**Specific heat capacity ratio (k)**is

**included**in the Equation [23] & [24] and [25] & [26] in API RP 521, 1997 where [23] & [24] and [25] & [26] are used to calculate the Mach number and Critical pressure of gas in the pipe respectively.

In the latest API Std 521 Jan 2007,

**Specific heat capacity ratio (k)**has been

**removed**from [27] & [28] and [29] & [30]...

I have made some surveys and derivation, k factor may be required in the equation. Read details

**HERE**.

This issue has been highlighted to API committee incharge and the response is those equations in current revision (2007) are

**CORRECT**(k factor should NOT appear in the equation).

Appreciate your advice and information.

JoeWong