Fatigue Improvement Techniques for Welds

Fatigue Improvement Techniques for Welds

The great majority of industrial machines, including their supporting structures, have to contend with changing loads over the course of their lifetimes. Most of these machines are at least partially assembled by welding, which requires that their welded joints sustain those fluctuating loads over the entire life of the machine. These machines may fail prematurely because of cracking due to fluctuating loads, even if they are designed with the correct safety factors against the static loads they handle.  

The Design Challenge

One of the biggest design challenges for industrial machines is the welding factor. Welding lowers the fatigue life of any structure, and weld defects can add undue concentrations of stress. Even though a certain number of defects are expected in every weld, the process of welding brings residual stresses into the structure, which affect the fatigue life of the structure.

Over the past thirty years, the trend in industrial machine design has been an increase in process flows, temperatures, pressures, speeds, and intervals between maintenance. At the same time, designers are implementing stronger, lighter, more durable construction. As a result, in general, we have machines with far fewer safety concerns and closer attention to detail than ever before. This is great – except that now, the fatigue life of a machine is a greater concern than it has been previously.

So the challenge is manufacturing the machine efficiently and maintaining its expected life at the same time.

What Is the Answer?

One way to address this challenge is to minimally alter the welds in the machine in ways that enhance the machine’s fatigue life. These methods fall into one of two categories: methods that address the geometric problems and those that address residual stress problems.

Weld geometry improvement has two options with two methods each, as follows:

  •      Material Removal
    • Burr Grinding
    • Disc Grinding
  •      Weld Toe Remelting
    • TIG Dressing
    • Plasma Dressing

The residual stress improvement method has two options, one with four methods and one with only one method, as follows:

  •      Mechanical
    • Hammer Peening
    • Ultrasonic Hammer Peening
    • Shot Peening
    • Vibratory Stress Relief
  •      Thermal
    • Thermal Stress Relief

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