Microcleanliness test a "heat" test? 5

[salmon2]

I came cross one problem at work and want to know what others think.

We are buying seamless steel tubes from many companies. There is this company we have beening purchasing for many years. A very big company in US, but I won't share it with you in case some people from the company may be here.

We always require microcleanliness test because properties in transver direction is pretty critical to our applications. Not very long ago, we accidently found out that the cleanliness test from this company is actually done on the bar, not on the finished tube. I went ahead to ask them why and is it possible for them to do the test on the tube vs bar. First, they said the hot piercing/rolling won't change cleanliness rating; then they admitted the rating could be possibly affected by rolling, but still insisted that cleanliness is a standard heat test which means they will do it only on the bar and kind of saying we are asking some special.

I was totally surprised by this because we are dealing many steel mills in the world and they are the only one who is doing the test on bar. Other mills either do the test on the finished bar or refuse to do it. Somehow, we have been under the impression that the cleanliess from them is on tubes, even though we didn't specifically required this in our Spec since this is kind of common sense to us. Why would we need a property measured in the middle stage? That is totally meaningless to me (OK, not totally, it is a quality control on step 1).

During conversation, I said since hot rolling will probably change the JK rating, which you have agreed, that is exactly why we need it to be done on finished tubes. Funny enough, they said that is exactly we wouldn't do it on finished tubes. I kind of lost my logic and didn't know how to argue back.

We still placed PO since we have no other alternatives on this product. But I want to know if cleanliness is really a heat test and usually done on bar vs tube, speaking of tubular products?

Salmon thanks everyone.

 

[IRstuff]

One possible perspective is that you never found any problems with their product in the "many years" that you've purchased from them. So either their product is sufficient clean as processed, or your requirement isn't really needed.

TTFN

FAQ731-376

 

[salmon2]

IRstuff, this is not really my question. But you are right that their steel has been very clean and our requiremnet, specific limits for each type, may be over specified.

But this is a quality control test, who knows if they will deliver some dirty steel next time. Regarding to the ratings, they refuse to gurantee anything anyway. I have been doing internal qualification using their reported cleanliness result. But it seems that we have to do our own cleanliness test after they delivered tubes. So really they are doing the test for nobody's good and actually I think we are carrying the test cost even though there is no seperate PO line for this test.

 

[TVP]

Do you specifically reference ASTM A 519 (seamless tubes) and E 45 (inclusion analysis)? If so, here are some relevant passages:

ASTM A 519

S2.4 Steel Cleanliness—When there are special requirements
for steel cleanliness, the methods of test and limits of
acceptance shall be established by manufacturer and purchaser agreement.


ASTM E 45

6.9 The size and shape of the wrought steel product tested
has a marked influence on the size and shape of the inclusions. During reduction from the cast shape by rolling or forging, the inclusions are elongated and broken up according to the degree of reduction of the steel cross section.

8.1 The minimum polished surface area of a specimen for
the microscopic determination of inclusion content is 160
mm2 (0.25 in.2). It is recommended that a significantly large area should be obtained so that the measurements may be made within the defined area away from the edges of the sample. The polished surface must be parallel to the longitudinal axis of the product. In addition, for flat-rolled products, the section shall also be perpendicular to the rolling plane; for rounds and tubular shapes, the section shall be in the radial direction.

8.3 Thin Sections (Product Section Sizes 9.5 mm (0.375 in.)
Thick or Less; Strip, Sheet, Rod, Wire, and Tubing)—Full cross section longitudinal specimens shall be cut in accordance with the following plan:

 

[salmon2]

TVP,

We didn't reference ASTM A519 because our tubing is neither standar mechanical tubing or API pipe/casing/tubing. But we did reference ASTM E45 as testing procedure and with our own limits.

E45 doesn't specify when the test should be done for tubular goods. So is it really a hole of E45 to be updated or it is a common sense that this test should serve as a final property, vs a middle stage measurement.

Thanks,

Salmon

 

[redpicker]

salmon2,

I can't comment directly why you got the answers you did from the steel mill you are dealing with (particularly since they are unnamed), but I have observed the following to be true (particularly from US steel mills).

They don't like to do heat qualification testing for cleanliness, hardenability, grain size--these characteristics they want to qualify through process control. If they have to hold the material for these test results, it interrupts the flow of material through the mill.

