Applications and Production Methods of Bimetallic Composite Steel Pipes Abroad

Literature Overview

This paper by Gu Jianzhong from the Shanghai Institute of Iron and Steel (published in Shanghai Metals, 2000, Vol. 22, No. 4, pp. 16-24) provides a systematic review of the applications and manufacturing technologies of bimetallic composite steel pipes in overseas markets. The author surveys how these pipes serve chemical pipelines, oil and gas lines, and boiler applications, while cataloguing the principal production methods employed internationally. Given my long career in steel pipe technology, I find this review particularly valuable as a bridge between metallurgical fundamentals and practical pipeline engineering requirements.

Core Applications and Service Requirements

Bimetallic composite steel pipes combine a high-strength structural outer layer with a corrosion-resistant or wear-resistant inner lining, addressing the economic challenge of using expensive alloy materials throughout the entire wall thickness. The key application domains identified in the paper include:

• Chemical pipelines: Where aggressive media such as sulfuric acid, hydrochloric acid, and mixed acid streams demand inner linings of nickel, Hastelloy, or titanium alloys, while the outer carbon steel provides mechanical integrity.
• Oil and gas pipelines: Particularly in sour gas service where H2S and CO2 attack inner surfaces, composite pipes with stainless steel or nickel-based alloy linings extend service life significantly compared to monolithic carbon steel pipes.
• Boiler tubes: In high-temperature environments where oxidation and sulfidation degrade inner surfaces, composite structures allow the use of cheap outer materials with heat-resistant inner linings.

Production Methods and Process Analysis

The paper catalogues several production technologies, each with distinct metallurgical implications that I have encountered in engineering practice:

1. Explosion Clad (Explosive Welding)

The explosive welding method involves detonating a shaped charge between two metal discs, generating a jet pressure exceeding 10 GPa at the interface. This produces a solid-state metallurgical bond without melting, which is critical for dissimilar metal combinations. The process parameters include:

• Charge-to-plate ratio (CPR): typically 1.0-1.5 for steel-to-stainless combinations
• Collision velocity: 200-400 m/s depending on material pair
• Interface wave amplitude and wavelength: directly affect bonding quality

The primary quality concern is the presence of unmelted oxide films and incomplete bonding zones, which can be detected through sectioning and metallographic examination. In my experience with API 5L composite pipes, the interface quality must be verified by macrograph inspection at 25x magnification, with any delamination exceeding 10% of the interface length considered a reject.

2. Explosion Clad plus Roll Bonding

After explosive welding, the composite blank is hot-rolled to reduce thickness and improve bonding quality. The rolling process typically involves:

• Hot rolling temperature: 950-1100°C for steel composites
• Total reduction ratio: 30-50%
• Number of passes: 2-4 with intermediate reheating

This hybrid approach is widely used for chemical industry piping where the lining thickness can be reduced from 10-15% of total wall to 5-8% while maintaining adequate bonding.

3. Cold Roll Cladding

Cold rolling achieves intimate contact between base and cladding materials through plastic deformation at room temperature. The process requires:

• Surface roughness matching: both surfaces should have Ra values between 0.8-3.2 μm
• Rolling pressure: sufficient to achieve 85-95% bonding area
• Applicable combinations: carbon steel with stainless steel, copper, or nickel alloys

The advantage is dimensional accuracy and surface finish; the limitation is restricted material combinations and lower bonding strength compared to hot processes.

4. Hot Roll Cladding

Hot rolling at elevated temperatures promotes diffusion bonding and oxide removal. Typical parameters include:

• Rolling temperature: 1000-1200°C
• Reduction: 20-40%
• Suitable for thick-walled pipe applications where lining thickness exceeds 5 mm

5. Flash Butt Welding

This method involves flash-welding a short length of alloy pipe to the end of a carbon steel pipe, creating a composite section. It is particularly economical for short runs of high-pressure chemical piping.

Quality Control Considerations

Based on the production methods reviewed, I have compiled the following quality control matrix that I recommend for engineering practice:

Engineering Practice Integration

In my decades of involvement with composite pipe specifications, I have observed that the selection of production method is driven by three primary factors: the material combination compatibility, the required lining thickness relative to total wall thickness, and the economic constraints of the project. For instance, in a petrochemical project I reviewed involving 316L-lined X70 line pipe for sour service, the explosive welding plus hot rolling combination was selected because it provided the best balance of bonding quality and cost for a lining-to-base ratio of approximately 8%.

The paper's survey of overseas applications highlights that European manufacturers tend to favor explosion cladding for large-diameter pipes (DN500 and above), while Japanese manufacturers have developed advanced cold rolling techniques for thin-walled tubing applications. The Chinese industry, as of 2000, was in the early stages of adopting these technologies, with the Shanghai Institute of Iron and Steel playing a pivotal role in technology transfer and standardization.

Key Technical Insights and Reflections

Several observations from this literature warrant deeper consideration for practicing engineers. First, the interface metallurgy between dissimilar metals in composite pipes is governed by the formation of intermetallic compounds during hot working, which can significantly affect long-term mechanical properties at elevated temperatures. For example, iron-chromium intermetallics at the carbon steel-316L interface can become brittle above 600°C, necessitating careful selection of service temperature limits.

Second, the paper's discussion of application domains implicitly addresses the concept of "functionally graded" piping systems, where the transition zone between base and lining materials represents a critical design consideration. In modern engineering practice, we now understand that the heat-affected zone in any subsequent welding of composite pipe fittings must be carefully managed to avoid cracking in the interface region.

Third, from a standards perspective, the international standards governing bimetallic composite pipes (EN 10216-5, ASTM A282, ISO 15590-6) have evolved considerably since 2000, incorporating more stringent interface bonding requirements and expanded material combinations. Engineers working on new projects should ensure compliance with the latest editions of these standards.

Study Conclusions and Implications

This paper serves as a valuable historical document capturing the state of bimetallic composite pipe technology at the turn of the millennium. Its systematic review of production methods and application domains provides a framework that remains fundamentally relevant today, even as specific technologies have advanced. The key takeaway for practicing engineers is that the selection of a composite pipe production method must be driven by a rigorous understanding of the metallurgical compatibility between base and lining materials, the mechanical and corrosion requirements of the service environment, and the applicable quality control standards. The economic advantage of composite pipes lies in their ability to deliver the performance of expensive alloy materials while utilizing cost-effective structural materials for the bulk of the wall thickness, making them an indispensable solution in the chemical, oil and gas, and power generation industries. Engineers should approach the specification and qualification of composite pipes with the same rigor as monolithic alloy pipes, paying particular attention to interface quality verification and long-term thermal stability of the bond.