Piping type for recirc lines

Do recirc lines require the copper pipes to be thicker? Type M or Type L ?

I was wondering if the constant movement of water would slowly corrode pipe faster.

How quickly might one expect errosion to penetrate the wall of copper tubing? In my proposed re-circulating system I'll be using Type L, 3/4" return line in a gravity flow system.

You should be fine with the 3/4" type L.

I was just reading an ASPE article yesterday on recircing systems. The author recommends not going smaller than 3/4" due to velocity and using balancing valves to control the flow as hj suggested.

Curious, on plans I always call for Type L copper for the water lines (when specifying copper anyway), do you typical use Type K?