If they are made to perform these tests for heat qualification, they want to do it as far upstream as they can so they aren't putting time and labor into a product a customer won't accept. It would seem, for their product, the bar stage is a convenient place for them to perform this test.

I doubt they have a problem meeting your cleanliness requirements (as evidenced by your successful use of their material), but they will object (with any reason they can come up with) to having to do it on the tube since that would turn their process flow upside-down.

I also doubt this is a "hole" in E45. In fact, I suspect E45 is specifically written to allow this practice. It wouldn't suprise me, if this is a "very big Company in US", that this company has employees in the ASTM workgroup that wrote (and/or revises) the standard to help make sure this is the case.

In the end, you are getting material that meets your needs. They are comfortable in using the testing methods they use to demonstrate compliance to your requirements. If you had an instance where you had performed testing on the final product that did not meet your cleanliness requirements, you would (in my opinion) would have a vaild complaint. But, until you do this, I don't think you will get any change in their stance.

rp

 

[CoryPad]

redpicker makes a great point - ASTM standards are predominantly written for the benefit of the manufacturer, while other standards (MIL, ISO, EN, etc.) are written to benefit the end user.

Regards,

Cory

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

 

[metengr]

salmon2;
We have and continue to buy boiler tubes as an end-user (for many years). I would say that other than the General Requirements under SA 450 which we require as part of an ASME boiler tube material procurement specification, I have never seen a specific microcleanliness test performed for boiler tubes at the various mills that I have audited, nor ever had a problem with cleanliness. The ASME tube material specifications have a significant amount of mechanical testing required to assure minimum quality requirements for satisfactory performance in boiler/heat exchangers.

 

[dbooker630]

It appears that your supplier has a good track record, so rather than mandate cleanliness testing on the finished tube, which will add cost to your product, perhaps you should cover this in your material specification by stating that "cleanliness testing is acceptable in the billet condition as long as end use fit or function is not affected."

 

[salmon2]

Thanks to everyone who has responded, especially redpicker who has probably said the same thing as what my supplier tried to tell me. But obviously redpicker did a much better job.

I understand the situation a little bit more now, but still not convinced because:

1) they are the only one doing test on bar vs tube. I am dealing at least 10 steel mills in this world. Usually we are dealing with their specialty tubing department since our products are not standard ASTM or API. We don't really quote ASTM A519 or API 5X.

2) yes, we haven't have any accident with their products. But that doesn't justify exemption on this test. Cleanliness is just as import as hardness and tensile to us. Should we exempt them from doing hardness and tensile test?

3) I admit our required limits are really demanding, zero for type A and C. I admit it is over-specified but I can't get our engineering to change it because nobody knows where to change or nobody wants to be responsible. To engineering, over-specifying is safer than the potential failure from loosing up. And now it is our manufacturing/sourcing's responsiblity if anything happened because obviously this company's product is not comforming to our Spec. Actually it is hanging upon my head because every time I have to put my name on the approval form. I have made strong recommendation to find replacement for this company.

4) I am going to begin doing cleanliness test by ourself on the finished tubes from this company since we just found this out. See what results turn out compared with our limits and their bar results.

I know you guys thinking I am dealing with US steel. To be fair for them, it is not them. It is another company with much bigger profile for clean steel.

 

[deadrange]

salmon2,

A couple of points that I think needs to be added to this conversation.

1) ASTM E45, if memory serves me correctly, E standards are methods. They describe how the test is completed, not when. Unless prompted the producing tube mill will order the material to your requirements and pass along the heat results from the steel mill. This is typically the case in automotive industries where material is supplied and cleanliness taken by the producing steel mill. On forged material they typically do not re-test the cleanliness of the forgings.

2) While piercing/rolling does have the potential of elongating the inclusions already in the steel, while doing so it also reduces the width. This is the case except for B type inclusions were are non-deformable from piercing or rolling. Also it should be added that the reduction of width may make the inclusion non-ratable based on the thickness of the inclusion. E45 specifies a minimum width of inclusion to be counted.


3) My experience with steel mills is that they typically take the inclusion samples from a rolled billet and not in the as-cast condition. They want the inclusions to roll and elongate since they typically provide better results. Heavys becoming Thin type inclusions.

