Hi,
I know that this possibly has a simple answer that everyone but me
knows, but is there any way I can prevent the unslightly brown "rust"
marks on my white hull paint from a welded fabricated stainless steel
fitting that is bolted on with stainless bolts?

I am about to spray on the white topcoat over the primer during a hull
repaint job and I'd like it to stay looking good.

I suspect that the drop ladder on the stern is not made entirely of
316. It has been 15 years since I fitted it, so that I can't recall
whether the bolt is 316, 304 or (unlikely) something else. There are
no 316 markings on the bolt heads.

We use oxalic acid powder mixed with water to get rid of it but it
always comes back. I am beginning to quote Lady MacBeth when I rub it
away ("out foul spot") and it's embarrassing when passersby overhear.
I know that there are several (expensive) "special" products to clean
it with but I would appreciate some knight on a white charger offering
me a permanent fix. It doesn't matter if he's young or old, handsome
or otherwise - I'm not playing Sleeping Beauty - so long as he or she
has the answer.

I wonder whether it would be possible to electrically isolate it with
say, a teflon washer?

cheers
Peter
(who actually sails places and doesn't pretend to)

Peter Hendra wrote:
Hi,
I know that this possibly has a simple answer that everyone but me
knows, but is there any way I can prevent the unslightly brown "rust"
marks on my white hull paint from a welded fabricated stainless steel
fitting that is bolted on with stainless bolts?

I am about to spray on the white topcoat over the primer during a hull
repaint job and I'd like it to stay looking good.

I suspect that the drop ladder on the stern is not made entirely of
316. It has been 15 years since I fitted it, so that I can't recall
whether the bolt is 316, 304 or (unlikely) something else. There are
no 316 markings on the bolt heads.

We use oxalic acid powder mixed with water to get rid of it but it
always comes back. I am beginning to quote Lady MacBeth when I rub it
away ("out foul spot") and it's embarrassing when passersby overhear.
I know that there are several (expensive) "special" products to clean
it with but I would appreciate some knight on a white charger offering
me a permanent fix. It doesn't matter if he's young or old, handsome
or otherwise - I'm not playing Sleeping Beauty - so long as he or she
has the answer.

I wonder whether it would be possible to electrically isolate it with
say, a teflon washer?

cheers
Peter
(who actually sails places and doesn't pretend to)
where is the rust comming from
the weld or the mounting point
or the bolts them selfs
Shaun

On Fri, 23 Mar 2007 19:22:33 +1100, Peter Hendra
wrote:

I know that this possibly has a simple answer that everyone but me
knows, but is there any way I can prevent the unslightly brown "rust"
marks on my white hull paint from a welded fabricated stainless steel
fitting that is bolted on with stainless bolts?

My first reaction would be to prime and paint the stainless but that
might have its own issues.

Probability is that the welds are not ground flat and smooth and
crevice corrosion is underway in the 'intersticies' of the weldment
(poor weld technique ... not a full penetration weld).

To be 'corrosion resistant' (chlorides, etc. attack stainless) all the
weld must be flat /smooth by grinding and then polishing/buffing to a
high mechanical mirror polish. Any 'weld-lap' or pin-hole in the weld
will be a source of 'rust' .... gotta be closed and then smoothed. .


In article , Peter Hendra
wrote:

Hi,
I know that this possibly has a simple answer that everyone but me
knows, but is there any way I can prevent the unslightly brown "rust"
marks on my white hull paint from a welded fabricated stainless steel
fitting that is bolted on with stainless bolts?

I am about to spray on the white topcoat over the primer during a hull
repaint job and I'd like it to stay looking good.

I suspect that the drop ladder on the stern is not made entirely of
316. It has been 15 years since I fitted it, so that I can't recall
whether the bolt is 316, 304 or (unlikely) something else. There are
no 316 markings on the bolt heads.

We use oxalic acid powder mixed with water to get rid of it but it
always comes back. I am beginning to quote Lady MacBeth when I rub it
away ("out foul spot") and it's embarrassing when passersby overhear.
I know that there are several (expensive) "special" products to clean
it with but I would appreciate some knight on a white charger offering
me a permanent fix. It doesn't matter if he's young or old, handsome
or otherwise - I'm not playing Sleeping Beauty - so long as he or she
has the answer.

