Oil line bonding

I hit a similar problem years ago with microbore heating pipes in bathroom supplementary bonding and ended up with something like these - https://uk.rs-online.com/web/p/earthing-straps/2365264 (I don't recall them being quite so expensive at the time!) I think those particular ones only take up to 6mm2 conductors so a bit shy for main bonding, but perhaps there's something in a similar range?

   - Andy.

The clips for 3/8 earth rods may be a solid way forward but you need the split kind as you cannot thread it on from the end of the pipe, as there will be an oil  tank in the way..

https://www.cef.co.uk/catalogue/products/23424-machined-brass-clamp-for-use-with-3-8-inch-earth-rod

 You can slightly adjust the grip of these by filing at the contact faces.

Brass or copper P clips are also a way forward - the kind for securing large 'pyro' cable would have been the way a while back , but its not the thing most folk have in the toolbox anymore.
maybe bend up some  plumbing saddle clips..

https://www.ebay.co.uk/itm/127460827028

or P clips

https://www.ebay.co.uk/itm/114326097638

Mike.