Preparation of technical inspection processes to prevent risk and cost of environmental pollution and gas waste due to gas leakage are the first and chief aspects of such reconstruction. To have an integrated gas network, the inspection is required during pipes production, fitting, installation level and even after gas injection in operation stage. These examinations have significant roles in the safety and proper function of gas distribution systems. Meantime destructive tests due to their characteristics and damaging nature are not affordable and could not be used for all couplers in gas pipe connections. Regarding to effect of instrument efficiency on the integrity of electrofusion welds, nondestructive test that could be perform on all electrofusion couplers is required. Using ultrasonic and thermography methods in the previous studies which conducted to assess electrofusion welds were acceptable in preliminary results on laboratory scale. However, because of the high equipment cost, operator skill requirements and the non- applicability of these tests, using these methods have been stopped in gas projects.

Research on the accumulation leak detection method of helium mass spectrometry based on low vacuum

Nowadays, the non-vacuum accumulation leak detection method and vacuum leak detection method are widely used for testing the total leakage rate of spacecrafts, such as the hermetic cabin. The vacuum leak detection method is often used for Russian spacecrafts. But the above two kinds of method are both used for American spacecrafts. Generally speaking, the non-vacuum accumulation leak detection method is used for spacecrafts which have low leakage rate demand, such as satellites and Node 1 of International Space Station. While the vacuum leak detection method is used for these spacecrafts which have high leakage rate demand, such as Airlock Module and Laboratory Module of ISS. In China, the non-vacuum accumulation leak detection method is often used in order to save the leak detection cost. As we all know, the method of non-vacuum accumulation leak detection has advantages of low construction cost, simple operation, and so on. But its leak detection sensitivity is low, and test period is long, generally more than 24 hours. While the method of vacuum leak detection has advantages of high leak detection sensitivity, short test period, but its construction cost is high, and operation is relatively complicated. Therefore, it is necessary to study a kind of accumulation leak detection method of helium mass spectrometry based on low vacuum, in order to improve the leak detection sensitivity while reduce the construction cost as much as possible. In this paper, the feasibility of accumulation leak detection method of helium mass spectrometry based on low vacuum was studied from theoretical aspect firstly. Secondly, the optimum vacuum degree of leak detection, repeatability of experiment results and leak detection sensitivity had been tested. The results show that the accumulation leak detection method of helium mass spectrometry based on low vacuum has a higher leak detection sensitivity and good repeatability.

Design and experiment of the noise-resistant and sound focusing accessory of ultrasonic leak detector for spacecraft on orbit

Ultrasonic signal produced by the gas leak is so week that it is difficult to detect, and easily interfered. So developing the noise-resistant and sound focusing accessory for the ultrasonic leak detector is very important for improving ultrasonic leak detector sensitivity and noise-resistant capability. Based on the theory analysis of the leak ultrasonic signal reverberation and anacampsis, the 5A06 aluminium alloy and nylon were selected as the material of noise-resistant and sound focusing accessory by calculation and compare. Then the circular cone trumpet structure was design as the accessory main structure, and the nylon expansion port, nylon shrinking port and aluminium alloy expansion port structures were manufactured. The different structure characters were shown by the contrasting experiment. The results indicate that the nylon expansion circular cone trumpet structure has better sound focusing performance and it can improve the testing sound pressure amplitude 10 times bigger than the detector without the accessory. And the aluminium alloy expansion circular cone trumpet structure has better noise-resistant ability than others. These conclusions are very important for the spacecraft leak detection and it can provide some references for the design of the noise-resistant and sound focusing structure.

The Leak Detector for Manned Spacecraft with Ultrasonic Sensor

In this paper, the mechanism of air gas leaking out from spacecraft into vacuum producing sound, sound transmitting in cabin air and sound signal detecting will be analyzed. An equation of the sound power, leak size and air gas pressure in the spacecraft is got, and the relationship between leak sound pressure and receiving direction and distance has been studied. The center frequency in millimeter diameter leak is more than 20 kHz. The simulation equipment of air leaking out from spacecraft to space has been set up and the experiment of different size leak and testing distance and direction has been done. The sound pressure is in direct proportion to the cosine of the angle of leak to sensor. The portable ultrasonic leak detector has been developed, whose minimal leak rate is 10-1Pam3s-1. The leak detector consists of the sensor, mainframe, structure, preamplifier, DSP, display and key-press circuit, power supply and batteries. The accuracy of distance for locating the leaks is less than 20 mm, the mass is 1.2kg, and the electric power is less than 2.2W.

