Dual certification refers to two different materials or standards certified together to meet both of them, the most common example is 304 and 304L stainless steel grades, which occupy the largest proportion for use in stainless steel because they have excellent properties to meet the most case.
304 304L Dual Certified
for stainless steel plate, 304 / 304L dual certified stainless steel conforms to ASTM A240, as a stainless steel tube % pipe manufacturer, we checked it in this aspect it is almost the same in chemical composition and properties, dual certification is always required in two very similar alloys, not for big difference grade, like 304 and 321 stainless steel.
Firstly, let us see 304 and 304L conforming to ASTM A269 specification for welded and seamless tubing, and comparing in difference, usually, we consider 304L to be low carbon 304, and variation from 304, “L” means low content in carbon element.
| Grade | C | Si | Mn | Cr | Ni | Mo | S | P |
|---|---|---|---|---|---|---|---|---|
| 304 | 0,08 | 1,0 | 2 | 18 – 20 | 8 – 11 | – | 0,03 | 0,045 |
| 304L | 0,035 | 1,0 | 2 | 18 – 20 | 8 – 12 | – | 0,03 | 0,045 |
From the above table, we can see that there are two differences in composition, Carbon and Nickel content, Nickel content ranges from 8 to 12% for 304L, and 304 Nickel content ranges from 8 to 11%, it is not so that important, carbon content of 304 / 304L dual certification must not exceed 0.035%.
Secondly, let us check 304 and 304L stainless steel mechanical properties in minimum value.
| Grade | Tensile Strength(Mpa) | Yield Point(Mpa) | Elongation(%) |
|---|---|---|---|
| TP304 | 515 | 205 | 35 |
| TP304L | 485 | 170 | 35 |
Versus 304L, 304 has a higher value in Tensile strength and Yield point due to high carbon content, so 304/304L dual certification limit to those two properties minimum 515 Mpa and 205 Mpa separately.
Important: 304 304L dual-certified stainless steel requires both chemical compositions fully complying with 304L grade and mechanical properties complying with 304 grade.
Different chemical compositions and mechanical properties affect other stainless steel properties, such as corrosion resistance, ductility, weldability, and low carbon dual certified grade has good resistance to avoid intergranular corrosion attack.
Typical dual-certified 304/304L stainless steel; tube and pipe.
Why Dual Certified Grade?
Although dual certification type is not stated by any standards organization, in practice, dual-certified material is more and more used for special applications, dual-certified grades have some benefits, the corrosion resistance of stainless steel should be guaranteed, and the strength of standard requirements should be met.
For End Users
End users can select dual-certified grades to meet strict requirements, dual-certification material possess both high strength and excellent corrosion resistance together.
For Manufacturers
With stainless steel refining technology improvement, the dual-certified alloy can be offered in both grades, which means dual certification grade can replace individual grade, which reduces the production cost.
Other Examples Of Dual Certified Term
- 1.4301 / 1.4307
- 316 / 316L stainless steel
- S31803 / S32205 duplex
- ASTM A249 / ASTM A269 for welded tube
- ASTM A213 / ASTM A269 for seamless tube
304 304L dual certified is for stainless steel material, dual certified standard has multiple requirements, such as test, tolerance, and mills must issue MTC to certify it is dual certified material and standard.