Stress Corrosion Cracking of Fasteners
Stress Corrosion Cracking of Fasteners
(OP)
Problem:
Steel fasteners under tension are failing. Lab results indicate stress corrosion cracking, multiple sites.
Environment includes Ammonium Nitrate dust or paste and
humidity and water(not immersed)
Hypothesis:
In the presence of the Ammonium Nitrate and the humidity, acids are formed chemically attacking the fastener.
Question(s):
Is this hypothesis plausible?
If so, what kind of coating/plating can reduce or eliminate the chemical attack?
Steel fasteners under tension are failing. Lab results indicate stress corrosion cracking, multiple sites.
Environment includes Ammonium Nitrate dust or paste and
humidity and water(not immersed)
Hypothesis:
In the presence of the Ammonium Nitrate and the humidity, acids are formed chemically attacking the fastener.
Question(s):
Is this hypothesis plausible?
If so, what kind of coating/plating can reduce or eliminate the chemical attack?





RE: Stress Corrosion Cracking of Fasteners
Give a little more description of the bolts, material, size and the number
RE: Stress Corrosion Cracking of Fasteners
I wouldn't trust coating/plating as a preventative measure on threaded fasteners. Barrier types, e.g., electroless nickel, can be damaged during installation. Sacrificial coating materials Cd & Zn are attacked by ammonia/ammonium ion, and I’m not sure whether they would help, anyway. Best to use resistant material.
Verify that chlorides are not present before switching to austenitic SS bolts. Note that high strength martensitic and PH grades of SS can suffer ammonium nitrate-induced SCC. If austenitic bolts are not available in the required strength, various treatments are available to improve the resistance of mild steel: Cold working to > 50% reduction (e.g., cold heading, with rolled threads) or alloying with > 1% Cr or Mo (while avoiding Ni < 2%). Also, quenching from 900-950oC and tempering at the relatively low temperature of 250oC minimizes susceptibility. ibid., pp. 127-130.