Welding Inspection Services

 

Non-Destructive Testing NDT

1. 1.      Concept

Non-Destructive Testing (NDT) or non-destructive evaluation, non-destructive inspection-NDI), or defect detection is the use of physical methods to find out defects in or on the surface of the object without influences its usability.

Non-destructive testing (NDT) is used to detect defects such as cracks, porosity, slag, layers splitting, lack of fusion and incomplete penetration of welds, metal abrasion tests, layers splitting of composite, material hardness test, concrete moisture test, material thickness measurement, size determination and reinforcement positioning in concrete….

1. 2.      Non-Destructive Testing (NDT)

NDT should be used in all stages of production and used for: from the selection of materials, quality control of the semi-products in different technological phases to the evaluation of quality finished product before shipment. Non-destructive testing is also used to detect and evaluate the appearance and development of defects in building products and structures during use.

Non-destructive testing method: NDT service helps customers to evaluate, check the technical status of metal, welding structures from the manufacturing process as well as during use. Non-destructive testing (NDT) consists of a number of different methods, divided into two main groups according to their ability to detect defects:

No	Detects inside of objects (and surfaces)	Detects on surface (and near surface) of objects
1	Radiography Testing (RT)	Liquid Penetrant Testing (PT)
2	Ultrasonic Testing (UT)	Magnetic Powder Testing (MT)
3		Eddy Current Testing (ET)

 

Ultrasonic Testing (UT):

Use an ultrasonic beam to infiltrate the metal and record the ultrasonic rays reflected from the metal surface as well as from defects within the metal. Based on the analysis of these reflections, it is possible to determine the metal thickness as well as the magnitude and location of defects within the metal.

Radiography Testing (RT) (X-Ray):

Using X-ray or gamma-ray bursts to take pictures of objects to be tested, radiographic imaging permits the recording of images within the subject's body due to the penetration of X-rays and gamma rays. If the ultrasound method requires data processing during the test, the method of radiographic imaging allows the film to be recorded at any time.

Liquid Penetrant Testing (PT)

To detect cracks on metal surfaces, welds after machining, especially non-magnetic materials such as stainless steel. We spray a liquid that is highly penetrant and has a distinctive color (usually red) on the surface of the object to be inspected. If there are very small cracks on the surface, the liquid material will penetrate and settle in the cracks and then continue to spray on the surface to test another substance called "colorant" to make the substance has penetrated the cracks are prominent and we recognize the very small cracks that the naked eyes can not detect. However, to be able to apply this method, the surface of the tested objects must be very clean and dry so it is not suitable for surfaces that are stained or rough.

Magnetic Powder Testing (MT)

Magnetic powder testing (MT) is a method that is more reliable and sensitive, does not require that the test surface be too clean and smooth, as in penetrant testing, can not be used with non- magnetic materials  such as stainless steel, MT is applied in the periodical inspection of boilers and pressure vessels with high risk of cracking after a period of using, such as NH3 storage tank, autoclave lids, gas desiccants, steam boilers of thermal power plants, furnace tube surfaces of boilers etc. On the other hand, we also apply MT as an additional measure for welds, machining parts after heat treatment.

1. 3.      Advantages of non-destructive testing methods (NDT) compared to methods of destructive testing (DT).

No	NDT	DT
1	NDT will not affect the usability of the sample later.	The sample will not be reused
2	NDT can test 100% of the test items, and ensure 100% of the quality products are passed.	Only check items that are used for destruction
3	NDT only results indirectly (by comparison with standard samples).	Direct results with the samples
4	NDT can easily detect defects from the processing stages, which can eliminate the semi-products, cost savings, repair errors.	New finished products are tested, which takes time and costs.
5	Non-destructive testing is also widely used to assess the integrity of industrial products and constructions. Due to early detection of damage, timely replacement of the repair, so we save on repair costs, avoid the disaster would be happened.	Not applicable
6	NDT is also an important tool in the research and development of new materials, optimization of production processes, the process of welding through the test, the detection flaws of design, materials and products.