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Pressure Vessel Inspection

COE - Acoustic Emission Testing Services Find Active Defects in a Broad Range of Vessels and Structures

As the world leader in Acoustic Emission (AE) technology, MISTRAS has performed thousands of field tests on pressure vessels, storage tanks, pipelines, valves, nuclear lift rigs, railroad tank cars, bridges, compressed gas cylinders, transformers, and much more. Our extensive database for interpreting the significance of AE signals, as they relate to flaws and leaks, has led to the development of knowledge-based systems such as MONPAC™, GasPAC™, TankPAC™, ADTI™, TT™, as well as the European-driven VPAC™ and IPAC™, all internationally recognized names.

AE testing is a nondestructive method for evaluating the condition of numerous structures including:
  • Metal pressure vessels
  • FRP vessels and pipes
  • Above ground storage tanks
  • Transportation vehicles - (railroad tank cars, aerial man-lift devices, NGV cylinders)
  • Bridges
  • Compressed gas cylinders and tube trailers
  • Nuclear components (valves, lift beams, steam lines)
  • Petrochemical supply lines
  • Main steam and hot reheat lines in fossil fuel plants (high energy piping)
  • Transformers
  • Aerospace components and structures
  • Reactors and hot circuit piping in refineries
  • Internal valve leak detection and assessment

Many codes and standards exist for AE testing of vessels, from transportation gas cylinders and railroad tank cars, to 30,000 ton storage tanks. The method uses sensors which detect the high-frequency signals that result from structural defects when subjected to load. The signals may result from local overstress, crack growth, corrosion product, and leaks. Normally, AE inspection is carried out during a controlled increase in operating load, during cool down or controlled temperature change where thermal stresses are significant. Because only active defects and deterioration produce AE, no time is wasted on inactive defects that do not threaten structural integrity.

Conventionally, vessels are inspected prior to original hydrotest, but then not again until after an in-service period. This means that any defects which develop during the hydrotest of a new vessel may only be discovered after some period of service. This makes it difficult to determine whether they are manufacturing defects or service-induced defects. AE can eliminate this problem by monitoring the original hydrotest so that the vessel condition is known prior to putting it into service. AE monitoring of the hydrotest also provides a "fingerprint" for comparison with future AE tests.
Acoustic Emission testing is now approved in many countries for the re-qualification of compressed gas cylinders and is particularly cost-effective on large tube trailer cylinders. The method is used during normal filling, usually every five years.
The American Association of Railroads requires that all stub-sill railcars must undergo testing. This involves not only the vessels, but also the highly stressed areas of the chassis which are loaded during the test using a twist bar. The test detects cracking in the chassis or vessel and corrosion in insulated vessels without the need for costly insulation removal.
Acoustic Emission testing is the most effective method of evaluating the structural integrity of FRP tanks and pipes. The AE test procedures, originally developed by SPI/CARP, are now written into ASTM and ASME codes. Testing involves attaching sensors to monitor the highly stressed areas while filling or pressurizing. AE may result from matrix crazing, debonding or fiber failure in the material.
MONPAC™ is an "expert system" for evaluating the condition of metal pressure vessels based on the experience from over 2000 tests. Monsanto developed the procedures that are now widely used in the oil and chemical industries. The same test procedures have been adopted in ASME Section V, Article 12 for acceptance testing of new metal vessels. Benefits of this method are seen in the reduced inspection costs and reduced downtime resulting from improved information about plant condition. MONPAC™ is particularly effective on spheres, columns and for tank shell integrity but is also used on complete process systems. It gives a "color coding" for severity of emission, complete with associated recommendations. Testing is carried out by engineers and technicians trained and certified to meet our inhouse qualifications for AE, Level II inspection.
When an emission is detected by two or more sensors, it is possible to locate the source by using arrival times. 3D location is used on concrete structures and power transformers for locating partial discharge. For more information, please visit our Substation Reliability COE.
On certain types of thick-walled, high temperature vessels, the three-dimensional loading, resulting from cool down, may be sufficient to stimulate defects to emit AE. In this case monitoring the cool down provides information for scheduling further inspection and maintenance, resulting in considerable reduction of downtime.
Reactors with refractory linings present a specific challenge for re-qualification because the removal of the lining to allow internal inspection is costly and can result in subsequent reliability problems. AE procedures for testing these vessels are used on-line or during pneumatic testing.
The cost of removing a large storage tank from service, decontaminating and cleaning for floor inspection can exceed several hundred thousand dollars. Companies often do this on a scheduled basis irrespective of internal condition, meaning that maintenance money is inefficiently spent. Good tanks are cleaned and inspected, and tanks in poorcondition may leak before their inspection becomes due.

Using our TankPAC™ testing method to prioritize tank floor maintenance yields considerable economic and environmental benefits. The inspectors at MISTRAS have tested thousands of tanks with proprietary technology that is continuously improved and updated with user feedback. The test takes only one half day per tank, after isolating the tank at high product level for a short period.
Losses due to internal valve leakage into the flare system in refineries can cost many hundreds of thousands of dollars per annum at an individual site. MISTRAS uses VPAC™, a proprietary method for quantifying these leaks at individual valves so that appropriate maintenance decisions can be made.
Acoustic Emission (AE) can be cost-effective for evaluating the condition of pipework, especially on insulated and buried lines. Corrosion in carbon­steel lines, stress corrosion cracking on stainless steel lines and leaks in all metal pipe can be detected under the right test conditions.
Using AE testing, the integrity of a Coke Drum may be evaluated without taking the unit out of service. Such inspections are becoming a high priority for plant operations.
MISTRAS also inspects the structural integrity of lift rigs in nuclear power plants. The AE test is designed to detect subcritical flaw activity that might occur during the in-service loading of the lift rig. Because AE propagates to all parts of the structure, this test method is not limited to surface flaws. It does not require disassembly of the rig to gain access to hard-to-reach areas. Also, the AE test requires less access and generates less waste than other NDT methods. Waste disposal is minimized by focusing waste-generating inspections (e.g. PT) onto only those areas where AE has shown relatively high activity and intensity.
Pressurized underground piping can be tested for leaks using MISTRAS' special "Buried Pipe Test Methods." The ability to determine the location of the leak, within several feet, provides an expeditious path to remediation.
MISTRAS uses state-of-the-art AE testing equipment that is manufactured under ISO-9001 Certification. The Company's AE systems and sensors are the latest designs and are calibrated and maintained by MISTRAS' highly trained staff.
MISTRAS maintains a staff with several Level III personnel that develop and control test procedures. Level II field engineers and technicians operate under fully-documented procedures for standard tests, assuring you of quality services. We are proud of the Written Practice that we maintain and the inspectors that we certify. The MISTRAS Group Inc. has always maintained a quality assurance program that covers all aspects of its operations, from manufacturing to the testing of vessels and structures.
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