It may be a company spec, but It's not in documents like API 5L, 5CT, etc. In ASME section II (04) Part A the tightest general variance is +- .005 for nitrogen per SA-6/SA-6M.
In part C SFA 5.1 through 5.26, no such tight tolerances are standard. (in saying that, you are correct in that there are some special circumstances in which the petrochem world uses it)
As for NACE 472 "Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments"
1.2 This standard covers only carbon steels classified as
P-1, Group 1 or 2. These classifications can be found in
the ASME Boiler and Pressure Vessel Code, Section IX,'
ASMEíANSI B31.3 Code for Pressure Piping, or API
Standards 620 and 650. It excludes steels over 480 MPa
(70,000 psi) minimum specified tensile strength. Other
materials may be vulnerable to cracking, but these
materials are outside the scope of this standard.
5.2.3 Maximum contents for each deliberately added
microalloying element (such as Cb, V, Ti, and B)
should not exceed the corresponding value on the
test sample. Deliberate additions are generally
considered to be greater than 0.01% for each of Cb,
V, and Ti, and greater than 0.0005% of B.
"Ladle Analysis
A term applied to the chemical analysis representative of a heat of steel as reported by the producer. It is determined by analyzing a test ingot sample obtained during the pouring of the steel from a ladle."
Which In America leads to ASTM A751 "Standard Test Methods, Practices, and Terminology for Chemical Analysis of Steel Products."
The edition I have is 01, current edition is 07, but I doubt much has changed in this regards.
In it is referenced E29 "Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications"
Starting with E29 There are two methods for listing the requirements. Those are absolute and rounded.
Absolute is as it implies, anything out of the specified range is unacceptable. For instance, a designation of .03 percent carbon max. The same works for minimums.
rounded being
"6. Rounding Method
6.1 Where Applicable--The rounding method applies where
it is the intent that a limited number of digits in an observed
value or a calculated value are to be considered significant for
purposes of determining conformance with specifications."
Using icp tolerances can get down to .0002. +-.0001 or with FT-ICR down to .00005 +-.00002
Care must be taken when speaking in terms of absolutes, and is addressed in E29.
The point of all this is, it's not as common as it is being made out to be. I wouldn't want someone reading this thread at a later date thinking this is common place because it is not, and could lead to some trouble down the road for that person. Having said that, in some very specific incidences, various industries will call for these tight tolerances, but it is most definitely not a usual part of the codes and standards. I have some experience with the "majors" as you call them in the area of materials testing, I have seen what you are stating, but again, it's a special circumstance, not run of the mill daily operation.
Regards,
Gerald
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