joeh
New member
i have observed a couple of small ( 2mm long ) hairline like cracks on my forestay lower terminal fitting ( stainless, stalok ). on rubbing with sandpaper they disappeared totally. any comments / suggestions ?
hairline cracks
- Thread starter joeh
- Start date
jfkal
Active member
Replace.
AndrewB
Well-known member
Replace it!
Short, hairline cracks are symptomatic of fatigue in stainless steel. Take a look at <A target="_blank" HREF=http://bosunsupplies.com/Fatigue.cfm>this advice</A>.
Bit odd they disappear totally on sanding though. Are you quite sure it isn't surface scratches or dirt? You might try a penetrating dye on one to check.
Short, hairline cracks are symptomatic of fatigue in stainless steel. Take a look at <A target="_blank" HREF=http://bosunsupplies.com/Fatigue.cfm>this advice</A>.
Bit odd they disappear totally on sanding though. Are you quite sure it isn't surface scratches or dirt? You might try a penetrating dye on one to check.
Plum
Well-known member
By abrading the surface you may have just disguised the cracks. Depends on what grade of abrasive you used. You need to restore the surface to a "mirror" like surface using progressively finer wet&dry abrasive paper working down to 5000 grade. Then, after thorough cleaning, use a dye penetrant spray for crack detection. Read the instructions on the can. If the cracks show up, replace it. Check all the others while you are at it! Is this a re-usable fitting? If so, remove it from the wire and mail it to Stalock for analysis.
chriscallender
Active member
I would replace it - you're never going to trust it 100% now, no matter how well it is checked or who tells you it will be OK, so for the peace of mind that it gives you its worth replacing.
I guess that when you sand they may get filled with very fine dust which temporarily causes them to disappear?
I guess that when you sand they may get filled with very fine dust which temporarily causes them to disappear?
charles_reed
Active member
I\'d second that
Done enough FMEAs to know that you're fairly far down the roar to having a bonk on the head from a falling mast.
Mind you it's probably a good idea to go thro' with your imminent garvity storm, you'll get every thing but the fatigue-failed object replaced by your insurers.
I caught my mast before it fell and am still arguing with underwriters.
Done enough FMEAs to know that you're fairly far down the roar to having a bonk on the head from a falling mast.
Mind you it's probably a good idea to go thro' with your imminent garvity storm, you'll get every thing but the fatigue-failed object replaced by your insurers.
I caught my mast before it fell and am still arguing with underwriters.
PeteMcK
New member
Third it
It's a common fallacy that it's the fatigue crack that gets you. It's almost always the fast fracture which does. All materials have a measurable property called fracture toughness. This determines whether, for a given combination of load and crack length, the crack will extend unstably (usually at something near the speed of sound). Fatigue causes the crack to initiate and grow in the first place in a fairly stable, possibly slow, incremental manner, with cyclic loading. Under the loads you've been giving the rig, the critical crack length for fast fracture isn't the 2mm you've measured, but it might be 2.1. Or the next load might be that 1% extra it needs. Unless you're sure, absolutely sure, it's not just cosmetic surface scratches you see, condemn the unit immediately. Take note, fatigue cracking aggravated by stress corrosion cracking, which is what you probably have, is exactly the type of serious degradation that highly loaded stainless is susceptible to in this type of environment. (And, bolstering Charles and his FMEA, this tuppenceworth's from a PhD in fracture mechanics.).
It's a common fallacy that it's the fatigue crack that gets you. It's almost always the fast fracture which does. All materials have a measurable property called fracture toughness. This determines whether, for a given combination of load and crack length, the crack will extend unstably (usually at something near the speed of sound). Fatigue causes the crack to initiate and grow in the first place in a fairly stable, possibly slow, incremental manner, with cyclic loading. Under the loads you've been giving the rig, the critical crack length for fast fracture isn't the 2mm you've measured, but it might be 2.1. Or the next load might be that 1% extra it needs. Unless you're sure, absolutely sure, it's not just cosmetic surface scratches you see, condemn the unit immediately. Take note, fatigue cracking aggravated by stress corrosion cracking, which is what you probably have, is exactly the type of serious degradation that highly loaded stainless is susceptible to in this type of environment. (And, bolstering Charles and his FMEA, this tuppenceworth's from a PhD in fracture mechanics.).
