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What's going on at sea cliffs: is magnesium oxide breaking down steel bolts?


Original Post
aikibujin · · Castle Rock, CO · Joined Oct 2014 · Points: 294

I'm not a bolter, and I don't have the education or experience to participate in the discussion that goes on in this sub-forum. However, I do like to read about this stuff, and hope that what I learned here can help keep me safe when I'm clipping bolts outside. So when I was listening to the Enormocast with Sam Lightner Jr posted almost a month ago, something Sam said really piqued my interest. The whole discussion about bolting started at about 46 minutes into the podcast if anyone wants to take a listen. In reference to what was happening with bolts failing in Thailand what he said was, "it was Magnesium oxide, heated up to over 140 degrees, breaks down steel 20 times faster than salt does, and it will break down virtually any kind of steel." This was something that I've never heard of, and a search of "magnesium oxide" or "MgO" didn't turn up any relevant discussion on MP. I know SCC (Stress Corrosion Cracking) has been discussed extensively here, but people usually talk about magnesium chloride. So did Sam just confused magnesium oxide with magnesium chloride, or is this new information?

slevin · · Unknown Hometown · Joined Jan 2001 · Points: 1,001
Mike Slavens · · Houston, TX · Joined Jan 2009 · Points: 35

Sam almost certainly meant Magnesium Chloride, just a simple mistake.  Its Chloride concentration, along with temperature, that causes SCC.  MgCl2, dissolved from the rock, will allow much higher chloride concentrations than NaCl which is one of the thoughts on why the SS of Thailand was failing where SCC would not normally be expected to occur.

https://www.researchgate.net/publication/225392704_Marine_Atmospheric_SCC_of_Unsensitized_Stainless_Steel_Rock_Climbing_Protection


aikibujin · · Castle Rock, CO · Joined Oct 2014 · Points: 294
slevin wrote:

https://www.climbing.com/people/built-to-last/

Magnesium oxide was not mentioned in that article at all. I'm really questioning if magnesium oxide is the latest breaking news, or did Sam confuse magnesium oxide with magnesium chloride.

C. Williams · · the Climber Cave · Joined Jul 2013 · Points: 1,152

Sam was talking about magnesium chloride. For MgO to be transferred to climbing bolts it would most likely be dissolved in water creating magnesium hydroxide. Magnesium hydroxide (and MgO) is not known to be corrosive to stainless steels. Magnesium chloride on the other hand is rather destructive to most stainless steels, even more so once temperatures pass 40 C.

Francis Haden · · Unknown Hometown · Joined Dec 2016 · Points: 9

1) Chlorides

2) A material susceptible to SCC

3) Stress within the material

The minimum 3 requirements for SCC. However it's more complicated since optimum humidity (producing the most aggressive salt concentration) and other factors are involved which is why SCC is occurring in non limestone climbing regions besides Southern Thailand.


Jim Titt · · Germany · Joined Nov 2009 · Points: 490

Magnesium oxide is good if you´ve got indigestion  

Guideline #1: Don't be a jerk.

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