Biaxially oriented pipe derived from beta crystalline polypropylene

Abstract

Process for preparing a biaxially oriented pipe comprising the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of ≤ Tc to obtain a precursor pipe, where Tc is the crystallisation temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Td °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe; wherein the drawing temperature Td is a temperature > Tc and ≤ Tc + 22°C; where Tc is the crystallisation temperature of the polypropylene composition, determined using Differential Scanning Calorimetry (DSC), and wherein the precursor pipe comprising the polypropylene composition is at least partially crystallised in the β-form having β-crystallinity of > 5.0%. Also disclosed is a biaxially oriented pipe obtained from the above process.

Description

BIAXIALLY ORIENTED PIPE DERIVED FROM BETA CRYSTALLINE POLYPROPYLENEFIELD OF INVENTION

[0001] The invention relates to a process for producing biaxially oriented polypropylene pipe in particular to a pipe processed from a beta nucleated polypropylene composition and to the biaxially oriented polypropylene pipe obtained from such a process.BACKGROUND

[0002] Polypropylene-based polymers have certain characteristics, which render them suitable for manufacturing pipes. In particular, polypropylene resins may be used for preparing pressure pipes, mainly for the transport of liquid, e.g. water or industrial fluids, during which the fluid can be pressurized.

[0003] One of the key performance criteria for pressure pipe is that pipe should have excellent long-term hydrostatic pressure performance. Long-term hydrostatic pressure performance can be measured in terms of time taken for failure, when a pipe of certain diameter and thickness is subjected to stress. A pipe having a good long-term hydrostatic pressure performance signifies long term durability of the pipe suitable for transporting industrial and agricultural fluid under severe conditions.

[0004] One possible way of increasing the long-term hydrostatic pressure performance of a pipe is by increasing the thickness of the pipe wall. However, processing of such pipes with thick walls as well as the amount of material required for manufacturing such a pipe puts a limit to the extent the pipe wall thickness can be can be increased. Further, with thicker wall, the time and energy required to heat and cool the different sections of the pipe make processing difficult and economically expensive.

[0005] Another possible way to improve pressure performance is by biaxially orienting the pipe during its production. A pipe can be oriented in the axial direction and in the peripheral direction (hoop direction) to improve its long-term hydrostatic pressure performance.

[0006] For example, a pipe made by a biaxial elongation of a polypropylene composition is known. US5910346 describes a drawn tube made from a tube of isotropic polypropylene (ICI grade GSE 108). Morath et al., Biaxially oriented polypropylene pipes, Plastics, Rubber and Composites 2006 vol 35 no 10, p.447-454 describes a biaxially oriented polypropylene pipe madefrom a random polypropylene copolymer with melt flow rate of 0.3 dg / min and an ethylene content of 4%.

[0007] In the past a possible technique for preparing a thick walled pipes from polypropylene involve the steps of melt processing a polymeric material into a billet followed by cooling the billet to a temperature below the crystallization temperature (Tc) of the polymeric material constituting the billet to obtain what may be referred to as precursor form of the pipe to be manufactured (“precursor pipe”). Subsequently, the precursor pipe is reheated to the desired drawing temperature (Td) for drawing the billet in solid state for the purpose of obtaining a biaxially oriented pipe. Industry practitioners typically desire the drawing temperature to be as high as possible in order to impart the desired properties of long-term hydrostatic pressure performance to the pipe that is being formed.

[0008] However, during production of the pipe, the step of increasing the temperature of the precursor pipe from a temperature below the crystallization temperature Tc to the drawing temperature Td, is an energy intensive process requiring a significant energy to be spent for heating the billet. Further, in a conventional continuous production line for the production of biaxial pipe, the line length required for heating the precursor pipe uniformly is large rendering such a process to be economically operationally challenging.

[0009] Accordingly, from an environmental point of view as well as from a process economics perspective, it is desired that the energy required to heat the billet is minimized while ensuring that the pipe once formed has the desired long-term hydrostatic pressure performance.

[0010] Therefore, it is an objective of the present invention to provide a process for producing a biaxially oriented pipe which can be drawn from a precursor pipe at a relatively low temperature while ensuring that the pipe once formed has the desired long-term hydrostatic pressure performance.

[0011] It is yet another objective of the present invention to provide a process which minimizes consumption of energy and can be produced at relatively smaller production lines. It is yet another objective, to obtain a biaxially oriented pipe that has excellent long-term hydrostatic pressure performance while being while being produced in an energy efficient manner.DESCRIPTION

[0012] Accordingly, the one or more objectives of the present invention is achieved by a process for preparing a biaxially oriented pipe, the process comprises the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Ta °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe;• wherein the drawing temperature Ta is a temperature > Tcand < Tc+ 22 °C, preferably > Tcand < Tc+ 20 °C; where Tcis the crystallization temperature of the polypropylene composition determined in accordance with ASTM D3418-15, using Differential Scanning Calorimetry (DSC) with a first heating at a temperature between -40°C to 230°C @ 10°C / min (3 min hold at the end temperature) and a cooling of 230°C to - 40°C @ 10°C / min at a heating and a cooling rate of 10°C / min for a 3-5 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle; and• wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% as determined using Wide Angle X-ray Diffraction technique.

[0013] The expression "second heating" means that the sample is heated according to ISO 3146 / part 3 / method C2 for a first time and then cooled to room temperature at a rate of 10 °C / min. The sample is then heated a second time, also according to ISO 3146 / part 3 / method C2. During the "first heat" all thermal history of the sample giving rise to different crystalline structure, which typically derived from different processing conditions and / or methods, is destroyed.

