Ultrasonic Inspection, (UT)

Ultrasonic inspection is a volumetric method of testing using high frequency sound waves to penetrate the test specimen. The equipment used converts the mechanical sound properties into electrical properties and presents the result on a screen in varying displays. Ultrasonic testing ranges from as simple as taking thickness measurements to highly specialized inspection methods such as Phased Array.

Phased Array Technology
A specialized method of detecting subsurface defects using either straight beam or shear wave technology. Phased Array induces multiple sound waves into the part which are pulsed independently. Whereas traditional ultrasonic testing uses an A-Scan presentation or time/base line, Phased Array results are displayed using advanced imagery and are instant/real-time. Phased Array is largely becoming accepted as a substitution for Radiography.

Angle Beam or Shear Wave Testing:
In this method ultrasonic waves are introduced into the test specimen at an angle to the specimen surface traditionally at 45°, 60°, and/or 70°. Shear wave testing is best suited for weld inspection to detect transverse defects such as cracking or lack of fusion.

Straight Beam or Compression Wave Testing:
Ultrasonic waves are induced into the test specimen at a zero degree angle or perpendicular to the test specimen surface. This application is best used for detection of planar defects or thickness testing.

Advantages:

• Can typically be conducted with just one technician

• The equipment is highly portable

• Volumetric inspection detecting both surface and subsurface defects

• Low cost in comparison to using Radiography

• Does not require evacuation of personnel as with Radiography

• Can be encoded for precise documenting

Disadvantages:

• Advanced training and experience is required

• Access to the test part surface is required and so insulation must be removed

• Equipment in some cases is expensive

Eddy Current and Remote Field Testing, (ET, RFT)

Eddy Current uses electromagnetic induction to detect flaws in conductive materials. A circular coil carrying alternating current is placed in proximity to the test specimen which generates a changing magnetic field interacting with test specimen and in turn generating eddy currents. Variations in the electrical conductivity or magnetic permeability of the test object, i.e. the presence of any flaws, will cause a change in eddy current and a corresponding change in the phase and amplitude of the measured current. This form of inspection is limited in terms of depth however can detect very small defects and is widely used for tubular and surface examinations.

Advantages:

• The equipment is highly portable and can be easily used in field applications.

• Can detect very small defects both in the form of cracking and corrosion. Changes in permeability can detect the loss of baffle plates in exchangers.

• Excellent application for inspection of tube bundles in exchangers and condensers.

• Defects in exchangers and condenser tube bundles can be detected on both the inside and outside surfaces.

• Requires minimal surface preparation.

• Can be used to detect changes in permeability for coating thickness measurements.

Disadvantages:

• The equipment can come at a high cost.

• Personnel require advanced training and experience.

• The depth of penetration is limited to the material’s conductivity.

Eddy Current Array

Eddy Current Array is a surface inspection technique to examine plate and welds for surface and subsurface cracking. Excellent application for detecting stress corrosion cracking in carbon or stainless steel vessels, tanks or piping. Not only does it enable measuring surface-breaking crack position and length, but also sizing cracks as deep as 7 mm (0.28 in). Allows simultaneously scanning the weld cap, toe area, and heat-affected zone for longitudinal and transverse cracks without surface preparation or paint removal. Semi-flexible ECA probes can adapt to a tank floor’s curvature and other geometric features, offering sufficient penetration to scan through thick aluminum/stainless steel, (over 0.250 in or 6.35 mm thick). So doing, the solution is capable of detecting and characterizing corrosion-related defects such as pitting and thinning affecting as little as 10 % of a plate’s thickness.

Advantages:

• High speed scanning capabilities and real-time results.

• Minimal surface preparation.

• Can detect and size defects up to 0.28” deep.

• Excellent application for detecting stress corrosion cracking in both carbon and stainless steels.

Disadvantages:

• The equipment can come at a high cost.

• Personnel require advanced training and experience.

• Must have access to the test piece surface.

Liquid Penetrant Inspection, (LPI)

Liquid Penetrant Testing is for detection of surface discontinuities in parts that range from the very small to as large as tanks or vessels and can be applied in the field or in-house. Field applications are very efficient as they are highly portable, require minimal training and are relatively inexpensive to perform. In-house applications can accommodate an entire production line with the use of large tanks in which to submerge test items.

Advantages:

• Field applications are highly portable

• The application is inexpensive

• Has high sensitivity

• Minimal training and experience hours are required

Disdvantages:

• Only discontinuities open to the surface can be detected

• Extensive cleaning may be required

• Temperature limitations. Temperature ranges are from 50°F to 125°F

Magnetic Particle Inspection, (MPI)

Magnetic Particle Testing is a method used for detection of surface and slightly sub-surface defects in carbon steels using magnetic fields introduced into the specimen. A magnetic field will always choose the shortest path of travel and in the case of flaws open to the surface that path is through and not around. This is call magnetic flux leakage and is the basis for the method of inspection. A medium which is typically iron particles either in dry form or carried in a fluid suspension, is dusted or sprayed onto the item being inspected and is attracted to the flux leakage presenting a defined defect pattern.

Advantages:

• Can be highly portable when used in field applications

• Is highly sensitive in fluorescent applications

• Dry powder form can be used at temperatures up to 700°F

• Is not limited by specimen size or configuration

• Can be used to process large volume of parts in laboratory environments

Disadvantages:

• Can only be used to detect flaws open to the surface or slightly subsurface

• Can only be used on ferrous materials

• Fluorescent applications require work to be done under black light conditions

• A power supply is required

Positive Material Identification, (PMI)

Positive Material Identification, (PMI) uses X-Ray fluorescence, (XRF) for analysis of a metallic alloy to establish composition by reading the quantities of its constituent elements by percentage. The method can applied to existing components to determine material properties or to verify alloy content of new materials.

Advantages:

• The equipment is highly portable

• Equipment costs are relatively inexpensive

• Minimal surface preparation is required

• Produces immediate results

Disadvantages:

• Component temperature can be a limiting factor

• Analyzers emit radiation and so some special training is required

Other Applications: