The 32-year-old Langeveldt, who took five wickets in South Africa's narrow one-wicket win over Sri Lanka last week, led the attack after Graeme Smith won the toss and put Ireland in.
In a match reduced to 35 overs a side, Andrew White top-scored with 30 and added 39 for the fifth wicket with Andre Botha (14) to lift Irish hopes after their tempo was broken by two rain interruptions of 48 minutes and two hours respectively.
South Africa were set a revised target of 160 off their 35 overs under the Duckworth-Lewis formula
After the start was delayed by 15 minutes, South Africa's pacemen exploited the wet and cloudy conditions.
Shaun Pollock dismissed openers Jeremy Bray (nought) and William Porterfield (14) to finish with 2-17.
Pollock, whose form was a worry after his costly and wicket-less bowling against Australia and Sri Lanka, now has 377 wickets in 279 matches -- joint fourth on the all-time list with Sri Lanka's Chaminda Vaas.
Eoin Morgan (28) and Niall O'Brien (25) built the innings through a 32-run third wicket stand. Morgan hit four boundaries before he fell off a short Andrew Hall delivery.
Left-hander O'Brien, who made a brilliant 72 in Ireland's three-wicket win which dumped Pakistan out in the first round, hit four boundaries before he became the first of Langeveldt's victims.
Langeveldt then dismissed Kyle McCallan and John Mooney off successive deliveries to finish with 3-41.
Dave Langford-Smith hit out in the slog overs to finish with 17 not out including a four and a six.
Ireland 152 for 8 in 35 overs ( Andrew White 30, Eion Morgan 28, Niell O'Brien 25, Johnston 17 n o; Pollock 2 for 17, Langeveldt 3 for 41, Hall 2 for 37) Vs South Africa (yet to bat).