[0014] The inventive process is designed in a way that the difference between the drawing temperature Ta of the precursor pipe and the crystallization temperature of the polypropylene composition is around 22°C, preferably around 20 °C. As a result, the energy required for heating the precursor pipe to the drawing temperature (Td) is relatively less as compared to a conventionalprocess, which does not use a precursor pipe having B-crystallinity of > 5.0% while producing a biaxial pipe having the desired failure properties.

[0015] This is an advantage, that not only helps in energy savings through operational costs for the manufacturer but also ensures a faster and a more efficient process for the production of the pipes. Surprisingly, the inventors found that the biaxially oriented pipe obtained from the inventive process has excellent long-term hydrostatic pressure performance or failure properties (i.e higher time to failure) even when drawn at a lower temperature.

[0016] In particular, the possibility to perform the drawing the pipe at a lower temperature while retaining its properties is advantageous in terms of time and energy required for heating the tube (precursor pipe). Such a process further allows for a reduced cooling time and smaller cooling baths to be used in a continuous process.

[0017] The precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% which in turn influences the crystallization temperature of the polypropylene composition. Preferably, the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 103 °C and < 120 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

[0018] Preferably, the process for preparing a biaxially oriented pipe, the process comprises the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Ta °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe;• wherein the drawing temperature Ta is a temperature > Tcand < Tc+ 22 °C, preferably > Tcand < Tc+ 20 °C; where Tcis the crystallization temperature of the polypropylene composition determined in accordance with ASTM D3418-15, using DifferentialScanning Calorimetry (DSC) with a first heating at a temperature between -40°C to 230°C @ 10°C / min (3 min hold at the end temperature) and a cooling of 230°C to - 40°C @ 10°C / min at a heating and a cooling rate of 10°C / min for a 3-5 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle; and

[0019] wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% as determined using Wide Angle X-ray Diffraction technique; wherein the crystallization temperature Tcof the polypropylene composition ranges > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 103 °C and < 120 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.Melt Processing of polypropylene composition to form a billet

[0020] The step of melt processing a polypropylene composition into a billet or a tube can be done by any known conventional process such as melt extrusion. In a conventional process system for the melt extrusion of polymeric pipes comprises an extruder, a nozzle, a calibrating device, cooling equipment, a pulling device, and a device for cutting or for coiling-up the pipe.

[0021] During melt extrusion, the molten mass of polymer flowing from the extruder is subjected to shear and elongation etc. in the axial direction of the pipe, creating a billet which is a uniaxially orientated pipe in its axial direction. The polypropylene composition may be suitably chosen to improve the efficiency of the melt processing.Polypropylene composition

[0022] The polypropylene composition that is melt processed or extruded comprises a propylene polymer. Preferably the polypropylene composition comprises a propylene polymer selected from heterophasic polypropylene, propylene random copolymer, and propylene homopolymer; and / or wherein the propylene polymer is present in an amount of > 95.0 wt.%, preferably > 97.0 wt.%, preferably > 98.0 wt.%, preferably > 99.0 wt.%, preferably 100.0 wt.%, with regard to the total weight of the polypropylene composition.

[0023] Preferably, the polypropylene composition comprises > 0 wt.% and < 5.0 wt.%, preferably > 0 wt.% and < 3.0 wt.%, preferably > 0 wt.% and < 2.0 wt.%, preferably > 0 wt.% and < 1.0 wt.%, with regard to the total weight of the polypropylene composition, of additives excluding beta-nucleating agents. Non-limiting examples of such additives, may be selected from UV stabilisers, anti-oxidants, color pigments, fillers and any combination thereof.

[0024] Preferably, the propylene polymer is a propylene random copolymer comprising polymeric units derived from propylene and polymeric units derived from a comonomer selected from ethylene and / or an a-olefin comonomer having 4 to 10 carbon atoms; preferably wherein the propylene random copolymer has:(a) polymeric units derived from propylene ranging from > 88.0 and < 100 wt.%, preferably > 90.0 and < 100 wt.%, preferably > 95.0 and < 100 wt.%, preferably > 95.0 and < 99.5 wt.%, preferably > 98.0 and < 99.5 wt.%, with regard to total weight of the propylene random copolymer; and(b) polymeric units derived from the comonomer ranging from > 0 and < 12.0 wt%, preferably > 0 and < 10.0 wt.%, preferably > 0 and < 5.0 wt%, preferably > 0.5 and < 5.0 wt%, preferably > 0.5 and < 2.0 wt%, with regard to total weight of the propylene random copolymer, preferably wherein the comonomer is selected from ethylene, 1- butene, 1 -hexene, 1 -octene and combinations thereof, preferably wherein the comonomer is ethylene.

[0025] Preferably, the propylene random copolymer comprises polymeric units derived from propylene ranging from > 98.0 and < 99.5 wt.%, with regard to total weight of the propylene random copolymer and polymeric units derived from ethylene ranging from > 0.5 and < 2.0 wt%, with regard to total weight of the propylene random copolymer.

[0026] Preferably, the propylene random copolymer has a melt flow index of > 0.1 and < 10.0 g / lOmin, preferably > 0.1 and < 4.0 g / 10 min, more preferably > 0.1 and < 1.0 g / lOmin, measured according to IS01133- 1 :2011 (230 °C / 2.16 kg).

[0027] The polymer composition may be obtained by melt-mixing the propylene-based polymer with any other optional additives.Precursor pipe

[0028] The billet once formed may be subjected to a cooling process to obtain the precursor pipe. For example the billet may be cooled to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition. The precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% as determined using Wide Angle X-ray Diffraction.

