APA Group's choice of internal candidate Rob Wheals to replace retiring Mick McCormack as chief executive is expected to spark a broader upheaval in the senior ranks at the gas pipeline giant, even as its prospects as a takeover target have lessened.

Mr Wheals, an 11-year APA veteran who leads the core gas transmission business, was seen by the market as one of the key contenders to succeed Mr McCormack, although possibly behind head of strategy Ross Gersbach.