It's too late for me to comment on most of it (yawn!) but note that unless you are writing to another speaker of Indian English, don't use "Kindly do the needful". No other variant uses it.
Could you please check this draft letter?
This is in reference to our submittal of revised WPS (Welding Procedure Specification), we await your response immediate. We want to qualify our welders based on approved WPS. Any further delay will affect our Double Tee Slab welding activities and overall project progress for Building units.
Kindly do the needful at the earliest.
Please correct my mistakes.
It's too late for me to comment on most of it (yawn!) but note that unless you are writing to another speaker of Indian English, don't use "Kindly do the needful". No other variant uses it.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.