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Longitudinal Charpy V Notch Position

  • 1.  Longitudinal Charpy V Notch Position

    Posted 07-30-2020 10:49
    ​Greetings all. I recently attended a joint ASTM/API meeting designed to develop acceptable recheck tolerances for mechanical properties. There was a lively debate as to whether the L-C or the L-R position should be specified for longitudinal testing of bar product, assuming the product code was silent. Does anyone have an opinion as to which position would be more appropriate? For the most part, the product would be in tension with possibly some bending.

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    Joel Russo
    Chief Materials Engineer 1
    TechnipFMC
    Houston, TX
    (281) 591-4247
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  • 2.  RE: Longitudinal Charpy V Notch Position

    Posted 07-31-2020 08:14
    I'm on the subcommittee for ASTM A370 and written the standard for tensile testing of round tubing, currently under ballot consideration.  This draft standard has received commentary, some affirmative, other negatives, from all over the industrial world because ASTM standards are widely used.  The CVN specimen for square or rectangular tubing is generally taken with its long axis in the same direction of the long axis of the tubing, never at welds or corners.  However, for round tubing, which could be pressurized, it makes sense to take the CVN specimens in both transverse and longitudinal axes of the tubing.  Hoop stresses in highly pressurized tubing can result in pressure bursts, especially if the interior is pitted or its fracture toughness is minimal.  Moreover, since tubing may exhibit "fibering" where there is grain elongation and magnification of the length of grain boundaries, a transverse CVN test specimen should be sampled.  ASTM is conservative about mandating specimen orientation, so most of the time this is left to the "purchaser" to require testing locations in the Ordering Information.

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    Christopher Hahin
    Engineer of Structural Materials & Bridge Investigations
    Illinois Department of Transportation
    Springfield IL
    (217) 522-4023
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  • 3.  RE: Longitudinal Charpy V Notch Position

    Posted 07-31-2020 09:18
    If considering assessment of circumferential surface flaws, L-R specimens would be relevant.

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    Su Xu
    CanmetMATERIALS
    Hamilton ON
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  • 4.  RE: Longitudinal Charpy V Notch Position

    Posted 08-01-2020 12:40
    I believe I was in the same meeting discussion. The answer depends on the size of the material being considered. For small diameters (the smallest diameter that can be tested is 9/16 inch diameter), the two orientations are effectively the same. For very large diameters (greater than about 8 inches), product yield considerations may make the CR, RL, CL, or RC orientations more desirable. The RL and CL orientations have the greater probability of encountering inclusion stringers and should therefore have the lowest toughness. 
    Looking at small diameter bars in tension or bending, The LR orientation corresponds most closely with the  probable fracture mode. 
    In the end, any test is better than none. 

    --
    John Grubb





  • 5.  RE: Longitudinal Charpy V Notch Position

    Posted 08-01-2020 12:41
    Virtually all commercial steel used now-a-days in NA is made using the continuous casting processing step.  Gone are the days of ingot casting.  Yet most textbooks and standards reflect information obtained from ingot-cast material.  Well this may shock you, but there are significant differences in residual non-homogeneities in rolled product when you compare CC-steel to ingot-cast steel.  One would think that to obtain a meaningful evaluation of the material, the Charpy V-notch would be aligned so as to propagate the failure-plane through the weakest region.  Of course, this requires some appreciation of what might be the weakest region in CC-steel (not discussed in the textbooks I have seen).  One example may be evaluation of line pipe steel (steel presently in place for the Keystone pipe line system).   The weakest portion of this steel is the centerplane, making through-thickness (not the hoop or longitudinal) the weakest direction.  If the Charpy V-notch orientation ignores this fact, the test may actually give a false sense of security.  That is why, the Keystone pipe line may be a disaster waiting to happen.  But it may take 20 to 30 years, so I really need not worry.

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    Edward Szekeres
    Principal Consultant
    Casting Consultants Inc.
    Rochester NY
    (585) 766-3536
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  • 6.  RE: Longitudinal Charpy V Notch Position

    Posted 08-03-2020 08:19
    I appreciate the comment that the through-thickness may be the weakest link in a thick-walled pipeline.  However, a CVN specimen is only 1 cm thick, so if the pipeline wall thickness is greater than 1 cm, multiple specimens would be required to sample the thick wall.  The specimen could be oriented in the longitudinal pipe direction or transverse, both of which would provide where a fracture would start based on its inherent toughness.  In forgings, your concept is used where the CVNs are often specified to be taken at the 2/3 R points of a round bar.

