metallurgy/failure question

[leftbrainstuff]

Brittle fracture occurred at the interface between the rusted and unrusted section. Using the surace area and an estimate of the material properties would allow a rough calc of the failure load.

The rusted section is where the initial crack has propogated. So a cyclic load has been applied. Assuming it was similar to the previous failure load calc and an approximation of the material props would allow a miners law plot to be plotted.

An optical analysis, approx 50x mag, would allow me to provide, a detailed assessment.

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[leftbrainstuff]

Originally Posted by Panope

Does the expanding rust (that forms in a crack) exert significant pressure that would tend to open the crack further?

Steve

No

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[hpeer]

Evans,

Allow me to blather on for a moment, not a metalurgest , as you can tell by the spelling.

The particular device you have, that manufacture, that metal may be newis but screw anchors in concept are very old and have held up a whole lot of Chesapeake light houses, without fracture.

And, similar screw anchors are used by the gazillions in line work for telephone and electrical lines. Look around and you will see them all over the place, greatly abused. They are run over, bent, hit by cars and trucks and snow plows, and BEND!

They are installed holding up high tension wire all across the world and never replaced.

They are installed in swamps (ones with oversized spirals are called "swamp anchors") and left forever.

They are sold as foundations for houses, obviously a very permanent installation. They hold back sheer embankments along highways.

So, just on a gut level, I'm going with these things should be permanent installations. Or maybe the exposed eye or shaft eventually rusts out and then it needs to be replace. But a break like you are showing, well that is just plain wrong.

Can you find out who the manufacturer was?

https://www.macleanpower.com/assets/...4D59691A0C.pdf

http://www.hubbellpowersystems.com/c...04-Anchors.pdf

[hpeer]

Here are a couple specializing in marine anchoring, mooring systems. Maybe give them a call.

Helix Anchors.com, LLC - Home of the Environmentally Friendly Mooring System

Home

The Benefits

High-Holding:

Our anchors derive their holding from the soils into which they are screwed. The Square Shaft anchors are installed with the aid of hydraulics to screw the anchor through resisting soils. Our anchors have been repeatedly tested by Mother Nature and tugboats with load measuring equipment.

The results of the first test (performed in Vineyard Haven, Massachusetts, under the watchful eye of area harbor masters, a marine industry reporter, and a representative of Boat/US) are typical of all the load tests performed.



Vineyard Haven, Pull Test Results
Mooring Type
Bottom Condition
Breakout Force
350-lb. Mushroom 5 ft. deep in mud 2,000 lb.
500-lb. Mushroom in sand bottom 1,700 lb.
3,000-lb. Concrete USCG block set in mud 2,100 lb.
6,000 lb. cement block on sand bottom 3,200 lb.
8/10 Helix soft clay mud 20,800+ lb.
Long Life:

Our high-load marine anchor is built on a solid, square shaft measuring 1 ¾” on a side. It is protected with hot-dipped galvanizing, and the termination includes a 1 1/8” shackle which encircles the shaft and connects to the anchor rode (Seaflex elastic rode, chain, rope, and cable have all been used successfully). Compare the mass of steel in our shaft with the steel in the eye of a mushroom or the staple in a deadweight block.

Environmentally Friendly:
Because these anchors don't drag around the harbor bottoms and can be effective with shorter scopes, these anchors are preferred in environmentally sensitive areas and have been recommended by some state agencies and scuba-diving tour companies.

[hpeer]

Here is one of interest, showing expected lifetimes under various conditions, for civil construction but you will get the idea.

If I'm reading it right you should expect 75 years from a properly designed pile anchor in a marine environment, for a 95% confidence level.

http://www.helicalpilebook.com/Files...ix%20piers.pdf

I'm betting that either this pile was a home brew concoction or it is a plain manufacturing defect. Especially if you don't see signs of the shaft being tortured in some way;bending, or twist, or whatever.

[estarzinger]

The mooring was in Red Brook Harbour in Ma. It is a decently (but not perfectly) protected harbour.

I dont know the chain, etc details, but it was a pro install, so I suspect all reasonable 'correct'.

It is a production helix mooring, not home brew.

I was exposed to Sandy, with high winds and an extraordinary water height. Right now I am guessing that exposed it to some sort of un-ordinary loading that caused a fracture. The rust in the original break area looks (to my uneducated eye) about that old. And that might suggest that many of the moorings in that NJ - RI area should be examined carefully.