All of the information that you've shared is appreciated. I will provide emergency shutdown valves at various places in the line so that the maximum "shut in" is 10,000 gallons. There are overpressure PSV's between each shutdown valve (and, in some cases, 2 PSVs).
I will uses A333 low-temperature carbon steel for the piping... and I had considered globe valves at one point but, as you say, those are a little too expensive. I'll use 4" of urethane insulation for the long run and have a 6" NH3 vapor line parallel to the 16" carrier line... PSV discharge will connect to the vapor line.
It looks to me as if gate valves are installed, but I'll take a closer look. I am mainly curious to know if 90° and 180° turns would create enough pressure drop to cause liquid to condense and, if so, is there a preferred method to handle the liquid.
Thanks for your time and knowledge... yep, it's the Port of Tampa...