Development of Large Diameter Thick-Walled TP347H Stainless Steel Pipe via Centrifugal Casting and Pilger Rolling

Literature Overview

The paper by Yin Renjie, Wang E'na, Bian Huachuan, Li Xu, and Zhang Tao, published in Steel Pipe (Vol. 38, No. 6, 2009, pp. 34–37), documents the successful development of a large diameter thick-walled TP347H stainless steel pipe with dimensions of Φ355.6 mm × 42.8 mm at Pangang Group Chengdu Steel and Vanadium Co., Ltd. This research addresses a significant industrial challenge: the domestic production of large diameter thick-walled austenitic stainless steel pipes that meet ASME A312 standards, a product category that was previously dominated by imports. The process innovation lies in the combination of centrifugal casting for billet preparation and Pilger mill rolling for tube formation, a dual-process approach that leverages the strengths of both manufacturing routes.

Core Technical Content

TP347H is a heat-resistant austenitic stainless steel alloy designed for high-temperature applications in power generation, petrochemical, and process industries. The alloy contains stabilized additions of niobium (Nb) to prevent chromium carbide precipitation at elevated temperatures, ensuring long-term resistance to intergranular corrosion. The specification of Φ355.6 mm × 42.8 mm represents a substantial wall thickness ratio of approximately 12.1%, placing this product firmly in the thick-walled category where conventional seamless tube production methods face significant geometric and metallurgical challenges.

Process Route Analysis

The centrifugal casting process produces a hollow billet with inherent soundness advantages over solid ingots, as the centrifugal force during solidification promotes a dense microstructure free from central porosity. This is particularly important for thick-walled tubes where centerline defects in solid ingots would propagate into the final product. The Pilger rolling process, which involves forward-backward motion of the tube through a reducing plug and dies, provides the flexibility to achieve the required wall thickness reduction from the cast billet dimensions to the final Φ355.6 mm × 42.8 mm specification.

Metallurgical Quality

The paper reports that the final product meets all technical requirements of ASME A312, including chemical composition, mechanical properties (tensile strength, yield strength, elongation), and dimensional tolerances. Critically, the authors emphasize that both longitudinal and transverse mechanical properties are uniform, which is a common weakness in centrifugal casting products where the axial direction may exhibit different properties from the circumferential direction due to the casting flow pattern. This uniformity is essential for applications where the pipe may experience multiaxial stress states, such as in high-temperature boiler tubes or heat exchanger components.

Engineering Practice Implications

For engineers specifying large diameter thick-walled stainless steel pipes, this research demonstrates that domestically produced alternatives to imported products are viable. The centrifugal casting plus Pilger rolling route offers a cost-effective solution that maintains metallurgical quality. However, specification engineers should ensure that the supplier provides comprehensive documentation of the centrifugal casting parameters, including pouring temperature, rotation speed, and cooling rate, as these factors directly influence the grain structure and inclusion characteristics of the final product.

The TP347H alloy is particularly relevant for applications in supercritical and ultra-supercritical power plants, where operating temperatures exceed 600°C and the risk of intergranular carbide precipitation is a primary concern. Engineers in the power industry should note that the heat treatment specification, particularly the solution annealing temperature and cooling method, is critical to achieving the required high-temperature creep strength and intergranular corrosion resistance.

Key Questions and Reflections

The paper does not provide detailed information on the microstructural characterization of the final product, such as grain size distribution, δ-ferrite content, or inclusion morphology. For high-temperature applications, these metallurgical features are critical to long-term performance. Additionally, the absence of long-term creep testing data is a limitation for engineers who need to assess service life under sustained high-temperature loading. The 2009 publication date also means that subsequent improvements in centrifugal casting technology and Pilger mill capabilities may have further enhanced the process.

This research represents a meaningful step toward the localization of large diameter thick-walled stainless steel pipe production in China. The dual-process approach of centrifugal casting and Pilger rolling is technically sound and provides a replicable manufacturing pathway. Engineers should consider this process route as a credible option for specifying TP347H pipes in large diameter thick-walled applications, subject to appropriate quality assurance protocols.