Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 01-12-2015, 17:55   #16
Registered User
 
leftbrainstuff's Avatar

Join Date: May 2011
Location: San Francisco and Australia
Boat: Liberty 458
Posts: 2,174
Re: metallurgy/failure question

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.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
__________________

leftbrainstuff is offline   Reply With Quote
Old 01-12-2015, 17:57   #17
Registered User
 
leftbrainstuff's Avatar

Join Date: May 2011
Location: San Francisco and Australia
Boat: Liberty 458
Posts: 2,174
Re: metallurgy/failure question

Quote:
Originally Posted by Panope View Post
Does the expanding rust (that forms in a crack) exert significant pressure that would tend to open the crack further?

Steve
No

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
__________________

leftbrainstuff is offline   Reply With Quote
Old 01-12-2015, 18:29   #18
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 5,255
Re: metallurgy/failure question

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 is offline   Reply With Quote
Old 01-12-2015, 18:44   #19
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 5,255
Re: metallurgy/failure question

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

Quote:
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 is offline   Reply With Quote
Old 01-12-2015, 18:55   #20
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 5,255
Re: metallurgy/failure question

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.
hpeer is offline   Reply With Quote
Old 01-12-2015, 20:13   #21
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,037
Re: metallurgy/failure question

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.
__________________

estarzinger is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
rig failure? irwinsailor Dollars & Cents 3 18-02-2008 07:26
Another Stainless steel failure delmarrey Construction, Maintenance & Refit 15 27-07-2006 15:58
Chain plate failure, dismasting in the Southern Ocean GrayGoose Construction, Maintenance & Refit 1 27-03-2005 07:19
In the Event of Rig Failure GordMay Health, Safety & Related Gear 0 01-08-2004 04:36



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.