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]

I am assuming that the tubing is a carbon steel grade, i.e. non stainless both then and now? And no change in applied coatings or conveyor lube? I can't think of any reason that low carbon steel would behave differently today than it did years ago--it will rust if given no corrosion protection.

 

[Maui]

What grade of steel did you purchase 15 years ago for this application? Are there any samples of it available (I assume that you can get samples since you identified customers who are in fact still using this product). A metallurgical analysis of the current material and the previously supplied material that did not exhibit this corrosion problem should be performed. This analysis will enable you to verify whether or not the chemistry, microcleanliness, and corrosion resistance of the steel from your supplier has changed.

Have your specification requirements changed? Are you still purchasing the same grade of steel from the same supplier for this same application? What type(s) of rust preventatives are applied to the stock material when it is shipped to you? Has your supplier chosen to use a different rust preventative than was used previously? What do you require per your specification?

Maui

 

[mshimko]

We had similar concerns, but with less real examples, a few years ago.

I do feel the following is a plasible possibility, and perhaps an explanation, using one alloying element in a hypothetical stainless steel alloy:
- Mo is more expensive than Cr and Fe;
- An alloy has an allowable range for Mo, say 6-8%
- The allowable range was developed years ago and was based partially on the precision of metal manufacturing.
- Hence, years ago the "average" amount of Mo in this alloy was 7%
- With time manufacturing processes improve and more precision becomes practical, and the cost of allowing elements increase,
- Today, the average Mo content may be 6.2%

Any thoughts on this possibility?

 

[moltenmetal]

Though it may be true that better process control in steelmaking permits vendors to limit alloying constituents to the bottom end of a particular spec's requirements and contaminants to the top end, it seems to me doubtful that this is the issue with atmospheric corrosion performance of basically unalloyed carbon steel.

If the tubing in question is being supplied by different manufacturers, there may be a difference in surface corrosion inhibitors or lacquers etc. applied by different manufacturers, which might explain the shelf/storage performance of your material. But that wouldn't explain the performance of your finished rollers in the field- presumably these are treated the same way as always.

So if you're not getting a straight answer from us, it's that we just plain don't have sufficient evidence to make a judgment! You need to do a more detailed review of what has changed and what has absolutely remained constant to understand just exactly what is going on in this case.

 

[Pressed]

The physical analysis of old metal compared to current is a good start as Maui stated.

Also think about the entire system, ie. everything that touches the steel. Once dissimilar metals come into contact (even different steels) it starts to create galvonic corrosion (electrolytic cell), especially in the presence of an electrolyte. Different metals have different corrosion potential or relative positions in the galvanic series. If your current system has metals selected from further apart on the corrosion potential chart than the old system, it will corrode the high potential metal faster [(-) negative metal or anode].

In the event that you cannot determine the cause, try to add a chunk of magnesium to the steel surface and see how much difference it makes. It would become your sacrificial anode.

[URL unfurl="true"]www.hghouston.com[/URL]      definitions

[URL unfurl="true"]www.assda.asn.au/asp/index.asp?pgid=18533[/URL]   corrosion chart

[URL unfurl="true"]www.ocean.udel.edu/seagrant/publications/corrosion.html[/URL]

According to the last link, you can measure the potential difference with a volt meter. If you can isolate the correct metals you can measure and compare the old to new systems. I hope this helps.


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[rob768]

I'd start to look at the increase of the pollution of the air over the last few years.

 

[EdStainless]

Do you do any machining to the outer surface?
You need to be treating material that you recieve with a rust inhibitor. Better yet your supplier should, but they cut that out to save money and now it is your problem.
Once there is some surface corrosion the surface is pitted. Even if you clean it off the pits will resume corroding easily.
This could be a function of inclusions in the steel, but more likely someone changed a process that effects the surface condition.

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

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

 

[btrueblood]

Ed,

Is the loss of corrosion protection also an environmental issue? It seems that years ago, we'd receive sheet/bar steel with a light oil coating as a matter of course, whereas now it comes "dry" from the supplier. Somebody told me this was an environmental issue to reduce the amount of oil dripping on the floor/ground and from there into drains.

 

[Compositepro]

Many factors contribute to rusting and many are an inherent part of steel and therefore can't be eliminated. The main way to prevent rust is to keep the steel clean and dry. So I would suspect some kind of hygroscopic salt contamination. You would think that that should be easily removeable by appropriate washing but if the salts are very finely distributed through the bulk of the steel as microscopic slag particles, then every time you machine or sand a surface it would be clean but it would also expose more salts. I would surmise that any impurity in the steel that is hygroscopic would worsen rusting. Sodium chloride and particularly calcium chloride would be very bad.

 

[EAllard]

Hello everybody,

1)
Wow, I am overwhelmed by how many and how good a response I am getting for my post.

2)
I am sorry I have not provided answers to your questions at this point. I have been working on other projects away from my computer.

3)
keep the good stuff coming, I should be able to answer back this afternoon.

Thanks again.

 

[swall]

EAllard--a lot of good points have been brought up, but I think focus ultimately needs to be on the tubing source. They need to be made aware of your desire to have tubing free of rust and must be in a situation to and have a desire to correct the problem. It may well be that the problem starts with the tubing manufacturer's steel source. If the steel strip from which the tubing is made is already pitted, then as EdStainless pointed out, rusting will shortly follow. And as I said in my previous post, carbon steel will rust if not protected.

 

[macmet]

I cannot provide a solution for your problem, but I have also heard of many similar problems. Many of our clients request information on where the steel is coming from before we fabricate any pieces. When asked why they say they do not want to get any asian steel because they have had a lot of problems with it - corrosion, failure, etc.

