On Sun, 11 Aug 2019 14:49:03 +0100
brian wrote:

I need to drill 30 odd 4.5mm holes in a stainless steel pipe; I'm
drilling a small pilot hole ~ 1mm first . Usual type blunt too
quickly 4 holes ! Pipe wall thickness is only 1mm and I thought I'd
get away with it.

Carbide tipped and cobalt seem to be recommended .

Will tile drills do ?

Wrong geometry, a sharp masonry drill would do better (but still not
well).

Any experience or advice ?

If it's just a one-off job and the HSS bit is working OK until it
blunts, I'd probably just deal with sharpening it a few times. If that
was too tedious or otherwise unsuitable I'd order a couple of cobalt
bits. https://www.ukdrills.com/ used to be competitive and quick, I've
not used them recently.