Had a 18" cooling water piping repaired; two holes within 10 feet. Is there any regulation/code/standard on how many repairs can be done for ___ feet of piping for underground piping?
No code or standard AFAIK. Depends what kind of repair, but this normally falls into the engineering judgment category and cost / time of two repairs versus whatever the alternative is.
If it's a fibre reinforced wrap then you can't overlap them, but otherwise it goes on size of the defects and overall cost and difficulty of repairs (i.e. patch up whilst still online or needing to de-commission and clear contents for a cut-out).
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way