Newest Requirements for LED UV Lamps used in Magnetic Particle and Penetrant Testing, their Background and Practical Relevance

The LED-Technology is strongly substituting the conventional bulb based UV source (Mercury-Vapor, Xenon and Metal-Halide) in the fluorescent NDT methods in all industries.

The NDT industry is getting more and more aware that the quality and characteristics of the LED UV lamps is essential to ensure at least the quality and performance of the inspection process as when using a 100W Mercury vapor lamp. There are also made big efforts by the Aerospace industry to explain the need and the technical background to the users in parts manufacturing.

A new and more restrictive Aerospace manufacturer standard has been released in the Aerospace industry that ensures adequate quality of the LED UV sources for mag and pen. It also requires that the user takes care about the proper function during the usage of LED UV sources on a regular basis.

The presentation will give an overview of the requirements and characteristics that came up, will explain the technical need of those to ensure a secure and reliable inspection process and will explain the new parametrization that has been established to describe easy and understandable the characteristics of LED UV sources for easy selection and good practical use of LED UV sources.

POD and other important parameters influencing risk reduction by in-service inspection

Nuclear piping and components are susceptible for degradation by different mechanisms, e.g. stress corrosion cracking (SCC) and fatigue which may cause leakage or failure. In order to justify continued safe operation of nuclear power plants (NPP) an effective in-service inspection (ISI) is required. Due to a great number of welds and other locations with potential degradation, it is also essential to have a reliable methodology for inspection program planning. For addressing this challenge, different methods for risk-informed planning of in-service inspection (RI-ISI) are under development.
ISI is typically accompanied by non-destructive testing (NDT) for monitoring the extent of potential degradation and/or for assuring the absence of unexpected degradation. It is commonly believed that a choice of suitable NDT method in combination with an appropriate inspection interval provides a significant contribution to lowering the probability for unexpected leakage and failure. There is on-going extensive development of advanced NDT methods that can offer a greater Probability of Detection (POD) and thereby allow for detection of smaller size flaws. Also, the simulation techniques for NDT testing are actively developed.
Development of probabilistic methods and structural reliability models (SRM) has allowed for quantitative assessment of leakage and rupture probabilities taking into account the actual piping dimensions, loads, material properties and damage growth under different degradation mechanisms. This paper presents some results based on probabilistic analyses with different SRM models. These analyses have demonstrated that POD and inspection interval, determining the ISI efficiency, are not the only parameters that govern the reduction of risk for leakage/rupture. The risk reduction also vary depending on the base and weld materials used in a pipe, loads, weld residual stresses (WRS), environment, etc.


Heat exchangers are critical components in many chemical processing plants. Currently, inspection of the tube-to-tube sheet welds in the heat exchangers is normally limited to various methods for surface inspection, while defects inside the welds remain undiscovered, which could compromise safety and could lead to failure and production stops.

FORCE Technology has developed an automated ultrasonic solution, which is capable of finding small embedded defects in the welds, is time efficient and provides detailed documentation of the inspected welds. This paper describes our solution and how we apply it. Inspection of tube-to-tube sheet welds are traditionally limited to visual, liquid penetrant and hydrogen leak testing. All these techniques only provide information about the surface condition of the inspected welds, such as surface cracks or other surface breaking discontinuities. The mentioned inspection techniques are not able to detect any internal weld defects such as lack of fusion or cluster porosity. Internal defects are crucial for weld integrity. FORCE Technology has developed an alternative technique based on standard ultrasonic examination principles, which is capable of detecting them.. The technique offers a lot of benefits for our customers and significantly increases the level of confidence they have in the examined heat exchangers. The technique is very fast, thus minimising downtime and provides full scanning of the welded volume. Therefore, defects such as lack of fusion, inclusions or clustered porosity are easily detectable. The technique makes it possible to save detailed data for each particular weld, including precise dimensioning and positioning of detected defects inside the weld. The data can either be used for on-site reporting or, if needed, at a later stage. The equipment is easily transportable and does not require any safety preparations prior to testing, except for those required by the customer