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

Bruce wrote:

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.

snip...
Bruce in Bangkok
(brucepaigeatgmaildotcom)


Hi Bruce,

I've just recently started building stainless
parts for my two sailboats. I'm using 316 SS and
316L SS exclusively and passivating with Citrisurf
which is a strong citric acid. It can also be
used for electropolishing, and I intend to try
using it for that in the future.

Google "Citrisurf". It is supposed to be better
and more environmentally friendly than nitric acid
paste. Several of the welders that post to
sci.engr.joining.welding have used it with good
results. I've only started using it about six
months ago, so the stuff I've built has not been
out in the salt spray long enough to tell how good
the passivation was.

Don W.

On Tue, 27 Mar 2007 06:52:12 +1000, Peter Hendra
wrote:

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.


Feel free to use it. :-)

I was really trying to say use a longer exposure to a weak brew and
don't use a concentrated mix just to get a quick result.



Eric Stevens

On Tue, 27 Mar 2007 17:35:18 GMT, Don W
wrote:



Bruce wrote:

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.

snip...
Bruce in Bangkok
(brucepaigeatgmaildotcom)


Hi Bruce,

I've just recently started building stainless
parts for my two sailboats. I'm using 316 SS and
316L SS exclusively and passivating with Citrisurf
which is a strong citric acid. It can also be
used for electropolishing, and I intend to try
using it for that in the future.

Google "Citrisurf". It is supposed to be better
and more environmentally friendly than nitric acid
paste. Several of the welders that post to
sci.engr.joining.welding have used it with good
results. I've only started using it about six
months ago, so the stuff I've built has not been
out in the salt spray long enough to tell how good
the passivation was.

Don W.

Don,


I've tried things ranging from purpose made passivating stuff to
vinegar. At the moment I am using a tile cleaner sold, here in
Thailand in every supermarket, that is 20% hydrochloric acid.

One comment I probably should make is that all the passivation
chemicals work by dissolving (eating) some material from the surface
of the piece being worked on. Of course this is how it works, removing
all the oxides and other rubbish from the just welded surfaces. BUT,
it also etches the nice shiny surface of the expensive piece of
stainless you just welded.

My experience is that if you don't polish the etched surface back to a
mirror finish you still get staining.

In another message I mentioned some dinghy lifting brackets I made
that stained. They had been left in acid overnight and were perfectly
clean but with a matt finish when I installed them -- thought the matt
finish would hold the paint better -- wrong.



















Bruce in Bangkok
(brucepaigeatgmaildotcom)

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

On Tue, 27 Mar 2007 06:52:12 +1000, Peter Hendra
wrote:

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.

I take back most of what I have written. I have just found a little
booklet about stainless steels I bought some years ago from New
Zealand's Department of Scientific & Industrial Research. Here is
their advice:
_____________________________
Pickling and passivation

Acid pickling effectively removes all surface blemishes of low
corrosion resistance, such as iron contamination, oxide scale, and
heat tints. The process involves using an etchant (hydrofluoric acid)
in the presence of an oxidising agent (nitric acid) which inhibits the
etching action. A typical formulation consists of 15% nitric acid and
1-3% hydrofluoric acid, which will remove most scales on immersion of
the stainless steel component for 5-30 min at ambient temperature. As
mentioned previously, passivation treatment involves the use of 15-30%
nitric acid on its own, to restore a passive film which may have been
damaged by heat treatment or contact with harmful chemicals. The
disadvantages of using concentrated chemical etchants, apart from the
handling of hazardous materials, include the risk of excessive
pickling at grain boundaries and hydrogen embrittlement of certain
grades of stainless steels.

Weld dressing and descaling are essential to enhance the corrosion
resistance of welds. If immersion of the welded component in an acid
mixture is not practicable, a weld-descaling paste may be used. This
is an inert base material containing nitric acid and hydrofluoric
acid, or, if a passivation treatment only is required, just nitric
acid. These weld-dressing pastes are applied over the weld in a thin
layer and then left for about 1 hour before the residues are cleaned
off.