[0029] The beta crystallinity may alternatively be also determined using Differential Scanning Calorimetry (DSC) in accordance with ISO 3146 / part 3 / method C2 with a scan rate of 10 °C / min and calculated from the second heat.

[0030] The crystallization temperature (Tc) may be construed as the crystallization temperature of the B crystals present in the polypropylene composition that constitutes the precursor pipe. The B crystals may be formed by the presence of beta nucleating agent present or compounded in the polypropylene composition itself prior to the melt processing.

[0031] Preferably, the polypropylene composition prior to melt processing, comprises B- nucleating agent present in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt.%, preferably > 0.003 and < 0.25 wt.%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition.

[0032] Alternatively, the B crystals may be imparted in the polypropylene composition by the addition of beta nucleating agents during melt processing.

[0033] In some aspects of the invention, B-nucleating agent is added during the step of melt processing the polypropylene composition. For example, the step of melt processing of the polypropylene composition comprises the step of adding B-nucleating agent in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt%, preferably > 0.003 and < 0.25 wt%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition.B-crystallinity and its measurement for the precursor pipe

[0034] Accordingly, the precursor pipe always has a B-crystallinity of > 5.0%, preferably> 10.0 %, preferably > 15.0 %, preferably > 20.0 %, preferably > 25.0 %, preferably > 30.0 %, preferably > preferably 35.0 %, preferably > 40.0 %, preferably > 45.0 % preferably > 50.0 %,preferably > 55.0 %, preferably > 60.0 %, preferably > 65.0 %, preferably > 70.0 %, preferably > 75.0 %, preferably > 80.0 %. The amount of fi-crystallinity is expressed in terms of the total amount of crystalline phase present in the polypropylene composition.

[0035] Preferably, the precursor pipe comprising the polypropylene composition has a fiery stallinity in the range of > 10% and < 90%, preferably > 25% and < 80%, preferably > 25% and < 75%, preferably > 30% and < 60%, preferably > 45% and < 55%, determined using Wide Angle X-ray Diffraction technique.

[0036] The WAXD (Wide Angle X-ray Diffraction) determination may be conducted on samples, mechanically prepared from billets of 1 mm thickness.

[0037] As P-nucleating agent any nucleating agent can be used which is suitable for inducing crystallization of polypropylene homo- and copolymers in the hexagonal or pseudohexagonal modification. Mixtures of such nucleating agents may also be employed.

[0038] Suitable non-limiting examples of P-nucleating agents are a) dicarboxylic acid derivative type diamide compounds from Cs to Cs-cycloalkyl monoamines or Ce to Ci2-aromatic monoamines and Cs to Cs-aliphatic, Cs to Cs-cycloaliphatic or Ce to Ci2-aromatic dicarboxylic acids, e. g. i. N,N'-di-C5-C8-cycloalkyl-2, 6-naphthalene dicarboxamide compounds such as N, N'-dicyclohexyl-2, 6-naphthalene dicarboxamide and N, N'-dicyclooctyl-2, 6-naphthalene di carb oxami de, ii. N,N-di-C5-C8-cycloalkyl-4,4-biphenyldicarboxamide compounds such as N, N'- dicyclohexyl-4, 4-biphenyldicarboxamide and N, N'-dicyclopentyl-4, 4- bipheny 1 di carb oxami de, iii. N, N'-di-Cs-Cs-cycloalkyl-terephthalamide compounds such as N, N'- dicyclohexylterephthalamide and N, N'-dicyclopentylterephthalamide, iv. N, N'-di-C5-C8-cycloalkyl-l,4-cyclohexanedicarboxamide compounds such as N,N'-dicyclo-hexyl-l,4-cyclohexanedicarboxamide and N, N'-dicyclohexyl-l, 4- cy cl opentanedi carb oxami de,b) diamine derivative type diamide compounds from Cs-Cs-cycloalkyl monocarboxylic acidsor Ce-Cn-aromatic monocarboxylic acids and Cs-Cs-cycloaliphatic or Ce-Cn-aromatic diamines, e. g. i. N,N-C6-Ci2-arylene-bis-benzamide compounds such as N,N'-p-phenylene-bis-benzamide and N,N' - 1 , 5 -naphthal ene-bi s-b enzami de, ii. N,N'-C5-C5-cycloalkyl-bis-benzamide compounds such as N,N'-l,4-cyclopentane-bis- benzamide and N,N'-l,4-cyclohexane-bis- benzamide, iii. N,N-p-Ce-Cn-arylene-bis-Cs-C8-cycloalkylcarboxamide compounds such as N,N'-1,5- naphthalene-bis-cyclohexanecarboxamide and N,N'-l,4-phenylene-bis-cyclohexanecarboxamide, and iv. N,N'-Cs-C8-cycloalkyl-bis-cyclohexanecarboxamide compounds such as N,N'-1,4- cyclopentane-bis-cyclohexanecarboxamide and N,N'- 1 ,4-cyclohexane-bis- cy cl ohexanecarb oxami de, v. amino acid derivative type diamide compounds from amidation reaction of Cs-Cs-alkyl, Cs-Cs-cycloalkyl-or Ce-Cn-arylamino acids, Cs-Cs-alkyl-, Cs-Cs-cycloalkyl-or Ce-Cn-aromatic monocarboxylic acid chlorides and Cs-Cs-alkyl-, Cs-Cs-cycloalkyl-or Ce-Cn-aromatic monoamines, e.g. N-phenyl-5-(N-benzoylamino)pentaneamide and N-cyclohexyl-4-(N-cyclohexyl- carb ony 1 amino)b enzami de .