To be honest, I have no idea how they would know the steel would be from asia, but they want north american steel only.

 

[kenvlach]

Too little information for a proper answer. What was the purchase specification -- ASTM A513, Type 1, AWHR (as-welded from hot-rolled steel)?

Re "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!"
-- Coatings are irrelevant here since worn off during use (unless going high end, e.g., chrome plating). A different chemistry or heat treatment may cause a difference in microstructure or resdiual stress. Some pearlitic steels 'flash rust' very quickly in the presence of moisture due to galvanic corrosion of the ferrite matrix (anodic vs. carbide).

Asia produces more 'good' steel than the US. Also, more crappy stuff. The volume of imports wouldn't be so high (see 'Imports Hit Second Highest Monthly Total in U.S. History' [in July 2006] at

http://www.steel.org

Problems arise when buying on the basis of price alone from bottom feeding distributors -- may sell reject material. Need a reputable supplier, and it is difficult for small buyers to know what is going on overseas.

 

[EAllard]

Thanks again everybody,

1)
Like I said earlier, I am overwhelmed by the number and the quality of the replies I revceived for my post. For this reason, it will be impossible for me to answer specifically to all the questions I received. Nevertheless, I see a lot of commonalities between some of your comments. I will try to answer to those.

2)
First, I guess I already have the answer to my question: "Is steel quality getting poorer?".

Although this is the feeling I am getting from comments I get from suppliers, customer, competitors, it seems it is not as generalized a problem as I would have expected.

Very few of you actually considered the GENERAL steel quality as the problem. Sure the specific quality I bought probably has something to do with my problem but it does NOT seem like this is a GENERALIZED problem.

If any one of you has comments on the GENERAL quality of steel these days, please keep comments coming.

2)
Now with the specifics of my problem

Tube is carbon steel (not stainless or fancy alloy)

When we purchase, we specify ASTM A513 type 2.
If I am not mistaking, this implies I am getting C1010 steel which is rolled into the shape of a tube using a cold rolling process.

There is no surface treatment on the tubing other than a light film of rust inhibitor when tubing is delivered to us. This films washes away very quickly once rollers are used by customer.

There is no machining done to the tube other than cut it to the proper lenght. Nothing done to the face of the tube.

3)
Before I put up my post, I was also of the opinion that the 2 better places to look were: supplier and composition of steel.

Supplier:
I am currently going through the tedious job of tracing back all the purchase orders of steel tubing for the last couple of years.

First news, suppliers vary a lot. Although it is +/- always the same 4 suppliers, we do not consitently buy from the same supplier. Purchasing criteria is usually price and availability.

According to my production people, no matter which supplier is picked or tubing size bought, they all have a rust problem. By that I mean: their tubing rusts a lot more quickly than it use to rust years ago.

Does that indicate that it is a generalized problem? Caused by the general quality of steel? or by the general change in manufacturing processes? or environmental constraints?

One thing for sure, going to cheapest bidder probably does not help our case!


Composition of steel:
I can get samples of the old and the new. I am presently in contact with a lab to get composition analysis. Furthermore, a local corrosion engineer has offered me to look at the result to help me identify what could be the cause of the problem.

4)
This is all I have to say for now. If you can comment about general quality of steel these days and/or manufacturing process changes and new environmental contraints, please do.

Thanks again,

EAllard.

 

[CoryPad]

The general quality of steel these days is equal to or better than steel in the past with regards to corrosion.

Regards,

Cory

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

 

[metengr]

Composition of steel:
I can get samples of the old and the new. I am presently in contact with a lab to get composition analysis. Furthermore, a local corrosion engineer has offered me to look at the result to help me identify what could be the cause of the problem.

Bingo - you are headed in the proper direction.

 

[mcguire]

Just as general information, steel mills always are trying to use steel made which is excess to orders. They sometimes overgrade by putting a higher alloy grade on a lesser order whose spec doesn't prohibit doing so. This happened more in the past when fiscal sloppiness was more the norm. So you could have previously gotten more than you expected or paid for.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

You are also correct, environmental issues have changed the practice of coatings and inhibitors. It used to be that steel was shipped dripping with inhibitor loaded oil. Not today.
You may need to consider adding a cleaning and surface treating step to your operation, since your suppliers have dropped it from theirs.

Over all steel quality (surface finish, chemistry control, mechanical properties, corrosion resistance) is better than it ever was. It is still true that the junk is junk, but the material from the good sources has continued to benifit from tighter process controls.

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

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

 

[EAllard]

Hello everybody,

1)
Many of you suggested I get an analysis of both the old material and the new to highlight any potential differences.

2)
I followed this advice and I got the results.

SAMPLE A:
Carbon = 0.10%
Manganese = 0.51%
Silicon = <0.01%
Phosphorus = 0.008%
Sulphur = 0.011%
Chrominium = 0.04%
Nickel = 0.05%
Molybdenum = 0.01%

Grade: Lab says it is AISI 1010


SAMPLE B:
Carbon = 0.07%
Manganese = 0.38%
Silicon = 0.02%
Phosphorus = 0.006%
Sulphur = 0.006%
Chrominium = 0.02%
Nickel = 0.02%
Molybdenum = <0.01%

Grade: Lab says it is AISI 1006 (Supplier says 1008)


3)
Let's make this fun.
For now, I won't tell you which of the 2 samples is the old tube (not rusting) or which is the new (rusting a lot).

Let's see what you have to say.

I your opinion, which of the 2 samples should experience more corrosion if subject to the same "normal" atmospheric conditions? and why?

Would you expect the difference to as dramatic as what I have been experiencing? and why?

Thanks again.