All pickling and passivation chemicals applied to welds must be
thoroughly rinsed off with fresh water after the appropriate residence
time for the chemical cleaning is completed.
Electropolishing is another batch process for post-fabrication shop
cleaning and passivation of stainless steel components and smaller
equipment. This technique removes heat tints on welds and surface
impurities such as iron contamination, and it also imparts a highly
corrosion-resistant finish with a pleasant dull-grey appearance to the
treated surface. Electropolishing must be carried out by trained staff
under carefully controlled conditions, because, as with the anodising
process on aluminium, it is possible to produce a defective finish if
the process goes out of control.
______________________________

What I said previously about hydrofluoric acid stands. Its a very nast
material. Treat it with very great respect, even in the diluted form.
See http://ptcl.chem.ox.ac.uk/MSDS/HY/hy...oric_acid.html and
http://adm.monash.edu/ohse/assets/do...acid-draft.pdf



Eric Stevens

On Wed, 28 Mar 2007 07:44:50 +0700, Bruce
wrote:


I've tried things ranging from purpose made passivating stuff to
vinegar. At the moment I am using a tile cleaner sold, here in
Thailand in every supermarket, that is 20% hydrochloric acid.

One comment I probably should make is that all the passivation
chemicals work by dissolving (eating) some material from the surface
of the piece being worked on. Of course this is how it works, removing
all the oxides and other rubbish from the just welded surfaces. BUT,
it also etches the nice shiny surface of the expensive piece of
stainless you just welded.

My experience is that if you don't polish the etched surface back to a
mirror finish you still get staining.

In another message I mentioned some dinghy lifting brackets I made
that stained. They had been left in acid overnight and were perfectly
clean but with a matt finish when I installed them -- thought the matt
finish would hold the paint better -- wrong.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

Thanks again Bruce,
There is just so much to learn
Peter

On Wed, 28 Mar 2007 13:29:59 +1200, Eric Stevens
wrote:

On Tue, 27 Mar 2007 06:52:12 +1000, Peter Hendra
wrote:

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
m...
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.

I take back most of what I have written. I have just found a little
booklet about stainless steels I bought some years ago from New
Zealand's Department of Scientific & Industrial Research. Here is
their advice:
_____________________________
Pickling and passivation

Acid pickling effectively removes all surface blemishes of low
corrosion resistance, such as iron contamination, oxide scale, and
heat tints. The process involves using an etchant (hydrofluoric acid)
in the presence of an oxidising agent (nitric acid) which inhibits the
etching action. A typical formulation consists of 15% nitric acid and
1-3% hydrofluoric acid, which will remove most scales on immersion of
the stainless steel component for 5-30 min at ambient temperature. As
mentioned previously, passivation treatment involves the use of 15-30%
nitric acid on its own, to restore a passive film which may have been
damaged by heat treatment or contact with harmful chemicals. The
disadvantages of using concentrated chemical etchants, apart from the
handling of hazardous materials, include the risk of excessive
pickling at grain boundaries and hydrogen embrittlement of certain
grades of stainless steels.

Weld dressing and descaling are essential to enhance the corrosion
resistance of welds. If immersion of the welded component in an acid
mixture is not practicable, a weld-descaling paste may be used. This
is an inert base material containing nitric acid and hydrofluoric
acid, or, if a passivation treatment only is required, just nitric
acid. These weld-dressing pastes are applied over the weld in a thin
layer and then left for about 1 hour before the residues are cleaned
off.

All pickling and passivation chemicals applied to welds must be
thoroughly rinsed off with fresh water after the appropriate residence
time for the chemical cleaning is completed.
Electropolishing is another batch process for post-fabrication shop
cleaning and passivation of stainless steel components and smaller
equipment. This technique removes heat tints on welds and surface
impurities such as iron contamination, and it also imparts a highly
corrosion-resistant finish with a pleasant dull-grey appearance to the
treated surface. Electropolishing must be carried out by trained staff
under carefully controlled conditions, because, as with the anodising
process on aluminium, it is possible to produce a defective finish if
the process goes out of control.
______________________________

What I said previously about hydrofluoric acid stands. Its a very nast
material. Treat it with very great respect, even in the diluted form.
See http://ptcl.chem.ox.ac.uk/MSDS/HY/hy...oric_acid.html and
http://adm.monash.edu/ohse/assets/do...acid-draft.pdf



Eric Stevens

Thanks for quote. I knew that stainless reacted with oxygen to form a
non-corrosive surface and that unless you had a flow of water the lack
of dissolved oxygen might result in crevice corrosion but somehow had
never related it to pasivating. I'll now use at least come nitric acid
as an oxidizing agent.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

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

Bruce wrote:

snip--Eric's good primer on pickling and passivation of austentetic stainless steels
Pickling and passivation


Thanks for quote. I knew that stainless reacted with oxygen to form a
non-corrosive surface and that unless you had a flow of water the lack
of dissolved oxygen might result in crevice corrosion but somehow had
never related it to pasivating. I'll now use at least come nitric acid
as an oxidizing agent.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

Bruce,

I'll try to steer you to looking into stainless
steel passivation using strong citric acid (ie
Citrisurf, etc.) once more. I've not time to
provide the relevant links at the moment.