[0039] Further, non-limiting examples of P-nucleating agents are a) quinacridone type compounds, e.g. quinacridone, dimethylquinacridone and dimethoxy quinacridone; b) quinacridonequinone type compounds, e. g. quinacridonequinone, a mixed crystal of 5,12- dihydro(2,3b)acridine-7, 14-dione with quino(2,3b)acridine-6,7,13,14-(5H, 12H)-tetrone and dimethoxyquinacridonequinone; and c) dihydroquinacridone type compounds, e.g. dihydroquinacridone, dimethoxydihydroquinacridone and dibenzodihydroquinacridone.

[0040] Still further suitable P-nucleating agents are salts of metals from group Ila of periodic system and imido acids of the formula:

[0041] wherein x = 1 to 4; R = H,-C00H, Ci-Ci2-alkyl, Cs-Cs-cycloalkyl or Ce-Cn-aryl, and Y =Ci-Ci2-alkyl, Cs-Cs-cycloalkyl or Ce-Cn-aryl-substituted bivalent Ce-Cn-aromatic residues, e.g. calcium salts of phthaloylglycine, hexahydrophthaloylglycine, N-phthaloylalanine and / or N-4-methylphthaloylglycine.

[0042] It is particularly preferred that the P-nucleating agent is a quinacridone compound. Preferably, the P-nucleating agent is a quinacridone compound selected from quinacridone, dimethylquinacridone and dimethoxyquinacridoneDrawing of the precursor pipe

[0043] The precursor pipe once formed is heated to a drawing temperature (Ta °C). The drawing temperature is selected according to the melt temperature of the polypropylene composition.

[0044] The drawing temperature is herein defined as the temperature at the surface of the precursor pipe after heating and just prior to biaxially stretching the precursor pipe. Prior to stretching, the mandrel and the precursor pipe may for example be heated to the desired drawing temperature. This may be done by heating the mandrel and the precursor pipe at the drawing temperature for a period sufficient to attain thermal equilibrium, e.g. 30 minutes (the temperature is preferably controlled within ±1 °C).

[0045] The drawing temperature may be selected to be lower than the lowest melt temperature (Tmi) of the polypropylene composition. Preferably, the drawing temperature (Td) ranges from (Tmi - 15.0) °C < Td < (Tmi -1.0) °C, preferably (Tmi - 10.0) °C < Td < (Tmi - 5.0) °C, wherein Tmi is the lowest melt temperature of the polypropylene composition determined in accordance with ASTM D3418-15 by using Differential Scanning Calorimetry (DSC) with a firstheating at a temperature between -40°C to 230°C @ 10°C / min (3 min hold at the end temperature) and a cooling of 230°C to -40°C @ 10°C / min at a heating and a cooling rate of 10°C / min for a 3- 5 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle.

[0046] The lowest melt temperature (Tmi) may be the melting temperature of the B-crystals present in the polypropylene composition. The polypropylene composition may have a lowest melt temperature (Tmi) of > 121 °C and < 175 °C, preferably > 121 °C and < 165 °C, preferably > 121 °C and < 165 °C, preferably > 126 °C and < 160 °C, preferably > 131 °C and < 163 °C, preferably > 131°C and < 155 °C, preferably > 131°C and < 150 °C.

[0047] Preferably, the polypropylene composition has a lowest melt temperature (Tmi) of> 131°C and < 150 °C and the drawing temperature (Ta) ranges from > 130 °C and < 148 °C.

[0048] Preferably, the polypropylene composition has a lowest melt temperature (Tmi) of> 131°C and < 150 °C and a drawing temperature (Ta) ranging from > 130 °C and < 148 °C, preferably > 130°C and < 140 °C.

[0049] Preferably, the drawing temperature (Ta) ranges from > 120 °C and < 160 °C, preferably >120 °C and < 150 °C, preferably >123 °C and < 142 °C, preferably >125 °C and < 145 °C, preferably > 130 °C and < 148 °C, preferably > 130°C and < 140 °C.

[0050] Preferably, the drawing temperature (Ta) ranges from > 120 °C and < 160 °C, preferably >120 °C and < 150 °C, preferably >125 °C and < 145 °C, preferably > 130 °C and < 148 °C, preferably > 130°C and < 140 °C; and / or the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 98 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 120 °C and < 128 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

[0051] Preferably, the drawing temperature (Ta) ranges from > 120 °C and < 160 °C, preferably >120 °C and < 150 °C, preferably >125 °C and < 145 °C, preferably > 130 °C and < 148 °C, preferably > 130°C and < 140 °C; and / or the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 120 °C and < 128 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably> 110°C and < 120 °C.

[0052] Preferably, the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 103 °C and < 120 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

[0053] Preferably, the drawing temperature (Ta) ranges from >125 °C and < 145 °C; and / or the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 123 °C.

[0054] Preferably, the drawing temperature (Ta) ranges from preferably >120 °C and < 160 °C and the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C.

[0055] Preferably, the drawing temperature (Ta) ranges from >125 °C and < 150 °C and / or the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 128 °C.

[0056] Preferably, the drawing temperature (Ta) ranges from >125 °C and < 145 °C and / or the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 123 °C.

[0057] Preferably, the drawing temperature (Ta) ranges from > 130°C and < 140 °C and / or the crystallization temperature Tcof the polypropylene composition ranges from > 108 °C and < 118 °C.

[0058] Preferably, the drawing temperature (Ta) ranges from > 130°C and < 140 °C and the crystallization temperature Tcof the polypropylene composition ranges from > 108 °C and < 118 °C.

[0059] Preferably, the drawing temperature (Ta) ranges from >125 °C and < 145 °C and the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 123 °C.

