Pipe systems having at least one layer comprising a semi-crystalline random polymer of propylene and 0.2 to 5 wt % 1-hexen and optionally a recurring unit selected from ethylene and a C4-C10 α-olefin in an amount from more than 0 to 9% by moles. The polymer exhibits broad molecular weight distribution, in terms of the ratio of weight average molecular weight to numeric average molecular weight formula (I), ranging from 5 to 11, molecular weight distribution of monomodal type and hexen-1 content in the fraction with an intrinsic viscosity of equal to or higher than 3.3 dl/g lower than the hexen-1 content in the fraction with an intrinsic viscosity of less than 3.3 dl/g. ( Mw/ Mn)   (I)