Mechanically Lined Pipes: A Comprehensive Guide

1. Material & Size:
   Mechanically lined pipes typically consist of an outer carrier pipe and an inner liner pipe. The carrier pipe is commonly made of carbon steel or low-alloy steel, while the liner pipe is composed of a corrosion-resistant alloy (CRA) material such as stainless steel, duplex stainless steel, or nickel alloys. The size range of mechanically lined pipes can vary, starting from small diameters up to larger dimensions, depending on the specific project requirements.
2. Backing Material:
   The backing material, which is the outer carrier pipe, provides structural support and is responsible for withstanding external loads and pressures. The selection of the backing material depends on factors such as the operating conditions, design requirements, and project specifications.
3. CRA Liner Material:
   The CRA liner material is selected based on its corrosion resistance properties to ensure protection against the transported fluids. Different CRA materials have varying levels of resistance to specific corrosive environments. The selection of the liner material depends on factors such as the fluid composition, temperature, pressure, and pH.
4. Technical Features of Mechanically Lined Pipes:
   Mechanically lined pipes are designed to provide a tight and secure mechanical bond between the inner liner and the outer carrier pipe. This bond is achieved through precision engineering techniques, such as hydroforming or other mechanical interlocking mechanisms. The tight fit ensures a reliable connection that can withstand external stresses, vibrations, and thermal expansion.
5. Mechanical Properties:
   Mechanically lined pipes must possess adequate mechanical properties to ensure structural integrity and withstand operational conditions. These properties include tensile strength, yield strength, elongation, impact resistance, and hardness. The mechanical properties are determined by the choice of materials and the manufacturing processes employed.
6. Material Selection and Standard Specification:
   The selection of materials for mechanically lined pipes is crucial and depends on factors such as the conveyed fluid, operating temperature, pressure, and environmental conditions. Various international standards, including API (American Petroleum Institute), ASTM (American Society for Testing and Materials), DNV (Det Norske Veritas), and ISO (International Organization for Standardization), provide specifications and guidelines for material selection, fabrication, and testing.
7. Tests and Inspection:
   Mechanically lined pipes undergo rigorous testing and inspection to ensure compliance with industry standards and project requirements. These tests include hydrostatic testing, dimensional inspection, visual inspection, non-destructive testing (such as ultrasonic testing or radiographic examination), and destructive testing (such as tensile testing or impact testing). These tests verify the integrity, mechanical properties, and corrosion resistance of the pipes.

In conclusion, enhancing pipeline integrity with mechanically lined pipes requires careful consideration of material selection, size, technical features, mechanical properties, adherence to standard specifications, and rigorous testing and inspection. By leveraging the advantages of mechanically lined pipes, such as corrosion resistance and mechanical strength, industries can achieve reliable and long-lasting pipeline systems.