Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 04-12-2015, 15:48   #1
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Boat: Outbound 44
Posts: 4,580
Helicoil into aluminum - corosion

I need to put some helicoils for stripped bolt holes on an aluminum mast base fitting. This regularly gets soaked with saltwater. Any thoughts on how to avoid corrosion between the stainless helicoil and the AL plate that they will be in?
__________________

__________________
Paul L
http://svjeorgia.blogspot.com
Paul L is online now   Reply With Quote
Old 04-12-2015, 15:57   #2
Registered User

Join Date: Nov 2013
Location: Nice, France
Boat: Hunter Marine 38
Posts: 281
Re: Helicoil into aluminum - corosion

Tefgel
__________________

__________________
sailormed is offline   Reply With Quote
Old 04-12-2015, 16:01   #3
Guy
Registered User

Join Date: Feb 2013
Location: So. Oregon, USA
Boat: Seafarer36c
Posts: 4,308
Re: Helicoil into aluminum - corosion

I have seen green locktite used to prevent corrosion in helicoil threads. I'm a big fan of anaerobic sealant. Kind of like locktite but does not get hard.
__________________
Guy is offline   Reply With Quote
Old 04-12-2015, 17:10   #4
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Helicoil into aluminum - corosion

Lanocote, Tefgel, Duralac.

b.
__________________
barnakiel is offline   Reply With Quote
Old 04-12-2015, 17:50   #5
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,374
Re: Helicoil into aluminum - corosion

If you want to remove it in the future, Tefgel. If you never anticipate taking it apart, use red or green Loctite.

By the way, I recently learned that Loctite recommends using their primer with what they refer to as inactive metals which includes SS, anodized Al, or pure Al. Not sure if that would include Al alloys common in marine usage like 6061.
__________________
The water is always bluer on the other side of the ocean.
skipmac is online now   Reply With Quote
Old 04-12-2015, 18:04   #6
Registered User

Join Date: Dec 2011
Location: Canada
Boat: 53' Amel Super Maramu
Posts: 221
Re: Helicoil into aluminum - corosion

Paul,
Is the application structural or just holding a cover on? If non-structural, or possibly just shear loads, have you considered using a Rivnut? I normally despise them from my days working on airplanes, but in this instance it would reduce the issue of galvanic corrosion with the mast as they're also aluminum.

You'd still have the issues of galvanic corrosion between it and the stainkess fastener, but with Tef-Gel it's reduced and they can be drilled out and replaced relatively easily and replaced if you do get some thread corrosion in a few years. Just a thought.

Mark
__________________
Hobie_ind is offline   Reply With Quote
Old 04-12-2015, 18:16   #7
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,045
Re: Helicoil into aluminum - corosion

Rivnuts are horrible things, spawn of the devil they are.
Seriously what happens quick is corrosion between the SS fastener and the rivnut, then you know what you have right?

I have much experience with Loctite, both green and blue, just do not use red. Astonished me when Forespar recommended Red to me to mount my whisker pole track. Red is stud and bearing mount, meant to be permanent. On the bottle it warns that it may take excessive force and or heat to remove.
I have a two ounce tub of Tefgel that I plan on using based solely on others recommendation. Sure looks a lot like Teflon pipe dope, just way more money, but if it works it's worth it.


Sent from my iPad Pro using Cruisers Sailing Forum
__________________
a64pilot is offline   Reply With Quote
Old 04-12-2015, 18:41   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Boat: Outbound 44
Posts: 4,580
Re: Helicoil into aluminum - corosion

I usually use tefgel. I was just thinking that there wouldn't be much left on the helicoil to base material side after installing the helicoil.
__________________
Paul L
http://svjeorgia.blogspot.com
Paul L is online now   Reply With Quote
Old 04-12-2015, 19:06   #9
Guy
Registered User

Join Date: Feb 2013
Location: So. Oregon, USA
Boat: Seafarer36c
Posts: 4,308
Re: Helicoil into aluminum - corosion

Quote:
Originally Posted by a64pilot View Post
Sure looks a lot like Teflon pipe dope, just way more money, but if it's worth it's worth it.
Sent from my iPad Pro using Cruisers Sailing Forum
I'm telling you they are not the same, it's worth it. If you don't believe me check the teflon content of both and also check the difference between Forespar and Tefgel because you will find Forespar has more Teflon.
__________________
Guy is offline   Reply With Quote
Old 05-12-2015, 09:10   #10
Registered User

Join Date: Oct 2015
Location: Crete, Greece
Boat: Dromor, Discovery3000, 33'
Posts: 4
Re: Helicoil into aluminum - corosion

Helicoils weren't always intended just to repair damaged threads. In the aircraft industry they were used in aluminium to prevent damage should a bolt require to be withdrawn frequently.

