I would suggest that you go back to the manual for your Thermal Dynamics A40....check out the mechanized cutcharts and follow them exactly in terms of which nozzle (tip) to use for best cut quality on each material type and thickness.
You state that you are using a 60amp tip running at 40 amps , 160 ipm on 16 gauge steel.....
1. If you are looking for best cut quality you should use the correct consumables for the material. Without having an A40 manual.....I would guess that either a 30 amp or 40 amp set of consumables would provide far better cut quality and consumable life on 16 gauge....and a 60 amp "tip".....should bve operated at or near 60 amps. Less amperage and you are reducing the arc energy density....which will make for a very ugly cut.
2. You mention arc voltage (so you must have a height control).....don't worry about the arc voltage that is listed in your manual....rather, adjust the arc voltage durring the cut so that the torch cuts at the physical height that your manual suggests. At 40 amps on 14 gauge...the torch should be cutting at around .06" (1/16") off the plate for good quality.
3. You don't mention what the consumables look like after a few cuts.....is the nozzle orifice damaged? Out of round, nicks in the orifice? If so....that is usually caused by piercing too close to the plate....or by allowing the nozzle (tip) to contact the plate during the cut.
I typically will get many hours of cutting, and average around 1400 pierces (on one nozzle) when cutting 16 gauge at 45 amps with my Hypertherm Powermax45.
Jim Colt Hypertherm