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

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 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 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.

Hi Keith,

Keith Hughes wrote:
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.

Well, my use of the term "new" is relative. A
decade takes us back to 1997, and I still think of
that as relatively "new".

For any given temperature and contact time, nitric works better.

I'm not sure that this is true...

I read an independent technical lab report on the
quality of passivation films formed by nitric acid
and citric acid when I was researching the
Citrisurf. It compared the CrO2? films at a
microscopic level for different passivation
techniques, and concluded that the quality of
passivation using citric acid was slightly better
than nitric acid.

IIRC the thickness of the passivation film using
any method is limited to some maximum because
eventually the reaction stops due to complete
oxidation of the surface.

The report is available on the web somewhere. I
did not bookmark it because I was only trying to
decide what technique to use for myself.

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).

I use Phosphoric for pre-cleaning, rust removal
and etch of regular (non-stainless) steel before
painting. It works well.

Hydrochloric acid (Battery acid) can be used with
a DC power supply for surface passivation of
aluminum. The process is called anodizing ;-)

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.

AFAIK Citrisurf does not claim to clean. You are
supposed to do a cleaning step (cleaner/degreaser)
before passivation. At least that is what I do.

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

Agreed.

Don W.