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Acoustic Emission Testing on Pressure Vessels and Machinery

Delivering real business benefits across key segments

Faster and more effective: acoustic emission testing

Technical malfunctions and failure caused by leakage, cracking, corrosion or defects pose serious risks for managers and operators of plants, pressure vessels and machines. Acoustic emission testing (AET) is a non-destructive test (NDT) method that reliably recognises impending problems and defects before they become serious.
Acoustic emission testing is not only ideal for localising cracks and leakage and for identifying corrosion and faults. It is also recommended for mandatory periodic technical inspections of pressure vessels and tanks in accordance with the German Regulation on Health and Safety in the Use of Work Equipment (BetrSichV), and in particular as a special test method replacing

  • visual examination within the scope of internal inspection,
  • hydrostatic strength testing by means of an AET-verified gas-pressure test.

Acoustic emission testing can generally be performed using the fluid stored in the tank. This has the advantage that pressure vessels or tanks need not be opened and drained prior to testing, so that AET is faster as well as more cost-effective and involves less organisational effort than conventional test methods.

Non-Destructive Testing (NDT) for Corrosion and Flaw Detection

Corrosion, cracks, and other such flaws in the material of your tubes, tanks, reservoirs, and containers grave potential threats to your assets. The maintenance and testing of these components thus becomes essential.

Non-destructive testing involves inspection, test, and/or evaluation of materials for detecting flaws. Components or assemblies can be checked for discontinuities or differences in characteristics without rendering the system or component unusable. With NDT methods like acoustic emission testing (AET), one can ensure the safety of their components. These tests ensure the quality, integrity, and reliability of in-service products in the manufacturing, construction, and fabrication industries. NDT procedures like acoustic emission inspection are used to ensure that the infrastructure used in the industry continues to serve its purpose while delivering consistent quality.

Acoustic emission testing – ideal for all types of equipment:

 

  • Simple Pressure Vessels (BetrSichV)

    Acoustic emission testing is ideal for simple pressure vessels, including:

    • Pneumatic systems
    • Hydraulic tanks and filling systems
    • LPG storage tanks
    • Oil separators
    • Filters

    AET offers the following advantages:

    • No contamination by water
    • No dismantling of components (e.g. removal of desiccant in the case of dryers)
    • Savings on consumables (e.g. no need to remove oil for testing)
    • No additional costs caused by disposal of test fluid (e.g. oily water)
    • No significant service operations
  • Complex Pressure Vessels (BetrSichV)

    Complex vessels are the other major type of pressure vessel. Complex pressure vessels can include various fittings and installations, geometries and diameters, many nozzles or an interstitial space, and are generally characterised by complex geometry.

    AET is also recommended for the periodic technical inspections required under the German BetrSichV.

    Examples:

    • Spherical pressure vessels for gas storage (including spherical accumulators)
    • Special pressure equipment, such as
      • Natural gas, LPG and H2 pressure vessels
      • Pressure equipment in hydraulic systems (bladder and piston accumulators and cylinders)
      • Steam-heated rotating cylinders (paper cylinders, dry cylinders)
      • Pressure equipment plus fittings and installations
    • Vessels such as sintering furnaces, autoclaves, curing ovens
    • Sterilisers for hospitals
    • Heat exchangers
    • Filter tanks
    • Pressure vessels in sub-stations
  • Flat-bottom tanks (WHG / AwSV)

    Corrosion testing of single-wall flat-bottom tanks

    The sensors are fastened to the tank’s outer wall in two rows. The sensor positions are defined before the test using the available drawing and must be safely accessible on site. The sensors are fastened to the bare metal surface.
    For the measurement process itself, the tank must be filled to a certain minimum level. The tank also needs to be taken out of service before measurement, i.e. no filling or draining processes may be performed. Any tank heating units or agitators must be switched off. If possible, all machines, pumps and devices in the direct vicinity of the tank should be switched off while measurement is performed.
    Once all preparations have been taken, measurement can be started. In addition to other criteria, the length of measurement also depends on the weather conditions. For example, measurement must be interrupted if rain starts, as even small droplets hitting the tank wall might cause sensors in the measurement chain to overload.
    Once measurements are completed the test equipment is removed from the tank, which is then reset to its baseline condition and returned to service. The measured data are then evaluated over the following days and documented in a report.

    Leak testing of flat-bottom tanks with interstitial space

    Flat-bottom tanks with interstitial space have a leak monitoring system. Detection of fluid in the interstitial space suggests leakage in the upper bottom, whereas collapse or dissipation of the existing vacuum without fluid ingress into the interstitial space indicates leakage in the lower tank bottom, which is not accessible for inspection. Given this, acoustic emission testing aims at localising leakage in the lower bottoms of flat-bottom tanks with interstitial space.
    For this type of application the sensors must be placed directly onto the upper bottom inside the tank. To do so, the tank must be taken out of operation, emptied and drained before the test.
    Measurement can be started as soon as all test preparations have been completed. In order to localise the leak, leakage must first be induced, for example by activating the available vacuum pump. The attempt to build up a vacuum state causes a flow at the point of leakage; in this case the external air is sucked inside, producing acoustic signals that can be localised using the AET method.
    Once measurement is completed, the test equipment is removed from the tank and measurement evaluated. The measurement results are presented in the report and any suspicious areas indicated.
    Generally, the test report is prepared according to the requirements of the DIN EN ISO/IEC 17025 standard; it outlines the general details of the tested equipment, the test results and the required actions.

  • Dangerous goods (ADR)

    Acoustic emission testing is also suitable for high-pressure tanks and tanks used in road carriage on trucks.

