NON DESTRUCTIVE TEST

ABSTRACT

The objective of this practical work is to find the discontinuity, cracks or defect present in the welded joint, using a method that does not involves destruction of the sample itself. The kind of test is call the NON-DESTRUCTIVE TEST.

Non-destructive testing are test carry out on material to check their quality control level, in this practical test we will be using liquid penetrant method in determining the defect or capillary in the surface of the material of choice.

Liquid penetrant testing is a widely used non-destructive testing (NDT) method for detecting surface defects on equipment or installations of various kinds. The method consists in applying a liquid capable of penetrating surface discontinuities onto the surface of interest, wiping off any excess penetrant and then applying a medium (developer) capable of absorbing any penetrant entrapped in the defects, thus magnifying the indication and making it visible

INTRODUCTION

There are several means of analyzing the materials properties among which are the stress-strain test, non-destructive test and other mechanical testing. However, Non destructive testing (NDT) is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage. The terms non destructive examination (NDE), non destructive inspection (NDI), and non destructive evaluation (NDE) are also commonly used to describe this technology. 

Liquid penetrant inspection reveals discontinuities that are open to the surface of solid and nonporous material. Indication of a wide spectrum of flaws can be found regardless of configuration of work piece and regardless of flaws orientation. Liquid penetrant look into any kinds of minute surface opening by capillary action. Because of this, the process is well suited for the detection all kinds of surface crack, laps, porosity and shrinkage area lamination and other discontinuity. It is extensively used for the inspection of wrought and cast product of both ferrous and nonferrous metal, powder metallurgy, ceramics, glass and plastic object.

In practice, the liquid process penetrant is always simple to utilize and control. The equipment used in liquid penetrant inspection can vary from an arrangement of simple tank containing penetrant, emulsifier, and developer to sophisticated computer-control automated processing and inspection system. Establishing procedure and standard for the inspection of specific part or product is critical for optimum result.

EXPERIMENTAL PROCEDURE

Below are the main steps of Liquid Penetrant Inspection:

1. Pre-cleaning: The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment. 

2. Application of Penetrant: The penetrant is then applied to the surface of the item being tested. The penetrant is usually a brilliant coloured mobile fluid with high wetting capability. The penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3. Removal of the Excess Penetrant Liquid: In the third step, we removes penetrant liquid from the surface by rag or cloth and uses back and forth rubbing to clean the surface. No red color should be visible after cleaning. Then we take a clean rag and sprays some cleaner on a cloth and then cleans the surface one more time. This is be done two or three times to remove all penetrant liquid from the surface.  by the capillary action; the penetrant liquid still is in the cracks or hot tear or any other imperfection. It didn’t come out by cleaning as described.

4. Application of Developer: In the fourth step, we  take the developer (LD7 Developer) spray can and agitates it and then sprays to the surface. Then he waits for 10 minutes dwell time. In this time, the defect will be visible, the developer material uses reverse capillary action and bleeds out the red penetrant, and all crack in the surface are seen appear in a red line within the white color covered by developer material.

5. Post-clean part: The part needs to be cleaned to remove all developer after the material has been evaluated

                                                                       

Fig 1: Pre-cleaning                                                               Fig 2: application of penetrant 

                                                                                               

                                                           

Fig 3: removal of excess penetrant                                      Fig 4: application of developer

                                                                                   

Fig 5: post cleaning                                                              Fig 6:  Red Penetrant

                                                                                               

Fig 7: Developer                                                             Fig 8: Penetrant remover

RESULTS AND DISCUSSION

After the application of the penetrant, at a given time of about 5 to 15 minutes, the penetrant bleeds out to indicate the areas with discontinuities.

The lengths of indications were measured and the sample given has a negligible indication size. Hence the defect observed is acceptable for quality control.

CONCLUSION

It can be concluded that liquid penetrant testing proves to be advantageous as its cost is low and speed of testing is high compared to other methods of testing. It should be noted that it detects only surface flaws, skin irritation, and the inspection is on a smooth clean surface where excess penetrant can be removed prior to being developed.

It can be seen from the result of the experiment that NDT method of testing is easy to check whether a material is good enough to go out for marketing. This also exhibit easy inspection of parts with complex shape with few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and conductive and nonconductive can all be inspected)