Wednesday, January 27, 2010

Functional methods

As we saw in the beginning, 2nd Section of technical diagnostics is about functional methods. They consist of:

• Evaluation of long term and short term statistical data such as, the temperature of the part/machine, Pressure of the hydraulic systems, fuel/air consumption etc… By analyzing such parameters, engineer can predict the economical use of the part/machine and prognosis future failures, so that it will be possible to remove it and put a new part/ or totally stop using the machine before a catastrophe.

• By analyzing the physical and chemical parameters such as the spectral analysis of oil in order to detect foreign particles (for example, small particles of metals can be found in oil system when a ball bearing is destroyed, and that can lead to a failure of the whole machine)

• Vibration diagnostics: where engineer analyses the vibration of machine and evaluate faults and trends. An experienced engineer watches the frequency spectrum of the vibration without even touching the machine, say where exactly problem is, and propose options to cure that defect.

Figure: An NDT engineer preparing instrumentation for a vibration analysis of a gas turbine engine

Wednesday, January 20, 2010

NDT methods

First of all let's have a brief look at some of the most common NDT/NDE methods,

•Visual inspection: Visual examiners follow procedures that range from simply looking at a part to see if surface imperfections are visible. He can use the help of a magnifying glass or computer controlled camera. It is the most basic method of all.

•Liquid penetrant Testing: Engineer evaluates defects on the material surface with help of liquids or sprays.

•Eddy Current Testing: Engineer uses equipment with electromagnetic induction to detect flaws in or on conductive materials.
•Acoustics methods (mainly ultrasonic, Acoustic emission, Impedance etc…): Engineer uses different forms of acoustic waves (such as sound, ultrasound and infrasound) in order to evaluate defects. You probably have heard of the Ultrasonic sonogram they use in medicine to see the gender of a baby before birth. It certainly is another use of NDT.
Figure: Ultrasonic Scanning of a T beam

•Magnetic particle crack detection: Engineer evaluates defects of ferromagnetic materials by applying a magnetic field and magnetic particles which are usually mixed with a liquid.

•X-Ray: Use electromagnetic radiation to detect defects as same as in Medicine. Every one of us has seen an X-Ray image. This is one of the most trusted ways of controlling an object.

•Thermography: Engineer uses a camera containing large numbers of sensors sensitive to infrared radiation.

Sunday, January 10, 2010

What is "Technical Diagnostics"?

Diagnostics! Well, yes, we all heard this word very many times in the medicine. There, diagnostics means, identification of the nature of an illness or other problem by examination of the symptoms.
As same as Buddha tried to find reason for sadness before cure, doctors try to find reason for illness before cure, Engineers do test and evaluate before thinking a cure for those mechanical objects. It is one of the most important parts of engineering which is closely linked to aerospace engineering, civil engineering, electrical engineering, material science and engineering, mechanical engineering, nuclear engineering, petroleum engineering, physics etc… It’s often used in both constructional and service sides.