As a core pressure-bearing component material in power plant boilers, the performance of P92 high-pressure boiler steel tubes directly affects the safe operation and energy efficiency of ultra-supercritical units. This new type of martensitic heat-resistant steel has achieved breakthroughs in high-temperature strength, creep resistance, and weldability through composition optimization and process innovation, and has now become a key material choice for units with steam parameters above 600℃ worldwide.
First, the material characteristics and technological innovations of P92 high-pressure boiler steel tubes.
P92 steel is an improved steel grade based on P91 with the addition of 1.7% tungsten and a reduction in molybdenum content. Its chemical composition system (Cr: 8.5-9.5%, W: 1.5-2.0%, Mo: 0.3-0.6%) achieves a creep strength increase of over 30% compared to traditional steel grades through the synergistic effect of solid solution strengthening and precipitation strengthening. In terms of microstructure, this material, through controlled rolling and cooling processes, forms a lath martensitic matrix. Combined with the dispersed distribution of MX-type carbonitrides and Laves phases, it maintains a creep strength of ≥100 MPa for 100,000 hours even at 650℃. Particularly noteworthy is the excellent match between its coefficient of thermal expansion (12.5 × 10⁻⁶/℃) and thermal conductivity (26 W/m·K), effectively mitigating thermal stress issues during unit start-up and shutdown.
Second, key breakthroughs in the production process of P92 high-pressure boiler steel tubes.
1. Employing EF+LF+VD triple smelting technology to control gas content to [H]≤1.5ppm and [O]≤20ppm.
2. Achieving precision forming with a wall thickness tolerance of ±5% using a radial forging mill in conjunction with a three-roll continuous rolling mill.
3. Utilizing a dual heat treatment process of normalizing (1080℃±10℃) + tempering (760℃±15℃).
4. Automatic ultrasonic flaw detection and eddy current testing to ensure a defect detection rate ≥99.5%.
According to data from the Jiangxi Testing Center, the fracture life of domestically produced P92 tubes under 620℃/29.4MPa conditions reaches 187,000 hours, exceeding the ASME standard requirement by 40%. Six years of operation tracking at a demonstration power plant showed that its annual creep rate was only 0.12%/kh, far below the design allowable value.
Third, a typical engineering application case of P92 high-pressure boiler steel pipes.
In the construction of a 1000MW ultra-supercritical unit in Guangdong, P92 steel pipes showed significant advantages when used in the main steam pipeline (design parameters 31MPa/605℃):
- Wall thickness reduced to 52mm (18% weight reduction compared to the P91 solution)
- Post-weld heat treatment window widened to 740-780℃
- On-site installation, welding first-pass yield increased to 98.6%
Operational monitoring data shows that the unit’s thermal efficiency reached 45.8%, an increase of 7.3 percentage points compared to subcritical units, reducing CO₂ emissions by approximately 120,000 tons annually.
Fourth, a breakthrough in welding technology for P92 high-pressure boiler steel pipes.
Addressing the welding difficulties of P92 steel, domestically developed special welding materials (such as CHH727 welding electrodes) were matched with a multi-layer, multi-pass welding process, increasing the joint toughness to 72J (-20℃). A key project adopted the following methods:
1. Preheating temperature 150-200℃
2. Interpass temperature control ≤300℃
3. Post-weld hydrogen removal treatment at 250℃ for 2 hours
4. Post-weld heat treatment at 760℃ for 4 hours. This resulted in a weld joint strength coefficient of 0.92 and heat-affected zone hardness controlled below 250 HV10. Furthermore, the laser-arc hybrid welding technology developed by Nanjing University of Technology further improved welding efficiency by 40% and reduced deformation by 60%.
Fifth, the construction of a quality control system for P92 high-pressure boiler steel pipes.
The industry has established a full-cycle quality monitoring network from raw materials to service:
- Raw materials: Implementing precise control of Nb/Ti microalloying (±0.01%)
- Manufacturing: Using infrared thermal imagers to monitor the heat treatment temperature field in real time
- Inspection: Introducing phased array ultrasonic testing to identify 0.5mm equivalent defects
- Big data platform: Integrating 32,000 sets of operating data from 56 power plants nationwide.
Sixth, cost-benefit analysis of P92 high-pressure boiler steel pipes.
Although the initial cost of P92 material is 20-30% higher than traditional steel grades, its life-cycle cost advantage is significant:
1. Increased design pressure allows for reduced wall thickness, reducing material usage by 15-20%.
2. Maintenance cycle extended to 8 years (compared to 5 years for conventional materials).
3. Reduced replacement frequency reduces downtime losses by approximately 12 million yuan per instance. Economic calculations from a power plant show that units using P92 pipes saw an increase in comprehensive revenue of 230 million yuan over a 10-year operating period.
VII. Future Development Trends of P92 High-Pressure Boiler Steel Tubes
With the advancement of 700℃ ultra-supercritical technology research and development, the improvement directions of P92 steel are concentrated on:
1. Adding 0.003% B to improve grain boundary strength
2. Developing nanoscale Y₂O₃ dispersion strengthening technology
3. Exploring the application of additive manufacturing in irregularly shaped pipe fittings
Preliminary research data from the Shanghai Materials Research Institute shows that the stress fracture time of modified P92 at 650℃ can reach 2.3 times that of traditional materials.
Currently, my country’s annual production capacity of P92 high-pressure boiler steel tubes has exceeded 80,000 tons, and the products are exported to more than 20 countries in Southeast Asia, the Middle East, and other regions. Driven by the “dual carbon” goal, this high-performance material will continue to provide key support for the upgrading of clean coal power technology, and its technological evolution path has also accumulated valuable experience for the application of next-generation nickel-based alloys. Industry experts predict that by 2030, the global market demand for P92 materials will maintain an average annual growth rate of 6.5%, and Chinese manufacturing, with its complete industrial chain advantages, is expected to occupy more than 40% of the market share.
Post time: Nov-11-2025