May be looking for the wrong cause..... Looks like it is preferentially
removing Cr (concentration is twice that of Fe). Is the corrosion
truly generalized, or is there an elevation (level) at which is worse or
not as uniform? Do you have stray current or some potential (even
irregularly) on the column? Could even be induced. I assumed the
packing is plastic, or perhaps a venturi scrubber. If you have metal or
metal coated catalyst, could be galvanic corrosion - if no or irregular
corrosion above the packing level, that is more evidence. If velocities
are enough, might even get some level of current induced with gas
passing thru column, and worse if column is running too dry (got to be
somewhat flooded). Stray or induced current is surprisingly difficult to
find. Ground the column, bonding it and everything else (pipe, pumps,
fans, etc.), to keep the potential at zero. Metal scrubber systems
should always be grounded (inlet duct to stack).
Could still be uniform pitting from halides or other pretreatment, but less likely than galvanic. Same stuff happends to metallic UG pipes, for the same reason.
... Bruce D. Bullough ...
Sebesta Blomberg & Associates, Inc.
2381 Rosegate
Roseville, MN 55113 USA
desk: 651-634-7344 fax: 651-634-7400
www.sebesta.com
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>]
On Behalf Of Arif Javed
Sent: Tuesday, April 11, 2006 8:34 AM
To: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>
Subject: RE: [PipingDesign] Acetic Acid and 316l [bayes][heur]
Bruce,
The original metallurgy was 304, which got corroded on the HAZ. Therefore it was decided to change the metallurgy to 316L as it was proven metal for Acetic Acid. But this time it is a generalized corrosion through out the metal and not on HAZ.
The temp is 70 to 75 deg C.
May be during construction or storage of the vent scrubber the chlorides ingressed into it. As there is no evidence to it and the only thing found in the lab analysis was as under:-
Please find below the results of the Catalyst Activator - I Vent Scrubber Sample given on 30/03/2006.
DATE 30-Mar-06
TIME 13:00
Description
Catalyst Activator- I vent scrubber sample
Acidity as Acetic Acid, wt %
0.25
Hexa. Chromium, wt %
NIL Iron, wt %
0.035
pH
4.10
Total Chromium, wt %
0.080
Zinc, wt %
<0.0001
Does this make any sense in guiding to right solution?
A J
Mechanical Engineer
From: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>]
On Behalf Of Bruce Bullough
Sent: 11 April 2006 16:19
To: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>
Subject: RE: [PipingDesign] Acetic Acid and 316l
AJ
My opinion is that you have provided (and probably only have) an incomplete or inaccurate "picture". If you have only acetic acid at pH 4.2 in an acceptable temperature range (I have no idea what "normal" is) in 316L, you will not have significant corrosion. If, however, the welds were done poorly resulting in metallurical changes, the heat affected zones might no longer be 316L, and corrode. 321 SS is strongly attacked by acetic acid (I've seen it before - a 321 pipe was supplied because the purchasing department could save some money, even though it was specified to be 316L). If the metal was passivated or "pickled" but inadequately cleaned afterward, the residual fluoride or nitrate (or other) could initiate the attack. If you have other things (such as chlorides, fluorides, etc.) that are also present only occasionally, corrosion occurs due to the "other things". There are many possibilties.
... Bruce D. Bullough ...
Sebesta Blomberg & Associates, Inc.
2381 Rosegate
Roseville, MN 55113 USA
desk: 651-634-7344 fax: 651-634-7400
www.sebesta.com
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>]
On Behalf Of Arif Javed
Sent: Tuesday, April 11, 2006 2:04 AM
To: <a href="/group/PipingDesign/post?postID=gAkYWj5l41_5Jm-BfAp5OvuzgrcELjIgGXkE3bRtX5A1jZ55NE-Kjh7ivRNbYU_51OW6GdOayAENkLTusP6jH4LQrgH4r70">PipingDesign@yahoogroups.com</a>
Subject: [PipingDesign] Acetic Acid and 316l [bayes][heur]
We have an vent scrubber made of 316L. This got corroded. Lab analysis showed presence of Acetic Acid 4.2 pH and acidity 0.25 wt %. Temperature is normal. My experience shows that this metallurgy should be OK for Acetic Acid. What is group's opinion?
A J
Mechanical Engineer
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