Use nitric acid if you like. It works also,
although not as well as citric acid according to
various studies. It is also much more hazardous
to transport and dispose of. Citric acid can be
diluted and legally flushed down the drain.

Citric acid passivation for SS is fairly new
technology, and Nitric acid is the traditional way
of doing it. Citric acid can also be used with a
power supply to electropolish stainless steel.

The people who turned me on to the citric acid
passivation do a lot of industrial and food grade
stainless welding and have switched over.

Good luck,

Don W.

On Wed, 28 Mar 2007 15:03:32 -0500, Don W
wrote:

Bruce wrote:

snip--Eric's good primer on pickling and passivation of austentetic stainless steels
Pickling and passivation


Thanks for quote. I knew that stainless reacted with oxygen to form a
non-corrosive surface and that unless you had a flow of water the lack
of dissolved oxygen might result in crevice corrosion but somehow had
never related it to pasivating. I'll now use at least come nitric acid
as an oxidizing agent.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

Bruce,

I'll try to steer you to looking into stainless
steel passivation using strong citric acid (ie
Citrisurf, etc.) once more. I've not time to
provide the relevant links at the moment.

Use nitric acid if you like. It works also,
although not as well as citric acid according to
various studies. It is also much more hazardous
to transport and dispose of. Citric acid can be
diluted and legally flushed down the drain.

Citric acid passivation for SS is fairly new
technology, and Nitric acid is the traditional way
of doing it. Citric acid can also be used with a
power supply to electropolish stainless steel.

The people who turned me on to the citric acid
passivation do a lot of industrial and food grade
stainless welding and have switched over.

Good luck,

Don W.

Don't get me wrong, I really appreciate your information. My reply was
supposed to indicate that while I knew that stainless needed a certain
amount of oxygen to be "stainless" I had never related that
information to the passivation process.

Citric acid may prove a problem though as I live in Thailand thousand
and some things are just not available. Add to this the (sometimes)
problem with translating technical terms and life sometimes becomes
very frustrating. However, when I return to Bangkok I'll stop by my
chemical supply place and see what is available.

One nice thing about Thailand is that it is still primitive enough
that people actually want to sell you things. You go to a large
chemical supply house and say, "I need a liter of a 6-1/3% solution of
nitric acid and distilled water and they never blink an eye. Just
apologize for not being able to hand it to you straight away and ask
you to come back tomorrow morning, about 09:00.


Bruce in Bangkok
(brucepaigeatgmaildotcom)

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

Don, Bruce,

While nitric acid is the historical method of passivation, citric acid
had been the standard for *well* over a decade - not new technology at
all. For any given temperature and contact time, nitric works better.
Citric acid is used since it's far less dangerous and environmentally
unfriendly. Phosphoric acid is also frequently used for ambient temp
passivation. Hydrochloric acid is NOT used for passivation of stainless
- ever. Neither is HF, unless you're pickling (i.e. removing
significant material - etching).

The Citrisurf material looks OK, but I have little faith in combination
products that both clean and passivate. Far better to remove all oils
*first* with a heavy duty surfactant (e.g. TSP), then passivate with
citric (or other) acid.

As has been previously discussed, mechanical polishing of non-orbital
welds (prior to passivation) is still a pre-requisite for prevention of
oxidation.

Keith Hughes

Don W wrote:
Bruce wrote:

snip--Eric's good primer on pickling and passivation of austentetic
stainless steels
Pickling and passivation


Thanks for quote. I knew that stainless reacted with oxygen to form a
non-corrosive surface and that unless you had a flow of water the lack
of dissolved oxygen might result in crevice corrosion but somehow had
never related it to pasivating. I'll now use at least come nitric acid
as an oxidizing agent.

Bruce in Bangkok
(brucepaigeatgmaildotcom)


Bruce,

I'll try to steer you to looking into stainless steel passivation using
strong citric acid (ie Citrisurf, etc.) once more. I've not time to
provide the relevant links at the moment.

Use nitric acid if you like. It works also, although not as well as
citric acid according to various studies. It is also much more
hazardous to transport and dispose of. Citric acid can be diluted and
legally flushed down the drain.

Citric acid passivation for SS is fairly new technology, and Nitric acid
is the traditional way of doing it. Citric acid can also be used with a
power supply to electropolish stainless steel.

The people who turned me on to the citric acid passivation do a lot of
industrial and food grade stainless welding and have switched over.

Good luck,

Don W.