Compatibility Study of Stainless Steel Seamless Pipe and Carbon Steel Seamless Pipe in Chemical Equipment

Compatibility Study of Stainless Steel Seamless Pipe and Carbon Steel Seamless Pipe in Chemical Equipment
In chemical equipment design, the choice of piping system directly impacts production safety, equipment lifespan, and operating costs. As two mainstream piping materials, stainless steel seamless pipe and carbon steel seamless pipe each have their own characteristics and applicable scenarios. This article compares and analyzes the compatibility of these two materials in chemical environments from multiple perspectives, providing a reference for project selection.

1. Core Requirements for Pipes in Chemical Equipment
Chemical production environments are often characterized by complex working conditions such as highly corrosive media (such as concentrated sulfuric acid, hydrochloric acid, and caustic soda), high temperatures, high pressures, and temperature fluctuations.2 These conditions require piping materials to possess the following:

Excellent corrosion resistance: Resistant to corrosion from various chemical media, preventing leaks and contamination caused by corrosion.

Sufficient mechanical strength and heat resistance: Maintaining structural stability under high temperatures and pressures, and resisting creep and deformation.

Good economics: Optimizing lifecycle costs by comprehensively considering initial investment, maintenance costs, and service life.

Reliable process performance: This includes weldability, formability, and consistent quality.

2. Characteristics and Applications of Seamless Stainless Steel Pipes
2.1 Core Characteristics
Seamless stainless steel pipes (common grades such as 304, 316L, and 2205) are renowned for their excellent corrosion resistance.3 Their key advantages are:

The Role of Alloying Elements: A chromium (Cr) content of typically ≥16% forms a dense passivation film, effectively blocking corrosion. The addition of molybdenum (Mo) (e.g., in 316L) significantly enhances resistance to chloride pitting corrosion.

High-Temperature Oxidation Resistance: Austenitic stainless steel maintains stable performance at relatively high temperatures (the specific temperature range varies by grade).

Hygiene and Aesthetics: The smooth surface resists scaling, making it suitable for industries requiring high cleanliness, such as food and pharmaceuticals.

2.2 Typical Applications in Chemical Equipment
Seamless stainless steel pipes are particularly suitable for the following chemical processes:

Transport of Highly Corrosive Media: Reactor Linings, Acid and Alkali Piping (e.g., Sulfuric Acid and Nitric Acid).3

High-Cleanliness Environments: Pharmaceutical Cleanroom Piping, Food-Grade Media Transport.3

Chloride-containing environments: 316L or duplex steel 2205 are used in seawater cooling systems, desalination equipment, or process fluids containing chloride ions.

3. Characteristics and Applications of Carbon Steel Seamless Pipes
3.1 Core Characteristics
Carbon steel seamless pipes (common grades 20#, 45#, and Q235) offer a low-cost, high-mechanical-strength option.16 Features include:

Good mechanical properties and weldability: High tensile strength and mature welding processes.6

Poor corrosion resistance: Susceptible to rust in humid or corrosive environments, typically requiring surface anti-corrosion treatment (such as galvanizing, plastic coating, or lining).36

Temperature resistance: Suitable for medium and low-temperature operating conditions (e.g., 20# steel for ambient temperature, low-pressure water and air transportation).3 Some grades, such as A106 Gr.B, can be used for high-temperature steam (≤450°C).3

3.2 Typical Applications in Chemical Equipment
Carbon steel seamless pipes are commonly used in the chemical industry for:

Structural support components: Platforms, frames, pipe galleries, etc.

Non-corrosive media transportation: Used for the transportation of non-corrosive or weakly corrosive media such as water, steam, air, and oil.

Composite pipe outer layer: Serving as the base of plastic-lined pipes, the outer steel pipe provides mechanical strength, while the inner plastic lining (such as PP, PE, PTFE) provides corrosion resistance. This offers both pressure bearing and corrosion protection, offering a high cost-effectiveness.

