Rust. Is steel quality getting poorer ?

[EAllard]

Hello,

1)
As it is often the case, I am new to this "Eng-tips" forum because I have a question nobody will give me a straight answer to. Hope you guys will help.

2)
To make a long story short...
I am working for a conveyor manufacturer. To fabricate our conveyor rollers, we have been using for years ERW tubing.

In a not so distant past, we would buy this tubing in large quantities. The tubing would stay on our racks for long periods without showing real signs of corrosion. After fabrication, the rollers could be used for years before they would have to be replaced because of rust.

These days, we have to buy tubing in much smaller quantities because it will rust so fast that we don't even have the time to fabricate rollers before the raw material rust. When rollers get to our customers, rollers rust very badly within a couple of months.

3)
The most dramatic example of the above happened recently.

One of our customers asked us to lenghten an existing system. The original system is 15 years old. original rollers are still in very good condition showing little to no sign of rust.

We supplied new sections of conveyor (same specifications). Within 4 months, new rollers were all rusted and looking like crap right next to 15 years old rollers that were still looking very good!

4)
Of course, I went back to our steel supplier to find out what is going on. Nobody has clear answer to give me.

On the other end, we are hearing all kinds of rumors that China is taking over the steel industry and that the steel they provide is full of impurities (lower quality).

Is there any truth to that rumor?
Am I the only one experiencing this kind of problems?
Any explanation to suggest?

Thanks.

 

[swall]

There is no reason, based on the chemistries you have reported, to expect a difference in corrosion performance between the two samples.

 

[unclesyd]

One might have to go for sample B due to it being purer Iron. The silicon is a higher than sample A and I have read somewhere that in pure Iron Silicon can make a difference in the corrosion rate.

 

[CoryPad]

Based upon the chemical compositions, there should not be any difference in corrosion performance.

You will need to look at surface contamination and surface protection practices (phosphating, oiling, etc.).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[stanweld]

Did you run an analysis for copper on both materials? Higher chromium, molybdenum and copper residuals in combination can provide more tightly adherent passivated oxide layers.

 

[EdStainless]

I vote with Cory, surface condition will control with these chemistries.

Ask your supplier, you might be able to get steel treated for better storage life.
Otherwise you need to clean and treat the steel yourself.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rconner]

This is an interesting exercise, but I'm not exactly sure where same is headed. I don't have a dog in this particular hunt, but I have been following same due to apparent allegations of “poor quality” of the material. Therefore, I got hold of and read a copy of ASTM A513, apparently the material specified by the conveyor roller vendor or Purchaser. In looking at all information that has been provided thus far including the chemical analyses, what I don’t see is any obvious evidence of poor quality, nor as others have stated any obvious reason many corrosion engineers would ascribe any degree of enhanced atmospheric corrosion resistance to either material, in an of itself. In this regard, I noticed also the A513 specification states, “When specified, tubing shall be coated with a film of oil before shipping to retard rust…” It would thus appear that the developers of this material specification anticipate that the tubing material, and perhaps maybe even that manufactured to quite high quality standards?, either will or can rust (in even shipment, before it even gets in service!, at least if this oil is not specified or after this protective oil has dissipated?)
Now, as to why the new one looks rustier than the old in service, I would think there might indeed be a reason(s) for this, but I don’t know what it is/they are. You mentioned that the rollers were somehow “washed”. Is the tubing by any chance in electrical contact with another material, e.g. some sort of steel trunnions or inner bearing rods etc. and exposed in some sort of manner to a fluid or moisture that might be acting as a corrosion agent or electrolyte? I would e.g. expect a carbon steel with even a little less intentional or unintentional “alloying” (of nickel, copper, chrome etc.) to be some “anodic”, and perhaps corrode at least a little more relative to another that is more cathodic (with even a little more of such alloying) steel, if immersed in an electrolyte etc. as in a galvanic cell. Though I personally would not have expected such very minor chemistry variations like you show here to cause much current flow, I think various tests can nevertheless be run to diagnose such relationships/tendencies.
In any case, you or your customer might eventually have to bite the bullet and go to some sort of special surface treatment or maybe even some special alloy steel material (of course probably at a little more initial material cost) to get a more consistent appearance (particularly if the “looking like crap” represents something more than an aesthetic problem in the application!)

 

[tomwalz]

I’m going with kenvlach.

In what we buy we see a great number of suppliers who are meeting specifications as written but who are running around the non-written parts to cut costs. More and more we are writing specifications for ourselves and our customers defining the specifications in terms of composition, manufacture and use.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[rconner]

Interesting dialogue -- the original inquirer has specifically stated "Purchasing criteria is usually price..." While I have not yet seen the proof on this particular thread that this is the case here, in such an environment it might appear the steel vendor who does the best job of "running around the non-written parts to cut costs" might actually have the best chance to quote the lowest price and thus win his/her order!! (I am certainly not saying this is right nor the case here, just that this is certainly a possiblity). When multiple vendors are allowed with the decision to purchase based on price, in the contemporary world it is perhaps increasingly hard to depend on vendors building a lot of "non-written" quality cost into their wares. On the other hand, sometimes the more that is "written" the higher the price or the less the availability (assuming of course that what extra is written can even be produced!) -- hard to "have ones cake and eat it too"!
With regard to the prior/good comments of kenvlach, it certainly might not be a bad idea to look at (have a detailed "microstructure examination" as well performed?) on samples of the two materials.

 

[Maui]

EAllard, do you have the answers to the other questions that appear in my original post? If you do, please share them with us.

Maui

 

[EAllard]

Hello everybody,

1)
I am sorry I have been away from this thread for so long and left you hanging with my "teaser".

Here is the answer to the question you have been waiting for...

Sample A is the "old" material. The one that shows much better resistance to corrosion.

Sample B is the "new" material. The one that is causing me a lot of trouble.

2)
The general concensus seem to be that the difference in steel composition is so small that it probably cannot justify such a difference in corrosion behavior. I have to look somewhere else.

3)
I think a lot of you have hit the nail right on the head. My main purchasing criteria being "price" I open myself to all those suppliers who are ready to cut corners to lower their prices. I could try to force them into a very precise specification but my purchasing volume being relatively low (not high volume), I probably would end up paying an arm and a leg, get forced into buying greater quantities with longer deliveries...not a very good deal.

4)
Conclusion (because at one point we have to draw conclusion):

In those applications where looks are not important, we are going to use the tube we have on hand and alert the customer to the possibility that roller tube may rust without affecting the functionnality of the roller.

In those applications where looks are important, we will propose that tube be electro-galvanized.

For future purchase of tubing, we will strongly consider the purchase of pre-galvanized (mill galvanized) tubing. Sure it will cost more but it is going to insure a quality product to our customer and eliminate a lot of aggravation with manufacturing and engineering (me).

5)
I won't be able thank to you enough for all the valuable input everybody put in my basic question. Thank you all.