Pressure pipes

1. A pressure pipe having increased long-term pressure resistance fabricated of a polypropylene composition comprising a random terpolymer of:

89.0-96.0 wt % propylene,

3 to 10 wt % of a C 4 -C 8 α-olefin, and up to

1 wt % ethylene,

wherein the random terpolymer is at least partially crystallized in the β-modification.

2. The pressure pipe of claim 1 wherein the C 4 -C 8 α-olefin is butene-1.

3. The pressure pipe according to claim 1 wherein the polypropylene composition has an MFR of 0.1 to 10 g/10 min at 230° C./2.16 kg.

4. The pressure pipe according to claim 1 wherein the amount of β-crystallinity of the random terpolymer, determined by DSC using the second heat, is at least 50%.

5. The pressure pipe according to claim 1 wherein the random terpolymer comprises a β-nucleating agent.

6. The pressure pipe according to claim 5 , wherein

the β-nucleating agent comprises at least one selected from the group consisting of a mixed crystal of 5,12-dihydro-quino(2,3-b)acridine-7,14-dione with quino(2,3-b)acridine6,7,13,14(5H, 12H)-tetrone, N,N′-dicyclohexyl-2,6-naphtalen dicarboxamide and dicarboxylic acid salts of metals of group II of the periodic table, and

dicarboxylic acids of said dicarboxylic acid salts contain at least 7 carbon atoms.

7. The pressure pipe according to claim 1 wherein the C 4 -C 8 α-olefin is comprised of

3 to 10 wt % of butene.

8. The pressure pipe according to of claim 1 wherein the random terpolymer comprises:

90.0-94.0 wt % of propylene, and

6 to 10 wt % of 1-butene, the pressure pipe having failure time vs. hoop stress relation at 95° C. before a knee-point which fits the following equation:

LOG(hoop stress)=(slope)*LOG(failure time)+(constant),

where (slope)≧−0.0250 when the failure is ductile and where the testing is performed according to ISO 1167:1996(E).

9. The pressure pipe according to claim 1 wherein the random terpolymer comprises:

89.4-95.9 wt % of propylene,

4 to 10 wt % of 1-butene, and

0.1 to 0.6 wt % of ethylene, the pressure pipe having failure time vs. hoop stress relation at 95° C. before a knee-point which fits the following equation:

LOG(hoop stress)=(slope)*LOG(failure time)+(constant),

where (slope)≧−0.0250 when the failure is ductile and where the testing is performed according to ISO 1167:1996(E).

10. The pressure pipe according to claim 1 wherein the random terpolymer comprises:

95-97 wt % of propylene, and

3 to 5 wt % of ethylene, the pressure pipe having failure time vs. hoop stress relation at 95° C. before a knee point which fits the following equation:

LOG(hoop stress)=(slope)*LOG (failure time)+(constant),

where (slope)≧−0.0250 when the failure is ductile and where the testing is performed according to ISO 1167:1996(E).

11. Multi-layer pipe where at least one of the layers comprises a pressure pipe according to claim 1 .

12. The pressure pipe according to claim 1 , wherein said pressure pipe is an extruded pipe.

13. The pressure pipe according to claim 6 , wherein the β-nucleating agent comprises a mixed crystal of 5,12-dihydro-quino(2,3-b)acridine-7,14-dione with quino(2,3-b)acridine6,7,13,14(5H, 12H)-tetrone.

14. Extruded pressure pipe with increased long-term pressure resistance comprised of a polypropylene composition wherein

the polypropylene composition is comprised of a random terpolymer which comprises:

89.0-96.0 wt % propylene,

3 to 10 wt % of a C 4 -C 8 β-olefin, and up to

1 wt % ethylene,

the random terpolymer is at least partially crystallized in the β-modification and the amount of β-crystallinity of the random terpolymer, determined by DSC using the second heat, is at least 50%, and

the random terpolymer comprises a β-nucleating agent.

15. Extruded pipe according to claim 14 , wherein the amount of β-crystallinity of the random terpolymer, determined by DSC using the second heat, is at least 80%.