  • High pressure gas pipelines (DVGW)

    Pipelines are also used to transport pressurised natural gas, biogas, liquefied gas and hydrogen, particularly over longer distances. These pipelines are subject to mandatory testing and inspection, for which acoustic emission testing is ideal. The AET advantages outlined above also apply to this use case.

  • Advanced materials

    Increasing use is being made of advanced materials, which offer certain advantages but also involve new challenges. Composite pressure vessels for example, have the advantage of resistance to corrosion. Equipment made from these types of materials is likewise suitable for acoustic emission testing.

  • Structure health monitoring

    If a defect or damage has been found on your equipment but delivery of the replacement vessel will take a few months, the defect can be monitored with the help of acoustic emission testing to ensure any propagation of the defect will be detected immediately.

 

Acoustic Emission (AE) Inspection

The procedure for Acoustic Emission Testing (AET) is fairly simple. A set of three transducer sensors is installed on the outer surface of the material. They detect inconsistencies or flaws in the material by triangulating the emitted acoustic waves.
The actual procedure is such:

Attenuation survey:
Before the acoustic emission inspection, the sensors are carefully positioned on the material’s surface. This positioning is critical for the results. The positioning of sensors must avoid disturbances in the signal.

Sensor responses:
The responses collected by the sensors are now evaluated to derive inferences on flaws and defects in the material.

Report:
After the evaluation, the AET providers deliver a report to the client detailing areas of defects and any required follow up non-destructive testing.

Different Acoustic Emission Test Methods

The acoustic emission testing procedure factors in the type of defect one can expect in the component. There are two types of acoustic emission testing methods based on the expected type of defect and other conditions. For testing gearboxes or detecting leaks, the continuous testing method is used. For components that are likely to suffer from cracks, the transient testing method is used.

Transient acoustic emission testing method:
AE bursts that exceed a certain threshold are recorded in this method. The transducer captures the peaks, strength, and duration of the signal. This data is can now be used to ascertain the condition of the test material.

Continuous acoustic emission testing method:
The continuous acoustic emission testing method records the entire signal for a set duration. The data provided in the method is in the form of means and RMS values of the signal. For example, the signal can be recorded for 1/10th of a second, and with this data, experts in AET will be able to determine the existence and nature of faults in the component.

OUR AET SERVICES FOR YOU

  • Visual examination of pressure equipment within the scope of internal inspection
  • Hydrostatic strength testing by means of AET-verified gas-pressure test
  • Localisation of cracking and leakage
  • Identification of corrosion and defects
  • Organisation and coordination of acoustic emission testing
  • Documentation of results in compliance with legal requirements
  • Assistance in selecting possible test methods and special procedures

ACOUSTIC EMISSION TESTING – YOUR BENEFITS

  • No need to fill your equipment with water, no concerns over corrosion, contamination or static loads
  • No need to open the tank or vessel for testing
  • No need to drain operating fluid. Testing can generally be performed with the operating fluid in place
  • Enhanced equipment availability and safety
  • Early information about flaws such as cracking or corrosion
  • Integral monitoring of complex pressure vessels for incipient cracking and crack propagation
  • Tracking methods enable acoustic emission sources to be localised
  • Cost savings based on combinations with other NDT methods for targeted verification
  • Expert partner with long-standing experience

Watch the video to learn more about the advantages and possible applications of AET in pressure-vessel testing in accordance with the German BetrSichV. Is acoustic emission testing also a suitable option for your pressure vessel? Talk to us – we will be happy to advise you.

WHY CHOOSE TÜV SÜD?

TÜV SÜD provides acoustic emission testing AET in India for pressure equipment. NDT is the preferred choice to check materials susceptible to corrosion, faults, defects, and cracks. By monitoring sound waves emanating from materials, AET sensors and transducers map the consistency of the component. This report can then be used to implement safety and preventive measures in case of any dangers.

We provide acoustic emission NDT for a wide range of areas and pressure equipment:

Tubes
Tanks
Spherical reservoirs
Fibre-reinforced materials
Gas station tanks and containers
Gas and hydrogen reservoirs

Our service engineers come to you with time-tested expertise in NDT procedures. The immense field experience has made us an industry leader. With early detection of flaws in the material, we can implement measures to prevent damage. We ensure conformance to industry standards EN 15495:2007 and EN 14584:2005 with our acoustic emission testing services. TÜV SÜD’s acoustic emission NDT inspections are a reliable, time and cost-efficient choice for safeguarding equipment integrity.

 

Frequently Asked Questions

  • Is the difference between acoustic emission and ultrasonic testing in non-destructive testing?

    Ultrasonic Testing is a non-invasive testing method, and so is acoustic emission testing. The difference between the two is that AET relies on sound waves generated from the material itself. No external energy is supplied to the system. A very sensitive sensor picks up these emissions from active defects. UT is a volumetric Non-Destructive Testing (NDT) method that actively probes the material.

  • How many types of acoustic emissions are there?

    There are two types of acoustic emissions: Burst and continuous. Continuous emissions result in sustained signals and are used to detect ductile material flaws at early stages. Flaws like fractured non-metallic inclusions, broken corrosion products, crack jumps in ductile metals can be detected by burst emissions.

  • How is Acoustic Emission Testing by TÜV SÜD more efficient?

    With the acoustic emission testing NDT method, TÜV SÜD offers a range of AET services that make it very efficient:

    • Visual examination of pressure equipment within the scope of internal inspection
    • Hydrostatic strength testing by means of AET-verified gas-pressure test
    • Localisation of cracking and leakage
    • Identification of corrosion and defects
    • Organisation and coordination of acoustic emission testing
    • Documentation of results in compliance with legal requirements
    • Assistance in selecting possible test methods and special procedures

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