There are many benefits to shot peening but I am wondering is there ever a time when shot peening would be harmful?

More specific to my application - I work in a plating shop. When in doubt, we peen. But now I am questioning is peening always the best solution.

There are two guidelines that I use when determining if peening is necessary. The first comes from AMS 2460. The chrome plating specification states "parts designed for unlimited fatigue life under dynamic loads are peened prior to plating." So if the part is dynamically loaded, we peen.

The second place I reference is AMS-S-13165 which states very thin sections should not be peened at high intensities. I use Table VI as a guideline and if the part is less than 0.090 inches (steel), I do not peen.

But sometimes we do not know if the part is dynamically loaded, and sometimes the thickness is right on the 0.090 inch. In these cases, is it ALWAYS better to peen if in doubt, or is there another factor I am not considering when trying to make this decision.

Thanks in advance.

My first thought...

The key to the AMS-S-13165 guideline is not to peen thin sections at high intensities. This could cause part deformation. Peen at a lower intensity to prevent deforming the part.

I'm not sure that there would be another detriment to peening when concerning thin sections so I anticipate further comments to your question.

Thanks Dave!

If you shot peen the ID of a barrel it induces compressive stresses on the surface of the ID. Will this inturn create unwanted tensile stresses on the OD?

I guess that is more of what I am looking for when I asked is there any reason you would NOT want to shot peen.

Not speaking from experience but just thinking it through: I imagine peening the ID of a barrel (only) should make the ID increase by a degree relevant to the the intensity. That would lead me to tensile stresses developing as the OD is stretched (ripped) to allow the dimensional change.

Again, I await for some knowledge from the "elders". :P

OD tensile stresses would develop under the stated conditions. The magnitude of the OD surface stress should usually be negligible. As a rough guide if the depth of the induced compressively stressed layer is a tenth of the wall thickness then the OD tensile stress would be about a tenth of the ID compressive stress. With a ratio of a hundredth then the tensile stress would be about a hundredth. This follows from having to have a balance of the longitudinal tensile and compressive forces.Hence, high-intensity peening is not recommended for very thin sections - as well as because of possible distortion problems. If induced OD tensile stress is a problem then the outside of the barrel should also be peened.