The distortion happens because you're mapping a trapezoid to a rectangle. Those quads are really two triangles, and the triangles get distorted differently, so you see that dodgy seam along the diagonal.
You can add more geo to make the trapezoid more like a rectangle, or you can make the UVs more like a trapezoid (try unwrapping using pelt rather than cylindrical mapping).
Generally for this stuff I just leave the distortion in there for the sake of neat UVs.
Maybe fiddle with the UV verts once you've got it unwrapped nice and rectangular, but I try and keep the edges that follow along the length of the pipe aligned all the way along.
Thanks for the reply, the reason i'm asking is because the model is not mine actually a small part of the actual model so that part is just small so it wont be that notable just asking to see if there's any option of fix it whit out adding geometry but i think i just leave it at it is. thanks for the help
edit: do i use the unfold option to get these line straight?
Keep the same seam under the pipe and just use the relax tool. Should just pull the pipe into a much more realistic shape, at the cost of being harder to texture. Probably the relax by face angles or whatever option. Is that Max, Maya...?
The only problem with this distortion is that it can be a bit noticeable sometimes. Often your best bet is to make the UV have a more consistent density. By that I mean that you should give the underneath corners of the pipes more texels than just the inside corner, warp your u/vs a little to counteract the density issue but keep keep your outside edges straight.
Replies
You can add more geo to make the trapezoid more like a rectangle, or you can make the UVs more like a trapezoid (try unwrapping using pelt rather than cylindrical mapping).
Maybe fiddle with the UV verts once you've got it unwrapped nice and rectangular, but I try and keep the edges that follow along the length of the pipe aligned all the way along.
edit: do i use the unfold option to get these line straight?
http://www.creativecrash.com/maya/marketplace/scripts-plugins/texturing/c/ninja-uv--2