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Metal compatibility "as a minimum"

  • 1.  Metal compatibility "as a minimum"

    Posted 26 days ago
    Several petrochemical standards require metal components to be "carbon steel, as a minimum" or "316/316L, as a minimum." For some very specific components, we understand what this means, but is this a good phrase to use? Is there some general knowledge of what "as a minimum" means?

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    John Merrill
    Principal Engineer
    EagleBurgmann
    Matthews NC
    7048407045
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    Journal of the Month


  • 2.  RE: Metal compatibility "as a minimum"

    Posted 25 days ago
    Yes it is - it tells were cost can generally be cut and were cost cannot be cut - "carbon steel as minium" does not prevent using a stainless steel in its place in a tough case of procurement.  Unfortunately there are no royal roads to understanding what materials will always work in a given applicaiton and GOOD engineering judgement - not common sense - is required.  Management will generally press for the cheapest route because they believe it part of their job - sometimes the only task they can claim due to ignornace.  You must be ready to stand up to them with the best knowledge, training, and experience you can muster - its you head on the chopping block not theirs. Good Luck.

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    Edward Vojcak
    Senior Metallurgical Engineer
    SGS North America
    Blue Island IL
    (708) 595-8734
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    Journal of the Month


  • 3.  RE: Metal compatibility "as a minimum"

    Posted 25 days ago
    I have never seen that, but I would not like it unless it specifies "minimum" relative to some specific property, like corrosion resistance for example.

    I don't even like "carbon steel" as a specification, but if you are going to say "carbon steel, as a minimum" why not just specify "steel"? Is there any steel more "minimal" than carbon steel?

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    Ken Kirby
    Snap-on, Inc.
    Kenosha WI
    (262) 748-3836
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    Journal of the Month


  • 4.  RE: Metal compatibility "as a minimum"

    Posted 25 days ago
    I am troubled by this because austenitic 316 is a completely different alloy with completely different properties than that a "carbon" steel. These alloys are not necessarily compatible with each other (depending on application). If any old carbon steel is good enough, why do you need at least 316/316L to meet the requirement. Are the applications calling this out really this indifferent to material property requirements?

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    Aaron Tanzer
    Senior Metallurgical Engineer
    Metallurgical & Materials Technologies
    Baton Rouge LA
    (407) 247-9557
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    Journal of the Month


  • 5.  RE: Metal compatibility "as a minimum"

    Posted 25 days ago
    Yes, very open to misunderstanding or poor interpretation.  On the 316/316L, what is equivalent or above the minimum.  Even if corrosion resistance is specified, is 2304 OK?  And of course 321 and 347 are higher numbers than 316, are they OK?   (Don't laugh at that, sadly it happens!) Let alone there are cases where 304L is better than 316L.

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    Gary Coates
    Manager, Technical
    Nickel Institute
    Mississauga ON
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    Journal of the Month


  • 6.  RE: Metal compatibility "as a minimum"

    Posted 25 days ago
    In my opinion, this is inadequate, and probably unenforceable - minimum for what property? For what service conditions? Given that the application is petrochemical, my default assumption is that this is regarding corrosion resistance, i.e. "something must be at least as corrosion resistant as 316" but even there you can't say that one material is blanketly more corrosion resistant than another because it depends on the service medium and mechanism of corrosion. For example, 316 is notably susceptible to pitting in the presence of chlorides, whereas "lesser" grades may not be (they'll suffer from general corrosion but last much longer in service). This is to say nothing of weldability, compatibility with mating materials to prevent galvanic corrosion, strength variation within generic categories like "carbon steel" (i.e. F60 vs. 1018), etc. 


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    Sean Piper
    Product / Process Metallurgist
    Ellwood Texas Forge Houston
    Houston TX
    (713) 434-5138
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    Journal of the Month


  • 7.  RE: Metal compatibility "as a minimum"

    Posted 24 days ago
    I used to approve supplier requests from vendors to substitute material for drawing specified. My fundamental was the substitute material had to perform at least as well as or better than the material we specified (I did not want to see this request come back to me years later in the form of a failure). The other fundamental rule was that it was unacceptable to change the material system. Using 316L austenitic stainless in place of carbon steel fundamentally could cause all sorts of problems in the system including the differences in thermal expansion (this was for gas turbines), weldability, and compatibility with other materials in the design, even though 316L might have been considered a "better" material.

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    Aaron Tanzer
    Senior Metallurgical Engineer
    Metallurgical & Materials Technologies
    Baton Rouge LA
    (407) 247-9557
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    Journal of the Month


  • 8.  RE: Metal compatibility "as a minimum"

    Posted 24 days ago
    In my travels, the most memorable "minimum" definition I have encountered was a rather ancient drawing, which had a single statement regarding the material to use.  It said " make from metal"

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    Anthony Giammarise
    consulting metallurgist
    MOSTLY METALS
    Erie PA
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    Journal of the Month


  • 9.  RE: Metal compatibility "as a minimum"

    Putnam Service Award
    Posted 24 days ago

    Minimum of Minimal……Time ? Thickness ? The term that drives me crazy is "unless otherwise specified"?

     

     Can you imagine what a procurement "person" might accept when challenged year to year to buy commodity metals at 10% less than the previous year? Safety over Service….availability! Did someone 

    say….weldablity? 

