What would be the effect of accidental introduction of larger shot due to sieve failure during peening? Should you re-peen the part?

As with most problems of this type "The Devil is in the details". If the peening intensity is still being maintained within the user's required range and if the shot mixture still satifies the specification for its size then there should be no need to re-peen. If these requirements are not being met then re-peening will only serve to hide the larger indentations - which is not advisable.

If there were about 20% larger shot in the machine by the end of processing, then I guess that the intensity would drop off.
With the same air pressure the larger shot will be slower & possibly 'choke' the pipes.

I'lll check start & finish arc height and see where we are then

thanks

Pete

Larger media with a given air pressure will increase intensity as the mass is larger while the velocity is the same.

If "choking" is significant enough to decrease CFM that would lead to lower velocities thus lower intensities. While possible, I wouldn't think a 20% increase in size would/should do that.

Sorry my last message was unclear. We've had S170 contaminated with about 20% of S280. With increase of x2 in volume & almost x3 in cross sectional area with the larger shot, I thought choking would be likely.

Sorry, I did misunderstand.

Choking aside, If you have 20% contamination of larger shot (determined via sieve testing) you're likely out of spec.

The discontinued AMS-S-13165 uses a single sieve for in-use media and would not disqualify the sample, however, it is a discontinued spec and you should follow AMS-2430.

AMS-2430 allows only 1/2% of the test sample on a #25 sieve, where you'll be clearly out of spec.

If the media does flow freely through the nozzle you still may achieve acceptable confirmation arc heights. You should generate new saturation curves. The larger media will increase the intensity but will take longer to saturate, thus resulting in a "double hump" saturation curve. If you chose to pursue this as a learning experience make sure to have extra Almen strip data points at longer than normal exposure times.

Have fun!