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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Original Message:
Sent: 04-30-2022 12:54
From: Michael Connelly
Subject: Metal compatibility "as a minimum"
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
Original Message:
Sent: 04-26-2022 09:36
From: John Merrill
Subject: Metal compatibility "as a minimum"
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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