area = pie x radius squared
volume = area x length = 12.57 in2 x 36 in = 452.52 in3 (cubic inch)
452.52 in3 x (1 L per 61.02 in3 ) = 7.42 Liter
What ever the local code says is legal
China is a large country to export steel pipe, if you want to buy steel pipe, you can import from China.
"4 inch" would usually refer to the diameter in such cases. You can multiply that by pi (which is about 3.1416) to get the circumference.
Australia makes steel pipe and tubes
Brazil exports steel pipe and tubes
Brazil makes steel pipe and tubes
California makes steel pipe and tubes
China exports steel pipe and tubes
China makes steel pipe and tubes
Illinois makes steel pipe and tubes
Japan makes steel pipe and tubes
Mexico exports steel pipe and tubes