Technical Diagnostics and NDT

Figure: Boeing 777 aircraft Commercial aircrafts are frequently inspected visually. There is a primary inspection called "walk around check" both in the line and the base, transit checks, daily check, weekly check, A check, B check etc… Line is the more about the quick checks while aircraft is in the park or in between flights. Base is mostly the hanger, where hard checks, repairs take place. A qualified engineer walk around the aircraft and inspect structural items visually. Engine is also checked during the walk around checks. There engineer watches for oil leaks, structural damages in the engine, inlet of the engine for composite parts fixtures to the structure, fan/first stages of the compressor, last stages of the turbine for deterioration or damages , or any unusual changes of the engine. In this example shows how, engineer/Pilot carry on a walk around inspection of a Boeing 777 aircraft. Figure: Walk around inspection of a Boeing 777 1. Left Mid Fuselage...

Gas turbine engines are widely used in different fields for generate energy. They are commonly used in aircrafts. If you watch a huge passenger aircraft, you can see the gas turbine engines are either hanging on the wing section or tail section. Those power plants gives enough energy to generate thrust which finally result the aircraft fly. Figure: An Airbus A340's 4 engines are situated on the wing, 2 in each side. Figure: A Tupolev 154 Aircraft where engines situated on the empennage  How does a gas turbine engine work? There are several sections inside of an engine. First one is the air intake and fan which direct the air to inside of the engine, then the compressor, which compress the air to a very high pressure while reducing its speed. Then air meets the combustion chamber, where kerosene (fuel) is spread as small particles and burned in a high temperature.  

Visual Inspection is one of the most common NDT methods used to evaluate the condition and provide a better quality of an item. Visual method is easily carried out, inexpensive and usually does not require special equipment. It entails reflected or transmitted light from a test object being imaged with a light-sensitive device, such as the human eye. Such a testing method requires proper vision, good lighting conditions and the knowledge of what exactly to look for.

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 ma...

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: ...

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.