Stubbon Nut!!

Around 2 months ago I started the job of replacing the exhaust downpipe.
I was dreading removing the 6 bolts from the manifold but they all came away without too much effort.. However at the catalyst end the lower of the 3 nuts just refuses to move..

I've been having a go at it every weekend for the last 2 months:
Its been soaked in WD40
The nut became rounded so
Mole grips - but they just damaged the nut further
I bought a Nut removal kit - but it just won't grip!
I bought a nut splitter but its got too rounded - and the flare at the bottom of the nut is stopping it from splitting.

So looks like its time to get the angle grinder out - but before I do, how easy is it to drill out the bolt? and will a standard nut and bolt work as a replacement or will it work loose?

Thanks

Why not to try a gastro burner? Worked well for me.
The angle grinder is a good idea, too. Maybe the best way for these rusted nuts.
Standard nuts, bolts and snapring should work okay. Never forget to use lots of copper grease!
Regards
Christof

I replaced the front pipe some years back..the 6 bolts on manifold came off a treat...I snapped a stud on the exhaust system and decided to remove the full system and do the job on the bench..they were tough to drill out after grinding them flush with the flange...glad I took it off....I replaced the fixed studs for bolts and nuts...with lashings of copper grease...thinking ahead to make it easier for myself if ever it has to come off again...nice new gaskets fitted and a splash of ht paint on silencer...stunk for a bit but smell wears off and it still looks as good now has it did in picture....saved me a lot of money has exhaust fitters just want to scrap a exhaust system which still has life left in it.

Try releasing oil like Plus Gas rather than WD40 (unless it's the WD40 release oil of course).

Nuts and bolts are fine when you put it back but have a look at using long nuts like these STAINLESS STEEL DEEP NUT HEX BAR CONNECTORS M5, M6, M8, M10, M12, M14, M16, M20 Buy It Now that cover the thread of the bolt. They will make it easier to remove in future.

I'm pretty sure that the studs just knock out of the flange.:yesnod:

If you grind off the nut, the stud will knock out ok, I had to do one earlier this year.
Good luck with the job!
Replace with stainless....and don't forget to replace the gaskets.

Sundance

I looked at knocking the studs out.has I've been successful doing that in the past.but they were solid and I think if I carried on blowing them with the hammer then the exhaust would of been in pieces..hence went for the drill.

Toolstation also do those nuts.

https://www.toolstation.com/search?q=connector%20nut

Thanks for the replies.
Finally got the downpipe off with the help of my angle grinder! - trouble is the supporting bracket from the back box came away as I released the pipe away.
I'm now liking the idea of removing the whole system as suggested - however looking at what's left the nuts connecting the cat to the back box its not going to be easy.
What I'd ideally like do is replace it all with stainless steel - just don't think I'll be allowed

If you take the exhaust system off..be aware if you move the car..a tf with no exhaust is extremely loud.when I started mine to move it ..the noise.stopped next doors dog barking...come to think of it I ain't heard it bark for some time since.