Abrasion. Description The mechanical action of rubbing, scraping, scratching, gouging or erosion. Probable CausesRemoval of a portion of the surface of the coating. Weld Reality presents the Pulsed MIG problems and resolutions. Pulsed MIG and robot information. Pulsed MIG and robots welding boiler tubes to headers. Pulsed MIG. Weldingdefects how to look for them. Between discontinuities and defects. Acceptance limits for harmless discontinuities. Visual and internal defects. Defect most. Rubber bands have been around since the middle of the 19th century. Weld Defects Causes, Consequences, PreventionAlexander L. Kielland Semi Submersible Drilling Rig Image Courtesy of Norsk Oljemuseum at https en. File AlexanderLKiellandandEdda2 7. CNOMF 0. 26. 63 1 6. Bad Welds Invite Tragedies March 2. Alexander L. Kielland Semi Submersible Drilling Rig at the Ekofisk Oil Field, Norwegian sector of the North Sea. A howling 4. 0 knot wind was driving rain onto the rig that had just been winched away. Over 2. 00 of the 2. Throat+Crack+Definition%3A+A+longitudinal+crack+located+in+the+weld+throat+area..jpg' alt='What Causes Crater Cracks In Welding' title='What Causes Crater Cracks In Welding' />Many were relaxing in the cinema and the mess hall. Just before 6 3. A little later they sensed some kind of trembling. Much like the slight tremors felt before an earthquake lets loose its full fury, the clap and trembling were only the beginning. Soon, the rig became the theater of the worst disaster in Norwegian offshore history since the Second World War. Five of the six anchor cables had broken and caused the sharp clap and trembling as the rig heeled by around 3. What stood between the crew and a total catastrophe was the sixth cable. Groove+Weld+with+Various+Other+Discontinuities.jpg' alt='What Causes Crater Cracks In Welding' title='What Causes Crater Cracks In Welding' />But that did not last for long. By 6 5. 3 pm, the last cable standing gave away and the rig capsized. Of the 2. 12 aboard, 1. What aggravated the crisis was a safety device that prevented the release of some life boats. And the standby vessel arrived an hour later. Anatomy of Collapse of the Alexander L. Kielland Semi Submersible Drilling Rig. Image Courtesy of Wiki Chris at https en. File ALKcolumnsfracturesenglish. Investigators blamed a fatigue crack in one of the six D 6 bracings. A small 6 mm filler weld with poor profile had precipitated the crack. The weld linked the bracing to a non load bearing flange plate. The devil truly is in the detail. Filling+the+Crater+At+the+end+of+the+weld%2C+the+operator+breaks+the+arc+which+creates+a+%E2%80%98crater%E2%80%99.jpg' alt='What Causes Crater Cracks In Welding' title='What Causes Crater Cracks In Welding' />Closer to home, shoddy welding of a bracket that supported a tray inside the reactor of a urea plant in Westlake, Louisiana caused an explosion on July 2. Such was the impact of the explosion that a fragmented shell of the column was blasted 9. The Fundamentals During welding, metals expand and contract. More than anything else, this introduces undesirables in the process brittleness, cracks, deformations, porosity, lack of penetration, and what not. Mild steel or low carbon steel is metal of choice for structural work because it retains its ductility despite journeying to extreme temperatures and back. Sadly, high carbon steel, aluminum, cast iron, stainless steel, and titanium are not so well endowed. Weld Defects are any of the myriad of imperfections that undermine the utility of a welded joint. ISO 6. 52. 0 classifies weld flaws while ISO 5. ISO 1. 00. 42 prescribe acceptable limits for such defects. Welding Failure Caused the Collapse of Seongsu Bridge in 1. Image Courtesy of at https en. File 1. 99. 4EC8. B1EC8. 89. 8EB8. C8. EAB59. 