I am getting closer to finishing my manifold and was wondering if it is recommended to weld the inside of the collector and flange joints? Would I do this with really low heat?

 

Just make sure to backgrind it with a die grinder to remove any carbon that might have blown by when you welded the filets on the flange.

If you backpurged this shouldnt be a problem tho.

 

It's a mild steel manifold. Doesn't need back purging.
So do I weld the inside of the joint our not?

 

It would depend if you got full penetration or not. There are some micro torches that would make it pretty easy. I can weld a 2" pipe from the inside 7" deep with a micro torch.

 

Yea, it wont hurt a thing if you weld the inside. If you have a joint without full penetration, and you can get to it to weld it, I would.

Also, I looked at your build thread. You should have removed the mill scale in the area where you was gonna weld. (that black coating on the outside of the pipe) Thats where all that brown residue came from on your welds. Also you have to use a shitload of heat to weld thru the scale, which makes it hard to keep a nice consistent bead.

 

I definately removed all the mill scale from where I was welding. I used a scotch pad on an angle grinder. The pipes were shiny silver before welding. Thats not where the brown is coming from.

All my welding has been done at around 40-50amps. As far as I'm aware that's not a shitload of heat.

 

Just because you weld at a low amperage dosnt mean you arent moving to slow and letting the metal get saturated with heat.

 

Yep, slow travel speed can put alot of excess heat into the metal.

The collector on this page could have used some better cleaning. yea see you used a scotch pad. Normally that will suffice for stainless but for mild you wanna use a sanding disc to really get all the mill scale off. basically a scotch pad will just shine the scale but not remove it.

http://www.preludeaustralia.com/foru...l=1#post723051

 

Ok, I've never read that I needed to hit it with a flap wheel.
do you think the current welds well hold up?

Why do they make it so difficult to remove the mill scale?
How do I know I've removed it all?

 

Well basically mill scale is a by-product of the steel being hot rolled/formed. The scale is left on there as a protective coating from corrosion. Usually the scale is about 1/32"(1mm) thick. Normally when you see shiny mild steel it has been pickled or cold rolled, that's why there is no mill scale.

The best way to remove it is with a grinding disc or an aggressive sanding pad. You will be able to tell when it's removed when your grinder starts having alot of long sparks shooting out instead of just a few small ones. I would only try to remove about 1/2"(1cm) width area along the joints on the collector. Don't remove more then that because that mill scale will help prevent rusting.

 

Idk how much torch time you have, but usually it is very apparent there is still scale on there by the way it welds. You will here fizzling sounds, you'll see the weld pool almost bubble, and you get that orange residue. Prep it until its shiny. Honestly it will probably hold. Just run it, if/ when it cracks you get a second chance. Get yourself some stainless though in such an instance! The fit up looks nice on the collector though!

 

Weld them and grind them to be as sharp as possible. Spatter pray might also be good to use to keep loose beads to a minimum.