Articles, particularly pressure pipes, having high strength as well as high stiffness and very good impact resistance even at low temperatures can be obtained by using a heterophasic polyolefin composition comprising (percent by weight) 70-90% of a random copolymer of propylene with 0.5-6% of 1-hexene, and 10-30% of a polymer of ethylene with a C3-C10 α-olefin and optionally a diene, wherein the polymer of ethylene has an ethylene content higher than 45% and an intrinsic viscosity [η] value from 3 to 5 dl/g.A particular advantage of the present invention is that articles comprising the above heterophasic polyolefin composition show a low ductile to brittle transition temperature (DBTT).