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CONTROL OF WELDING

CONTROL OF WELDING . I-95 Bridge at Delaware. I-95 Bridge at Delaware US . Hoan Bridge Milawaukee. Unacceptable weld on recent project. WELDING. Defects can cause problems after acceptance Not possible to identify many built-in defects by later testing

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CONTROL OF WELDING

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  1. CONTROL OF WELDING

  2. I-95 Bridge at Delaware

  3. I-95 Bridge at Delaware US

  4. Hoan Bridge Milawaukee

  5. Unacceptable weld on recent project

  6. WELDING • Defects can cause problems after acceptance • Not possible to identify many built-in defects by later testing • If a problem exists then repair may be prohibitively expensive, may damage the product and • Some defects can only be revealed by destructive testing • Thus welding needs to be a controlled process to minimise rejection of end product

  7. Welding Defects • Hydrogen Embrittlement • Reduces ductility • Reduce load carrying capacity • Can occur suddenly Can occur with only slight corrosion. Potential not readily identifiable afterwards

  8. Welding Defects • Cracks • Stress concentrators • Can grow until fracture • Variety of causes including weldability issues

  9. Welding Defects • Porosity • Stress concentrators, problems for coatings • Caused by impurities, air inclusion • PQR may reveal this as a potential problem • Corrosion problem

  10. Welding Defects • Incomplete penetration • Lack of weld strength • Caused by current, travel speed, angle weld • Review of PQR will reveal this as a potential problem

  11. Welding Defects • Lack of fusion • Lack of weld strength • Caused by poor weld technique • Review of PQR will reveal this as a potential problem

  12. Welding Defects • Undercutting • Lack of weld strength • Caused by poor weld technique • Review of PQR will reveal this as a potential problem

  13. Welding Defects • Inclusions • Potential Crack initiator • Caused by poor weld technique • Review of PQR will reveal this as a potential problem

  14. Welding Defects • Arc strike • Crack initiator • Caused by carelessness • Needs to be treated as a weld and assessed

  15. Control of Welding • RTA controls: • Prequalification • Notes on drawings of weld type (GP, SP, FP) • Requirements for welders, supervisors and inspectors • RTA inspectors • RTA specifications B80, B200, B204 etc

  16. Types of Welding • Reinforcing steel: • Non-load bearing tack welds • Load bearing tack welds incl lifting • Structural welds such as splices • Structural complex • Structural routine

  17. History of Reinforcement Welding 1965-1977 Only Hydrogen controlled electrodes 1978-1991 Generally not field weldable due to preheat requirements 1992-1999 Almost any electrodes 2000-2005 Low hydrogen electrodes

  18. Reinforcement Welding Non-load bearing tack welds • May now use non hydrogen controlled electrodes as long as an approved PQR used

  19. Reinforcement Welding Load bearing tack welds • Welds being lifted, transported etc • Must use hydrogen controlled electrodes • Welds must be designed by engineer • Lifting points on drawings and on assembly • Weld to spec and code

  20. Reinforcement Welding Structural reinforcement welds • Welding for strength transfer, fitting welding etc • Must use hydrogen controlled matching strength electrodes • Welds must be designed by engineer • Weld PQR required to spec and code

  21. Structural Welding Three types of weld may be shown on drawings: GP-general purpose SP-weld stressed > 50% or subject dynamic loading FP-fatigue adds additional testing & acceptance Different level of testing requirements Decreasing tolerance for level of defects

  22. Welding -Specification Requirements B80 • 500L (mesh) not to be field welded • Not near prestressing tendons B204 • Personnel • Weld procedures • Prototypes • Consumables

  23. Welding -Specification Requirements (cont) B204 • Control of distortion • Run-on/run-off tabs • Inspection requirements GP least with FP greatest • Non conformances

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