[0060] Preferably, the drawing temperature (Ta) ranges from >123 °C and < 142 °C; and wherein the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 120 °CBiaxial stretching

[0061] After the precursor temperature has attained the drawing temperature Ta the precursor pipe may be stretched in the axial and the peripheral (hoop) direction at specific draw ratios to obtain the biaxially oriented pipe.

[0062] The biaxial orientation of the pipe may be carried out in various ways, for instance mechanically by means of an internal mandrel, or by an internal pressurized fluid, such as air or water or the like. Alternatively, a further method for carrying out the biaxial process involves orienting the pipe by means of rollers, for instance by arranging the pipe on a mandrel and rotating the mandrel and the pipe relative to one or more pressure rollers engaging the pipe, or via internally arranged pressure rollers that are rotated relative to the pipe against an externally arranged mould or a calibrating device.

[0063] Preferably, wherein the step of bi-axially stretching the precursor pipe is performed at an axial draw ratio of > 1.1 and < 5.0 and at an average hoop draw ratio of > 1.1 and < 3.0.

[0064] Preferably, the precursor pipe is drawn at an axial draw ratio of > 1.1 and < 4.0, preferably > 1.1 and < 3.6, preferably > 1.1 and < 3.2. It is preferred that the axial draw ratio is larger for obtaining a biaxially oriented pipe with a higher outer diameter.

[0065] The axial draw ratio of the drawn pipe is defined as the ratio of the cross-sectional area of the starting isotropic tube (precursor pipe or Tube) to that of the biaxially oriented pipe (i.e. Product), that is,(Tube OD)2- (Tube ID)2Aaxial“ (Product OD)2- (Product ID)2

[0066] OD stands for outer diameter and ID stands for inner diameter.

[0067] In case of expanded tube drawing, the hoop draw ratio of the product varies from the inner to the outer wall. These draw ratios are defined as:1 Product ID

[0068] > yvhoop, inner Tube IDProduct OD

[0069] ■hoop, outer Tube OD

[0070] The average hoop draw ratio can be defined as: rnn71l —TotalDraw Ratio lTotaI1 JAaverage hoop Axial Draw Ratio Xax.alWhereTube (precursor pipe) Wall ThicknessProduct (biaxial pipe) Wall ThicknessBiaxially oriented pipe

[0072] The biaxially oriented pipe according to the present invention may be a pressure pipe or a non-pressure pipe. The preferred pipe is a pressure pipe.

[0073] The biaxially oriented pipe may typically have a wall thickness of 0.3 mm to 10 cm. The biaxially oriented pipe may typically have an outer diameter (OD) of 10 mm to 2000 mm. In some examples, the biaxially oriented pipe has an outer diameter (OD) of 10 mm to 10 cm and a wall thickness of 0.3 mm to 3 mm, preferably 1 mm to 3 mm. In some examples, the biaxially oriented pipe has an outer diameter of 20 mm to 50 cm and a thickness of 1 mm to 10 mm.

[0074] In an aspect of the invention, the invention relates to a biaxially oriented pipe obtained by or obtainable by the process of the present invention.

[0075] Preferably, the biaxially oriented pipe comprises > 95.0 wt.%, preferably > 98.0 wt.% of the polypropylene composition with regard to the total weight of the biaxially oriented pipe.

[0076] Preferably, the polypropylene composition comprises B-nucleating agent present in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt.%, preferably > 0.003 and < 0.25 wt.%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition. Preferably, the B-nucleating agent is a quinacridone type compound. Preferably, the B-nucleating agent is a quinacridone type compound selected from quinacridone, dimethylquinacridone and dimethoxyquinacridone.

[0077] Preferably, the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 120 °C and wherein the polypropylene composition has a lowest melt temperature (Tmi) of > 131°C and < 150 °C.

[0078] In an aspect of the invention, the biaxially oriented pipe comprises > 95.0 wt.%, preferably > 98.0 wt.% of the polypropylene composition with regard to the total weight of the biaxially oriented pipe; wherein the polypropylene composition comprises B-nucleating agent present in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt.%, preferably > 0.003 and < 0.25 wt.%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition; wherein the B-nucleating agent is a quinacridone type compound selected from quinacridone, dimethylquinacridone and dimethoxyquinacridone; and wherein the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 120 °C and wherein the polypropylene composition has a lowest melt temperature (Tmi) of > 131°C and < 150 °C.

[0079] The presence of B-nucleating agent in the biaxially oriented pipe obtained from the process of the present invention originates either from the B-nucleating agent added during melt processing of the polypropylene composition or is present in the polypropylene composition prior to melt processing.

[0080] Preferably in an aspect of the invention, the invention relates to a biaxially oriented pipe obtained by or obtainable by the process comprising the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Ta °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe;• wherein the drawing temperature Ta is a temperature > Tcand < Tc+ 22 °C, preferably > Tcand < Tc+ 20 °C; where Tcis the crystallization temperature of the polypropylene composition determined in accordance with ASTM D3418-15, using Differential Scanning Calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23°C to 200°C and at a heating and a cooling rate of 10°C / min for a 5-10 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle; and• wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% determined using Wide Angle X-ray Diffraction technique.

[0081] Preferably in an aspect of the invention, the invention relates to a biaxially oriented pipe obtained by or obtainable by the process comprising the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Ta °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe;• wherein the drawing temperature Ta is a temperature > Tcand < Tc+ 22 °C, preferably> Tcand < Tc+ 20 °C; where Tcis the crystallization temperature of the polypropylene composition determined in accordance with ASTM D3418-15, using Differential Scanning Calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23°C to 200°C and at a heating and a cooling rate of 10°C / min for a 5-10 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle; and• wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% determined using Wide Angle X-ray Diffraction technique; and• wherein the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably> 103 °C and < 120 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

[0082] Advantageously, the pipe obtained has excellent long term hydrostatic pressure performance by modifying the process with which the pipe is manufactured.

