API Standard 537. Heat Transfer Equipment Standards for Refinery Service
Binder. Standard. Edition. Section. Inquiry #. Question. Reply. 530. 2nd Edition. A
.2.3.
API Standard 537 Heat Transfer Equipment Standards for Refinery Service Binder
Standard
Edition
Section
Inquiry #
530
2nd Edition
A.2.3
537-2010-1
Question I am writing to report what I consider to be an error in API 537. The issue is the conversion of units for the calorific value of gases. For example in para. 8.2.3, page 43 of API 537, Second Edition, the following appears :- ... a minimum calorific value of 11 175 kJ/Nm3 (300 Btu/scf)..... The conversion here seems to be based on a straight calculation of values, where : 1 Btu = 1.05506 kJ 1 m3 = 35.3147 ft3 This results in 300 Btu/scf = 11,177.7 kJ/Nm3. This results in 300 Btu/scf = 11,177.7 kJ/Nm3, which is indeed very close to the above. However, the fact is that Nm3 is based on standard conditions of 0°C and one atmosphere, whereas scf is based on standard conditions of 60°F and one atmosphere. Consequently we have : 1 Nm3 = 37.326 scf (not 35.3147 scf). Therefore 300 Btu/scf is equivalent to 11,814 kJ/Nm3. Please advise on whether you agree with my interpretation.
Reply The applicable basis is defined in ISO 5024 as follows: “The standard reference conditions of pressure and temperature for use in measurements on crude petroleum and its products shall be 101,325 kPa (absolute) and 15 °C, with the exception of liquid hydrocarbons having a vapour pressure greater than atmospheric at 15 °C, in which case the standard pressure shall be equilibrium vapour pressure at 15 °C.” The quoted numbers in ISO-25457/API-537 are in compliance with this definition.