     

    Conclusion: those of us who function as failure analyst likely will continue to be very busy ! MurDoc



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    Frederick Schmidt - Past President ASM & ASMu
    DIRECTOR MATERIALS TECHNOLOGY
    Advanced Applied Services,Engineering Systems Incorporated
    New Port Richey FL
    (630) 207-3900
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    Journal of the Month


  • 10.  RE: Metal compatibility "as a minimum"

    Posted 23 days ago
    Could a better material possibly create higher failure risk for end user? Although we also provide coating services for some petrochemical requirements, at Hitemco, a Thermal Spray Coating service, we are mostly insulated from this " as a minimum " type of request by specification conformances. Aerospace, ( and other markets ), usually require coatings to an existing coating specification, where even the powdered metal alloy or ceramic material used in the process must its own specification. However, a very apropos instance comes to mind: where one of our 'newer' coating processes uses the same material as an older, competitive, proprietary coating technology. But, our coating exceeds that of the older competitive coating in comparison to a number of physically measurable properties, because of the different coating process used. We made a presentation, same material but better coating, to a very astute engineer at an OEM aerospace customer. His simple answer was most enlightening. Something like; if your better coating replaces the existing coating on this component to make it last longer and resist failure in this system of moving parts, that may not be best because; we must now discover what other flight critical component in the entire system of moving parts will fail instead. He went on to state the million$ cost for a risk analysis flight test. So, be aware;  " as a minimum " may not always create better engineering.

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    Noel Gibilaro
    Customer Relationship Specialist/New Business
    Hitemco, LLC
    North Branford CT
    (203) 430-7755
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    Journal of the Month


  • 11.  RE: Metal compatibility "as a minimum"

    Putnam Service Award
    Posted 22 days ago
    John,
    I've been on the flip side of this argument, and it can be very painful to all parties.  First off, the language is terrible.  I've seen this type of thing with fasteners and during the bid process the lowest cost generally wins the bid.  When you take into account volume and if the part is purchased overseas you wind up with an equivalent that technically meets the drawing requirement.  The part(s) get rejected by the customer for whatever reason and now you're stuck with thousands of dollars of inventory that meet requirements.

    Michael B. Connelly, FASM, CQE
    Adjunct Professor - Richard J. Daley College

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    Michael Connelly
    Connelly Consulting
    Chicago IL
    (312) 972-8556
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    Journal of the Month


  • 12.  RE: Metal compatibility "as a minimum"

    Posted 21 days ago
    There are many interesting and informative responses in this thread. I think there is consensus that the language in the callout is too vague, too open, and too subject to interpretation (and misinterpretation!) to actually appear on a drawing.

    So - an amusing story, if you wish to waste some time.

    A number of years ago I got a call from a machine shop / vendor about a material callout on a drawing. New vendor, not much history making oilfield parts, callout was too strange (he could have met it easily but wanted to understand it),

    The callout was: "1018 or 4140 28-36 HRC"

    At first glance it is absurd and contradictory, but the one commonality between the steels is that excess bar stock of each will certainly be on he shelf in any machine shop that makes oilfield parts.

    "In the old days" there was a callout for '4140 at 28-26 HRC, 108 ksi min yield', which was known as "commercial heat treat" - 4140 quenched and tempered at the mill, with an enormous range of acceptable hardness and an easily-met min. yield. In fact, some drawings called out "4140, commercial heat treat" and the machine shops understood what was required and how to source it.

    So the drawing was calling for, in effect, "Steel, any, whatever is on the shelf that you can sell me cheap". This would be clear to anyone in the oilfield industry but opaque to anyone who knew anything about machining, steels or Engineering.

    After speaking with a Senior Designer (who knew the ropes and understood what was being called for) I sat down and wrote a spec for "Steel, Any, Lowest Cost" and in the very first paragraph made it quite real clear that if any particular strength, toughness, ductility, or indeed any mechanical properties were required, it was the wrong spec to use. If cheap steel was required instead of wood, aluminum, brass, zinc, or any other material - maybe to prevent galvanic corrosion - but none of the mechanical properties of any particular steel were required, it was the spec to call out.

    Modern day people may not believe this story but it is true.

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    Andrew Werner
    Chief Metallurgist, Perforating - Retired
    Schlumberger - Retired
    East Bernard TX
    (832) 563-3489
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    Journal of the Month


  • 13.  RE: Metal compatibility "as a minimum"

    ASM-IIM Vist. Lect.-NA
    Posted 20 days ago
    Yes, the drawing notes with "at a minimum" is ambiguous and leaves doubts whether the bid will be accepted even if it meets the technical requirements. However, in general it leans the metal component must meet the engineering property requirements of the part/component in the drawing. Now, that confuses manufacturers as they may not know the application of the part and what engineering properties must be met "at a minimum". In the example of "carbon steel", it would generally mean Yield, Tensile, elongation and possibly toughness (for petrochemical) from a metallurgist perspective. While in case of "316/316L" it would mean corrosion and weldability characteristics must be met at a minimum. Therefore, ask what characteristics/properties must be met at a minimum. In defense of the design engineers, I would say this is prompted by drawing notes requiring the minimum properties which is the best way to put a requirement and some uninformed engineers take it as granted what it means thinking of minimum mechanical properties.
    If one uses alloy steel for carbon steel it will meet all the mechanical properties minimums, but cost will be high and the bid will not accepted.
    Hope it makes sense.

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    Prabir Chaudhury
    President
    Education and Consulting LLC
    Phoenix AZ
    (480) 577-0772
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    Journal of the Month


  • 14.  RE: Metal compatibility "as a minimum"

    Posted 13 days ago

    The problem is that the manufacturer may not know the application, so even guessing why materials were chosen may not be valid. 

    -"While in case of "316/316L" it would mean corrosion and weldability characteristics must be met at a minimum."
    You don't know what corrosion minimum, there also may be mechanical property minima. If a spec calls for 316 at a minimum, would 316H or 316L be preferential? Unless minimum properties are specifically called out, "minimum" is a nonsense word and has no place in material specification.



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    David Sapiro
    Senior Materials Engineer
    Seattle WA
    dosapiro@gmail.com
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    Journal of the Month