Given two 4x4's with a 1/2" steel pipe running through the middle, how much weight can the posts support? Is there a chance the wood will split?
Axial compressive strength of a worst-case 4x4 post exceeds 3,000 lbs., could be as high as 13,000 lbs, depending on the height and type of wood. Yes, the wood can possibly split, but that's always a risk with wood. As mentioned, the pipe is likely the weakest link here, but we still don't know your purpose so this is all still theoretical.