With the continuous expansion of the application field of polyethylene (PE) pipe, PE pipe is also facing many problems brought by different use environments, such as the damage of termites to the pipe; How to prevent static electricity, the pipeline damage cannot be detected in real time, and the overall performance cannot be guaranteed under bad construction environment; How to add other new functions in the application of plastic pipes to adapt to the new use environment needs to promote the development of the whole polyethylene pipe industry through continuous innovation.

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1. Product and performance of coated pipe
As the working part of pressure bearing and transportation, the working layer of coated pipe plays a protective and auxiliary role, and can be stripped from the pipe body when in use.
According to the requirements of GB / T 15558.1-2015 and GB / T 13663.2-2018, the working pipe in the coated pipe shall meet the performance requirements specified in this standard, such as size, hydrostatic strength, oxidation induction time, resistance to slow crack growth, etc.
1.2 PE pipes with peelable thermoplastic protective layer coated on the outer wall
PE pipe with peelable thermoplastic protective layer coated on the outer wall (hereinafter referred to as coated pipe) refers to the pipe that takes single-layer PE pipe as the working pipe and extrudes a protective layer of different materials outside the working pipe through multi-layer coextrusion technology. As a part of pressure bearing and conveying medium, the protective layer plays a protective role, and the port part can be stripped from the working pipe during welding.
1.3 main characteristics of coated pipe
The coated pipe solves the problem that the PE pipe is easy to scratch in the trenchless process, and can effectively protect the working pipe. The key technology is the protective layer. In terms of raw material use and structure, the use of high elastic modulus polypropylene (PP) material can not only improve the scratch resistance of the protective layer, but also prevent it from bonding with the working pipe and facilitate stripping. In the production stage, the protective layer with a length of 300 mm at both ends of the cladding pipe shall be prefabricated and indented to facilitate the stripping of the protective layer during construction. In terms of crater protection, the stripped protective layer is restored to the stripped section after welding and wound with fiber-reinforced tape.
1.5 Material properties of coated pipe
By comparing the typical performance parameters of PE raw materials and PP raw materials, the tensile strength, bending modulus and hardness of PP materials are higher than those of PE materials. The scratch resistance of PP materials is that PP materials are harder than PE materials.Therefore, PP material is used as protective layer to avoid scratching the outer surface of PE working pipe in trenchless construction.

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2. Product performance advantages
For polyethylene pipes widely used in gas and water supply industries, the damage to pipes caused by pipe transportation, loading and unloading, construction and environmental factors is inevitable. Coated pipes can effectively protect working pipes, systematically solve various problems encountered in practical application through specific scraping tools and welding methods, and reflect the following advantages:
Protect the working pipe, effectively reduce scratches and improve the safety factor of the pipeline. The outer protective layer can effectively resist the aging of the working tube caused by ultraviolet rays and prolong the storage time of the working tube. The coating also has expansibility, such as adding anti-static, anti termite, positioning, detection and other functions.
3. Application of coated pipe in trenchless laying
The traditional excavation laying pipeline construction method has been more and more limited due to the inconvenience to the city and the strict requirements of municipal management. The trenchless construction technology continues to develop and popularize. At the same time, with the emergence of coated pipe, it can effectively increase the hardness of coated layer, which can better meet the requirements of trenchless laying and steel pipe interspersed repair.
CJJ 358-2018 polyethylene pipe for Trenchless Engineering (submitted for approval) adds coated pipe products, and puts forward requirements for the material performance of peelable polypropylene (PP) protective layer coated on the outer wall of trenchless engineering.

It effectively solves the problem of damage caused by scratching of underground rock during transportation and installation, especially in the process of trenchless crossing, and provides the possibility of horizontal directional drilling crossing with pipes larger than SDR11 Series in the future. These create opportunities and conditions for giving full play to the advantages of polyethylene (PE) and for the renewal and repair of old pipes in sections that are not suitable for excavation.

4. Summary
The coated pipe provides a new solution to the pipe scratch problem of PE pipe in transportation and construction, especially in trenchless construction. Coated pipe has great advantages in trenchless laying of pipeline. With the increasing construction of trenchless laying of natural gas pipeline, the coated pipe has a broad market prospect.
Qingdao Sainuo Chemical Co.,Ltd. We are manufacturer for PE wax, PP wax, OPE wax, EVA wax, PEMA, EBS,Zinc/Calcium Stearate…. Our products have passed the REACH, ROHS, PAHS, FDA testing. Sainuo rest assured wax, welcome your inquiry! Website：https://www.sanowax.com
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