1_58_PDFsam_02.Intermediate Weld Discontinuities _compressed.pdf

cem WSS Study Guide WD2.1 rhHN nh Intermediate Weld Discontinuities Hydrogen-induced cold cracking (HICC) can occur in the weld metal or the heat-affected zone and in any orientation with respect to the weld axis. Commonly observed positions of hydrogen-induced cold cracks in groove and fillet w...

cem WSS Study Guide WD2.1 rhHN nh Intermediate Weld Discontinuities Hydrogen-induced cold cracking (HICC) can occur in the weld metal or the heat-affected zone and in any orientation with respect to the weld axis. Commonly observed positions of hydrogen-induced cold cracks in groove and fillet welds are shown in Figures 45 and 46. Crater crack Transverse crack Longitudinal crack Transverse crack. HAZ Toe crack HAZ Fusion line cracking Underbead Root crack G45] crack HAZ Location oƒ hydrogen-induced cold cracks in groove welds x Root crack Toe crack Underbead crack mm Location oƒ hydrogen-induced cold cracks in fillet welds WSS Study Guide WD2.1 CWBï acorn An iniriauve of the cwbgroup Intermediate Weld Discontinuities Transverse cracks in the weld metal may extend into the heat-affected zone of the parent plate and beyond. Heat-affected zone cracks are usually longitudinal and most often occur at the root or the toes of the welds. Under some conditions longitudinal cracks may be very long, sometimes running the entire length of the weld. Cold cracking may also manifest itself as fine micro-cracks, difficult to detect by normal inspection and nondestructive test methods. The presence of micro-cracks may be symptomatic of a more serious condition, such as a high hydrogen level, that could lead to more serious cracking. Cracks may be detected by visual examination if the cracks are open to the surface and large enough, or by nondestructive methods suitable for detecting surface discontinuities. Subsurface cracks may be detected by nondestructive methods capable of detecting subsurface discontinuities. Due to their geometry, cracks are always considered a defect and must be repaired. The repair must ensure that the crack is completely removed, usually by excavating the weld or base metal to remove the crack. Then nondestructive testing is carried out agaïn to ensure that the crack is completely removed. Re-welding is performed following repair procedures and nondestructive testing is tựypically carried out again to ensure that new cracks did not form from the repair welding. Nondestructive examination shall be delayed as long as practicable and preferably not less than 48 h after completion of the welds. 4. Design-Related Discontinuities Sometimes discontinuities arise from problems within the design of the structural details or in choosing the wrong type of weld joint for a given application. lf the problem is attributed to the design of the weld joint and then welding is performed, the resulting discontinuity or defect is considered design-related. Page 60 9 2015 CWB Group Industry Services WSS dải Gủide WD2.1 Intermediate Weld Discontinuities Specific mechanical and chemical properties are required of all welds made in any given weldment. These requirements will depend on the codes or specifications involved and departure from these specified requirements is considered a defect. Properties are generally determined with specially prepared test plates but may be made on sample weldments taken from production procedure qualifications. Where test plates are used, the inspector should see that specified welding procedures are followed, otherwise the results obtained will not necessarily indicate the actual properties of the weldments. Mechanical properties that may be defective ïf procedures are not followed are: tensile strength, yield strength, ductility, hardness and impact. Chemical properties may be deficient because of incorrect weld metal composition or welding procedure and both of these may result in lack of corrosion resistance. Not all of these defects are due to improper welding conditions, since many such difficulties can be caused by the base metal. Properties of the base metal that may not meet the requirements are chemical composition, internal conditions (laminations and stringers), surface conditions (mill scale, grease, paint, oil, etc.) and mechanical properties. In the case repair will prepared. weldment Page 61 | Copyright © 2015 CWB Group Industry Services | of defective properties of usually involve the welded lf there are problems with may not be acceptable for weld metal and/or base metal, joint being removed and a new joint the base metal, the entire use. WSS Studv Guide WD2.1 cwbgroup Intermediate Weld Discontinuities Guides and Exam Exercise To obtain maximum benefit from this study guide we suggest that you follow this guide and complete the exercise as indicated. It is important that you work through the text methodically, studying each section thoroughly before moving on. The exercises are designed to give you an indication of whether vou have learned the material and can move on or whether you need to go back and study the section again. Do the exercises honestly. They will not help vou unless you take them seriously. lf you get a question wrong, go back through the text until you understand where you have gone wrong and know the correct answer. The length of time required to complete the module will vary from student to student. Find you own pace. Do not rush. Remember you are trying to teach vourself something, not win a race. Some people like to underline sections when they read a text. We suggest that you use caution ïf vou do this. What you think is important first time you read ït may be different after reading it three times. We suggest you read a section three times thoroughly before highlighting anvthing. The exam exercise is designed to give you an indication of whether you are ready to take the closed-book exams. The exercise questions are of a similar standard to the official exams. Do not take the exam until vou feel you are ready. You may wish to study several modules before taking the exams on each. lf you have any difficulties with this module do not hesitate to ask for help. Vou may contact us at 1-800-844-6790, fax us at 905-542-1318 or email us [email protected]. Page 62 Copyright © 2015 CWB Group Industry