If he has been allotted a Social Security Number by the Employees' Provident Fund Organisation, that number can be retained. For a centralized pay system wherein an employee's pay is released in Hyderabad, and contributions are deducted and deposited there but transferred to the Delhi office of the same organization, the number will still be retained. However, if these two establishments have different PF numbers, then the number will change.
The EPF account number has prefixes such as the Regional Code (indicating the region where the establishment is located) and an establishment code (representing where an employee works), which will be common to all employees under such an establishment. Upon assuming duties in Delhi, he will be allocated a new number. However, his past PF accumulations can be transferred to the new account by submitting Form 13, duly signed by the current employer.
Regards,
Madhu.T.K