304/304L Stainless Steel

 304 Stainless is a low carbon (0.08% max) version of basic 18-8 also known as 302. Type 302 has 18% chromium and 8% nickel.

ASTM A213 TP304 Stainless Steel Seamless Tube is manufactured by seamless process used in high pressure environment, stainless steel TP304 grade is the most used material due to its high strength and excellent corrosion resistance.

Type 304 has slightly lower strength than 302 due to its lower carbon content. Type 304 finds extensive use in welding applications because the low carbon permits some exposure in the carbide precipitation range of 800°F - 1500°F without the need for post-annealing operations.

However, the severity of corrosive environments may necessitate annealing after welding or the use of 304L.

Type 304L has a carbon content of 0.03% or less. This alloy can be used in the as-welded condition without becoming susceptible to intergranular corrosion.

Specifications - Stainless Steel 304/304L

• ASTM:A312, A376,A358, A269,A249, A403, A182, A351
• ASME: SA312, SA376
• Pressure SA358,SA269, SA249,SA403, SA182, SA351

The main constituents of 304 stainless steel - other than iron - are Chromium and Nickel.

304 contains 18 - 20% Chromium (Cr). Chromium is the essential chemical in all stainless steel and it is that which forms the thin passive layer that makes the metal "stainless"

304 also contains 8-10.5% Nickel (Ni). This is added to make the Austenitic structure more stable at normal temperatures. 

The nickel also improves high-temperature oxidation resistance makes the steel resistant to stress corrosion cracking.

Where the steel is to be stretched formed a lower percentage (8%) of nickel should be selected. If the steel is to be deep drawn a higher percentage is better (9% or more).

In addition a number of other chemicals may be present but these are expressed as maximum permited levels with the exception of the increased quantity of carbon required in 304H - i.e. a minimum of .04% and a maximum of 0.10%

*Maximum carbon content of 0.04% acceptable for drawn tubes

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What’s the Difference Between Grade 304 ,304L & 304H Stainless Steel?

There are hundreds of different grades of stainless steel on the market. Each of these unique formulations of stainless steel offer some degree of corrosion resistance above and beyond that of plain steel.

The existence of these stainless steel variants can cause some confusion—especially when the names & formulations of two stainless steel alloys are almost the same. This is the case with grade 304 and 304L stainless steel.

Chemical Composition - Stainless Steel 304/304L

Element	Percentage by Weight Maximum Unless Range is Specified
	304	304L	304H
Carbon	0.08	0.030	0.04-0.10
Manganese	2.00	2.00	2.00
Phosphorus	0.045	0.045	0.045
Sulfur	0.030	0.030	0.030
Silicon	0.75	0.75	0.75
Chromium	18.00 20.00	18.00 20.00	18.00 20.00
Nickel	8.0 10.50	8.0 12.00	8.0 10.5
Nitrogen	0.10	0.10	0.10

These three alloys are remarkably similar—but there is one key difference. In grade 304 stainless, the maximum carbon content is set at 0.08%, whereas grade 304L stainless steel has a maximum carbon content of 0.03%. The “L” in 304L can be interpreted as meaning extra-low carbon.

This difference of 0.05% carbon content produces a slight, but marked, difference in the performances of the two alloys.

The Mechanical Difference

Grade 304L has a slight, but noticeable, reduction in key mechanical performance characteristics compared to the “standard” grade 304 stainless steel alloy.