Some aircraft find themselves in pretty hostile environments, corrosion-wise, much worse than our beloved boats. We engineers had to make sure minimal corrosion, coupled to demountability. Thus, whilst we used stainless steel helicoils against stainless steel bolts we avoided stainless against aluminium. The maxim being that potential between two metals must be as low as possible but never more than 0.5 volt. I do not recall the actual figures (I could look it all up, but you can have fun doing the!), stainless to aluminium is 0.9 volts and consequently a high potential and electrolytic action in a wet environment (basically you have a battery corroding away) by electro-plating the helicoil with cadmium, which would stay in place between the helicoil and the aluminium and have less than 0.5 volt potential to each. The cadmium would wear away between the bolt and the helicoil, but that didn't matter...they were the same metals/potential difference. While I am a fan of loctite and the rest, metal to metal contact is inevitable although electrolyte (sea water) is lessened. It might be better to avoid it, just in case one day you want to take that dogged little helicoil out. Merry Xmas!
__________________
FATS is offline   Reply With Quote
Old 05-12-2015, 09:18   #11
Registered User

Join Date: Oct 2015
Location: Crete, Greece
Boat: Dromor, Discovery3000, 33'
Posts: 4
Thumbs up Re: Helicoil into aluminum - corosion

I forgot to say that these days cadmium plating is considered too toxic to be commercially viable but I believe zinc plating does much the same job, potential-difference-wise.
__________________
FATS is offline   Reply With Quote
Old 05-12-2015, 10:27   #12
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jan 2012
Location: vessel sold at LAKES ENTRANCE to a local. Currently nursing my 93 Y/o mother in Sydney. Next boat probably will be bought in the U.S.
Boat: triton 721 24' x 9' 1985 Cutter rigged.
Posts: 922
Re: Helicoil into aluminum - corosion

Been helicoiling seriously expensive alloy cylinder cylinder heads (Merc, bmw, ferrari etc) for 5 decades. Yes, the environmental electrolyte in automotive is different, little or no salt, temps well in excess of boiling must be tolerated and in the early days glycol didn't exist.
You'll have permanent success with Loctite or Duralac.
in any case, the masts aluminium will try to produce its own ( preventative) oxide.
If only ALL mast tappings were Helicoiled.
Appy the stuff liberally and forget it.
FWIT, in automotive... 3 metals are present...HT steel, alloy, s/steel....all in a terribly hot environment.
Worldwide standard practice for over half a century. Fact.
Sleep well.
__________________
brianlara 3 is offline   Reply With Quote
Old 05-12-2015, 14:57   #13
Registered User

Join Date: Aug 2011
Posts: 8
Re: Helicoil into aluminum - corosion

No one's mentioned copper free marine anti-seize. I've installed SS screws into an aluminum mast and was able to remove and replace the screw 5 years later without any problems. Boat was a 46' ocean going catamaran.
__________________
rostan1 is offline   Reply With Quote
Old 05-12-2015, 17:08   #14
Registered User

Join Date: Feb 2011
Posts: 2,105
Re: Helicoil into aluminum - corosion

In a pinch use silicone sealant. Good to have on any long distant voyage for sealing whatever. We re bedded an entire mast rack with it. Mildly adhesive. Clear tubes best all around use.
__________________
reed1v is offline   Reply With Quote
Old 06-12-2015, 05:39   #15
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Helicoil into aluminum - corosion

They make titanium, inconel, and other types of threaded inserts if you want to go that far.

Mark
__________________

__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Reply

Tags
oil

Thread Tools
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
Aluminum Chainplates Catamount Construction, Maintenance & Refit 11 09-03-2010 16:15
Aluminum Finishes Sandero Construction, Maintenance & Refit 6 27-04-2006 18:30
Aluminum boats irwinsailor Construction, Maintenance & Refit 12 06-10-2005 21:42
Aluminum spar damage. irwinsailor Construction, Maintenance & Refit 2 01-05-2004 21:52
Repairing an aluminum spar Sonosailor Construction, Maintenance & Refit 6 12-12-2003 03:46



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 01:33.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.