Quality Assurance in Welding: Module 6

Objective:

  Know the effect of welding in terms of shrinkage, residual stresses and
  distortion.
  And know how to minimise distortion before, during and after welding.

Scope:

• The thermal cycle in welding
• Development of residual stresses due to solidification, cooling and shrinkage
• Effects of restraint on residual stress
• Significance of residual stress
• Preheating, postheating
• Relationship between heat input and shrinkage, residual stress and distortion.
• Development of distortion; effect of heat input, weld size, penetration, and number of runs singleand doublesided fillet welded joints and in butt welds
• Corrective measures, procedure, welding technique, sequence, joint preparation, presetting
• Correction of distortion after welding

Expected results:

• Describe the thermal cycle during welding.
• Describe distortion resulting form shrinkage.
• Describe residual stresses.
• Name measures to minimise distortion.
• Describe the main causes for weld shrinkage.
• Outline the main effects on a weld due to residual stresses.

List of Contents

1. Preheating, interpass and post heating to prevent hydrogen cracking
2. Preheat