Typical Mechanical Properties-Stainless Steel 304/304L

Grade	Tensile Strength Rm N/mm²	Yield Strength Rp 0.2, N/mm²	Elongation (%)
304 Annealed	500-700	195	40
304L Annealed	460-680	180	40

Physical Properties

Data	Metric	English
Density	8 g/cc	0.289 lb/in³

 Mechanical Properties

Hardness, Brinell	123	123	Converted from Rockwell B hardness.
Hardness, Knoop	138	138	Converted from Rockwell B hardness.
Hardness, Rockwell B	70	70
Hardness, Vickers	129	129	Converted from Rockwell B hardness.
Tensile Strength, Ultimate	505 MPa	73200 psi
Tensile Strength, Yield	215 MPa	31200 psi	at 0.2% offset
Elongation at Break	70 %	70 %	in 50 mm
Modulus of Elasticity	193 - 200 GPa	28000 - 29000 ksi
Poisson's Ratio	0.29	0.29
Charpy Impact	325 J	240 ft-lb
Shear Modulus	86 GPa	12500 ksi

Electrical Properties

Electrical Resistivity	7.2e-005 ohm-cm	7.2e-005 ohm-cm	at 20°C (68°F); 1.16E-04 at 650°C (1200°F)
Magnetic Permeability	1.008	1.008	at RT

Thermal Properties

Design Features - Stainless Steel 304/304L

• Oxidation resistance up to 1650°F for continuous service and up to 1500°F where cyclic heating is involved.
• General purpose corrosion resistance.
• Non-hardenable except by cold working.
• Non-magnetic except when cold worked.
• May be susceptible to chloride stress corrosion cracking.
• Used where field working is employed.

Typical Applications - Stainless Steel 304/304L

• Sanitary
• Dairy and food processing
• Heat exchangers, evaporators
• Feedwater heaters

Tensile Requirements - Stainless Steel 304/304L

• Tensile Strength (KSI): 70
• Yield Strength (KSI): 25

Each alloy represents an excellent combination of corrosion resistance and fabricability. This combination of properties is the reason for the extensive use of these alloys which represent nearly one half of the total U.S. stainless steel production. The 18-8 stainless steels, principally Alloys 304, 304L, and 304H, are available in a wide range of product forms including sheet, strip, and plate. The alloys are covered by a variety of specifications and codes relating to, or regulating, construction or use of equipment manufactured from these alloys for specific conditions. Food and beverage, sanitary, cryogenic, and pressure-containing applications are examples.

Alloy 304 is the standard alloy since AOD technology has made lower carbon levels more easily attainable and economical. Alloy 304L is used for welded products which might be exposed to conditions which could cause intergranular corrosion in service.

Alloy 304H is a modification of Alloy 304 in which the carbon content is controlled to a range of 0.04-0.10 to provide improved high temperature strength to parts exposed to temperatures above 800°F.

For example, the ultimate tensile strength (UTS) of 304L is roughly 85 ksi (~586 MPa), less than the UTS of standard grade 304 stainless, which is 90 ksi (~620 MPa). The difference in yield strength is slightly greater, with 304 SS having a 0.2% yield strength of 42 ksi (~289 MPa) and 304L having a 0.2% yield strength of 35 ksi (~241 MPa).

This means that if you had two steel wire baskets and both baskets had the exact same design, wire thickness, and construction, the basket made from 304L would be structurally weaker than the standard 304 basket.

Why Would You Want to Use 304L, Then?

So, if 304L is weaker than standard 304 stainless steel, why would anyone want to use it?

The answer is that the 304L alloy’s lower carbon content helps minimize/eliminate carbide precipitation during the welding process. This allows 304L stainless steel to be used in the “as-welded” state, even in severe corrosive environments.

If you were to use standard 304 stainless in the same way, it would degrade much faster at the weld joints.

Basically, using 304L eliminates the need to anneal weld joints prior to using the completed metal form—saving time and effort.

In practice, both 304 and 304L can be used for many of the same applications. The differences are often minor enough that one isn’t considered massively more useful over the other. When stronger corrosion resistance is needed, other alloys, such as grade 316 stainless steel, are usually considered as an alternative.

ASTM A213 / ASME SA213

ASTM A213 / ASME SA213 is a America specification for stainless steel boiler, super heater, heat exchanger tubes, executed by most world stainless steel seamless tubes mills and factories, minimum wall thickness required in A213 seamless tube, or average wall thickness as customers requirement, tight tolerance of outside and wall thickness stated as A213 standard or A1016

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