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    Christopher Hahin
    Engineer of Structural Materials & Bridge Investigations
    Illinois Department of Transportation
    Springfield IL
    (217) 522-4023
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  • 7.  RE: Longitudinal Charpy V Notch Position

    Posted 08-30-2020 12:27
    Edited by Carrie Hawk 09-08-2020 10:03
    Pipeline failures per mile and unit (gallons, cubic feet) are very low compared to other transportation methods. They do not fail in the axial (through wall direction). Even with centerline segregation, you end up with two hoops that just reinforce each other. This is why pipeline operators install tight fitting sleeves over general corrosion. When they do fail, they generally either 1) leak (due to corrosion) which has little or nothing to do with toughness or 2) they rupture due to hoop (circumferential) stresses or 3) they're damaged by backhoes, bulldozers or farm equipment and then the failures are controlled by tri-axial stresses and toughness in two or three orientations.         ​

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    John Cline
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  • 8.  RE: Longitudinal Charpy V Notch Position

    Posted 08-03-2020 08:19
    The position and orientation of CVN test specimens obtained from bar products should depend on the relevant failure modes based on notched stresses in the final part. I have encountered instances where failure initiates in the transverse direction at the surface or subsurface of heat treated shafts from bending stresses. I have also observed longitudinal fractures initiating at the surface from imposed torsional stresses. I have also encountered longitudinal fractures at the centerline that propagate outward in the transverse direction from transverse tensile stresses imposed during heat treating. As already noted, specimen orientation on small bar less than about 1" is restricted by the geometry. For intermediate diameters, specimen orientation is limited to the longitudinal orientation. The orientation of the notch as to longitudinal or circumferential should be specified based on the application. Also, the location of the specimen should be specified relative to the depth from surface to centerline. Furthermore, if the orientation of the notch is circumferential, then the location of the notch should be specified as to whether it is toward the outer surface or inner surface of the bar. For larger diameter bars, the notch location and orientation will be further restricted by geometry and the location from surface to center should be further specified. 
    It would seem that the value of conducting the CVN test will depend on many factors in addition to those above. Standardization should be limited to the terminology of test prior heat treatment and specimen location/orientation with the selection of appropriate details left up to the user and producer.

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    Robert Cryderman
    Research Associate Professor
    Colorado School Of Mines
    Erie MI
    (734) 735-3093
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  • 9.  RE: Longitudinal Charpy V Notch Position

    Posted 08-03-2020 13:18
    Dr. Cryderman - You are correct, but the original question related to a specification (ASTM A370)  requirement. When the material is produced and tested, the end use and loading mode generally is unknown. Individual product specifications can establish their own requirements that supersede the general testing requirement, but the problem of limited knowledge of future usage remains.  

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    John Grubb





  • 10.  RE: Longitudinal Charpy V Notch Position

    Posted 08-04-2020 09:02
    The position(s) of where the CVN specimens should be taken are generally based on either a traditional stress analysis, or a finite element analysis if available.  Of course this is ideal, but many designers without sufficient background neglect these basic preludes to good specifications.  In any specification or inclusion of a particular standard like A370, the purchaser (or manufacturer of the product) needs to have some basic idea where failure would likely initiate.  That's why Ordering Information, located in ASTM specifications, should not be neglected because the general requirements and product standards do not always dictate where CVN specimens shall be taken.  In many of them, CVN is either a supplemental requirement if specified by a purchaser, or it isn't even present.  Let's face the fact that many designers to this day do not understand fracture toughness or crack initiation and its implications for product life.

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    Christopher Hahin
    Engineer of Structural Materials & Bridge Investigations
    Illinois Department of Transportation
    Springfield IL
    (217) 522-4023
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  • 11.  RE: Longitudinal Charpy V Notch Position

    Posted 08-15-2020 11:15

    Position and orientation choices on large, rotating power generation components (generators, turbines, etc.) are usually based on a worst case for depth and orientation, relative to the large forging, plate and/or bar that the component is made from, as well as a consideration of principal stresses. For example, a large generator rotor might have radial specimens taken at some depth into the rough machined rotor, in order to meet requirements that are based on a worst-case orientation and depth combination. Keep in mind that these could be rotors with a main body diameter of 70 inches, among other components.

    With turbomachinery, that worst case location/orientation tends to be carried through to all other critical metallic components. By the way, "longitudinal" is quite often a best-case location; i.e., optimistic.

     

    Neil Kilpatrick

    Genmet LLC

    neil@genmetallurgy.com

    +1 407 760 7293






  • 12.  RE: Longitudinal Charpy V Notch Position

    Posted 08-17-2020 08:48
    This is an extension of my earlier post: The orientation / location situation for large open-die forgings, such as large turbines and generators for power generation is much different than what we face with smaller components. ASTM specifications for these components include A469 (generator rotors), A470 (steam turbine rotors) and A471 (steam turbine discs and wheels). Normal practice is to specify location and orientation. This is done by the purchaser, who generally chooses the worst-case location and orientation.

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    Neil Kilpatrick
    Owner
    GenMet LLC
    Winter Springs FL
    (407) 760-7293
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