Stainless steels are essential in modern industries, from chemical plants and shipbuilding to oil and gas systems. Among the many available grades, SS 316 and SS 329 are two commonly used materials that often cause confusion among buyers and engineers. Both are known for their excellent corrosion resistance, yet they differ significantly in microstructure, mechanical properties, and performance.
This article, prepared by SAKYSTEEL, a global stainless steel supplier, explains in detail the difference between SS 329 and SS316, covering their chemical composition, corrosion resistance, strength, and suitable applications. Understanding these distinctions helps engineers and purchasing professionals make the right material choice for specific working environments.
SS316, also known as AISI 316 or UNS S31600, is an austenitic stainless steel. It is part of the 300-series family and is widely used due to its excellent corrosion resistance, good formability, and ease of welding.
The defining element of SS316 is molybdenum (2–3%), which improves resistance to pitting and crevice corrosion, especially in chloride-containing environments such as seawater. SS316 is often called “marine-grade stainless steel,” though its resistance to saltwater is moderate compared to duplex grades.
It is non-magnetic in the annealed condition and retains toughness even at cryogenic temperatures, making it a versatile and reliable material for chemical, food, and marine industries.
SS329, or UNS S32900, is a duplex stainless steel, meaning it contains a balanced mixture of austenite (γ) and ferrite (α) phases. This dual-phase structure gives SS329 a unique combination of high strength and excellent corrosion resistance, especially against chloride stress corrosion cracking (SCC).
With higher chromium (≈25%) and lower nickel (≈4%) compared with SS316, SS329 can perform in environments where standard austenitic stainless steels like 316L might fail.
It is commonly used in offshore platforms, desalination plants, heat exchangers, and high-pressure pipelines, where both mechanical strength and corrosion performance are critical.
The chemical balance defines how each steel performs. Below is a simplified breakdown (without a table, as requested):
SS316 Composition: 16–18% Chromium, 10–14% Nickel, 2–3% Molybdenum, with small amounts of Manganese, Silicon, and Carbon (<0.08%).
SS329 Composition: 23–28% Chromium, 2.5–5% Nickel, up to 1.5% Molybdenum, and a trace of Nitrogen to stabilize duplex structure.
SS329 contains much higher chromium and less nickel, giving it stronger corrosion protection and higher yield strength.
SS316, with its higher nickel and molybdenum, is more ductile and formable, suitable for intricate shapes and polished finishes.
The major difference between SS329 and SS316 lies in their microstructure:
SS316 is fully austenitic, meaning its crystal structure is face-centered cubic (FCC). This gives it excellent toughness, non-magnetic properties, and good weldability.
SS329 is duplex, composed of roughly 50% ferrite and 50% austenite. The ferritic structure (body-centered cubic) adds strength and chloride cracking resistance, while the austenitic part preserves ductility.
Because of this, SS329 is almost twice as strong as SS316 but less easy to form and machine.
The mechanical differences are significant:
Yield Strength: SS316 ≈ 205 MPa, SS329 ≈ 450 MPa
Tensile Strength: SS316 ≈ 515 MPa, SS329 ≈ 620 MPa
Elongation: SS316 ≈ 40%, SS329 ≈ 25%
This means SS329 provides higher load-bearing capacity and fatigue resistance, making it ideal for pressure vessels and offshore components. SS316, on the other hand, offers greater flexibility, better surface finish, and easier cold working for decorative or low-stress applications.
Both grades are corrosion-resistant, but in different environments:
SS316 can crack under prolonged chloride exposure at high temperatures.
SS329 resists chloride stress corrosion cracking, making it suitable for seawater and brine applications.
SS316’s molybdenum improves resistance to pitting, but only up to moderate chloride levels (≈300 ppm).
SS329 performs better even in higher chloride concentrations due to its higher chromium and duplex phase.
SS316 is good for acids like acetic, phosphoric, and sulfuric (dilute).
SS329 handles oxidizing acids and alkalis better, especially in mixed chloride-acid conditions.
Both are resistant when properly heat-treated. However, SS329 must be carefully processed to prevent sigma phase formation that can reduce toughness.
In short:
For marine or chemical applications, SS316 works well in moderate chloride levels, while SS329 is the superior choice for offshore or desalination environments.
