EMT pipe can hold hundreds of pounds - plenty strong for photographic equipment. The limiting factor will be the plastic components.
When supported at one end, a typical arm (reaching out 2 or 3 feet, 50-70cm) should support a few pounds, the weight of an SLR or a reflector. More than that would risk breaking the plastic of the pipe coupler.
A camera arm supported at one end
https://static.wixstatic.com/media/7b82c0_e69dceb4fb2f4461a748a0b24598df3f~mv2.jpg
Supported at two ends, however, the system is much stronger. If you build a frame with two supports, the system will hold at least 30 pounds (14kg), and possibly much more.
A frame supported at both ends
https://static.wixstatic.com/media/7b82c0_0c64b4ff92ab4dd8a62dd0c65c62912b~mv2.jpg
If you need more strength than plastic components can provide, I suggest looking for parts from the fine folks at Maker Pipe,(https://makerpipe.com/) who provide a steel system also designed to work with EMT conduit.