What is the difference between "prior to" and "in prior to" ?
What is the difference between "prior to" and "in prior to" ?
Do both mean "before"?

Also, please check if this sentence is correct.
"On-site welding shall be done prior to the floating test."

Thanks,

Question

What is the difference between "prior to" and "in prior to" ?
What is the difference between "prior to" and "in prior to" ?
Do both mean "before"?

Also, please check if this sentence is correct.
"On-site welding shall be done prior to the floating test."

Thanks,

Answer

The phrase is "prior to".

The examples I've found which have "in" before the phrase are part of a phrasal verb: [check in] prior to, the form must be [filled in] prior to...

Your sentence is correct.