Ring-Groove Concentricity for API Type 6B Flanges 1

[Gilmiril]

For Type 6B flanges, the current 20th edition of API 6A specifies that, "Ring groove shall be concentric with bore within 0,010 total indicator runout." Given that these R/RX ring grooves are dimensioned by pitch diameter (P), width (F), depth (E), and the angles of the sides walls (23 degrees +/-0.5), what would be the preferred method(s) to show this on a drawing?

 

[Gilmiril]

Perhaps I should add that we've been callling out a Total Runout on both side walls of the ring groove. But how does that work in conjunction with the 23.0+/-0.5 degree directly toleranced angles of these sidewalls? Does Total Runout require these angles to be basic?

 

[powerhound]

Gilmiril,

I worked in your industry a few years back so I know the rings you're referring to. At least I think I do. The sealing rings that go between two flanges. Some are high pressure (BX) and some not. The answer to the first question in your second post is: It does not work in conjunction with the +/- degree callout at all. The answer to your second question is: Maybe. Total runout is fully supported in the standard when the specified surface is cylindrical but not when the surface is conical relative to the datum axis. Still, the GD&T standard does not explicitly prohibit it's use with a conical surface so there are those who would argue that it's not illegal to do so. If it's not illegal then, by definition, the angle would absolutely have to be basic.
Keep in mind that some standards still use specifications that were determined up to 80 years ago or so...way before the development of GD&T.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
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[Gilmiril]

John, yes, you're talking about the correct rings. API 6A specifies two types of flanges: Type 6B which use R or RX ring gaskets, and Type 6BX which use BX ring gaskets. As an aside, R/RX ring gaskets are also used in ASME flanges with RTJ facings, and BX ring gaskets are also used in API Type 17SS flanges (the subsea version of 5000 Type 6B flanges to API 17D).

Any suggestions for how this requirement is best handled on a detail drawing? I'm tempted to use Circular Runout instead, but the API spec explicitly states Total Indicator Runout. From a functional point of view, it really only needs to control coaxiality, but that's not how it's worded.

Your point on standards that predate GD&T is well taken...

 

[Gilmiril]

...or am I misunderstanding "Total Indicator Runout"? Does this simply mean the value of Circular Runout when measured with a dial indicator? (i.e. the word "Total" simply means the difference between the high and low values and thus does not imply Total Runout?)

 

[CheckerHater]

You are not alone.
The term "Total Indicated Run-Out" (TIR) is historically the oldest one (see John's comment about some standards going wa-a-ay back).
Later TIR was interpreted as "Total Indicator Reading" - broader definition which includes "Total Indicated Run-Out" as well.
Today TIR is replaced with FIM ("Full Indicator Movement") applied to controls including Runout. So some discrepancy between older API standards and modern drafting standards definitely takes place.
As a personal opinion (not an expert in petro), I would specify Total Runout for cylindrical part of the groove and Circular for the walls. (and by definition it would be measured FIM (or TIR)).

 

[Belanger]

Yes, Gilmiril, your last post is a correct statement. The term TIR in those "old days" is most akin to circular runout in today's GD&T, not total runout, despite the use of the word total in both terms.
That's because the "total" in TIR is talking about the absolute value of the total travel of the dial indicator's point throughout one revolution. The "total" in total runout takes that notion and stretches it over the total length of the part as one tracing.
As CH mentions, FIM is a better term (though it is only a verbal thing and not actually spec'd on the drawing as FIM).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems