DESTRUCTIVE TESTING OF WELDS IN WPS / PQR PREPARATION
WELDING PROCEDURE SPECIFICATION ( WPS ) – A WPS is a written qualified welding procedure prepared to provide direction for making production welds to Code requirements. All the numerous welding process variables are described described in the WPS with sufficient detail to permit reproduction of the weld and afford a clear understanding of the parameters for performing the production weld. PROCEDURE QUALIFICATION RECORDS ( PQR ) – A PQR is a record of the welding data used to weld the test coupon and the results of testing the t he specimens cut from the test coupon. The purpose of the WPS and the PQR is to determine that the weldment proposed for construction is capable of having the required properties for its intended application
QUALIFICATION OF THE WPS ASME IX – All ASME IX WPS must be qualified. The basic steps in the qualification of a WPS based on ASME IX are as follows • Preparation of WPS. • Welding of test coupon following all the variables variables from the WPS. • Testing of cut cut specimens specimens from the test coupon. • Evaluation of overall preparation, welding, testing, and end results. • Possible changes in procedure. • Approval.
AWS D1.1 – The AWS AWS D1.1 employs the concept of prequalified weld joints. By following a number of welldefined variables, the user of this Code does not have to qualify the procedure. Instead, the values of the specific variables are recorded. Qualification is required only if any of these variables are changed beyond their specified limits.
REQUALIFICATION OF A QUALIFIED WPS If a Fabricator that has a qualified WPS has to change any essential variable at some later date, it is necessary to requalify the WPS. This requalification requalification establishes that the revised WPS will produce satisfactory results. Such requalification tests are not required if there are changes in non-essential variables. variables. They are required, however, however, if there are changes in essential variables variables which will alter the properties of the resulting welds.
TWO TYPES OF WPS: GENERAL – Broad, general type that applies to all welding processes of a given kind on a specific material. SPECIFIC – Narrower, more definitive type, as when a WPS has to be requalified to allow an essential variable be changed . ESSENTIAL / NON-ESSENTIAL VARIABLES ESSENTIAL VARIABLES – Changes in some variables are considered critical that will affect the mechanical properties of the weldment and will require requalification requalification of the WPS. NON-ESSENTIAL VARIABLES – Changes to other variables will require that the WPS be rewritten rew ritten to recognize the change, but will not require requalification.
ESSENTIAL VARIABLES • Welding Process or Method of Application Application – A change from the welding process or method of application established in the procedure specification. • Base Material – A change in base materials of two different material groups. • Diameters and Wall Thicknesses – The range of outside diameters and wall thicknesses over which the procedure is applicable shall be indentified. • Joint Design – The specification shall include a sketch or sketches of the joint that show the angle of bevel, the size of the root face, and the root opening. • Filler Metal and Number of Beads – The sizes and classification number of the filler metal and the minimum number and sequence of beads shall be designated. • Electrical Characteristics – The current and polarity shall be designated, and the range of voltage and amperage for each electrode, rod, or wire shall be shown.
• Time Between Passes – The maximum time between the completion of the root bead and the start of the second bead, as well as the maximum time between betw een the completion of the second bead and the start of the other beads, shall be designated. • Position – The specification shall designate roll or position welding. • Direction of Welding – The specification shall designate whether the welding is to be performed in an uphill or downhill direction. • Pre- and Post-Heat Treatment – The methods, temperature, temperature-control methods, and ambient temperature range for the pre- and post-heat treatment shall be specified. • Shielding Gas and Flow Rate – The composition of the shielding gas and the range of flow rates shall be designated. • Shielding Flux – The type of shielding flux shall be designated. • Speed of Travel – A change in the range for speed of travel.
DESTRUCTIVE TESTING, is used to describe an evaluation process of a weld by a technique that of necessity destroys the test specimen or destroys its ability to function function in its design application. application. They are performed on sample weldments made with procedures duplicating those used in the fabrication of the actual welded structures. The destructive destructive testing techniques can can be classified classified as three general types: chemical, metallographic, and mechanical.
