Non destructive testing (NDT) in haiphong vietnam

NON DESTRUCTIVE TESTING

Ultrasonic Testing  (UT) 

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more. To illustrate the general inspection principle, a typical pulse/echo inspection configuration as illustrated below will be used.

A typical UT inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface. The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen. In the applet below, the reflected signal strength is displayed versus the time from signal generation to when a echo was received. Signal travel time can be directly related to the distance that the signal traveled. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.

Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of ultrasonic inspection that are often cited include:

 + It is sensitive to both surface and subsurface discontinuities.

 + The depth of penetration for flaw detection or measurement is superior to other NDT methods.

 + Only single-sided access is needed when the pulse-echo technique is used.

 + It is highly accurate in determining reflector position and estimating size and shape.

 + Minimal part preparation is required.

 + Electronic equipment provides instantaneous results.

 + Detailed images can be produced with automated systems.

 + It has other uses, such as thickness measurement, in addition to flaw detection.

As with all NDT methods, ultrasonic inspection also has its limitations, which include:

 + Surface must be accessible to transmit ultrasound.

 + It normally requires a coupling medium to promote the transfer of sound energy into the test specimen.

 + Materials that are rough, irregular in shape, very small, exceptionally thin or not homogeneous are difficult to inspect.

 + Cast iron and other coarse grained materials are difficult to inspect due to low sound transmission and high signal noise.

 + Linear defects oriented parallel to the sound beam may go undetected.

 + Reference standards are required for both equipment calibration and the characterization of flaws.

Magnetic Particle Testing - (MT)

Magnetic particle inspection (MPI) is used for the detection of surface and near-surface flaws in ferromagnetic materials. A magnetic field is applied to the specimen, either locally or overall, using a permanent magnet, electromagnet, flexible cables or hand-held prods. If the material is sound, most of the magnetic flux is concentrated below the material's surface. However, if a flaw is present, such that it interacts with the magnetic field, the flux is distorted locally and 'leaks' from the surface of the specimen in the region of the flaw. Fine magnetic particles, applied to the surface of the specimen, are attracted to the area of flux leakage, creating a visible indication of the flaw. 

The materials commonly used for this purpose are black iron particles and red or yellow iron oxides. In some cases, the iron particles are coated with a fluorescent material enabling them to be viewed under a UV lamp in darkened conditions.

Penetration Testing - (PT)

          Much of the confusion surrounding penetration testing stems from the fact it is a relatively recent and rapidly evolving field. Additionally, many organisations will have their own internal terminology (one man's penetration test is another's vulnerability audit or technical risk assessment).

At its simplest, a penetration-test (actually, we prefer the term security assessment) is the process of actively evaluating your information security measures. Note the emphasis on 'active' assessment; the information systems will be tested to find any security issues, as opposed to a solely theoretical or paper-based audit.

The results of the assessment will then be documented in a report, which should be presented at a debriefing session, where questions can be answered and corrective strategies can be freely discussed.