Non Mettalic Inclusions in Carbon Steel Pipe Material

The test certificate accompanying the consignment?

The very reason why we are looking for a positive method as we have the experience of receiving material with clean certificates but were found with an unacceptable level of inclusions during a faailure investigation.

It's time to change supplier.

As Milo said: there are nonmetallic inclusions in all steels. Therefore you have to specify what is the dimension of the "minute size" that you wish to look for, and details regarding the pipe that you intend to check ( diameter, thickness and surface status as minimum information - even manufacturing process of the pipe will be helpful ). After that someone may advise you to choose an adequate method of testing.

Also, I will say that the expression "unacceptable level of inclusions" is not clear to me: unacceptable against what ?

If you are talking about definition in AWS B1.10 point 2.4.1

Then Rt is OK (Better with film D4).

WP

There are minute nonmetallic inclusions in all steels. Astm e45 method c is a typical mill practice for characterizing. What standard did you specify for the product? This will help me determine what method may be practicable. Frankly, i would cut test coupons and send to lab, unless you are talking about serious entrained slag from caster. Just how bad was the inclusions in phioe batch. Milo

I was only looking for an NDT method to detect inclusions. I will give details of my problem for your information anyway.

We have heaters with horizontal tube coils on the two walls and the material is A106 Gr. A. Opearting temperature is around 280 deg.C. These are shut down every 6 years only and we had no initial record of inclusions. After being in service for 6 years we found scattered inclusions on many tubes which were wrongly interpreted as metal loss by the UT technicians. Only after sectioning the tubes we found them to be inclusions. Hope this explanation is clear.

Sorry, my last answer is not for this. for this Type of problem may be AE test is useful. ASME V Articles 12-13 and 14. Also check MONPAC in internet. Sorry again. WP

No worries. We all learn a lot daily. Contributions are all well received.Thanks again.

So, your problem is not to detect the inclusions ( the best method you have already: UT). The real problem is to differentiate between the indications that you have: change in wall thickness or lamination, and this is not quite easy, especially for inspection in field.

Generally speaking the UT operator is "blind" and cannot see what is the remaining thickness below the signal that he receives, therefore at that point it might happen to have localized corrosion.

If you think that it worth the risk, consider that the material under the "inclusion" is sound.( I personally will take this risk only if in the tube is water and and there is not very much damage that can happen either to the equipment or even most important to the personnel - see temperature 280°C - in case if the tube will leak. But I assume that in your case we are speaking about some hydrocarbon , and the potential consequences are quite different ).

To look from an other perspective it will worth to take a look at this page:

http://www.ndt.net/article/apcndt01/papers/7/7.htm

Thanks very much.

A skilled operator - is not blind!!

He sees the remaining thickness ! His only restrictions is the UT Wave length

(beneath it- the signal is not clear)

The most important issue is to establish the inclusions size allowance. This must

be considered by a metallurgist with a speciallized functional field experience....

The strictest solutions will be preferrentially based on wall thickness versus Inclusion

Size (length +diameter+dispersion) allowed

Use ASTM-E213 Std

You give sound advice.

The issue remains as to what are the proper criteria, as you mentioned in an earlier post and as the OP has 'mentioned' in his earlier response to me.

My point is that YES there are nonmetallic inclusions. Normal expectancy.

The critical thinking that was missing about them is "So what?" The issue was raised, and now people have fear, but no causality or criteria to failure have been established. That is a description of a witch hunt, not sound engineering.

I concur with your advice regarding ASTM E 213.

Milo

@ Jacob Klepatch

The OP mentioned that this issue come as a result of an corrosion check.

Of course the operator is not blind. If he's blind he cannot be NDT operator at all, no matter how skilled he might be.

I used "blind" figuratively speaking - ( note the quotation marks ). What I was trying to suggest is that on the other side of the discontinuity looking from the UT probe side, there will be always a "shadow" area where is difficult to obtain reliable information. How big is this area depends on many factors related to the discontinuity itself ( size, position, pipe thickness) and related to the method used (probe type, diameter, frequency).

Around the discontinuity is an other matter, and based on the behavior of the response that he receives from the discontinuity and around it, he might have an educated guess that it is unlikely to have corrosion at this place, and must be "inclusion". For a new product is not an issue because you do not expect to have corrosion, but for a heater that has a service life of 6, 12 … or who knows how many years, always is a risk that sideway pits may occur. ( Not only this type of pits may occur, but these are those that I am concerned that cannot be differentiate from "inclusions" with an acceptable level of confidence using UT method in a practical way.)

To be better understood see below sketches that are showing the inner side of the pipe :

Sideway Pits (corrosion-doctors.org/Forms-pitting/shapes.htm)

• Subsurface (left side) Undercut (center) Horizontal grain attack (right side)
  

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If the problem of OP is as I perceive it ( corrosion check of pipe => UT signals from certain depth => rejection of the "corroded pipe" => cutting pipe and verify the remaining thickness => "sorry it is not corrosion , there are inclusions" ), ASTM E 213 is not the right answer.

ASTM E213 is comparing the response from the tested pipe with the response from some artificial notches with different shapes -U, V, square - and in case if the level is exceeding certain value the pipe is rejected. Is not making any reference to the type of discontinuity that produce that signal.

It is a great and simple tool to be used for new pipe, but to use it for a pipe that you expect to have the inner side corroded is totally an other matter. One reason is that because after the first reflection of UT beam you do not have confidence that the UT beam is going where you think that will go , and also because beam dispersion is increased with an amount that you are not aware. Therefore the angle beam technique is not a reliable choice for the test of corroded pipes.

The answer to OP problem will be monitoring the behavior of the "inclusions/corrosion" in time. Establish the minimum size of discontinuities that has relevance for them. Take a carefully snapshot of the problematic areas at a certain moment, marking location, depth and size of all the relevant discontinuities and compare it with the answer after certain amount of time. For sure , if it is inclusion will remain there unchanged and every one is happy - they have inclusions there , but they can live with them ("So what?"). In case if discontinuity is increasing as size or depth ... most probably it is corrosion, ( I am not excluding the possibility to have UT operator error either on the initial snapshot or on the later examination ) and they have to treat the problem with corrosion acceptance criteria.

It will remain to choose the period of time between the checks - enough to produce discernible changes if corrosion occurs - and if the heater may be put safely back in service for this period of time. But this is an analysis that shall be done by engineering team knowing details of the design of heater and the process involved there.

Dear crstn

Point well taken!!

As you stated the UT examination is most effective on new tubes !!

Other problem - the surface in depth of 5-6mm is quite impossible to check inclusions and other discrepancies with UT equipment!!

The more pragmatic approach is to use Magnetic Tests (see:ASTM-E1444 + AMS-2301)

-for surface inclusions / pinholes etc.

Also,in the last decade the Thermal Tests is used instead of both Tests-very efficient!

(see ELKEM System!- good for surface discontinuities too!!)

As a "thumb rule",for high (5,000 Atm !!) pressure tubes ,is used UT Class:"A" Size definition (i.e.:Single discontinuity:5/64" ,Multiple Disc.:3/64" etc.)

Regards: Klepatch

NB

"Blind" operator - of course not literally taken....

THERE OK....How big is this area depends on many factors related to the discontinuity itself ( size, position, Steel pipe thickness) and related to the method used (probe type, diameter, frequency)/.

What is on your mind ?

Every NDT standard DEFINES THE AREA / REGION TESTED !!

But it is your choice of what to test !!