5.4　Piston Rod and Gas Loading

5.4.1　The compressor piston rod and gas loading shall be in accordance with 6.6.1 through 6.6.5 of API Std 618-2007.

5.4.2　Combined loading（inertial loading and gas loading）of the rod，crosshead pin，or bushing shall be calculated using normal suction and discharge pressures with one compressor valve failed in any location.When the calculated loading for this upset case exceeds the maximum allowable continuous combined rod load，the vendor shall provide methods to protect the compressor，for example，a differential pressure safety valve.

5.4.3　For variable speed compressor train，the rod loading at any scheduled temporary hold points required during the train startup shall be included in the loading analysis.