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Common Mistakes When Using Stainless Steel Fasteners

December 13, 2019

Before using stainless steel fasteners, there are a few issues to keep in mind. First and foremost is the alloy going to react adversely when placed in a given environment? Rust inducing conditions come to mind here, so an oxidization resistant fastener is vital when such conditions prevail. Poorly finished screw shanks are another potential cause of fixing element failure, with those coarse surfaces trapping dirt and dust until a once functional layer of chromium-oxide is impaired.

A Failure to Assess the Fitting Conditions

Ultimately, the first mistake is a lack of situational awareness. Alternatively, the person who is responsible for sourcing a job's stainless steel fasteners wrongly assumes that all grades of this alloy are equally corrosion-resistant. That's simply not the case. Chromium and nickel-rich steels should be selected when screws or bolts are fitted in corrosive environments. And remember, water corrodes steel, so even an outdoors setting will eat away an alloy-hardened steel fitting. To sidestep such installation blunders, use 304 or 316 stainless steel.

Mistakenly Ignoring Airborne Contaminants

A rustproof stainless steel alloy is in use, but a box of screws has an unusually coarse finish. Flecks of dust adhere to this rough surface, then they settle in for the long haul. Left like this, the foreign matter causes a fatigue-like effect. The protective chromium-oxide sheath coating the fastener eventually breaks down, then the underlying steel oxidizes. Smoother, polished finishes provide no purchase for dust particles. Furthermore, if this is a working machine room of some kind, the smooth coating won't allow floating iron filings any purchase, either.

A Failure to Recognize Material-Specific Weaknesses

This time around, there are no environmental contaminants to blame. The slip-up belongs to the installation tech. Perhaps he's unaware of the difference between two metals in use on a particular job. Because the two metals are so dissimilar, a potential difference develops between them. A small electrical current flows, then electrons are lost from one of the alloy parts. This is how galvanic corrosion occurs. Either the fastener stainless steel or the parts being fastened must be similar, and the installer must take action to break the electrical circuit. A nylon washer between each fastener head and the dissimilar metal should be enough to offset this effect.

Clean steel parts and keep dust and iron filings away from stainless steel fasteners. Check and double-check a job for galvanic issues. Remember, even with a nylon washer installed, that current will still flow if the fastener screws into a dissimilar metal. Finally, low-nickel steels should not be used in settings where oxidization conditions dominate. Galvanic coatings, hot-dipped in zinc, are one option. Such coatings can fail, though, but a good 304 or 316 graded stainless steel will natively resist corrosion.

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TCI Fasteners - Topcope
13 Slater Parade, Keilor East VIC 3033 Australia

Telephone: (03) 9336 0155

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