4) With additional reduction:

A type inclusions are rated as a function of total sulfide inclusions per field of view. Not by length. The additional reduction would probably not have a significant impact on the rating of the A type inclusion
B type inclusions already stated above typically do not elongate since they are non-deformable. They sometimes beark apart based on the field of view and their shape and size are not going to be greatly effected by the additional reduction
D type inclusions (globular) are also counted as total per field of view. The additional reduction would not greatly change the total number, except maybe to reduce the total count since they have to be of a certain size. Additional reduction will reduce the size thereby decreasing the overall count
C type inclusions, that I initally skipped, is sort of the catch all in the standard. They are typically thought of as silicate inclusions, but can be of all compositions. These inclusions are deformable, and rated as a function of length. Clean steel practices typically limit the amount of these inclusions through minimized re-oxidation by way of good synthetic slag. These inclusion will elongate and may be reated slightly worse in the tube form as opposed to the bar form, but again by elongating the inclusion it is also being thinned out, possibly to the point of being unratable.

Long story short, I do not really see much of a difference in rating in the bar form versus tube form. But that is only my opinion.

 

[salmon2]

deadrange,

Our application put tubes under very high and quick internal pressure/load in the hoop direction. That is why type A and C will kill us but type B and D are much more tolerable to us.

If calcium addition in ladle or any other inclusion shape control in place, hot rolling won't necessily change the including shape which is what we prefer and want to verify by doing the cleanliness test on the finished tubes.

The way I understand the rating procedure is: 1) categorize 4 types by morphology; 2) determine thin/heavy by width (A,B,C) and diameter (D) and 3) determine severity by total length (A,B,C) and number (D). So a little bit different from you on Type A - it is by length to me. Thanks to let me know that type B is non-deformable, I didn't know that. I think type B and D may become type A and C as a result of rolling depending on if any inclusion shape control was used and also how much reduction.

If the difference before/after rolling is ratable, that is interesting to find out. I said I will be doing that. If indeed negligible, I will probably be satisfied, even though there are two possiblities: either inclusion shape control is effective or reduction is not high enough. But we don't specify what is billet size to start with for our tubing.

Last, cleanliness can only give me a gut's feeling - we don't have any calculation model to use them for let's say to calculate transver Charpy. If anybody knows any models or paper about this, please share with me.

Thanks,

Salmon

 

[swall]

Deadrange--very enlightening.

 

[EdStainless]

Cory, ASTM standards are written by consensus. The committees are balanced. You wouldn't believe how hard it is to get end users to participate. Pay your $85, get a free book, and vote electronically. It is easy and painless and you will know about revisions ahead of time.
ISO and EN standards are written by bureaucrats whose main objective is restricting trade.

When we look at cleanliness for thin sheet the tests are done on either cast slab or hot rolled bands. We like this since the cold rolling will serve to break up most inclusions, so the numbers reported are worse case.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[deadrange]

Salmon2,

Calcium in the ladle assuming it is being added in sufficient quantities to change the inclusion shapes will indeed change your A ratings. This is the primary mechanism of the Ca addition. It makes MnS inclusions (typically A inclusions) into round D type inclusions. I haven't done enough research into if it changes the morphology during the rolling operation since in my mind, it looks like it is going to elongate, but for some reason I remember working in the steel mills, when rating a 6x6 from a 12x14 as-cast calcium treated sulfide inclusions were still globular.

I whole heartly agree that E45 only gives a gut feeling since it is only a single plane of view, and only a fair representation of the actual cleanliness. However, there isn't a better method of determining the overall cleanliness of the material. There are several other inspection procedures (UT primarily) but they also have their own sets of limitations.

Good luck on your study. My guess is that you won't see a significant change in the cleanliness, but if you see otherwise please let us know.

 

[salmon2]

Yes, I will try to remember post my any results. But the material won't be delivered by 2009 Q1.

I think the mechanism is that the Ca addtion, one or two lbs per ton, will form Mn/S/Ca/Al inclusion which is harder than Mn/S inclusion and won't be elongated into stringer during rolling, instead it will stay globular. Therefore, we got more D type instead of A.

Thanks a lot to everyone. See that I hasn't been steel industry long enough. It has been very informative discussion.

 

[steelmtllrgst]

Just some info on Ca addition - initial add in liquid modifies aluminates in to calcium aluminates, makes B-types into D types.

The effect on MnS only will occur if Ca is still present during solidification of liquid steel in which case it acts as an innoculation site for MnS. MnSxCa inclusions form which are LESS deformable than MnS alone, but still deformable.

 

[salmon2]

Yes, I heard from our steel mill suppliers that Ca is not easy to apply because its solubility is very low.