Field Inspections
Acoustic Emission (AE)

Acoustic Emission (AE) testing is a powerful method for inspecting and monitoring the behavior of equipment and materials performing under stress.

Materials "talk" when they are in trouble. Through AE testing, MISTRAS "listens" to the sounds of cracks growing, fibers breaking, and many other modes of active damage in stressed materials.

Small-scale damage is detectable long before failure, so AE can be used as a non-destructive testing (NDT) inspection technique to find defects during structural proof tests and plant operations before serious damage occurs.

AE inspection is distinct from other NDT inspection methods in a few ways. Most notably, rather than supplying energy to the asset in question and detecting the changes to determine the presence of defects, AE listens to the energy that occurs naturally when damages occur. This ensures that any active concerns to structural and operational health are detected.

MISTRAS’ provides AE inspection and monitoring services and equipment. Some common defects that MISTRAS’ AE inspection services and equipment are used to detect include:

• Active Corrosion
• Behavior of materials: metals, ceramics, composites, rocks, concrete, etc.
• Crack Propagation
• Creep
• Fatigue
• Fiber Delamination
• Fiber Fracture
• Stress Corrosion
• Yielding

Acoustic Emission (AE) Benefits

Because only active defects and deterioration produce AE, no time is wasted on inactive defects that do not threaten structural integrity, minimizing plant downtime and unnecessary repairs.

Other AE Inspection benefits include:

• Early detection of active damages
• Real-time asset monitoring
• Able to pinpoint defect location
• Inspections and monitoring performed while asset remains online

Acoustic Emission (AE) Inspection Applications

As the world leader in AE technology, MISTRAS has performed thousands of field tests to assess structural integrity and to enhance safety in a wide range of structures from fiberglass tanks to bucket trucks, from bridges and aircraft to high-pressure gas cylinders.

For process monitoring, some of the most common AE applications include leak detection, particle impacts, electrical discharges, and a variety of friction-type processes. MISTRAS VPAC II inspection system is an industry-leading tool to detect and quantify through-valve leaks in process facilities. Other areas of interest include higher-frequency machinery health monitoring and predictive diagnosis. 

At the frequencies we use, the distance between the AE source and the sensor could be as little as a few inches or as much as hundreds of feet. In monitoring applications, MISTRAS’ AE subject matter experts work directly with our clients to determine optimal sensor positions to ensure damages are detected as early as possible.

Some typical applications of the Acoustic Emission principle in testing assets and materials include:

During Manufacturing Processes

• Cool-down testing
• Deforming processes – rolling, forging, extruding
• Defects such as pores, quenching cracks, inclusions, etc.
• Fabrication
• Material processing
• Phase transformation in metals and alloys (martensitic transformation)
• Through-valve leak detection of water and gases
• Weld monitoring for process control

Acoustic Emission (AE) Monitoring

• Continuous structural health monitoring (SHM) - bridges, metallic structures, mines, etc.
• Periodic testing - pressure vessels, pipelines, bridges, cables, storage tanks
• Stator vane cracking
• Transformer reliability monitoring
• Tube leak monitoring

Other AE Inspection & Monitoring Applications

• Aircraft and aerospace - fatigue cracks, corrosion, composite structures, etc.
• Electronics - loose particles in electronic components, bonding, substrate cracking
• Petrochemical and chemical plants - storage tanks, reactor vessels, offshore platforms, drill pipe, pipelines, valves, hydro-treaters
• Power generation and T&D facilities - nuclear reactor vessels, piping, steam generators, ceramic insulators, transformers, aerial devices