SHOT PEENING AND FATIGUE/CFC/SCC

[jackboot]

Is there an expert on shot peening and its effects on: stress corrosion cracking, corrosion fatigue, and just pure mechanical fatigue.

I have been to the

http://www.shotpeener.com

and combed their library- I got a lot of good information.

However, I was wonder if anyone had any real experience with the process and the beneficial effects that it imparts.

jackboot

 

[metengr]

Jackboot;
We have used shot peening to increase fatigue life of weld repairs performed on low pressure steam turbine blading and rotating shafts in certain power industry applications.

The main benefit derived from shot peening is the compressive residual stress on the surface of the part. If done correctly, the compressive stress will be uniform and reduce susceptibility to mechanical fatigue crack initiation. I would expect similar resistance to stress corrosion cracking, as well.

NOTE - the benefit of residual stress diminishes as service temperature increases. So, the best situation is when the component that has been shot peened does not see service temperatures that would reduce these beneficial stresses over time. Secondly, coverage of shot peening is critical for success. Inconsistent coverage will result in local residual tensile stresses in the location that you want to protect.

Several of our weld repairs that were shot peened to provide increased fatigue resistance are still in service (with no problems) after 15 years. The initial fatigue failures ocurred within 2 years after being placed into service.

 

[jackboot]

THANKS METENGR-

We have a localized high stress area that will fail- everytime at the same location. Many areas are seal locations so we can't peen everywhere. We did try to cover as much of the critical area as possible. Hopefully, this will fix a headache.

 

[TVP]

Roller burnishing is an excellent alternative to shot peening when residual compressive stresses are necessary, but the resultant surface finish from shot peening is not adequate. Perhaps this is an option to pursue. Also, there is a huge amount of technical information available on shot peening available at the following website:

http://www.shotpeening.org/ICSP/confrns.htm

Click on the papers from the various conferences to access the .pdfs.

 

[jackboot]

TVP - thanks, I thought this library was the same as the one on

http://www.shotpeener.com.

But - it has a good many papers that I have not seen.

 

[rmw]

I had to have some gears shot peened for fatigue resistance once, and while visiting the peener's plant, I noticed that a lot of OEM helicopter blade assembly parts were being peened by this process in the same shop. That spoke volumes to me regarding the process, and validated it for me, as I was a skeptic early on.

rmw

 

[EdStainless]

Peening can be very helpful in fatigue situations. I would be less eager to rely on it for SCC resistance. The problem is htat SCC requires active local corrosion sites. The peened surface will not have any better corrosion resistance. Any local crevice or pitting corrosion may change the local stresses enough for SCC to proceed.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[jackboot]

I have read several papers on shot peening and SCC. And SCC life cycles were extend 70% to several times out. It is notable to say that most of the studies depicted that SCC life improved more so than the fatigue life.

There were cases (solutions) where peening was detrimental though versus a non-peened version.

jackboot

 

[unclesyd]

I have had success with peening of 304L SS to improve IGC resistance and limited success on delaying or preventing IGSCC and TGSSS. It was hard to measure the improvement achieved due to the extreme corrosive nature of the process exposure. The corrosive nature of the media that a material is going to be exposed to greatly effect the results. I was mainly trying to improve or slow the initiation of the onset of IGC of 304L in our service.

The most dramatic results were with 430 SS with very small holes. This was a punched hole .0090"dia. in the bottom of 60° coined hole. The resultant hole was surrounded by very tight circular grain boundries and the corrosion mechanism was IGC . By employing shootpeening of this area prior to finishing the hole we practically eliminated the corrosion damage by disconnecting the grain boundries.

Checkout the following site.

http://www.metalimprovement.com/