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)

CORROCTION of metals

ABSTRACT

In order to appreciate losses accruable to engineering structures from the interaction with various environments, the report was written to give the effects of aerial ammonia on metal corrosion.

This test was conducted using nine different samples under normal atmospheric conditions at three different ammonia concentrations (1.5moldm­­­-3, 1.0moldm­­­-3, and 0.5moldm­­­-3) on three types of metal (aluminum, copper and iron).

INTRODUCTION

Most metals used by man are subjected to attack by the environment they encounter.  The attack which progresses in many cases slowly is as a result of interaction between the metallic materials and their environments. This interaction is of vital importance in the performance of materials of construction.

A common interaction herein discussed is the corrosion of metallic materials.

Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal, and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.

Corrosion is defined as the destruction or deterioration of material because of reaction with its environment. Some insist there the definition should be restricted to metals but often the corrosion engineers must consider both metals and non-metals. Ceramics, rubber and other non-metallic materials, deterioration of paints and rubber by sunlight or chemicals, fluxing or lining of steel making furnace and attack of solid metal by another molten metal (Liquid metal Corrosion) are all considered to be corrosion. Corrosion can be fast or slow.   Corrosion of metal can be considered as extractive metallurgy. Rusting is a term reserved for steel and iron corrosion, although many other metals form their oxides when corrosion occurs. Practically all environments are corrosive to some degree. Air, moisture, fresh distilled, salt  and mine waters, rural or urban and industrial atmosphere, steam and other gases such as NH3, Cl2, H2S, SO2, fuel gases, inorganic acids, organic acids, solvents, petroleum oils cause corrosion environment. Inorganic materials are more corrosive than the organics. High temperature and pressure involve more severe corrosion conditions. Anodizing of aluminum is another beneficial corrosion process used to obtain better and uniform appearance in addition to a protective corrosion product on the surface.

EXPERIMENTAL PROCEDURE

1.      Standard pieces(iron, copper and aluminuim) of size 6cm by 3cm is  cut into 3 pices each, makeing a total of 9 samples.

2.      The specimens are grinded and polished to create a clean surface and prevent any form debris from interfering with the experiment.

3.      After grinding a hole is drilled into each sample to allow the sample to be suspended, to prevent the sample from resting on container which would interfere with the results.

4.      A hot condition/situation is perfectly avoided

5.      And the samples were partially immersed in the reagent solution.

6.      The samples were observed at first to recognized spots where corrosion is rapid and vigorous.

7.      After the recognitions, other samples were left for 48 hours.

8.      The masses of the metals were reweighted and recorded.

9.      The samples were then observed for the last time after 72 hours of immersion and the liquid solution was pour off into a watching-glass.

10. The liquid color was observed

11. The metal was then rinsed with water and corroded areas were inspected.

DATA AND RESULTS

1.5moldm­_­­^-3

	Initial weight(W0)	Weight after 48 hours(W2)	Weight after 72 hours (W3)
Aluminuim	4.105	4.105	4.099
Copper	18.816	16.792	14.758
Iron	12.610	11.603	11.591

1.0moldm­_­­^-3

	Initial weight(W0)	Weight after 48 hours	Weight after 72 hours
Aluminuim	3.150	3.133	3.121
Copper	13.856	13.829	13.812
Iron	11.052	11.050	11.040

0.5moldm­_­­^-3

	Initial weight(W0)	Weight after 48 hours	Weight after 72 hours
Aluminuim	4.570	4.560	4.545
Copper	14.033	13.987	13.920
Iron	11.072	11.024	11.015

DISCUSSION

Corrosion of copper, Aluminum, and steel in the form of small plate has been studied in different medium by weight loss method. Three different concentrations ( 0.1M, 0.2M, 0.05M) of NH₃  were used for different timings.

From the study the following conclusions have been arrived.

i)                   The rate of corrosion increases with increasing the concentration of the acid.

ii)                 The rate of corrosion increases with increase in time.

Corrosion rate on iron steel is the highest, followed by copper and finally by aluminum.

QUESTIONS AND ANSWERS

Why is it that iron hand-rails on the stairs rarely rust, while the under-supports of bridges do?

This question can answered by considering the kind of treatment to the iron has been subjected. As in the case of hand-rails, the iron used has been chemically treated with chromium which helps in prevent the iron from having direct contact with the oxides. However for the under-support in the bridges, the iron is used as composite, in which case oxides and other corrosion factors are made in contact with iron hence rust occurs.

Why is it that metal statues seem to shed a blue-green stain on their stone bases? What metal is used for such statues?

These blue-green strains are cause by the action of corrosion and the dissolution of the metal itself when subjected to acidic solution, water quality ( acidic water) and improper electrical grounding hasten corrosion.

Metal that exhibit this statues are copper, brass etc.

What is the white bloom that appears on the aluminum and on lead when exposed to the weather?

In actual reality, aluminum and lead doesn’t rust but when exposed to weathering the two corrode by a process called oxidation. During which a white bloom powders are formed ton their surface. The powders are the oxides of aluminum and lead respectively. The oxides appeared as coating to harden and protect the layer from corrosion.

Where does rusting first set in on corrugated galvanized iron or steel sheet, used for roofing? Why do you think it occurs there?

Corrosion first set in at the surface. This is because the metal sheet surface is exposed to the atmosphere and when it rains, the surface because moist since rain water could contain some element of acids and oxides like sulphate, nitrate and chlorides.

Methods of preventing rusting in iron or steel:

Galvanizing

COR-TEN or weathering

Alloying

Proper pre-designing

Bluing

Regular maintenance

FOZZ

Powder coating

Organic coating and etc.

 The most effective one has always been galvanizing with considerable regular maintenance.

CONCLUSION

With this result it is very clear that environment affect material a lot, as a Material Engineer corrosion is one of the area to monitor very well, the kind of environment to use a material and the kind of prevention to use in that kind of environment. Since corrosion cannot be 100% prevented but it can only be minimize.

A common way to minimized corrosion as reported herein is galvanizing anchored with regular maintenance.