Rust formation on 316 bolt

[arunmrao]

A failed 316 bolt used near an oil well in the Middle East had come for failure analysis. The findings of the lab was that the bolt was not passivated properly . The lab recommended suitable procedure which was adopted by the manufacturer. However, within 2 months a rediish brown scale appeared on the surface of the bolt similar to earlier supplies.The lab confirms that now this is a protective layer which is impervious and further corrosion will not occur!!. I request the members to offer their insight.

I shall not be able to reveal details beyond what has been described.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[btrueblood]

Arun,

Any hint on what the chemistry of the scale is?

 

[EdStainless]

Well, if the bolt was touched with steel tools or subjected to rubbing/fretting/wear after passivation you would get this result.
What was the failure mode? Crevice corrosion? CSCC? We need to know what you are trying to prevent.
Personally, I have never used 3xx bolts. It is just the wrong combination of properties and risks.

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Rust never sleeps
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[btrueblood]

Ed,

But if the problem is iron contamination/embedment in the 316, you'd also say that the "rust" is not a "stable oxide layer", right?

 

[unclesyd]

I think the lab might be correct in that the coating/oxide will protect the fastener.

This is from experience.
It is quite common for Austenitic SS, 316 in this case, to form a protective oxide coating when exposed to different environments. In fact we deliberately forced the oxide (red) as routine measure to ensure compatibility with our process. In this process it involved both temperature and environment.
In another area where we used 316 SS spinneretts, extrusion jets, again we forced an oxide (blue) coating with a steam air oxidation. As we remove the polymer by pyrolysis it was essential that the oxide be present to prevent the deterioration of the capillary edges.
In both areas no cleaning was allowed that would remove the oxide coating.
The worst thing you could see was shinny SS in either of the above areas.

Anecdotal:
I used to do a little commercial Red Snapper fishing and we used 316 SS cable on or reels. The cable was 3/64" 7x19 McWhite, aircraft control cable. Several times I've witnessed that after putting a brand new cable on a reel and after less that an hour use, the cable would part underwater. Metallurgical examination of the cable revealed SCC of the finest kind. The cable could fail anytime and place.
The muffler on this boat was made from scrap 316 SS pipe (10" and 4") and sits exposed to the weather. In heavy seas you see the salt spray frying on the surface. It is 30 years old with no cracking. I fought off every attempt to clean it up.

Shinny SS around boats or salt water usually mean trouble unless they are in place wher they get polished often.

 

[arunmrao]

Thanks for the useful comments all.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[bob330]

Unclesyd,

I am absolutly shocked that you saw SCC in water that was probably no more than 80F or so. This should pretty much be an impossibility? Are you sure about this? Were you really seeing corrosion fatigue of some sort?

bob

 

[unclesyd]

I can guarantee that the failure was from chloride induced SCC. The material was 7X7 316 SS 3/32 dia.

As stated above we used SS aircraft control cable on commercial fishing reels. The cable was made by the McWhyte or Hackensack Co's specifically for aircraft control cable. One thousand feet of the cable is wound on 12" dia wooden/Bakelite spools. It completely isolated from any stray currents. The spool is exposed to the elements at all times. Other than hauling fish the normal load was a 7 lb weight.

It was not uncommon to get a rapid failure of the SS cable once exposed to sea water.
The ultimate failure, old age, of the cable was always corrosion and or SCC after period of time that varied greatly, though it was not unusual for a particular cable to last 4 or 5 years.

I was able to check several of the broken ends in our metallurgical lab, both by optical and SEM. Boiling MgCl[sub]2[/sub] would fracture the cable in minutes using a figure 8 knot to generate high stress.

I have another one where the failure was in a 316 SS roller guide I made for using the cable on a boat rod. The guide was made form 316 strip and after fabrication by welding all the guides were quenched annealed, mechanically polished, and put on a boat type rod. Between trips I noticed that the first guide from the reel had a few rust spots. I removed the guide and upon further examination revealed SCC. The other guides from the set are still on the rod and look good, 40 years later.

 

[EdStainless]

I have seen ambient (summer) temp CSCC in 304 and 316. It does take a lot of Cl and high stress, a bit of S helps, and it will go.

A red/orange layer is never a protection. This material is a mixture of oxides and hydroxides. It will be porous and moist and will not aid in the formation of a true chome oxide passive film under it. This red/orange layer is always an indication of improperly cleaned or handled stainless steel.

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Rust never sleeps
Neither should your protection

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[bob330]

EdStainless,

When you say improperly cleaned or handles, what exactly do you mean? Is it impossible to get the red corrosion products if the steel had been passivated correctly or can certain environments bring it out regardless?

Also, does stainless steel really need to be passivated prior to service since I hear that it will form the passive layer even in moist air?

bob

 

[EdStainless]

The real function of passivation is to remove imbedded iron from the surface. If a stainless part blushes orange in humid air then it has not been properly prepared.

There are some environments that will cause stainless to rust as a result of active corrosion attack. These will lead to early failure. They are usually low pH and high Cl. In this case you need a better stainless.
How about bolts in 2205? Just remember the temperature limits.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

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