weld quality & weld testing. what is unique about the eisenhower interstate highway system? one...
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Weld Quality & Weld Testing
What is unique about the Eisenhower Interstate Highway System?
One in every 5 miles is straight, this can be used as airstrips in times of war and other emergencies
Each Weldment Should Be:• Adequately Designed to meet the intended service for the required life• Fabricated with specified materials and in accordance with the design concepts• Operated and maintained properly
Welds are examined in regard to:• Size• Shape• Contour• Soundness• Other Features as Specified
Effect of Discontinuities on Properties
• Discontinuities in a welded joint can influence mechanical properties
• Codes establish size limits for acceptable discontinuities
• Discontinuities unacceptable by a given code are called defects and are subject to repair
Welding Code
Classification of Weld Joint Discontinuities
• Welding Process or Procedure Related Discontinuities• Metallurgical Discontinuities• Design Related Discontinuities
Welding Process or Procedure Related Discontinuities
Geometric•Misalignment•Undercut•Concavity or Convexity•Excessive Reinforcement•Improper Reinforcement•Overlap•Burn-through•Backing left on•Incomplete Penetration•Lack of Fusion•Shrinkage•Surface Irregularities
Other•Arc Strikes•Slag Inclusions•Tungsten Inclusions•Oxide Films•Spatter•Arc Craters
Classification of Weld Joint Discontinuities
Metallurgical Discontinuities
Cracks or Fissures•Hot•Cold or Delayed•Reheat
•Stress-Relief•Strain-age
•Lamellar Tearing
Porosity•Spherical•Elongated•Worm-hole
Heat-Affected Zone Microstructural Alterations
Weld Metal & HAZ Segregation
Base Plate Laminations
Classification of Weld Joint Discontinuities
Design Related Discontinuities
Changes in Section & Other Stress Concentrators
Weld Joint Type
Classification of Weld Joint Discontinuities
http://www-iwse.eng.ohio-state.edu/we300/Discontinuity/discontinuity.aam
Open the web page under “Demonstrations” and do the exercise entitled “Discontinuities
Pages 364 through 367 of the Welding Handbook list table of Common Causes and Remedies like the one on the Right. Review these tables to gain insight about Discontinuities
Turn to the person sitting next to you and discuss (1 min.):• From a general point of view, how would you rank the following discontinuities in their severity to weld properties: Hot Cracks, Change in section size, Porosity, ? Why
Porosity
• Porosity is the entrapment of small volumes of gas in solidifying weld metal
• Prevention– Drying consumables– Cleaning, degreasing material being welded– Electrode or filler metals with higher level of
deoxidants– Sealing air leaks, reducing excess shielding gas
flow
Welding Discontinuities
0.1.1.4.2.T7.95.12
Slag inclusions
• Slag inclusions are irregularly shaped, not spherical like porosity
• Prevention– Position work and/or change electrode/flux to
increase slag control– Better slag removal between passes– Dress weld surface smooth if it is likely to cause
slag traps– Remove heavy mill scale on plate
Welding Discontinuities
0.1.1.4.2.T8.95.12
Lack of Fusion
• Lack of fusion is caused by incorrect welding conditions
• Prevention– Procedure for complete fusion should be
verified by testing– Increased energy input– Correct electrode angle and work position
Welding Discontinuities
0.1.1.4.2.T9.95.12
Incomplete Root Penetration• Incomplete root penetration can be caused by
– Excessively thick root face, insufficient root gap– Incorrect welding conditions– Misalignment of second weld
• Prevention– Improved joint preparation– Test weld verifications for correct parameters– Reassessment of back gouging
Welding Discontinuities
0.1.1.4.2.T10.95.12
Overlap
• Overlap is an imperfection at the weld toe or root caused by metal flowing onto the surface of the base metal without fusing to it
• Prevention– Adjust electrode manipulation to ensure fusion
of base metal– Limit size of fillet to 9-mm leg length
Welding Discontinuities
0.1.1.4.2.T11.95.12
Undercut• Undercut is an irregular groove at the weld toe in the
parent metal or previous pass caused by– excessive weaving
– melting of top edge of fillet weld with high current
• Prevention– Weld in flat position
– Change shielding gas to one which produces better wetting
– Terminate welds so they don’t finish at a free edge
Welding Discontinuities
0.1.1.4.2.T12.95.12
Excessive Penetration
• Excessive penetration is caused by – Incorrect assembly or preparation
• Edge preparation too thin to support weld underbead
• Excessive root gap
– Energy input too high– Lack of operator skill
• Prevention– Control of preparation, backing bars
Welding Discontinuities
0.1.1.4.2.T13.95.12
Root Concavity
• Root concavity is caused by – Excessively thick root face– Insufficient arc energy for penetration– Excessive backing gas pressure
• Prevention– Reduce root face thickness, control backing gas
pressure– Establish a procedure by test welding
Welding Discontinuities
0.1.1.4.2.T14.95.12
Spatter
• Spatter consists of small droplets of electrode material that land beside the weld and may or may not fuse to the base material
• Prevention– Reduce energy input
– Shorter arc length
– Reposition current return clamp to reduce magnetic arc blow or switch to AC current
Welding Discontinuities
0.1.1.4.2.T15.95.12
Turn to the person sitting next to you and discuss (1 min.):• We have just looked at a list of discontinuities and preventative measures. How does this information effect the opinions of people involved in writing codes for proper welding conditions?
Weld Test Samples Help Reveal Discontinuities and Defects
Fatigue Appearance
• Distinct fracture surface has a characteristic texture– Concentric line
pattern– Smooth portion
referred to as clamshell texture
multiple initiation sites
Fatigue Design