Corrosion of Stainless Steel 3

[DaveAtkins]

I have a client who is wondering why some of their stainless steel guardrails/handrails are showing signs of surface corrosion after one winter. These are exterior guardrails. The stainless steel is Type 304, with a light sandblasted finish.

DaveAtkins

 

[JedClampett]

It might be poor workmanship. If you wire brush or grind the surface with a tool that has been used with carbon steel, the iron particles will embed themselves in the stainless pipe and corrode. Is the corrosion near areas that were tool finished?

 

[TXStructural]

As Jed says, surface contamination is the likely culprit. If bending or grinding was done with tools used for fabricating carbon steel, or the blasting grit was contaminated with iron/steel, the surface was contaminated.

Even without initial contamination from tools, the surface would typically need to be acid pickled to remove surface iron after manufacture. Pickling removes the iron exposed on the surface, exposing chromium. The chrome oxidizes quickly to form the characteristic chrome oxide layer that protects high-chromium stainless from weathering.

Also, residual stresses from fabricating stainless steel can result in stress corrosion cracking.

Uncontrolled, the pitting corrosion may continue deeper into the steel. As with any steel, chlorides can increase the incidence of corrosion.

 

[rowingengineer]

I'm betting it is tea staining, see attached

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[Ron]

Surface contamination is a possibility, but also look at environmental influence as well. Many stainless steels, including 304, are susceptible to chloride corrosion, as TX noted. If this is a coastal application or near a roadway in the winter, you might look into chloride influence.

The pattern of corrosion will also help to determine its cause. Both TX and JC noted that.

Check the finishing process. If acid washed, check the type of acid used. If nitric acid was used, that could be an issue.

 

[dik]

Is the corrosion occuring in areas that have been welded? Good article rowingengineer...

Dik

 

[rowingengineer]

following on from ron with a few more ideas; Are we sure it is all 304? 316 combined with 304 and sea water will cause the 304 to become a corrosion target.

Also if the handrails are riveted often the mantle in these rivets are normal steel, staining everything in their path.


An expert is a man who has made all the mistakes which can be made in a very narrow field