Development Issues and Technical Challenges in Composite and Bonded Steel Pipe Manufacturing

Literature Overview

This paper by He Defu and Wang Jingying from Shanghai Jiuli Industry and Trade Development Co., Ltd. provides a comprehensive examination of composite and bonded steel pipe development, focusing on metallurgical composite pipes versus mechanical bonded pipes, internal CRA overlay welding challenges, weld quality optimization, heat treatment standards comparison, and material selection criteria. Published in the journal "Steel Pipe" (钢管), this article addresses critical technical issues that practitioners in the oil, gas, and chemical industries must understand when specifying and fabricating corrosion-resistant alloy lined pipes.

Core Technical Points

Metallurgical Composite vs. Mechanical Bonded Pipes

The fundamental distinction between metallurgical composite and mechanical bonded pipes is central to understanding their performance and application limitations. Metallurgical composite pipes achieve atomic-level bonding between the base material and the corrosion-resistant alloy (CRA) layer through controlled melting and diffusion during manufacturing, resulting in superior bond strength and resistance to delamination under thermal cycling. Mechanical bonded pipes, on the other hand, rely on physical contact and pressure to maintain the interface, which can be susceptible to hydrogen-induced blistering and delamination under certain service conditions.

Internal CRA Overlay Welding Challenges

The direct overlay welding of CRA layers on the internal surface of steel pipes presents several significant technical challenges:

• Welding procedure qualification: The thermal input must be carefully controlled to prevent excessive dilution between the base material and the CRA overlay, which can compromise the corrosion resistance of the overlay layer. Typical dilution limits are 5-15% depending on the CRA grade and application requirements.
• Longitudinal seam weld quality: The interaction between the pipe's longitudinal weld seam and the CRA overlay creates a complex metallurgical zone that is prone to cracking, porosity, and inadequate fusion. The welding groove preparation at the seam location requires special attention.
• Filler metal selection: The filler metal composition must be compatible with both the base material and the CRA layer to ensure proper metallurgical compatibility and avoid intermetallic compound formation that could reduce toughness.
• Post-weld heat treatment: The PWHT requirements differ significantly between domestic and international standards, with implications for the bond quality and mechanical properties of the composite interface.

Weld Quality Optimization Methods

The authors propose several methods to optimize the quality of composite or bonded pipe welds:

1. Pre-weld preparation: Thorough cleaning and surface preparation of the pipe interior to remove oxide scale, contaminants, and residual hydrocarbons that could cause porosity or bonding defects.
2. Welding sequence control: Implementing a back-step welding technique or alternating weld passes to minimize residual stress accumulation and distortion.
3. Interpass temperature control: Maintaining interpass temperatures within a narrow window (typically 50-150°C for most CRA overlays) to control the cooling rate and prevent cracking.
4. Post-weld inspection: Employing a combination of magnetic particle testing (MT), dye penetrant testing (PT), and ultrasonic testing (UT) to detect subsurface defects at the bond interface.

Heat Treatment Standards Comparison

The differences in heat treatment requirements between domestic Chinese standards and international standards such as ASTM and EN can lead to significant variations in the final mechanical properties and corrosion resistance of composite pipes. Engineers must carefully review the applicable standard for each project and ensure that the heat treatment specification is clearly defined in the procurement documentation.

Bond Quality Inspection Methods

The bond quality of composite pipes is typically verified through the following methods:

• Peel test: A mechanical test where the CRA layer is peeled from the base material, with the fracture mode (ductile vs. brittle) indicating bond quality.
• Bond strength test: A shear or tensile test measuring the force required to separate the composite layers.
• Visual inspection: Examination of the bond interface for cracks, delamination, or incomplete bonding.
• Ultrasonic testing: Advanced UT techniques can detect subsurface voids and delaminations at the bond interface.

Material Selection Criteria

The selection of base material and CRA overlay material must consider the service environment, including the type of corrosive medium, operating temperature, pressure, and potential for hydrogen-induced cracking. For sour service environments containing H₂S, compliance with NACE MR0175/ISO 15156 is mandatory, which imposes strict limitations on the hardness and microstructure of both the base material and the CRA overlay.

Summary and Outlook

This paper provides essential guidance for engineers and manufacturers involved in the specification, fabrication, and quality assurance of composite and bonded steel pipes. The technical challenges identified—particularly regarding CRA overlay welding, longitudinal seam quality, and heat treatment standard harmonization—represent ongoing areas of research and development. Engineers must adopt a systematic approach to material selection, welding procedure qualification, and quality inspection to ensure the long-term reliability of composite pipe systems in demanding service environments. The convergence of international standards on heat treatment and bond testing requirements would significantly reduce technical barriers and facilitate global procurement of composite pipe products.