I wonder whether it would be possible to electrically isolate it with
say, a teflon washer?

cheers
Peter
(who actually sails places and doesn't pretend to)

On Sat, 24 Mar 2007 12:44:13 GMT, Rich Hampel
wrote:

Probability is that the welds are not ground flat and smooth and
crevice corrosion is underway in the 'intersticies' of the weldment
(poor weld technique ... not a full penetration weld).

To be 'corrosion resistant' (chlorides, etc. attack stainless) all the
weld must be flat /smooth by grinding and then polishing/buffing to a
high mechanical mirror polish. Any 'weld-lap' or pin-hole in the weld
will be a source of 'rust' .... gotta be closed and then smoothed. .


This has just made sense as only one of the bolt on "feet" for the
ladder suffers from the problem. I'll try it.

Thanks very much to all who responded.

regards
Peter Hendra

"Peter Hendra" wrote in message
...
On Sat, 24 Mar 2007 12:44:13 GMT, Rich Hampel
wrote:

Probability is that the welds are not ground flat and smooth and
crevice corrosion is underway in the 'intersticies' of the weldment
(poor weld technique ... not a full penetration weld).

To be 'corrosion resistant' (chlorides, etc. attack stainless) all the
weld must be flat /smooth by grinding and then polishing/buffing to a
high mechanical mirror polish. Any 'weld-lap' or pin-hole in the weld
will be a source of 'rust' .... gotta be closed and then smoothed. .


This has just made sense as only one of the bolt on "feet" for the
ladder suffers from the problem. I'll try it.

Thanks very much to all who responded.

regards
Peter Hendra

A friend has gone thru this with his stainless. People at his workplace
that know about his sort of thing told him he needed to passivate the welds.
They gave him some solution to paint on the welds. I believe this is
hydrofluoric acid, perhaps a mixture with other acids. Requires very
carefull application. It took away the surface shine. Don't recall the
final result but I can ask him.

On Mon, 26 Mar 2007 17:56:36 GMT, "Gordon Wedman"
wrote:



A friend has gone thru this with his stainless. People at his workplace
that know about his sort of thing told him he needed to passivate the welds.
They gave him some solution to paint on the welds. I believe this is
hydrofluoric acid, perhaps a mixture with other acids. Requires very
carefull application. It took away the surface shine. Don't recall the
final result but I can ask him.


Thanks for this Gordon,
At the moment the offending articles are sheathed by masking tape as I
am halfway through spray painting the hull.

I would very much appreciate you asking your friend if it is not too
much trouble. The more information about this, the better.

When it was welded, it, like all other Stainless welds was brushed
with that nitric acid gel solution that then is washed off with water,
and which removes the discolouration from the tig/mig/arc welding
process. Is this the same thing? I can't recall getting anything
"passivated".

Thanks and cheers
Peter

On Mon, 26 Mar 2007 17:50:22 +1000, Peter Hendra
wrote:

On Mon, 26 Mar 2007 17:56:36 GMT, "Gordon Wedman"
wrote:



A friend has gone thru this with his stainless. People at his workplace
that know about his sort of thing told him he needed to passivate the welds.
They gave him some solution to paint on the welds. I believe this is
hydrofluoric acid, perhaps a mixture with other acids. Requires very
carefull application. It took away the surface shine. Don't recall the
final result but I can ask him.


Thanks for this Gordon,
At the moment the offending articles are sheathed by masking tape as I
am halfway through spray painting the hull.

I would very much appreciate you asking your friend if it is not too
much trouble. The more information about this, the better.

When it was welded, it, like all other Stainless welds was brushed
with that nitric acid gel solution that then is washed off with water,
and which removes the discolouration from the tig/mig/arc welding
process. Is this the same thing? I can't recall getting anything
"passivated".

Thanks and cheers
Peter

The acid treatment was "passivating".

My experience is that unless the stainless is polished to a mirror
bright finish you will get staining. All the bits have to be polished;
Assuming that it is a bolt on fitting the bolts and washers that are
exposed to sea water need to be polished.

I've been making things out of stainless and putting them on boats for
quite a number of years and I have found that if the part has all the
welds ground smooth (so the welding ripples don't show), no pin holes
or voids in the weld and then polished bright I seldom get staining.
If I don't do this I always get staining.

