Multiple "If" statements for equation variables

Hey guys,

I'm currently working through some engineering problems which have slightly different equations based on two input variables (see below).

My previous experience with mathcad "if" statements led me to try and produce a multiple lined "if" statement like the one below for "alpha" but this does not seem to be working correctly as it is only picking up the lower "if" statement. The equation is based on the two variables "external pipe diameter" and a range of frequencies.

Any help with this would be greatly appreciated.

Regards,

Nick