If the bits are set out as in this link then probably be ok providing corrosion from removing the galvanising will be OK. http://www.tuopeek.com/insulator.html
Don't know if a build up of iron oxide over the years will affect the insulation properties with contamination.
Not the sort of thing you want to go and replace early, i imaging the cost implications would be huge.
I'm no fabricator but I'd imagine the consequences of something like this falling from height, either onto hv cables or all the way to the ground wouldn't be good.
I appreciate the likelihood of it actually hitting someone would be highly unlikely as pylons are not generally situated where people congregate but still...
What are the likely maximum wind forces going to be acting on this while its up there? Even if it doesn't get directly damaged by wind - 10 years of being buffeted by wind and it decides to crack?
There are some things you'd say "yeah, ok I'll take a chance with that". Personally, I'd say this wouldnt be one of them. It's not like power companies are exactly strapped for cash.
Once modified they'll be stripped and re-galved.
I would imagine they'll be something like that but the drawing showed many components. Far more than usual so they must be for something slightly different.
The link shows a very basic setup but essentially they all do the same job.
It might be ok if its tight and can not possibly move and is sandwiched between a large washer or part covering the full surface. But i would make sure the customer is fully aware of the dimensions and the amount of material remaining.
time permitting & all that,it could be sent to a testing house where it could have simulated loads applied equivalent to real life time & then given a lifespan.
I'd say that part would be seriously weakened by the proposed hole size.
Whether that means there's a risk of failure depends on the forces involved which we don't know but it's going to be considerably weaker than it currently is. And what's hard to work out isn't whether it'll fail with x load but whether that load will cause it to fatigue crack over time. Some pretty chunky bits of metal bend and break after a few years.
I'd say, no. The overengineering that goes into pylon stuff is don for a reason. They have to be able to withstand constant weather abuse for decades. I've never seen such thick galvanising on stuff as that which comes from pylons.
As above, loosing the galve, thinning the walls, add in a bit of rust and some von Carmen vortex action on the bar and youre set up to fatigue the hole edges.
New bit of appropriate flat with 18mm holes, chop the old one off, weld the bar on and re-dipped? More time consuming but less than making from scratch...maybe
With things like this context is everything. If it was a lever holding someones back gate shut, you'd have a go. Something involving 400kv elctrickery and great height(However unlikely you think it may be to fail)? No thanks!!
I think you have the right idea getting someone else to take responsibility for it. If the worst were to happen (Again, as unlikely as that may be) then I wouldn't want my name anywhere near a modification like this.