[0083] As is shown in the examples, a biaxially oriented pipe drawn at same temperature but without using a precursor pipe having of having > 5.0% of beta crystallinity, did not show thedesired pressure performance (i.e low time to failure). Surprisingly, the pipes obtained or obtainable by the process of the present invention has improved pressure performance over that of commercially available beta crystallized polypropylene pipe.

[0084] Preferably, the biaxially oriented pipe has a time to failure of > 100 hours, preferably > 400 hours, preferably > 1000 hours, preferably > 1200 hours, preferably > 1400 hours, determined in accordance with ISO 1167-1 at a stress level between 10 to 20 MPa, preferably at a stress level of 20 MPa, and measured at a temperature of 20°C.

[0085] Preferably, the biaxially oriented pipe has a time to failure of > 100 hours, preferably > 400 hours, preferably > 1000 hours, preferably > 1200 hours, preferably > 1400 hours, according to ISO 1167-1 determined at a stress level of 10-20 MPa, preferably at a stress level of 20 MPa and measured at a temperature of 20°C. Preferably, the test is performed on a biaxially oriented pipe having a diameter from 19 to 32 mm, preferably 32 mm; and a wall thickness of 1.5 mm to 3 mm.

[0086] Preferably, the biaxially oriented pipe has a time to failure of > 1000 hours, preferably > 1200 hours, preferably > 1400 hours, according to ISO 1167-1 determined at a stress level of 10 to 20 MPa, preferably at a stress level of 20 MPa and measured at a temperature of 20°C, wherein the test is performed on a biaxially oriented pipe having a diameter from 19 to 32 mm, preferably 32 mm; and a wall thickness of 1.5 mm to 3 mm; wherein the biaxially oriented pipe is derived from drawing the precursor pipe drawn at a drawing temperature (Ta) ranging from > 120 °C and < 160 °C, preferably >120 °C and < 150 °C, preferably >125 °C and < 145 °C, preferably > 130 °C and < 148 °C, preferably > 130°C and < 140 °C; and wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0%.

[0087] Preferably, the biaxially oriented pipe has a time to failure of > 1000 hours, preferably > 1200 hours, preferably > 1400 hours, according to ISO 1167-1 determined at a stress level of 10-20 MPa, preferably at a stress level of 20 MPa and measured at a temperature of 20°C, wherein the biaxially oriented pipe is derived from drawing the precursor pipe drawn at a drawing temperature ranging from > 130 °C and < 148 °C, preferably > 130°C and < 140 °C; and wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0%, wherein the crystallization temperature Tcof the polypropylenecomposition ranges from > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

[0088] The biaxially oriented pipe obtained from the process of the present invention may be formed of polypropylene composition having a certain degree of B-crystallinity or may be substantially free of B-crystallinity. For example, the biaxially oriented pipe comprising the polypropylene composition has a B-crystallinity in the range of > 0% and < 50.0%, preferably > 0% and < 30.0%, preferably > 0% and < 20.0%, determined using Wide Angle X-ray Diffraction technique.

[0089] Preferably, the biaxially oriented pipe comprising the polypropylene composition having a B-crystallinity in the range of > 0% and < 20.0%, preferably > 0% and < 10.0%, preferably > 0% and < 5.0%, preferably > 0% and < 2.0%, determined using Wide Angle X-ray Diffraction technique.

[0090] Preferably, the polypropylene composition forming the biaxially oriented pipe is substantially free of B-crystallinity. It is believed that in certain situation while drawing and stretching the precursor pipe, the pipe may lose it’s B-crystallinity or the amount of B-crystals is low.

[0091] Although the polypropylene composition comprising the precursor pipe and the biaxially oriented pipe is substantially identical from a chemical composition, the polypropylene composition may differ in the degree of B-crystallinity owing to processing.

[0092] The biaxially oriented pipe once obtained may be further annealed to relax out unwanted stresses and improve shrinkage resistance of the pipe.

[0093] For example, in an aspect of the invention, the process further comprises the step of subjecting the biaxially oriented pipe to an annealing temperature Tafor a time period of > 0 mins and < 30 mins and subsequently cooling the biaxially oriented pipe.

[0094] Preferably, the biaxially oriented pipe is cooled to a temperature of at most 145 °C below the drawing temperature (Ta), preferably at most 120 °C below the drawing temperature (Ta), preferably at most 80 °C below the drawing temperature (Ta), preferably at most 50 °C below the drawing temperature (Ta); and wherein the annealing temperature Ta< the drawing temperature Ta.

[0095] The invention will now be demonstrated with the following non-limiting examples.EXAMPLES

[0096] Purpose: To evaluate the long term hydrostatic pressure performance of polypropylene compositions based biaxial pipes.

[0097] Material: Polypropylene composition RPP 1 and RPP2 were used for preparing the pipes. RPP2 had beta-crystallinity of about 45% and contained 80-500 ppm by weight of beta nucleated agents derived from quinacridone type of compounds. RPP1 was a polypropylene composition which was free of beta nucleating agent. RPP2 was prepared from RPP1 by compounding RPP1 with the quinacridone type of beta-nucleating agent.

[0098] The lowest melt temperature (Tmi) was determined by differential scanning calorimetry (DSC) in accordance with ASTM D3418-15. The DSC measurements were performed using a DSC TA Q20 and an Intracooler configured to reach -90°C.

