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API 6D face-to-face dimensions: where they come from

Guide · API 6D · ASME B16.10

Face-to-face is the distance between the flange faces of a flanged valve; end-to-end is the same measurement for a valve with welding ends. API 6D sets these dimensions by reference to ASME B16.10. Read the ASME B16.10 table for the valve type, size, class and end connection in your purchase order.

Draft guide. Dimension values are shown as “To be confirmed” until each one has been checked against the ASME B16.10 edition named in the purchase order. Do not use this page for fabrication.

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How to check a face-to-face dimension in six steps

  1. 01Identify the valve type and the boreBall, check, gate and plug valves each have their own table in ASME B16.10. Note whether the bore is full or reduced, because the table and the pattern can differ.
  2. 02Read the size and the pressure classTake the NPS and the ASME class from the datasheet, not from the pipeline class name alone. A DN size and a PN class have to be converted to the ASME equivalents the table uses.
  3. 03Fix the end connectionFlanged RF, flanged RTJ, butt weld or another end: the dimension is measured between the end preparations, and the table may give separate values for each.
  4. 04Choose the patternShort-pattern and long-pattern valves have different dimensions. The purchase order or piping class should say which pattern the line needs; do not assume the factory default.
  5. 05Look up the table and compare it with the drawingTake the value for that combination from ASME B16.10 and compare it with the general arrangement drawing. If the drawing is outside the table value, treat it as a custom dimension and get the difference agreed in writing.
  6. 06Record the edition and the measurement basisWrite the standard edition and the measurement basis into the approved drawing: to the flange face, to the ring groove for RTJ, or to the weld bevel. Two valves can be dimensionally identical and still be recorded differently.
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Face-to-face and end-to-end, defined

Face-to-face (F2F) is the distance between the two flange faces of a flanged valve. End-to-end (E2E) is the same distance for a valve with welding ends. Both are measured along the valve axis with the valve closed, and they decide whether the valve fits between the flanges or spool pieces already in the line.

Flange outside diameter, bolt circle and facing are different dimensions, set by the flange standard such as ASME B16.5 for the common sizes. Do not use a flange dimension in place of a face-to-face dimension.

03

API 6D sets the dimension by reference to ASME B16.10

API 6D defines the design, testing and documentation of pipeline and piping valves. For the valve types and end connections within its scope, it requires face-to-face and end-to-end dimensions to follow ASME B16.10, so the dimension table you read is the ASME B16.10 table.

ASME B16.10 tabulates these dimensions by valve type, size, pressure class and pattern. The edition matters: the purchase order should name the edition, and the drawing should state the same edition.

That is why an “API 6D face-to-face dimension” is normally an ASME B16.10 dimension. The two standards are used together, and a drawing that quotes API 6D without a dimension edition is incomplete. Check the clause list of the edition in your purchase order for the exceptions it allows.

04

Dimension lookup

The table shows the lookup an order needs, not published values. Each dimension is to be confirmed from the ASME B16.10 edition named in the purchase order before it is used on a drawing.

Face-to-face lookup by size, class and pattern. Every value is To be confirmed until it is read from the cited ASME B16.10 edition.
Size (NPS)ASME classEnd connection and patternFace-to-face (mm, ASME B16.10)
2150Flanged RF, long patternTo be confirmed
4150Flanged RF, long patternTo be confirmed
6150Flanged RF, long patternTo be confirmed
8150Flanged RF, long patternTo be confirmed
2600Flanged RF, long patternTo be confirmed
4600Flanged RF, long patternTo be confirmed
6600Flanged RF, long patternTo be confirmed
4900Flanged RTJ, long patternTo be confirmed
05

What can move the number

Pattern and design: short-pattern valves save space in tight skids; long-pattern valves match older piping classes. A factory that offers only one pattern cannot necessarily match both.

Bore and design: a reduced-bore valve is not automatically shorter than a full-bore valve of the same size and class. Check the table for the exact combination rather than assuming the bore has no effect.

End preparation: a ring-joint flange, a raised-face flange and a weld bevel are measured differently, and the gasket groove or bevel is part of the agreed dimension.

Custom or extended designs: extended bonnets, actuators, double block and bleed bodies and non-standard lengths are outside the standard tables. They need a drawing dimension agreed in writing and marked as non-standard.

Tolerances: the standard and the purchase order define the permitted tolerance. State it on the drawing rather than assuming the table value is the only acceptance criterion.

06

Frequently asked questions

Where do API 6D face-to-face dimensions come from?
From ASME B16.10, which API 6D references for the valve types and end connections in its scope. The purchase order should name the ASME B16.10 edition, and the approved drawing should quote the same edition.
Are API 6D and ASME B16.10 face-to-face dimensions the same?
For the valve types and ends covered by the tables, the dimension is the ASME B16.10 value. A design outside those tables needs a drawing dimension agreed in writing. Check the exceptions listed in the edition your order names.
Does a full-bore valve have the same face-to-face as a reduced-bore valve?
Not always. The table value depends on the valve type, size, class and pattern, so compare the exact combination instead of assuming the bore makes no difference.
Can a factory make a valve to a non-standard face-to-face?
Yes, but it becomes a custom dimension. It has to appear on the approved drawing, be agreed in writing and be marked as outside ASME B16.10. Do not accept a verbal assurance that it “matches”.
Why can the RTJ dimension differ from the RF dimension?
The ring-joint groove changes the face where the dimension is measured. Check whether the drawing dimension is to the flange face or to the groove, and use the same basis when you compare two valves.
Can I use this page as a dimension table?
No. Every value on this page is marked To be confirmed. Use the ASME B16.10 edition named in your purchase order and the approved drawing for fabrication, and verify the drawing revision before the valve is machined.
07

Standards cited

  • API Spec 6D: Pipeline and piping valves: design, manufacture, testing and documentation of ball, gate, plug and check valves.
  • ASME B16.10: Face-to-face and end-to-end dimensions of valves. Edition quoted to: ASME B16.10-2022.
  • ASME B16.5: Pipe flanges and flanged fittings, NPS ½ to NPS 24.
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