Lifespan of 304 and 316 stainless steel plate

[pbc825]

I've recently been asked to estimate the lifespan of a proposed stainless steel plate structure. Our firm does mine reclamation work in northern Saskatchewan, Canada, and we've done a number of mine hole covers in the past with 316L stainless steel based on the client's recommendation. Following field fitting and assembly, the older mine covers were pickled and passivated to maximum longevity.

We're now in the proposal stage for a number of new covers. The new client has asked that we define which steel to use (we've narrowed it down to 304 or 316 stainless steel), and that we estimate the lifespan of the plate structures. For the most part, the structures will be subject to ground snow load (in the 60psf range) yearly and otherwise be untouched and unloaded as the covers are extremely remote. In lieu of sabotage, does anyone care to venture an educated guess at lifespan for a 304 stainless steel product that has been properly pickled and passivated in the field? And for a 316 product?

Any opinion I bring to the client's attention will likely need to be backed up either by calculation or literature in the area.

Thank you in advance.
pbc825

 

[kingnero]

Will there be salt thrown around against freezing underground? This might be something to consider.
As for the lifetime, I've got absolutely no idea what could be a representative annual weight loss...

 

[IRstuff]

If there's no corrosion, then there really isn't anything that limits life for a metal that does not experience cyclical bending stress. You could argue that there is some bending, due to thermal stresses, but they should be below the infinite life stress value, or made to be.

The more germane question would be what the life requirement is? Is it 20, 50, 100, or 500 yrs. What does the cover need to do over that time?

TTFN
faq731-376
Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[pbc825]

I'd assume there will be no salt as there is really no civilization around the covers.

The cover needs to simply exist over the lifespan. The client is responsible for estimated future replacement cost; therefore, if I say it's good for 1000 years then the capital required at turn over is much less than if I say it's good for 100 years given the time-value of money.

 

[IRstuff]

There may be salt air from being close to the ocean, or it may be prone to being pooped on by birds.

But, what is the required lifespan? If the required lifespan is 20 years, it'll be irrelevant. If the required lifespan is 5000 yrs, then neither is adequate. And that doesn't necessarily account for the basic cost of the cover with different lifespans, since the lower lifespan cover might be substantially cheaper to make, and might even cover the cost of the replacement, as an example.

TTFN
faq731-376
Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx

 

[pbc825]

I see your point IRstuff, but essentially I'm looking for someone to say a structure 400 miles away from the ocean and civilization would begin to corrode no more than say 10% of it's thickness in blank number of years. It would only influence the design based on the corrosion allowance we provide.

 

[JStephen]

I estimate 47.3 years. Feel free to quote me.

 

[SAIL3]

SS is not so immune to corosion as I had first thought....in the absence of oxygen and some other conditions it can deteriorate quite quickly....it seems that there is a protective layer on the surface from it's interaction with oxygen....a polished finish on SS removes this layer and can actually make matters worse....the OP should do some research into this topic to ensure that none of these conditions exist in this particular application....

 

[Retrograde]

http://www.parrinst.com/wp-content/...1/07/Parr_Stainless-Steels-Corrosion-Info.pdf

This reference suggests corrosion rates of less than 0.1 mm/year are typical.

 

[IRstuff]

Note that the rate would be dependent on temperature, so some Arrhenius curve would need to be applied.

TTFN
faq731-376
Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:

http://www.engineering.com/AskForum/aff/32.aspx