Non-Destructive Testing Methods to Ascertain the Quality of the Entire Weld - Report Example

Non Destructive Testing 485713) Introduction Testing of welded joints form an important part of the Quality Control process in an Oil and Petroleum Refinery site. This is mainly due to the nature of liquid that is carried through these pipelines. Incorrect welding techniques and uncontrolled welding processes may hamper the quality of the welds which ultimately affect the functioning of the plant. This is because leakage of oil through weld seams poses serious risks in an oil installation. Fires may be caused due to this leakage. This affects both man and material wastage in a refinery plant. Also, incorrect welding of structural parts may also affect the entire integrity of the structure posing grave danger to life. It is due to these serious consequences that a number of methods of inspecting weld joints have been developed. It is however physically impossible to inspect each and every weld joint. Since the welding is done only by qualified welders who have been approved by client, it forms an additional backup for improving weld efficiency. Depending on the application and the thickness of the material involved a set of weld seams are selected for inspection. These are tested using Non-destructive testing methods to ascertain the quality of the entire weld. (Interim Guidelines: Evaluation, Repair, Modification and Design of Steel Moment Frames, n.d) The Testing methods to be employed The common non-destructive methods are 1. Radiographic Method 2. Magnetic Particle Examination 3. Ultrasonic Examination 4. Dye Penetrant Testing However for the purpose of designing a portable kit, magnetic particle testing and dye penetrant testing are the most suitable methods that could be used. 1. Standard Liquid Penetrant Testing Procedure The liquid penetrant examination method is an effective method for detecting discontinuities which are open to the surface of nonporous metals. The common discontinuities that can be detected by this method are cracks, seams, laps, cold shuts, laminations and porosity. Prior to each liquid penetrant examination, the surface to be examined and all adjacent areas within 1 inch (25.4) shall be dry and free of dirt, grease, lint, scale, welding flux, weld spatter, paint, oil and free of surface defects that may hide these discontinuities and interfere with the examination process. A liquid penetrant is applied uniformly over the surface that is to be inspected using a brush or by spraying. This allows the penetrant to seep into the discontinuities. The time allowed for this penetration is 5-10 minutes. The excess penetrant is then removed using a cloth or absorbent paper moistened with solvent repeating the operation until the traces of penetrant has been wiped clean. Typical cleaners may which may be used are detergents, organic solvents, descaling solutions and paint removers. The area is then dried by blowing air and the developer applied. (Interim Guidelines: Evaluation, Repair, Modification and Design of Steel Moment Frames, n.d) The non-aqueous liquid developer shall be applied by spraying and the time interval between excess penetrant removal and application of the developer should not exceed 10 minutes. The developer should be thoroughly agitated to ensure that particles are well dispersed. The developer should be sprayed in the form of a thin even coat. Insufficient coating may not draw out the penetrant from the discontinuities and excessive coating might mask the indications. The developer acts as a blotter that absorbs back the penetrant from the discontinuities thus providing a contrasting background. With a colour contrast the developer forms a reasonably uniform white coating. Surface discontinuities are indicated by bleed-out of the penetrant forming a red colour that stains the developer. This increases the visibility of the penetrant indications. The materials that can be effectively examined using this technique are aluminium, magnesium, steel, titanium and high temperature alloys. The commonly used items in DP testing are Dye: Checkmor 222 Cleaner: S-72 Developer: LD-3S Crack Visualised by Dye Penetrant Test 2. Standard Wet Magnetic Particle Testing Procedure This technique is used to detect cracks and other discontinuities that are on the surface of ferromagnetic materials. Typical types of discontinuities that can be examined by this method are cracks, laps, seams, cold shuts and laminations. In principle this method involves magnetizing an area to be examined and applying ferromagnetic particles to the surface. The particles will form patterns on the surface where cracks and other discontinuities cause distortions in the normal magnetic field. (Bednar H Henry, 1986) The surface preparation is similar to that of dye penetrant testing. The area covered should be sufficient to permit a magnetic paticle portable AC Yoke to make contact with the prepared surface. The colour of the wet particles should provide adequate contrast with the surface being examined. The particles shall be suspended in a suitable liquid medium with the temperature not exceeding 57ºC. White contrast Paint Magnaflux WCP-2 ELY Contrast paint 712 Black Ink Magnaflux 7H-F ELY Supramor 4 black The Yoke leg spacing shall be a maximum of 8 inches (203.2 mm). Shorter spacing may be used to meet the limitations of geometry or dimensions of the area being examined or to increase sensitivity but leg spacing less than 3 inches (76.2 mm) is not allowed.