A few double wall vs. single wall questions

So I pulled apart my DSP brand stove pipe yesterday to clean it and realised that the last person to re-assemble it used long self-drilling screws that penetrated both layers. I put it back together exactly as it was and now I've got a few air leaks at the joints. According to the manufacturer I should be replacing it and using the correct short screws.

This doesn't fit into my budget at the moment so I looked at single wall pipe with heat shields. That works out to less than 50% of the DSP materials. I have enough clearance on the straight pipe with a shield (it's a corner installation) but the two 45's up top are a concern. The upper 45 seen in the attached pic is exactly 9 inches from the wall and the lower one looks like it could radiate heat towards the ceiling. Can single wall pipe be used if elbow heat shields are installed?

Thanks for any advice!

begreen said:

Explain the leaks at the joints. Where are they? At the screw holes?

Click to expand...

Right where two sections of pipe join, between the 3 screws. I'm wondering if a long screw failed to actually get back in the previous hole drilled through the inner pipe and managed to bend/push inner pipe inwards. I'll have time to pull it apart this weekend, again. I'm headed into town today and will price out replacement DSP components at 3 large stores.

Thanks!