Ok, lets begin with the "Y" Junction

Step 1: Create a cylinder, doesnt matter what size aslong as its not too small for hammer, I made mine 32l, 32w, 156h, 16 sides:



Step 2: Duplicate that cylinder, and make it horizontal to the original with one end sticking half way into the original:



Step 3: Now using the clipping tool, cut the horizontal cylinder vertical along the inside edge of the original (make the outside of that cylinder invisible)



Step 4: now you will need to cut the visible part of the horizontal cylinder into pieces (half the number of sides)



Step 5: And lastly you will need to take each piece and morph it to fit the edge of the original cylinder:



Now, the final product: "Y" Junction:



Now you Should all have realized by now how to make the "X" Junction, but for those of you who havent, it's real simple.

Step 1: after completing the above steps for the "Y" Junction, simply double up the final product. You could even change it up a bit, add some style to the design.



Final Note: Do you, and your players a favor, use this wisely, and func_wall all the pieces to help your r_speeds (see various tutorials for an explanation)

Without reading it all, i will say.. 1) i never bisect the same size pipes, it looks shoddy, 2)and i always copy/paste a small portion if the pipe i insert and turn it into a func_wall to reduce splitting.. i copy/paste the small portion to also reduce the ugly func_wall-no shadow the lights cause..
/2cents

That Y-Junction looks alot like a T. Minor detail I know, but they really are different shapes. Also I didn't know func_walls split faces on other func_walls. Ya learn something new everyday, unless you are lazy.

So when are people gonna learn to use models to create pipes.
they look ugly as brushes cos they dont have smoothing on them.

The tutorial explains the subject fine, except that CM should've been mentioned and that both parts would better be put into seperate func_walls, but aside from that, nice.

But I wonder... do pipes really break apart at such intersections? Or at the connections with another pipe part? Since these intersections are usually a special pipe part, and I suppose the connections between pipe parts are the weakest spots in pipelines...

Make step 5 a little clearer by telling people either to use vertex manipulation or the clip tool. 'Morph' mightn't mean much to a newbie.

Well guys ive given this some thought, and yes you are all right in that aspect, however if i were going to be doing some complecated things like having the top half of the pipes burst open in flames(which i am currently working on, and the reason for me writing this tut), my technic would be absolutely neccisary. but for simple pipes in a map, yes it would be better to just func_wall the section that meets.

16 sided pipe!?! jesus go 8 it looks fine and takes THAT MUCH POLYGONS LESS

It should look the same whether they overlap OR meet like in your method, and if they overlap its much simpler on the compiling process AND uses less faces, so is, if anything, going to have a lower polycount. Don't mean to rain on your parade, I just think its unnecessary and long winded to use the method you describe in this situation.

You all can go func_wall yourselves...ah hahaha

well i guess its more work the needed, but it does look nice and once you prefab that morphed section, its a breeze