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The advantages of high-strength duplex steel flanges (e.g. Super Duplex S32750, S32760, etc.) over carbon steel, ordinary stainless steel (e.g. 304/316), low alloy high-strength steel and other materials such as flanges are mainly embodied in the core dimensions of mechanical properties, corrosion resistance, structural efficiency and full-cycle costs as follows:
I. Mechanical Properties: The Dual Advantages of High Strength and High Toughness
Yield Strength is Significantly Higher than that of Similar materials
The yield strength of high-strength duplex steel (≥450MPa) is more than twice that of 304 stainless steel (205MPa), and is close to 1.3 times that of low-alloy high-strength steels (such as Q345). This allows it to withstand higher working pressures in high-pressure piping systems (e.g., more than 10MPa), or thinner flange structures under the same pressure, reducing the amount of material. For example, in DN100, PN16 flange design, the thickness of high-strength duplex steel flanges can be reduced by 30% compared with 304 stainless steel, and the weight can be reduced by 40%, which directly reduces the cost of materials and transportation and installation costs.
Better fatigue and impact resistance
Duplex steel's ferritic - austenitic two-phase organization gives it both high strength and high toughness (impact work ≥50J), and it is not easy to crack in vibration, alternating loads (such as compressor pipelines) or low temperature environments (below -40℃). In contrast, carbon steel flanges are prone to brittle fracture at low temperatures, and ordinary stainless steel flanges may leak due to fatigue cracks under high stress.
Second, corrosion resistance: the core advantage to deal with extreme corrosive environments
Anti-Chloride Stress Corrosion (SCC) ability to crush ordinary materials
In the environment containing chloride ions (such as seawater, salt spray, chemical halides), 304/316 stainless steel is susceptible to stress corrosion cracking, and high-strength dual-phase steel due to the alloying ratios of high chromium (25% +), high molybdenum (3% ~ 5%) and nitrogen elements, SCC resistance performance to enhance 10 times more. For example, if 316L stainless steel is used for the flanges of offshore platforms, they usually need to be replaced in 2~3 years, while the flanges of high-strength duplex steel can be in service for more than 15 years, which saves the downtime loss and labor cost of frequent replacement.
Outstanding resistance to pitting and intergranular corrosion
Its pitting corrosion equivalent (PREN) ≥ 40 (ordinary 316L is about 28), in acidic media (such as sulfuric acid, hydrochloric acid) or sulfide-containing oil and gas environment, pitting corrosion resistance is significantly better than carbon steel and low-grade stainless steel. For example: in the petroleum refining of sulfur-containing pipelines, carbon steel flanges need additional spray corrosion protection layer (cost increase of 10% to 20%), while high-strength dual-phase steel can be used directly, and does not require regular maintenance of the coating.
Structure and Cost: Lightweight Design and Full Cycle Cost Optimization
Flange Thickness Reduction to Achieve Lightweight and Installation Efficiency Improvement
Due to the high-strength characteristics, flanges can adopt thinner sealing surface and neck design, which not only reduces the amount of material used, but also reduces the requirements of flanges on bolt preload, and the matching bolt specifications can be reduced (e.g., from M20 to M16), which further saves the cost of accessories. For example, a set of DN500 high-strength duplex steel flanges is about 50% lighter than carbon steel flanges of the same specification, which reduces the investment in lifting equipment and labor costs by 30% during installation.
Significant Advantages in Life Cycle Cost (LCC)
Although the procurement cost of high-strength duplex steel flanges is 50%~80% higher than that of 316L stainless steel, the LCC is even lower due to its long service life (3~5 times longer repair cycle), low maintenance (no need for anticorrosion coatings), and high reliability (leakage risk reduced by 90%). Calculated on a 10-year cycle, the total cost of ownership (TCO) of high-strength duplex steel flanges in offshore engineering is more than 40% lower than that of 316L stainless steel.
IV. Special Scenario Adaptability: Irreplaceable under Extreme Working Conditions
Reliability in High Pressure, High Temperature and Low Temperature Environments
In deep-sea oil and gas exploitation (water depth over 1000 meters, pressure over 10MPa), high-strength duplex steel flanges can directly withstand the pressure of seawater and chloride corrosion, whereas carbon steel flanges need to be matched with heavy pressure-resistant shells, and the overall cost is more than 3 times.
In - 196 ℃ liquefied natural gas (LNG) pipeline, its low-temperature impact toughness (-196 ℃ impact work ≥ 40J) than most of the low alloy steel, to avoid the risk of low-temperature brittle fracture.
Resistance to hydrogen embrittlement and sulphide corrosion
In oil and gas fields containing hydrogen or hydrogen sulphide (e.g. high sulphur gas wells), high-strength duplex steels are structurally stable and not susceptible to hydrogen-induced cracking (HIC) or sulphide stress corrosion (SSC), whereas ordinary carbon steels require complex hydrogen-resistant treatments (e.g. NACE certified) at an increased cost, and still have limited performance.