Rust on stainless steel

[Gazza]

Have had a continuing and irritating problem of rust marks on the transom from various "stainless" steel bolts/fittings.

I've removed all the nuts and bolts and can replace them with the appropriate grade of SS, but the boarding ladder is more of a problem. The threaded studs seem to be very rusty where the threads join the tubing. I can, of course, clean them up and replace the nuts/washers, but I'm wondering if there is any more permanent solution. Getting to all the above involves removing the gas locker, so I'm keen for a long-term answer.

I intend using Loctite or similar on all fittings when replacing. Is there anything else that might work, particularly on the boarding ladder. I'd rather not have to buy a new boarding ladder.

Any help gratefully received.

Gary Miller

 

[Birdseye]

All stainless rusts to some degree in salt water but 316 type (A4) is much better than 304 type (A2) or even 302. You probably have boarding ladder studs made of the cheapest 302 or even mild steel.

Suggest you clean the GRP of rust stains with weak oxalic acid solution and thoroughly bed the boarding ladder on a sealant. I prefer silicon rubber, but the mareine stuff not kitchen version. There is a real difference in spec as well as price.

Wouldnt use loctite. Not a good enough sealant for what you want. Use silicone on the threads.

Resign yourself to having to repeat the job but if you do it right it will be every few years.

 

[tcm]

um, the boarding ladder would be rusty in a week if it was made of mild steel. It can't be mild steel really, can it?

1) all the nuts and bolts must be A4 (=316) not A2(=306) - loads of boatbuider use A4 in some places and A2 in others.

2) you have toget rid of the rust as birdeye says with oxalic acid, and rinse it off.

3) you may have to rub at the item to remove the rust: do not use any steel tool on this as you will include more carbon and make the surface a carbon (rustable) steel - use copper, brass brush plastic panscrub or other tools, but not steel on stainles steel - not wire wool either, frexample.

3) the higher the standard of polishing, the less easily crevice corrosion makes a start. Get things shiny. Use a machine and experimen with increasingly fine pastes. The round circles are evidence that people have moved to quickly through the grades of sanding/polishing - you need to be able to "turn" all the preceived scratches with a couple of wipes from one way to another before moving to the next finer grade.

4) product such as Witchinox can be used to repassivate the stainless steel surface once you've got it shiny.

5) with some things which are too rustyy to retrieve, a bit of engineering/welding work may be necessary and is not too ridiculously expensive.

 

[alant]

Stainless Steels will rust almost as quickly as mild steel if you prevent oxygen rehealing the surface - hence the rust stains.
So if any sealant is used, you are creating almost anaerobic conditions, preventing this healing even in the best grades. Threaded sections (bottle screws), or hidden surfaces (rigging wire core) not receiving sufficient oxygen will be seen to rust, as we have all experienced.
Best if sealing, to think of the s/s now as mild steel & try to make sure it is completely protected against moisture/water contact. Movement in a boat can crack hard sealants, so flexible materials must be best, so select with care maybe testing it first to make sure it 'cures' satisfactorily.
Any sections where any sealant is defective, can also undergo accelerated corrosion.

 

[bluedragon]

I took the stainless steel fixing screws out of my teak mast step block today. I was amazed by the corosion and loss of thickness. I don't know when these were fitted and what grade SS they were...but it's made me realise that SS screws in wood exposed to the weather don't have an unlimited life! When I replace these in the weeks ahead, I'll be thinking carefully how to seal them. In fact, there may be no option other than draw one or two after a few years and maybe replace the whole lot if needed. Any ideas anyone??

 

[enterprise]

TCM, tried search on "wichinox" & found that it does as you say but can't seem to find a UK supplier or chandlery to purchase some.
Any ideas or is there a simillar UK product?
Thanks

 

[Birdseye]

[ QUOTE ]
I took the stainless steel fixing screws out of my teak mast step block today. I was amazed by the corosion and loss of thickness. I don't know when these were fitted and what grade SS they were...but it's made me realise that SS screws in wood exposed to the weather don't have an unlimited life! When I replace these in the weeks ahead, I'll be thinking carefully how to seal them. In fact, there may be no option other than draw one or two after a few years and maybe replace the whole lot if needed. Any ideas anyone??

[/ QUOTE ]

There's no answer to this problem - you have stainless steel trapped in a damp anaerobic atmosphere. Same thing happens if you have stailess buried in GRP unless the sealant is good and flexible as alant has mentioned. Thats almost impossible to achieve in wood, so the best thing is to replace them with hot dip galvanised steel bolts.

 

[Birdseye]

wouldnt worry too much about the wichinox. stainless self passivates in air. if the bolts you are getting rust on are in fact stainless (some fabricators weld mild steel studs into the legs of things like pulpits where they bolt through the deck - bad practise but cheap) then the only practical way of stopping it is to ensure that they are totally sealed since they cant be totally exposed to fresh air. since the pipework on most boats is not really rigid, the sealant needs to be flexible and very adhesive.

 

[poriordan]

Hi Gazza !

Wonder if the addition of one or two small anodes on the ladder mountings might help to slow things down a little bit !

 

[richardandtracy]

.. or larger sized bronze bolts.

Regards

Richard.