4. Core Comparison of Stainless Steel and Carbon Steel Seamless Pipes
The following table compares the differences between the two materials in chemical applications from multiple perspectives:

Characteristics Stainless Steel Seamless Pipe Carbon Steel Seamless Pipe Compatibility Analysis
Corrosion Resistance Excellent (especially 316L and duplex steel resist chloride ion corrosion) Poor, requiring surface corrosion treatment or lining Stainless Steel: Strong acid, strong alkali, and chloride environments.
Carbon Steel + Lining: Specific corrosive media, when cost is a priority. Mechanical Strength: Medium (typical 304: σ_b ≥ 515 MPa, σ_s ≥ 205 MPa) 3 Higher (typical 20#: moderate strength; 45#: tensile strength ≥ 590 MPa) Carbon Steel: General pressure-bearing structures and high-strength support components.
Stainless Steel: Generally strong enough to meet the requirements of most chemical pressure piping.
High-Temperature Performance: Excellent (austenitic stainless steel resists high-temperature oxidation) Limited (susceptible to oxidation and strength loss at prolonged high temperatures) Stainless Steel: High-temperature heat exchange tubes and furnace tubes (e.g., 15CrMoG resists 550-650°C).
Carbon Steel: Typically used in medium- and low-temperature applications.
Low-Temperature Toughness: Excellent (austenitic stainless steel exhibits good low-temperature resistance) Average, prone to brittle fracture at low temperatures. Stainless Steel: Cryogenic equipment and LNG pipelines.
Initial Cost: High (approximately 3-5 times or more that of carbon steel pipe) Low 6 Carbon Steel: Applications with limited budgets, non-corrosive environments, or for large-diameter pipelines. Stainless steel: Although the initial investment is high, lifecycle costs may be lower.
Maintenance Costs: Low (corrosion-resistant, requiring no frequent replacement or maintenance) High (requires regular anti-corrosion maintenance, and the plastic lining requires inspection) Stainless steel: Suitable for equipment with long operating cycles and infrequent maintenance.
Carbon steel: Suitable for applications where maintenance is easy and costs are manageable.
Processing and Welding: High requirements (needs to control heat input to prevent intergranular corrosion) Mature process, good weldability6 Carbon steel: Easier to process and manufacture.
Stainless steel: Requires specialized welders and processes.
Hygiene and Cleanliness: High (smooth surface, easy to clean, antibacterial) Low (prone to rust and contaminate media) Stainless steel: Suitable for food, pharmaceuticals, and high-purity chemicals.
5. Selection Considerations and Trends
Chemical pipeline selection requires a systematic evaluation based on the media composition, concentration, temperature, pressure, expected lifespan, and total budget.3 The following are some key considerations and trends:

Media Corrosivity: This is the primary factor. Carefully evaluate the corrosive components (such as Cl⁻, H₂S, and acidic substances) in the medium, their concentrations, and temperature.

For highly corrosive environments: Stainless steel (such as 316L, duplex steel 2205) or nickel-based alloys (such as Hastelloy) are preferred.

For specific corrosive media: Carbon steel-lined plastic-coated pipes (such as PTFE-lined and PP-lined) effectively resist a variety of strong acids and alkalis and are a cost-effective option.

Temperature and Pressure:

High temperature and high pressure: Alloy steel (such as 15CrMoG) or high-alloy stainless steel are more suitable.

Ambient temperature and pressure/medium and low pressure: Carbon steel offers a high cost-effectiveness. If the medium is corrosive, consider carbon steel-lined plastic-coated pipes.

Economical considerations: Don't just focus on initial cost. The life cycle cost (LCC) is more important, including installation, maintenance, replacement costs, and downtime losses. Data shows that the total cost of plastic-coated pipe over 10 years can be approximately 50% lower than that of alloy pipe.

New Standards and New Materials:

Standard Upgrades: For example, GB/T 9948-2025, "Seamless Steel Pipes for Petrochemical and Chemical Plants," integrates multiple standards and imposes higher requirements on material properties and testing (such as phased array ultrasound and HIC testing).

Composite Applications: Carbon steel + corrosion-resistant lining composite pipe technology is increasingly mature, offering an excellent balance between strength, corrosion resistance, and cost.

6. Conclusion
In the selection of chemical equipment piping, stainless steel seamless pipe and carbon steel seamless pipe (including those with plastic linings) are not simply substitutes, but rather complementary and coexisting.

Stainless steel seamless pipe, with its excellent all-round corrosion resistance, good high-temperature performance, and high cleanliness, is the preferred choice for harsh corrosive environments, high-risk operating conditions, and high product purity requirements, despite its higher initial cost.

Carbon steel seamless pipe (especially plastic-lined carbon steel pipe) boasts excellent mechanical strength, low initial cost, and the corrosion resistance of composite materials. It holds a clear advantage in budget-sensitive applications involving non-extremely corrosive media, specific acidic and alkaline environments, and is a powerful tool for achieving cost reduction and efficiency improvement.

The final decision should be based on specific process parameters, strict compliance standards (such as GB/T 9948-2025), and a thorough lifecycle cost analysis. Close collaboration with materials engineers and, if necessary, corrosion testing are recommended to ensure the safe, stable, and economical operation of the selected piping material throughout the chemical plant's lifecycle.