User talk:Equinox2

SCC
I query your suggestion that pure metals are not susceptible to SCC. Acids and alkalis will attack many pure metals and pure copper is attacked by ammonia. Peterlewis (talk) 16:14, 3 June 2008 (UTC)

Hello Dr. Lewis. It's nice to meet you. Let's discuss this and end up with a page we are both happy with. It's clear that both of us are knowledgable in this field.

First off, note that my statement says that "generally", thus a few exceptions may occur, but this is not the norm. Next, could you clarify about your statement "Acids and alkalis will attack...". I fully agree that they will "attack" many pure metals, but are you saying that they cause pure metals to undergo SCC?

About the Cu, which alloy designation do you mean (such as alloy C11000, which is ETP pure copper)? The susceptability of various copper materials are listed on pg. 7-38 of the ASM handbook, and it lists the higher purity alloys as having an SCC susceptability of 0 (compare to, say, alloy C35300, which has a susceptability of 1000). Sometimes I've seen alloys of Cu referred to as "copper". Perhaps this is what is happening here?

I want to rely more on referencable sources than on personal experience, but I haven't seen any pure metals SCC, and have seen quite a bit of SCC over the years. Equinox2 (talk) 16:31, 3 June 2008 (UTC)
 * The reason SCC is or has not been commonly seen in pure metals is surely that pure metals are rarely used as structural materials. Most SCC papers come from practical problems such as season cracking with brass cartridges. There is no inherent reason why pure metals should be less susceptible to SCC than alloys. Peterlewis (talk) 22:51, 3 June 2008 (UTC)


 * Thanks for the reply. While I agree that alloys are used more often than pure metals, there are plenty of applications for pure metals, such as electrical components of pure Cu, Ag, etc, as well as piping (such as pure Ni (Ni200), Ta, etc.  Are there specific situations you are thinking of for the SCC of pure metals?  Maybe I'm unaware of the specific examples you are thinking of.  Also, were you going to get the alloy designation for the copper SCC you referred to in your first post?  Thanks-  Equinox2 (talk) 12:39, 4 June 2008 (UTC)

One of the problems with SCC is that relatively little seems to be published. But absence of evidence is not evidence of absence. SCC involves chemical reaction of a metal with any number of different chemicals at low concentrations, and I see no reason why pure metals should be exempt from attack. Peterlewis (talk) 15:09, 4 June 2008 (UTC)


 * It's certainly true that the full mechanism of SCC (any SCC, either in alloys or pure metals) isn't known for certain based on published materails. However, empirically noted trends (such as the dependance on specific chemicals like Cl- in SS) are valid things to be listed in the wiki.  At the same time, mechanisms have been discussed.  At metallurgical conferences I've heard various reasons for the lack of SCC in pure metals discussed, such as the fact that SCC is linked to stress, and the creation of a stress field around solute atoms (there's much more to it than that greatly simplified description).  Many have noted that pure metals generally don't undergo SCC, and many reasons have been discussed. We don't just have a lack of evidence, we do have evidence of absence.  There are many cases of SCC reported, and many cases of pure metals being used in all kinds of environments, yet many of us materials scientists have noted, and written about, the fact that pure metal SCC is rare.  Do we agree that that's not just an absence of evidence?


 * If you don't have an alloy designation for the copper you mentioned, nor any other evidence of SCC in a pure metal, that's fine. Did you not mean SCC anyway?  Please let me know that so we can move on.  Equinox2 (talk) 17:06, 4 June 2008 (UTC)

Dear Dr. Lewis-

Being that we've had time to look this over, I'd like to wrap our discussion up. It seems that we do have a recognized pattern - that SCC of pure metals is rare, even though pure metals are used in corrosive environments. I hope that I've addressed your concerns above, and in light of our discussion, it's probably good for me to reference the fact that this empirical observation (that SCC is rare in pure metals) has been made and can be referenced. Also, note my addition to the page, both in the past and now, only mentions the empirically and widely recognized observation that SCC is rare in pure metals, not that it can't or never happens. So, unless there are new concerns, I propose that I'll include the pure metals statement on the SCC page by Friday June 20th. Thanks for your attention to this matter - without good discussion between metallurgists like us, the quality of wikipedia would not be as high. Equinox2 (talk) 21:37, 18 June 2008 (UTC)

Response
I would be happy to include your point, especially if you can give some good refs to the problem. I was originally a chemist and have seen some mention of pure metals being less readily attacked but can't find the source(s). Do you have a good recent review for example of SCC in general? I have previously put some external links in the season cracking article I wrote about SCC in copper alloys and noted a link to a paper on SCC in copper itself. Peterlewis (talk) 06:00, 19 June 2008 (UTC)


 * Yes, I found a reference in a book. Boyer, H., Gall, T., Editors, “Metals Handbook, Desk Edition”, ASM International, 1997


 * pg. 32-24 has a list of things to look for to suspect SCC. They are: 1.  a tensile stress, 2. generally alloys (rarely pure metals), 3. presence of one of a few specific ions for a given alloy system.  4.  (#3 can be in low concentrations).  5.  SCC is more common in temperatures above room temperature.  6.  The alloy is usually mostly inert in the environment.  7. A macroscopically brittle fracture.  8.  Microscopic fracture mode is different from that of a plane-strain fracture.  9.  Stress must be above the minmum threshold for SCC.  I don't think the whole list is needed, but this does provide a reference for the alloys thing.

Antoher reference I have is Kolb, et al, "ASM Handbook Volume 13: Corrosion", ASM International, 1998, pg 146


 * I'm in a rush now (a meeting coming up), so I can work it in tomorrow if we like, or feel free to take a stab at it if you prefer. 97.87.24.50 (talk) 20:36, 19 June 2008 (UTC)

Added subject as discussed and updated reference list. sorry for the long delay, I was on a family vacation (took the kids to Epcot).Equinox2 (talk) 16:37, 8 July 2008 (UTC)


 * The changes are fine by me, but I think we should be cautious about excluding possible failures in pure metals (like the example I cite in the season cracking article of a copper pipe). The problem of SCC is insidious, and I wish engineers were more aware of the environments into which they put their products! You are right in general terms about very pure metals, but such are rare beasts in general engineering. Even "pure Copper" in pipes will have some minor elements present, which are enough to trigger attack. Peterlewis (talk) 18:35, 8 July 2008 (UTC)

I agree that we need to be cautious, and not make people think that by using that by using a pure metal they are completely safe from SCC. I thought of some things to add to cover that, but they each seemed to add length without adding real content. To that end, I think we have already made that clear in the article. It doesn't say pure metals are immune, only that SCC isn't as common in them, and it does say plenty of warning statements like "common for SCC to go undetected prior to failure", "SCC often progresses rapidly", "often leading to devastating and unexpected failure", etc. I think we are in good shape. Let me know if you still feel uneasy. Equinox2 (talk) 16:44, 9 July 2008 (UTC)