What is peening?

What is peening?

• A. It is the repeated impact of a peening hammer onto the surface of the solidified weld to create compressive stresses in the impacted area.
• B. It is a method of surface cleaning.
• C. It is a technique to increase weld speed.
• D. It is the process of applying a protective coating.

Answer: (A)

Peening is a mechanical surface finishing process that intentionally plastically deforms the surface to introduce compressive residual stresses. By delivering repetitive impacts—such as hammer blows or blast with abrasive media—the outer layer is work-hardened and forced into compression. This compressive layer counteracts the tensile stresses that arise during service, especially at welded joints, making the material more resistant to crack initiation and crack growth, thereby improving fatigue life. In welding practice, peening is commonly applied to weld toes or heat-affected zones to relieve residual tensile stress and enhance durability. The description in the option matches this mechanism and purpose: repeated impacts on the weld surface create compressive stresses in the impacted area. The other activities—surface cleaning, increasing weld speed, or applying a protective coating—do not involve inducing compressive residual stresses and are not what peening is.

Peening is a mechanical surface finishing process that intentionally plastically deforms the surface to introduce compressive residual stresses. By delivering repetitive impacts—such as hammer blows or blast with abrasive media—the outer layer is work-hardened and forced into compression. This compressive layer counteracts the tensile stresses that arise during service, especially at welded joints, making the material more resistant to crack initiation and crack growth, thereby improving fatigue life. In welding practice, peening is commonly applied to weld toes or heat-affected zones to relieve residual tensile stress and enhance durability.

The description in the option matches this mechanism and purpose: repeated impacts on the weld surface create compressive stresses in the impacted area. The other activities—surface cleaning, increasing weld speed, or applying a protective coating—do not involve inducing compressive residual stresses and are not what peening is.