SCC stainless
SCC stainless
(OP)
I have a piece that is exhibiting cracks(some small, some large). I'm trying to come up with an initial cause of these failures before we send them off for further analysis, and I'm wondering if it's possible to eliminate SCC as a cause of these cracks without access to metallographic equipment?
The pieces were in service for 4-5 years, and remain in decent shape except for cracks forming across the corners. I was initially told they were in service for <1 year so I thought it might be casting defects, but now I'm not so sure because of the longer service time.
Enviro is 600-700 deg. C, chlorides present, SS/austenitic, small tensile forces present.
The pieces were in service for 4-5 years, and remain in decent shape except for cracks forming across the corners. I was initially told they were in service for <1 year so I thought it might be casting defects, but now I'm not so sure because of the longer service time.
Enviro is 600-700 deg. C, chlorides present, SS/austenitic, small tensile forces present.





RE: SCC stainless
Do they see an temperature cycling?
Next to CSCC all of the other failure mechanisms have little chance. Mechanical or thermal fatigue? Doesn't sound likely.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SCC stainless
There is no evidence of pitting, but there is a region of porosity that looks like a casting defect. The holes are uniform in size, and there are two parrallel rows.
The material is not magnetic.
RE: SCC stainless
RE: SCC stainless
Complete shutdown happens once a year, ideally.
RE: SCC stainless
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: SCC stainless
RE: SCC stainless
-The service environment is oxidizing
-They are made of astm a297-hh
what is the most important factor in the cycling that may lead to the cracking? Temperature range? Cooling/heating rate? Cycling times?
RE: SCC stainless
RE: SCC stainless
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: SCC stainless
These pieces are about 1meter in length, and about .15 wide, with varying height(from .10m to .15). The forces act along the longer axis.
I'm fairly new at my position, and this is the first failure like this that I've seen. I'm just trying to learn from this case so I can understand and learn what to expect in the future.
RE: SCC stainless
If you can't find a way to control the cooling/heating rate, you'll need to redesign.
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: SCC stainless
I was just told by our supplier that HH tends to age harden which leads to the cracking. Can anyone tell me how common this problem is? We have had many of these components in service and never seen this time of problem before.
Also, they suggested upgrading to HK material. In the past I have conducted an experiment on various HK alloys, I found that HK had excessive spalling when there was cycling conditions. Has anyone seen similar or different results?
RE: SCC stainless
RE: SCC stainless
Would reheat cracking be apparent from large grains near the crack?
RE: SCC stainless
The flaking/spalling in HK may be a chemistry issue. This alloy has better strength at temp and should be very stable. Of course higher strength would work against you if you are having thermal fatigue issues.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SCC stainless
Would cycling have no effect on the spalling of HK? Why does higher strength have a negative effect on thermal fatigue? I would have thought differently.
RE: SCC stainless
1100C is pushing either of them temperature wise it is at the limits that we suggest for 310 stainless which is the wrought equivalent to HK. For 309 or HH we suggest an upper limit of around 1025 to 1050C. Depending on the design if the design can be done with a fabricated wrought product you would get better ductility. The drawback is wrought alloys like 309 or 310 have lower creep rupture properties than their cast equivalents. Also they tend to be more expensive than castings.
Below is a link to a case history on some cast grids that cracked. You might want to take a look at it and see if it looks similar to your problem.
http://www.rolledalloys.com/trc/hrcasehist.aspx
select the case history titled RA330 grids.
RE: SCC stainless
HK should be more stable. Less scale and it should be tight. If you are cycling though the higher strength of HK may not really help much. It may be a casting or design issue and the higher stresses will cause failures somewhere.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm