Pienaar is one of eight changes made by coach Mark Anscombe for the Pro12 top-of-the-table clash against the Welsh side who are nine points adrift of Ulster in second place.
Apart from the injured Stephen Ferris (ankle) and skipper Johann Muller (arm), full-back Jared Payne (groin) is also missing while hooker Rory Best is given another week’s rest ahead of the Heineken Cup games at the end of the month and John Afoa is on the bench.
The good news for Ulster is that lock Dan Tuohy is back after a calf injury and he partners Lewis Stevenson in the engine room while skipper Chris Henry is joined in the back-row by Robbie Diack and Nick Williams. Adam Macklin again stands-in for Afoa at right-head while Rob Herring wears the number two jersey.
Paddy Wallace is again named on the bench with Luke Marshall partnering Darren Cave in midfield and Adam D’Arcy continuing at full-back. With Paul Marshall getting married tomorrow, Michael Heaney is Pienaar’s shadow on the bench.
Pienaar, meanwhile, is just happy to get back playing again after a short family holiday gathering at Christmas, and can’t believe he has hit the 50 milestone for Ulster.
“I just can’t believe it to be honest. It’s been a very enjoyable time and to get to 50 appearances so quickly is something special particularly playing at Ravenhill too,” said Pienaar.
ULSTER: A D’Arcy; A Trimble, D Cave, L Marshall, C Gilroy; P Jackson, R Pienaar; T Court, R Henning, A Macklin, L Stevenson, D Tuohy, R Diack, C Henry, capt, N Williams.
Replacements: N Annett, C Black, J Afoa, N McComb, R Wilson, M Heaney, P Wallace, R Andrew.
SCARLETS: D Newton, G North, G Maule, J Davies, capt, K Phillips, A Thomas, T Knoyle, P John, E Phillips, J Adriaanse, S Timani, R Kelly, J Turnbull, J Edwards, R McCusker.
Replacements: K Myhill, R Jones, D Manu,T Vallejos, C Price, G Davies, S Williams,A Warren.
Referee: Leighton Hodges (WRU).