Propylene-Hexene Copolymer Pipes for High-Pressure Creep Resistance
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Solution Overview
Problem
Conventional pipe systems made from polypropylene materials lack sufficient creep resistance and impact strength, leading to inferior performance in high-pressure applications and outdoor installations, where resistance to rock impingement and slow crack growth are critical, and require additional protective measures like sand beds, increasing installation costs.
Innovation Solution
The use of semi-crystalline random polymers of propylene and 1-hexene, with optional recurring units from ethylene and other α-olefins, offering improved burst pressure resistance, rigidity, and stress-crack resistance, reducing the need for protective sand beds and lowering installation costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polypropylene materials are used for pipe systems, then manufacturing simplicity is maintained, but creep resistance and impact strength are insufficient for high-pressure applications
Solution Approach 1:
The patent applies parameter changes by modifying the molecular structure of polypropylene through copolymerization with α-olefins (1-butene, 1-hexene, or 1-octene) at controlled comonomer contents (2-10 wt%). This changes the crystallinity and molecular weight distribution parameters to achieve superior creep resistance (over 10,000 hours at 95°C) and impact strength while maintaining processability
Solution Approach 2:
The patent creates a composite polymer material by blending two different copolymers: a first copolymer with high molecular weight (Mw ≥ 100,000) and comonomer content 3-10 wt%, and a second copolymer with lower molecular weight and comonomer content 2-6 wt%. This composite structure synergistically improves both creep resistance and impact strength
2Strength
If polypropylene pipes are used for outdoor installation, then chemical resistance is maintained, but resistance to rock impingement and slow crack growth is insufficient
Solution Approach 1:
The patent optimizes the comonomer content parameter (2-10 wt%) and molecular weight parameter (Mw ≥ 100,000) to achieve a balance between flexibility and strength. The controlled incorporation of α-olefin comonomers creates a semi-crystalline structure with improved stress crack resistance while maintaining chemical resistance, enabling the pipes to withstand outdoor environmental stresses including rock impingement
3Object-affected harmful factors
If sand bed protection is added to protect polyethylene pipes from mechanical forces, then rock impingement resistance is improved, but installation cost and complexity increase
Solution Approach 1:
The patent makes the pipe material itself self-protecting by incorporating high impact strength and rock impingement resistance directly into the polypropylene copolymer composition. The material's inherent toughness (impact strength ≥ 10 kJ/m²) and resistance to mechanical forces eliminate the need for external sand bed protection, simplifying installation while maintaining durability
Solution Approach 2:
The patent extracts the protection function from the external sand bed system and integrates it into the pipe material itself. By incorporating α-olefin copolymers with specific molecular characteristics, the pipe gains intrinsic resistance to rock impingement and mechanical forces, removing the requirement for separate protective layers
Data Source
AI summary
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)