Welding SS316 is straightforward with all conventional processes (TIG, MIG, SMAW), and post-weld heat treatment is rarely required.
SS329, being duplex, requires more precise heat control during welding to maintain its phase balance. Excessive heat input can lead to brittle phases that lower corrosion resistance. Using matching filler metals and proper shielding gases is critical.
When it comes to forming and machining:
SS316 is easier to bend, roll, and polish.
SS329’s high strength makes it more difficult to form but suitable for robust structures.
SS316 retains its strength and corrosion resistance up to about 870°C (1600°F) in continuous service.
SS329, while strong at room temperature, may form brittle phases if exposed to prolonged high temperatures (above 300°C). However, it performs excellently in moderate-temperature environments under mechanical stress and chloride exposure.
Therefore, SS316 is preferred for high-temperature service, while SS329 is ideal for high-stress, medium-temperature, corrosive environments.
Generally, SS329 is more expensive than SS316 due to its complex production process and controlled heat treatment requirements. However, it offers longer service life and lower maintenance costs in aggressive environments, making it cost-effective over time.
SS316 is widely available and produced globally, making it a standard and economical choice for general-purpose use.
If your project involves seawater pipelines, chemical tanks, or oil rigs, investing in SS329 will save future maintenance costs. For kitchen equipment, architectural panels, or mild marine use, SS316 remains a practical and affordable option.
SS316 is found in almost every industry thanks to its balance of corrosion resistance, workability, and aesthetics. Common applications include:
Marine fittings and fasteners
Food and beverage equipment
Chemical and pharmaceutical process lines
Heat exchangers and evaporators
Architectural facades and railings
Medical instruments and surgical tools
Its bright finish and formability make it especially popular in industries demanding both function and appearance.
Due to its strength and corrosion resistance in aggressive conditions, SS329 is preferred in:
Offshore oil and gas pipelines
Desalination plants and seawater systems
Pulp and paper digesters
Chemical process tanks
Heat exchangers exposed to chloride solutions
Structural components in marine platforms
Its duplex structure ensures high mechanical strength even under dynamic loads and pressure fluctuations.
SS316:
Type: Austenitic
Strength: Moderate
Corrosion Resistance: Excellent (medium chlorides)
Formability: Very good
Welding: Easy
Typical Use: Food, chemical, architectural, mild marine
SS329:
Type: Duplex
Strength: Very high
Corrosion Resistance: Superior (high chlorides, seawater)
Formability: Moderate
Welding: Requires control
Typical Use: Oil & gas, offshore, desalination, industrial
In summary, the key difference between SS316 and SS329 is the balance between strength and corrosion resistance. SS329 offers greater mechanical and chloride resistance, while SS316 provides better formability and thermal stability.
Selecting the right stainless steel depends on operating conditions:
If strength and chloride resistance are priorities, choose SS329.
If fabrication ease and surface finish matter more, choose SS316.
For chemical plants, desalination systems, or seawater exposure, SS329 is superior.
For kitchenware, architectural parts, or low-chloride chemical processes, SS316 is sufficient.
Working with a knowledgeable supplier helps ensure proper material selection, correct welding procedures, and consistent quality.
As an experienced stainless steel manufacturer and exporter, SAKYSTEEL provides both SS316 and SS329 in forms such as round bars, plates, sheets, and tubes.
We offer:
Certified materials (EN 10204 3.1 / 3.2)
NACE MR0175 and ISO 15156 compliance for oil and gas service
Precise machining and customized lengths
Fast global delivery and technical support
Our products are widely used in marine, petrochemical, and construction industries across Europe, the Middle East, and Southeast Asia.
For every project, SAKYSTEEL ensures strict quality inspection, reliable traceability, and professional export packaging.
The difference between SS 329 and SS316 extends far beyond chemistry — it defines their performance, durability, and field of use. SS316 remains the industry’s workhorse for corrosion-resistant, easily fabricated components, while SS329 represents the next level of strength and reliability in harsh environments.
Understanding these differences allows engineers and buyers to select the right alloy for the right job — reducing maintenance, increasing longevity, and ensuring safety under challenging conditions.
When sourcing stainless steel materials, choose suppliers with proven expertise and certified quality assurance. Partner with SAKYSTEEL for consistent, high-performance stainless steels that meet global standards and exceed your expectations.