Influence of lack-of-fusion defects on load capacity of MAG welded joints
Pressure vessels operating at elevated temperatures and pressures are made of creep resisting plate and welded from individual components using the MAG welding process. The paper proposed focuses on the occurrence of lack-of-fusion defects in MAG welded plate components of pressure vessels. Lack of fusion, which is a planar defect and is, therefore, difficult to detect by common NDT methods, can result in catastrophic consequences since the latter do not only damage a pressure vessel but also jeopardize the environment and workers' health. The present paper deals with a research on the influence of a welding speed in welding of plate components made of S235JR steel of 8 mm in thickness, special care being taken to deliberately produce lack-of-fusion defects and possibly other weld defects. Test pieces prepared so as to contain various lack-of-fusion defects were subjected to destructive tensile testing. The force required for a weld failure was compared to actual weld defects. In the test pieces produced with lower welding speeds, a failure occurred in the welded joint and along a lack-of-fusion defect. In the test pieces produced with higher welding speeds, however, a fracture occurred outside a weld, although lack of fusion was present in the weld. Parallel to the tensile tests, radiographic examinations of lack-of-fusion defects were conducted and relevant micro sections were analysed. The aim of the study conducted was to elaborate a guideline for quality welding of plate components of pressure vessels.
Analysis of Ultrasonic Indications in Lack of Fusion Occurring in Welds
Lack of fusion is a very dangerous weld defect in a welded structure. Because of the notch effect, a crack may further propagate under the smallest load applied. This type of defect is very difficult to detect with non-destructive testing methods. For the purpose of the present study, lack-of-fusion defects were artificially produced in a multi-pass welded joint. The aim was to find out how ultrasonic devices can sense this type of defect in a butt weld. In addition radiography was used to detect the occurrence of lack of fusion in the welded joint. In the ultrasonic examination 60° and 70° angle probes were applied. They showed lack of fusion at the opposite side-walls of the groove. A normal probe was then used to detect the occurrence of inter-run lack of fusion. The weld defects provided a multiple reflection of ultrasonic waves, which confirmed the presence of lack of fusion in a certain depth. This was additionally confirmed by an ultrasonic thickness measuring gage. Finally, micro sections of the weld were made to establish the actual location and shape of lack-of-fusion defects.
Determination of iodide with 1,3-dibromo-5,5-dimethylhydantoin (DBH) in comparison with the ICl-method. Analytical methods of pharmacopeias with DBH in respect to environmental and economical concern. Part 3.
USP 1995 (The United States Pharmacopeia, 23rd Edit., (1995), potassium iodide p. 1265, sodium iodide p. 1424), PH. EUR. 1997 (European Pharmacopoeia, third ed., Council of Europe, Strasbourg, (1997), potassium iodide p. 1367, sodium iodide p. 1493) and JAP 1996 (The Japanes Pharmacopoeia, 13th ed. (1996), potassium iodide p. 578, sodium iodide p. 630) determine iodide with the ICl-method (J. Am. Chem. Soc. 25 (1903) 756-761; Z. Anorg. Chem. 36 (1903) 76-83; Fresenius Z. Anal. Chem. 106 (1936) 12-23; Arzneibuch-Kommentar, Wissenschaftliche Erläuterungen zum Europäischen Arzneibuch, Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, Govi-Verlag - Pharmazeutischer Verlag GmbH, Eschborn, 12th suppl. (1999), K10 p. 2), using chloroform, which is toxic and hazardous to environment. Without the application of chlorinated hydrocarbons USP 2000 (The United State Pharmacopeia, 24th ed. (2000), potassium iodide p. 1368, sodium iodide p. 1535) and Brit 1999 (British Pharmacopoeia London, (1999), Appendix VIII C, p. A162) titrate iodide with the redox indicator amaranth. A titration with potentiometric indication giving two end-points at the step of I(2) and [ICl(2)](-) is described. Due to the high concentration of hydrochloric acid required for the ICl-method, the determination with DBH (1,3-dibromo-5,5-dimethylhydantoin; 1,3-dibromo-5,5-dimethyl-2,4-imidazolidinedione) can be recommended and is performed easily. Similarly, the iodide content of gallamine triethiodide may be analyzed with DBH by application of a visual two-phase titration in water and ethyl acetate or with potentiometric indication in a mixture of 2-propanol and water. During the removal of the excess of DBH 4-bromo-triethylgallamine (2,2',2"-[1-bromo-benzene-2,3,4-triyltris(oxy)]N,N,N-triethylethanium) is formed.