[0099] The measurements were done under the flow of nitrogen to avoid sample degradation. The methodology followed was: First Heating: -40°C to 230°C @ 10°C / min (3 min hold at the end temperature), Cooling: 230°C to -40°C @ 10°C / min, Second Heating: -40°C to 230°C @ 10°C / min, sample used were between 3 and 5 mg. Lowest melt temperature (Tmi) was reported from the second heating cycle.

[0100] The Beta crystallinity was determined using WAXD (Wide Angle X-ray Diffraction), mechanically prepared from billets of 1 mm thickness. The WAXD patterns were measured on a SAXSLAB GANESHA equipped with a XENOCS microfocus source (CuKa) coupled to a multilayer optics. The primary beam is shaped via 3 sets of JJXRAX 4-blade slit systems with single-crystal anti-scatter slits to increase the signal to noise ratio.

[0101] After radial integration was carried out on the raw data, an amorphous halo, was determined by fitting a Gaussian area Aam on the tails of the diffraction pattern that was subtracted from the overall diffraction pattern. Subsequently, the peak areas Ai,cwere obtained from the crystalline fraction and was used to determine the overall crystalline fraction Xc:

[0102] where Xc stands for the fraction that is crystalline, Ai,cis the area of integrated crystalline fraction, and Aam is the area of amorphous fraction.

[0103] The relative P-crystallinity Kp was determined) using the formula given below (Obadal et al. Macromol. Rapid Commun. (2005) 26 1253:

[0104] The absolute P- crystallinity was derived by multiplication with the overall crystallinity:5 Xp = Kp* XcTable 1

[0105] Preparation of biaxially oriented Pipe: Precursor pipes were derived from RPP 1 andRPP2 using extrusion. The precursor pipes were drawn over an expanding conical mandrel having 10 an exit diameter of 33 mm with a semi angle of 15 degrees. The draw temperature was 135°C with a draw speed of 100 mm / min. The target axial draw ratio was 3.2 and the target average hoop draw ratio was 1.25.

[0106] The processing parameters are as provided below along with the results from the pressure performance test that was performed in accordance with the standard ISO 1167.15 Table 2

[0107] From Table 2 it is evident that at a given drawing temperature Td, the inventive biaxially oriented pipes (Inventive 1-4) derived from a precursor pipe having beta crystallinity > 5% (i.e 45% beta crystallinity) demonstrated excellent pressure performance (i.e higher failure time) over that of the pipes prepared from comparative samples. For example, the sample Inventive1 even though subjected to identical stress and having comparable dimension, the pressure performance of Inventive 1 over that of Comparative 2 was significantly high (i.e ~ 33 times higher). In other words, when the pipes for the comparative samples were drawn at a relatively low temperature identical to the inventive pipes, the resultant pipes did not demonstrate the desired long term hydrostatic pressure performance.

[0108] In conclusion, although the inventive and comparative samples were drawn at same temperature, the inventive samples obtained by the process of the present invention showed much higher resistance to failure indicated by the longer time taken for failure.

[0109] The standard Beta PP pipes were those beta-nucleated polypropylene based pipes that were commercially available in the market (RA7050 from Borealis). The standard beta PP pipes were not biaxially oriented. The improved performance for the inventive pipes (Inventive samples 1-4) over that of the standard Beta PP pipes is evident from the data related to the time to failure.

[0110] Accordingly, inventive biaxially oriented beta pipes (Inventive samples 1-4) has improved failure properties over that of standard beta pipe. Advantageously, the pipe production process involving the use of a precursor pipe having B-crystallinity of > 5.0%, along with the choice of specific processing conditions of draw temperature in relation to the crystallization temperature Tc of the polypropylene composition and the subsequent biaxial orientation, imparted the desired performance to the inventive biaxial pipes.

Claims

CLAIMS1. A process for preparing a biaxially oriented pipe, the process comprises the steps of: a) melt processing a polypropylene composition into a billet; b) cooling the billet to a temperature of < Tc°C to obtain a precursor pipe, where Tcis the crystallization temperature of the polypropylene composition; c) heating the precursor pipe to a drawing temperature (Ta °C); and d) bi-axially stretching the precursor pipe in the axial direction and in the peripheral direction to obtain the bi-axially oriented pipe;• wherein the drawing temperature Ta is a temperature > Tcand < Tc+ 22 °C, preferably > Tcand < Tc+ 20 °C; where Tcis the crystallization temperature of the polypropylene composition determined in accordance with ASTM D3418-15, using Differential Scanning Calorimetry (DSC) with a first heating at a temperature between -40°C to 230°C @ 10°C / min (3 min hold at the end temperature) and a cooling of 230°C to - 40°C @ 10°C / min at a heating and a cooling rate of 10°C / min for a 3-5 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle; and• wherein the precursor pipe comprising the polypropylene composition is crystallized in the B-form having B-crystallinity of > 5.0% as determined using Wide Angle X-ray Diffraction technique.

2. The process of claim 1, wherein the process further comprises the step of subjecting the biaxially oriented pipe to an annealing temperature Tafor a time period of > 0 mins and < 30 mins and subsequently cooling the biaxially oriented pipe.

3. The process according to any one of claims 1-2, wherein the precursor pipe comprises the polypropylene composition having a B-crystallinity in the range of > 10% and < 90%, as determined using Wide Angle X-ray Diffraction technique.

4. The process according to any one of claims 1-3, wherein the biaxially oriented pipe comprises the polypropylene composition having a B-crystallinity in the range of > 0% and < 50.0%, preferably > 0% and < 30.0%, preferably > 0% and < 20.0%, as determined using Wide Angle X-ray Diffraction technique.

