The new SH/T standard explicitly requires that the flange stud threads be processed by “rolling”

Thread Content

SH/T3231-2024 \"Pipe Flanges and Manway Flanges for High-Pressure Hydrogen-Handling Equipment in Petrochemical Industries\" (draft for approval) is a new SH industry standard compiled by Sinopec Guangzhou Engineering. It is primarily used for carbon steel and low-alloy steel pipe flanges and manway flanges with pressures ranging from PN110 to PN420 in high-pressure hydrogen-handling equipment in petrochemical plants. Obviously, the requirement that \"the threads of the studs shall be manufactured by rolling\" is intended for high-pressure flange studs. Then why is this requirement specified for high-pressure pipe flanges? The following content is excerpted from a literature source: Fang Wei. Manufacturing technology of thread rolling dies for rolled piston rod threads. Compressor Technology, 2000(6). Compared to the traditional turning method for creating threads, the thread rolling method has several advantages: 1. The thread rolling process is a plastic deformation technique; it causes plastic displacement of the metal volume without damaging its fiber structure, thereby enabling chip-free metal forming. This not only improves the mechanical properties of the threads but also helps conserve metal materials. 2. After plastic deformation, the strength and hardness of metals increase, while their plasticity decreases. When rolling threads, the metal fibers in the threaded portion are not cut; they only deform along the thread profile. The rolled metal material is relatively dense, with a cold-worked hardened layer and a residual stress layer formed on its surface. As a result, the wear resistance of the parts after rolling is significantly improved, and the fatigue strength of the threads is also greatly enhanced. 3. During the rolling process, the material of the part and the tool undergo continuous relative sliding, which enables the threaded surface to achieve or exceed the roughness level obtained through grinding; a higher surface quality enhances the cyclic strength of the thread. 4. When metal materials undergo plastic deformation, sliding occurs within each grain of the metal; the grains near the slip planes become distorted, and these grains are also broken into many fragments. This disordering phenomenon makes further sliding difficult. For the slip to continue, an external force must be applied in order for a new slip system to emerge. This cycle repeats itself, and in terms of the mechanical properties of metals, it means that as the degree of deformation increases, their strength also increases. Therefore, compared to threads turned, the rolled threads exhibit a certain degree of improvement in both tensile strength and shear strength. 5. Rolling threads offer good economic benefits, especially for bulk or long-run production. In summary, rolling processing of the stud threads can meet the requirements for high strength and high fatigue resistance.