I. Core Application Scenarios
Q1: What environments are Grade 3 steel pipes suitable for?
A: Designed for ultra-low temperature conditions of -100℃, it is mainly used in key facilities such as liquefied natural gas (LNG) equipment, cryogenic storage tank pipelines and cryogenic heat exchangers to ensure resistance to brittle fracture under extremely cold conditions.
II. Chemical composition characteristics
Q2: What are the special requirements for its composition?
A: High nickel content is the core feature:
Carbon ≤0.19%, Silicon 0.18%-0.37%, Manganese 0.31%-0.64%
Nickel 3.18%-3.82% (core strengthening element)
Phosphorus and sulfur are both ≤0.025% (strictly control impurities)
III. Mechanical performance standards
Q3: What are the key mechanical indicators?
A: Must meet:
Tensile strength ≥ 450MPa, Yield strength ≥ 240MPa
Elongation: longitudinal ≥ 30%, transverse ≥ 20%
-100℃ impact test mandatory standard (Charpy V-notch)
IV. Manufacturing process control
Q4: What are the special requirements for the production process?
A: The core process includes:
Metallurgy: deep deoxidation and slag removal in electric furnace/converter to ensure the purity of molten steel
Forming: seamless hot rolling or welding process (certification required)
Heat treatment: normalizing above 815℃ (or normalizing + tempering) to optimize low-temperature toughness
V. Quality verification items
Q5: What key items are included in the factory inspection?
A: Three core tests are mandatory:
-100℃ impact test (verify low temperature toughness)
Hydrostatic pressure test (pressure holding time ≥5 seconds)
Non-destructive testing (ultrasonic/eddy current testing, detection of ≥5% wall thickness defects)