5. The process according to any one of claims 1-4, wherein the step of bi-axially stretching the precursor pipe is performed at an axial draw ratio of > 1.1 and < 5.0 and at an average hoop draw ratio of > 1.1 and < 3.0.

6. The process according to any one of claims 1-5, wherein the polypropylene composition comprises a propylene polymer selected from heterophasic polypropylene, propylene random copolymer, and propylene homopolymer; and / or wherein the propylene polymer is present in an amount of > 95.0 wt.%, preferably > 97.0 wt.%, preferably > 98.0 wt.%, preferably > 99.0 wt.%, preferably 100.0 wt.%, with regard to the total weight of the polypropylene composition.

7. The process according to claim 6, wherein the propylene polymer is a propylene random copolymer comprising polymeric units derived from propylene and polymeric units derived from a comonomer selected from ethylene and / or an a-olefin comonomer having 4 to 10 carbon atoms; preferably wherein the propylene random copolymer has:(a) polymeric units derived from propylene ranging from > 88.0 and < 100 wt.%, preferably > 90.0 and < 100 wt.%, preferably > 95.0 and < 100 wt.%, preferably > 95.0 and < 99.5 wt.%, preferably > 98.0 and < 99.5 wt.%, with regard to total weight of the propylene random copolymer; and(b) polymeric units derived from the comonomer ranging from > 0 and < 12.0 wt%, preferably > 0 and < 10.0 wt.%, preferably > 0 and < 5.0 wt%, preferably > 0.5 and < 5.0 wt%, preferably > 0.5 and < 2.0 wt%, with regard to total weight of the propylene random copolymer, preferably wherein the comonomer is selected from ethylene, 1- butene, 1 -hexene, 1 -octene and combinations thereof, preferably wherein the comonomer is ethylene; andpreferably wherein the propylene random copolymer has a melt flow index of > 0.1 and < 10.0 g / lOmin, preferably > 0.1 and < 4.0 g / 10 min, more preferably > 0.1 and < 1.0 g / lOmin, measured according to ISO 1133- 1 :2011 (230 °C / 2.16 kg).

8. The process according to any one of claims 1-7, wherein the step of melt processing of the polypropylene composition comprises the step of adding B-nucleating agent in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt%, preferably > 0.003 and < 0.25 wt%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition.

9. The process according to any one of claims 1-7, wherein the polypropylene composition prior to melt processing, comprises B-nucleating agent present in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt.%, preferably > 0.003 and < 0.25 wt%, with regard to the total weight of the polypropylene composition.

10. The process according to any one of claims 1-9, wherein the drawing temperature (Td) ranges from (Tmi - 15.0) °C < Td < (Tmi -1.0) °C, preferably (Tmi - 10.0) °C < Td < (Tmi - 5.0) °C, wherein Tmi is the lowest melt temperature of the polypropylene composition determined in accordance with ASTM D3418-15 by using Differential Scanning Calorimetry (DSC) with a first heating at a temperature between -40°C to 230°C @ 10°C / min (3 min hold at the end temperature) and a cooling of 230°C to -40°C @ 10°C / min at a heating and a cooling rate of 10°C / min for a 3-5 mg sample, using a nitrogen purge gas at flow rate of 50 ± 5 mL / min, followed by a second heating and cooling cycle identical to the first heating and cooling cycle.

11. The process according to any one of claims 1-10, wherein the drawing temperature (Td) ranges from > 120 °C and < 160 °C, preferably >120 °C and < 150 °C, preferably >123 °C and < 142 °C, preferably >125 °C and < 145 °C, preferably > 130 °C and < 148 °C, preferably > 130°C and < 140 °C.

12. The process according to any one of claims 1-11, wherein the crystallization temperature Tcof the polypropylene composition ranges from > 98 °C and < 138 °C, preferably > 100 °C and < 128 °C, preferably > 98 °C and < 128 °C, preferably > 100 °C and < 128 °C, preferably >103 °C and < 123 °C, preferably > 103 °C and < 120 °C, preferably > 108 °C and < 120 °C, preferably > 108 °C and < 118 °C, preferably > 110°C and < 120 °C.

13. The process according to any one of claims 1-12, wherein the drawing temperature (Ta) ranges from >123 °C and < 142 °C and wherein the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 120 °C.

14. A biaxially oriented pipe obtained by or obtainable by the process as claimed in any one of the claims 1-13, preferably wherein the biaxially oriented pipe comprises > 95.0 wt.%, preferably> 98.0 wt.% of the polypropylene composition with regard to the total weight of the biaxially oriented pipe; preferably wherein the polypropylene composition comprises B-nucleating agent present in an amount of > 0.0001 and < 2.0 wt.%, preferably > 0.003 and < 0.3 wt.%, preferably> 0.003 and < 0.25 wt.%, preferably > 0.006 and < 0.08 wt.%, with regard to the total weight of the polypropylene composition; preferably wherein the B-nucleating agent is a quinacridone type compound; preferably wherein the crystallization temperature Tcof the polypropylene composition ranges from > 103 °C and < 120 °C and wherein the polypropylene composition has a lowest melt temperature (Tmi) of > 131°C and < 150 °C.

15. The biaxially oriented pipe of claim 14, wherein the biaxially oriented pipe has a time to failure of > 100 hours, preferably > 400 hours, preferably > 1000 hours, preferably > 1200 hours, preferably > 1400 hours, determined in accordance with ISO 1167-1 at a stress level between 10 to 20 MPa, preferably at a stress level of 20 MPa, and measured at a temperature of 20°C.

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