0EBB69. EAB4B4EC8. ACEAB3A0. Issues with welding have been around for decades. The following factors influence and aggravate them Ignorance on Weld Processes. Absence of Process Ownership. Needless Belief in Salespersons. In order to prevent failures of welded structures, the American Welding Society AWS develops comprehensive welding codes and standards. These define the dimensions, shape, and allowable level of defects. Other bodies such as the American Society of Mechanical Engineers ASME, American Society for Nondestructive Testing ASNT, and American Petroleum Institute API make suggestions for the code. Improper welding procedure causes most weld defects. According to ASME, following factors bring about weld defects Poor Process Conditions 4. Operator Error 3. Incorrect Technique 1. Faulty Consumables 1. Unsound Weld Gloves 5You can trace most weld defects to two general areas Ill Advised Training and Workmanship is overcome by providing a detailed Welding Procedure Specification WPS that adheres to the fundamentals of welding. Unwarranted Weld Design andor Material Choice is nullified by complying with basic design principles and practices. Ignorance is No Bliss in Welding, its Deadly. Image Courtesy of Path. Doc at shutterstock. You can simplify the causes as Flimsy Joint Design. Incorrect Shielding Gas or Flow Rate. Faulty Machine or Settings. Erroneous of Defective Electrode Wire. Incompatible Ambient Temperature or Humidity. Types, Causes, Prevention Metallurgically speaking, bad welds are a manifestation of Hydrogen Embrittlement. Residual Stresses. Please note, hydrogen embrittlement and residual stresses are complementary they feed and fatten each other. By eliminating one, you control the other too. Oxygen and hydrogen are the nemesis of welders. Corrosion, rust, and millscale on the base metals are a result of oxidation. These interfere with welding. Moisture i. e. water in any form invites hydrogen embrittlement water contains hydrogen and oxygen. Hydrogen Embrittlement is the entry and spread of hydrogen in a metal structure. It makes metals brittle and causes them to crack. Hydrogen embrittlement manifests as a sizable fall in the ductility of metals during the slow bend or tensile tests. Solubility of hydrogen in iron and therefore steel increases at elevated temperatures. Welding operations provide such high temperatures. Hydrogen remains trapped when metals solidify. Being highly mobile, hydrogen atoms diffuse freely in the metal and gather wherever possible. Hydrogen Induced Cracking HICImage Courtesy of CEphoto, Uwe Aranas CC BY SA 3. File Steel with Hydrogen Induced Cracks 0. There is no consensus among researchers on how hydrogen causes brittle fractures. The conventional explanation an increase in hydrogen concentration builds up pressure and causes cracks explains only a limited number of fractures. In order to prevent such embrittlement clean and dry steels before weldingemploy baking treatments to liberate trapped hydrogenfollow preheat schedules and prescribed inter pass temperature for high strength low alloy steels. Residual Stresses are those that linger in a material even after you remove the cause for the stress. Such stresses are a major reason for premature failure of metal structures. Three main causes of residual stresses in metals are Cyclic Temperature Changes. Plastic Inelastic Deformations. Structural Phase Transformations. Weld operations cause the base and filler metal to heat up and expand. After you remove the source of heat, the weld and base material cool down and contract. Methods to Measure Residual Stress. Image Courtesy of Dcave. File ResidualStressMeasurement TechniquesComparison. Some areas cool and contract more than others. Such uneven cooling introduces residual stresses. This creates large tensile stresses in some parts of the weld that are balanced by compressive stresses in other parts of the same weld. Typical weld defects include Lack of Fusion. Incomplete Penetration. Excessive Penetration. Porosity. Inclusion. Cracks. Undercuts. Lamellar Tearing. Other defects include Overlap. Distortion. Arc Strikes, Spatter, and Other Surface Disruptions. Activation Adobe Master Collection Cs6 Torrent. These defects can introduce stresses and cause failures below the design load. In case of cyclic loads, they cause failures before the predicted number of cycles. Weld Bead. Image Courtesy of wi. Weld Bead is the filler metal deposited in the weld joint. It can be Stringer Bead a narrow bead created by straight dragging or light oscillatory motion of the consumable.