3i has made an annualised return of more than 30% on the sale of ECM, a French industrial furnace maker, to Astorg, the French mid-market buy-out house, for around €50m ($60m).

The deal will result in 3i's investors getting back almost 2.5 times their original investment in ECM. The UK-listed European private equity firm bought the French group in November 2000 when it backed the son of the company's founder.