( Parker Research Corp, n.d) The yoke shall be preferably placed parallel to or perpendicular to the weld axis. The wet magnetic particles suspended at a recommended concentration and properly agitated by spraying over the areas to be inspected during the application of magnetizing field current. If there is excess magnetic particle, the suspension may be controlled by lightly blowing the suspension from the inspected area. The examination shall be conducted with sufficient overlap to assure 100 percent coverage of the area of interest at the required sensitivity. (Chuse Robert et al, 2004) Indications will be revealed by the retention of magnetic particles. Only indication’s which have any dimension greater than 1.6mm shall be considered relevant. Broad areas of particle accumulation which might mask indications from discontinuities are prohibited and such area shall be cleaned and re-examined. 3. Portable Hardness testing instrument This can be effectively used in testing hardness at certain locations on the surfaces of materials. This works on the principle of Leebs’ rebound method. (Frank Stefan & Schubert Hermann, 2003) This is measured by the amount of energy that is absorbed from an impact body when it strikes a test specimen. The impact object has a carbide metal tip and is accelerated using a spring towards the test surface at a definite speed. This impact causes certain degree of plastic deformation and as a result the kinetic energy of the impact body is reduced. (Qualitest, 2010)This causes the impact body to rebound back at a lower speed. The ratio of the induced voltage before and after the impact can be related to a hardness equation according to Leeb as HL= VB/VA*1000 4. Testing of Polymer Composites The Barcol Tester is an instrument that can be used to measure the hardness of polymer composite materials. The hardness is measured by measuring the amount of resistance to penetration of a sharp steel point under a spring load. This instrument gives a direct reading on a 0 to 100 scale. The hardness value obtained gives us information regarding the degree of cure of the reinforced and non-reinforced plastic. The procedure involves placing the specimen under a Barcol hardness tester and applying uniform pressure on the specimen until the dial indication reaches the maximum limit. The depth of penetration is calibrated into a set of Barcol numbers thus giving us the degree of hardness of the polymer. The polymer is considered cured when the hardness value is greater than or equal to 90% of the surface harness value. The idea of this portable kit is to design a tool box which could be used for easy inspection of weld joints at the site and also to have all the necessary basic tools that could enhance the utility of the kit. (The Barcol Impressor, 2008) Design-1 of the kit The first kit shall ideally contain the all equipments like magnifying glass and other telescopic instruments that help in the visual inspection of specimens since this is the most primary and fundamental inspection that is carried out before further tests are carried out. Other instruments in this kit include (i) Equipments like developer, dye and the cleaning agent that form part of Dye Pentrant Testing. The weight of these items would be approximately 0.5 kg and the cost of the DP package priced at 400 pounds. (ii) Wet Magnetic Particle testing accessories like the AC Yoke and the magnetic particles along with the immersing solution is the next part of the package. A standard AC Yoke would weigh 6.5 kg and cost about 500 pounds and would of course vary with each vendor. A weight above 5 kg is necessitated due to the integral parts of the structure being made of iron. (iii) The Portable Hardness Tester forms the next part of the package. This tool is available in many variants and is priced at 700 pounds. The weight of this product is 1.4 kg Summing up the entire package the weight of the kit would be approximately 10 kg and the cost would be around 1615 pounds including the weight and price of the magnifying glass. Design-2 of the kit The next kit apart from having all the above testing instruments should also have an instrument for examining polymer composites like the Barcol hardness Tester. This costs about 480 pounds and weighs approximately 1.8 kg. The kit-2 would have a weight of 11.8 kg costing about 2095 pounds. Conclusion The 2 kits designed have a myriad of operational uses and can be effectively used in Petroleum sites for quick and effective non destructive testing. Reference Lists 1. “Non Destructive Testing”, Interim Guidelines: Evaluation, Repair, Modification and Design of Steel Moment Frames, n.d, p.p 1-6 2. Frank Stefan & Schubert Hermann, Portable Hardness Testing, 2003, p.2 3. Bednar H Henry, Pressure Vessel Design Handbook, 1986, p.28 4. Chuse Robert et al, Pressure Vessels: The ASME Code Simplified, 2004, p.p 203-205 5. Parker Research Corp, n.d, Available at: [ Accessed on 17th December, 2010] 6. The Barcol Impressor, 2008, Available at: http://barcol-impressor.com [Accessed on 17th December 2010] 7. Qualitest, 2010, Available at: http://worldoftest.com [Accessed on 16th December 2010] Read More