What are the main manufacturing processes used for producing high-pressure resistant stainless steel

The manufacturing process of high-pressure resistant stainless steel pipes needs to take into account the material strength, dimensional accuracy and corrosion resistance. The key lies in ensuring the stability of the pipe material under high-pressure conditions through processing and treatment. Here is a detailed introduction to the main manufacturing process: 

I. Raw Material Preparation and Pre-treatment

Material Selection and Smelting: Select specific grades of stainless steel (such as 316, 321, 347, etc.) based on pressure resistance requirements. Smelt using an electric arc furnace or vacuum induction furnace, controlling the content of alloy elements such as carbon, chromium, nickel, and molybdenum (for high-pressure scenarios, the carbon content needs to be reduced to minimize the risk of intergranular corrosion), ensuring the purity of the steel billet.

Steel Billet Rolling: Heat the smelted steel billet to 1100-1250℃, and roll it into round tube billets (rough tubes) using a primary rolling machine to lay the foundation for subsequent shaping. 

II. Forming Process

Hot Rolling Tubes:

Heat the round tube billet to the austenitization temperature (approximately 1050 - 1150℃), pass the solid billet through a piercing machine to form a hollow tube, and then roll it through a rolling machine (such as a continuous rolling machine or a cyclic tube rolling machine) to the desired wall thickness and diameter. This process can enhance the density and mechanical properties of the tube material, and is suitable for large-diameter, thick-walled high-pressure tubes.

Cold Rolling / Cold Drawing Tube Making:

Perform cold processing on the hot-rolled tubes:

Cold Rolling: Roll the tubes at room temperature using a cold rolling machine, precisely controlling the dimensional accuracy (tolerance can reach ±0.05mm), improving the surface finish (Ra ≤ 0.8μm), and simultaneously increasing the strength through work hardening (tensile strength can be increased by 10% - 30%).

Cold Drawing: Use molds to forcibly draw the tubes through a specific diameter, further refining the grain structure, suitable for small-diameter, thin-walled high-pressure tubes (such as precision tubes with an outer diameter of ≤ 50mm).

Welded Tube Making (for specific scenarios):

Roll and weld stainless steel sheets (such as TIG welding, laser welding), forming the tube material, and then through expansion, straightening, etc. processing. Suitable for large-diameter high-pressure tubes, but requires extremely high welding quality (avoiding pores, cracks, and ensuring the weld strength is consistent with the base material). 

III. Performance Optimization Process

Heat Treatment:

Solution Treatment: Heat the pipe to 1050-1150℃ (depending on the material), hold for a period of time, then quickly cool with water to ensure that alloy elements (such as chromium, nickel, and molybdenum) are uniformly dissolved in the matrix, eliminating processing stress and restoring corrosion resistance and toughness.

Tempering Treatment: For some martensitic or precipitation hardening stainless steels (such as 17-4PH), heat for 480-620℃ to promote the formation of strengthening phases (such as Cu-rich phases), significantly increasing strength (tensile strength can reach above 1100 MPa), meeting the requirements of ultra-high pressure.

Surface Treatment:

Acid Washing and Passivation: Use a nitric acid - hydrofluoric acid mixture to remove surface oxide scale, forming a passivation film (Cr₂O₃), enhancing corrosion resistance (salt spray test can last for over 1000 hours without rusting).

Polishing: Reduce surface roughness (Ra ≤ 0.02 μm) through mechanical or chemical polishing, reducing medium retention and corrosion risks, suitable for clean high-pressure fields such as food and medicine. 

IV. Quality Inspection Process

Non-destructive Testing: This includes ultrasonic testing (for detecting internal defects), eddy current testing (for detecting surface defects), water pressure test (maintaining pressure at 1.5 times the design pressure for 30 minutes without leakage), and flattening test (to verify plasticity and welding quality). These tests ensure that the pipe materials have no cracks, voids, etc. as potential hazards.

Mechanical Performance Testing: Sampling tests are conducted to measure tensile strength, yield strength, elongation rate, etc., to ensure compliance with ASTM, GB, etc. standards (for example, the yield strength of 316L high-pressure pipe needs to be ≥ 205 MPa, and the tensile strength needs to be ≥ 520 MPa).

The combination application of these processes enables high-pressure stainless steel pipes to meet the pressure requirements (from tens of MPa to hundreds of MPa), temperature requirements (-270°C to 650°C), and corrosion environment requirements in various scenarios, which is the core guarantee for its reliable application in the high-pressure industrial field.