A couple of years ago I built a new stitch and glue dinghy. Welded up
a couple of plates with a lifting eye; dosed them with a 20% acid bath
until all the discoloration was cleaned off; gave them a lick with a
sanding disk on a high speed grinder; mounted them and gave them two
coats of epoxy primer and two coats of two part poly urethane
(spelling?). Got "rust" stains. Should have polished them.

By the way, I get my stainless polished at the local chrome shop,
Cheaper then the "stainless shop".

I also take care to bed everything with either 3M or Sikaflex. Much
better then household "silicone" sealant.

I've been reading some of your other posts -- do you reckon that your
paint job is cheaper, or more expensive then it wold be in Malaysia?



Bruce in Bangkok
(brucepaigeatgmaildotcom)

--
Posted via a free Usenet account from http://www.teranews.com

On Mon, 26 Mar 2007 17:56:36 GMT, "Gordon Wedman"
wrote:


"Peter Hendra" wrote in message
.. .
On Sat, 24 Mar 2007 12:44:13 GMT, Rich Hampel
wrote:

Probability is that the welds are not ground flat and smooth and
crevice corrosion is underway in the 'intersticies' of the weldment
(poor weld technique ... not a full penetration weld).

To be 'corrosion resistant' (chlorides, etc. attack stainless) all the
weld must be flat /smooth by grinding and then polishing/buffing to a
high mechanical mirror polish. Any 'weld-lap' or pin-hole in the weld
will be a source of 'rust' .... gotta be closed and then smoothed. .


This has just made sense as only one of the bolt on "feet" for the
ladder suffers from the problem. I'll try it.

Thanks very much to all who responded.

regards
Peter Hendra

A friend has gone thru this with his stainless. People at his workplace
that know about his sort of thing told him he needed to passivate the welds.
They gave him some solution to paint on the welds. I believe this is
hydrofluoric acid, perhaps a mixture with other acids. Requires very
carefull application. It took away the surface shine. Don't recall the
final result but I can ask him.

It won't be Hydrofluoric Acid, which is one of the nastiest nasty
chemicals on the face of this earth. It's much more likely to be a
50~50 mixture of Hydrochloric and Nitric acids plus, sometimes, a
little Phosphoric acid. You should somewhere find an expert and read
http://www.assda.asn.au/asp/index.asp?pgid=17982
Whatever you do, you don't want a strong brew and you should let time
be your friend.



Eric Stevens

On Tue, 27 Mar 2007 20:51:00 +1200, Eric Stevens
wrote:

On Mon, 26 Mar 2007 17:56:36 GMT, "Gordon Wedman"
wrote:


"Peter Hendra" wrote in message
. ..
On Sat, 24 Mar 2007 12:44:13 GMT, Rich Hampel
wrote:

Probability is that the welds are not ground flat and smooth and
crevice corrosion is underway in the 'intersticies' of the weldment
(poor weld technique ... not a full penetration weld).

To be 'corrosion resistant' (chlorides, etc. attack stainless) all the
weld must be flat /smooth by grinding and then polishing/buffing to a
high mechanical mirror polish. Any 'weld-lap' or pin-hole in the weld
will be a source of 'rust' .... gotta be closed and then smoothed. .


This has just made sense as only one of the bolt on "feet" for the
ladder suffers from the problem. I'll try it.

Thanks very much to all who responded.

regards
Peter Hendra

A friend has gone thru this with his stainless. People at his workplace
that know about his sort of thing told him he needed to passivate the welds.
They gave him some solution to paint on the welds. I believe this is
hydrofluoric acid, perhaps a mixture with other acids. Requires very
carefull application. It took away the surface shine. Don't recall the
final result but I can ask him.

It won't be Hydrofluoric Acid, which is one of the nastiest nasty
chemicals on the face of this earth. It's much more likely to be a
50~50 mixture of Hydrochloric and Nitric acids plus, sometimes, a
little Phosphoric acid. You should somewhere find an expert and read
http://www.assda.asn.au/asp/index.asp?pgid=17982
Whatever you do, you don't want a strong brew and you should let time
be your friend.



Eric Stevens

Thanks Eric,
A great site and I love your phrase "let time be your friend" -
poetic. May I have your permission to use it in future - yes, I'll
cite you as the originator? I don't want to get flamed.

cheers
Peter