CHEMICAL TESTS – are conducted on the specimen to determine its chemical composition. METALLOGRAPHIC TESTS – are used to determine the following: • The soundness of welds. • The distribution of nonmetallic inclusions in the weld. • The number of weld passes. • The metallurgical structure in the weld and fusion zone. • The extent and metallurgical structure of the heataffected zone. • The location and depth of penetration penetration of the weld. MECHANICAL TESTS – are used to determine weld strength. • Tensile Strength. Strengt h. • Impact Strength. • Bend Tests. • Hardness Tests.
UNIVERSAL TESTING MACHINE
TENSILE-TESTED SPECIMEN Standard – 70,000 psi minimum.
GUIDED BEND TEST JIG
SIDE-BEND TESTED SPECIMEN
VARIOUS BEND-TESTED SPECIMENS – Side Bend Double-V Groove – Face Bend – Side Bend Single V-Groove – Root Bend
Acceptance Criteria – One rounded indication maximum of 2.5 mm. Any appearance of crack is rejectable.
IMPACT TESTING MACHINE
IMPACT TESTING MACHINE
ANVIL FOR HOLDING IMPACT TESTING SPECIMEN
IMPACT TESTING SPECIMEN
IMPACT TESTED SPECIMEN Standard Impact Values – 47 joules minimum .
Carbon Steels, at lower temperatures, exhibit coarse-grained structures, and are are more brittle. Carbon Steels, at higher temperatures, have finer-grain structures, and give higher Impact Values.
Hardness is the property of a material m aterial that enables it to resist plastic deformation, deformation, usually by penetration. However, However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting. The Brinell Hardness Test method consists of indenting the test material with a 10 mm diameter hardened steel or carbide ball subjected to a load of 3000 kg.
The Rockwell Hardness Test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. indenter. The indenter is forced into the test material under a preliminary minor load, usually 10 kgf. kgf. When equilibrium equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration. When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, recovery, so reducing the depth of penetration. The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell Hardness Number. Number.
The Vickers Hardness Test Test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface surface of the indentation is is calculated. The Vickers Hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation.
BRINELL HARDNESS TESTERS
ROCKWELL HARDNESS TESTERS
VICKERS HARDNESS TESTERS
DIFFERENT INDENTORS FOR DIFFERENT HARDNESS VALUES.
VICKERS HARDNESS TESTER INDENTATION ON TEST SPECIMEN .
PREPARING PREPARING A METALLOGRAPHI METALLOGRAPHIC C SPECIMEN SP ECIMEN FOR MICROSTRUCTURE ANALYSIS • Cut a section of the test specimen for macro / microstructure analysis. • Grind the specimen in successively finer silicon Carbide abrasive grits of 120 / 320 / 600 / 1200. • Polish the finely ground specimen on napped polishing cloths in, first, colloidal chromium oxide suspension, then, in colloidal aluminum oxide suspension. • Dip the buffed specimen in a 3% nitric acid solution. solution. • The specimen is now now ready ready to be viewed viewed under a metallographic microscope.
METALLOGRAPHIC MICROSCOPE WITH DIGITAL CAMERA
MACROSCOPIC EXAMINATION
MICROSCOPIC MICROSCOP IC EXAMINATION AT AT 25 X MAGNIFICATION
THE ATOMIC ABSORPTION SPECTROMETER TECHNIQUE TYPICALLY USES A FLAME TO ATOMIZE THE METAL SAMPLE. A BEAM OF LIGHT PASSES PASSES THROUGH THIS FLAME, ABSORBING A SET OF QUANTITY OF ENERGY ( LIGHT OF A GIVEN WAVELENGTH WAVELENGTH ). ) . EACH WAVELENGTH WAVELENGTH IN THE SERIES IS SPECIFIC TO ONLY ONE PARTICULAR ELEMENT.
