API 661 Vibration Testing on air coolers

[MarioColorado]

Hello,

I have a question regarding vibration testing on air coolers, according to 7.3.2.1 section: "Structural members shall be designed to minimize vibration. The maximum amplitude of vibration over the design fan-speed range shall be 0.15 mm (0.006 in.) from peak to peak, as measured on primary structural members and machinery mountings", is it possible to use other units like RMS vibration velocity in inches per second instead of peak-to-peak values? I'm concerned if this will comply with the standard

Finally, are those primary structural members and machinery mountings mentioned above the beams and steel supports of the air cooler structure?

Thanks all, hope you can help me