Stainless Steel

[vyv_cox]

Yep, I am not used to seeing rust stains on what is supposed to be 316. I think my original 316 pushpit/pullpit were far in excess of the 316 standard. They never need a polish. May be once every few years. The Metals 4U stuff is crap by comparison. Only installed for a few months and brown rust stain on it

Corrosion resistance, and rusty appearance, is mostly dependent upon chromium content. The nominal minimum Cr content for 316 is 18% but top quality stuff has 20%. Cr paring is inevitable for cheaper supplies. Similarly, nickel will be 10% in the best alloys with a minimum of 8%. A slight reduction in this can result in the presence of ferrite, which also rusts.

 

[John the kiwi]

The L designation as in 304 L or 316 L indicates Low carbon. This is not a "superior" grade as such but very important for welding. With regular stainless 304 or 316 with normal carbon levels welding will cause precipitation of carbides in the heat affected zone. This is normally evident in failure alongside the weld where the parent material is a bit wasted. I have seen a number of stainless steel chemical tanks that have failed prematurely from being built from normal rather than L grade material.

The fastest corrosion of stainless steel i have seen was where 304 dairy tube had been used for ordinary steam condensate return from a heat exchanger to a steam boiler. Initially welded joints leaked then the pipe itself. The consensus was that the condensate was just acidic enough with carbonic acid to clean off the oxide layer, but the condensate had no dissolved oxygen to replenish it.
Its certainly an interesting material in all its various forms.

 

[flaming]

Corrosion resistance, and rusty appearance, is mostly dependent upon chromium content. The nominal minimum Cr content for 316 is 18% but top quality stuff has 20%. Cr paring is inevitable for cheaper supplies. Similarly, nickel will be 10% in the best alloys with a minimum of 8%. A slight reduction in this can result in the presence of ferrite, which also rusts.

What we've noticed over many years is that the mill certificates that come with our material are getting "better and better". What I mean by this is that quite clearly they are increasing the control of their processes, and are able to much more accurately control the exact amount of all the different elements present in the alloy. Because of this, where they used to aim for the middle of the spec for any given element, they are now able to aim at the bottom and reduce their spend on the exotic stuff. So all our material is still in spec, but you can argue that on average it's not quite as good as it used to be.

 

[John the kiwi]

What we've noticed over many years is that the mill certificates that come with our material are getting "better and better". What I mean by this is that quite clearly they are increasing the control of their processes, and are able to much more accurately control the exact amount of all the different elements present in the alloy. Because of this, where they used to aim for the middle of the spec for any given element, they are now able to aim at the bottom and reduce their spend on the exotic stuff. So all our material is still in spec, but you can argue that on average it's not quite as good as it used to be.

Many years ago i worked at Thatchers Cider in Sommerset. Old John Thatcher told me one day that in the old days out of 10 tanks of cider, one would be rubbish, 8 would be middling and 1 would be superb. Now with strict QC you get 10 middling tanks that all taste the same. Kind of like your stainless production story - its progress of a sort.

 

[[70521]]

Many years ago i worked at Thatchers Cider in Sommerset. Old John Thatcher told me one day that in the old days out of 10 tanks of cider, one would be rubbish, 8 would be middling and 1 would be superb. Now with strict QC you get 10 middling tanks that all taste the same. Kind of like your stainless production story - its progress of a sort.

That's not been my experience of his product! I found that 10 out of 10 tanks are rubbish. I recommend Hancock's of South Molton, Devon if you want decent cider.

 

[John the kiwi]

That's not been my experience of his product! I found that 10 out of 10 tanks are rubbish. I recommend Hancock's of South Molton, Devon if you want decent cider.

 

[AntarcticPilot]

That's not been my experience of his product! I found that 10 out of 10 tanks are rubbish. I recommend Hancock's of South Molton, Devon if you want decent cider.

If you want REALLY good cider, there used to be a farm that sold its own produce on the road from the M4 to Minehead. That was some years back, though!

 

[Rhylsailer99]

i bought 316 m8 nuts and bolts to go through my skeg to attach a rudder bottom bracket and after just a few months they're rusting , I was shocked as i though they would not rust.

 

[vyv_cox]

i bought 316 m8 nuts and bolts to go through my skeg to attach a rudder bottom bracket and after just a few months they're rusting , I was shocked as i though they would not rust.

Try polishing them. It is not unusual for new products to develop a rusty appearance, rigging wire is well known for it. This is due to micro cracks that develop crevice corrosion on a very small scale. Polishing can solve this by removing the cracks.

 

[Little Dorrit]

i bought 316 m8 nuts and bolts to go through my skeg to attach a rudder bottom bracket and after just a few months they're rusting , I was shocked as i though they would not rust.

I can confirm the previous comments ; I purchased some expensive hatch hinges about 5 years ago which did rust a little after the first season but after a polish have showed no sign of any since.