ASTM A403 WP304 Stainless Steel Fitting Elbow Buttwelded Seamless B16.9
ASTM A403 WP304 stainless steel fittings are one of the most widely used austenitic stainless steel fittings. The ASTM A403 standard specifies strict requirements for chemical composition, mechanical properties, heat treatment, dimensional tolerances, non-destructive testing and marking for wrought butt-weld, socket-weld and threaded fittings manufactured from UNS S30400.
Fitting Classes for WP Grades
| Class | | Nondestructive Examination |
| S | Seamless | |
| W | Welded | Radiography or Ultrasonic |
| WX | Welded | |
| WU | Welded | |
ASTM A403 WP304 Stainless Steel Chemical Composition
| WP GRA. | UNS GRA. | CHEMICAL COMPOSITION % |
| C | MN | P | S | Si | NI | Cr |
| WP304 | S30400 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 8.0-11.0 | 18.0-20.0 |
| WP304L | S30406 | 0.035 | 2.00 | 0.045 | 0.030 | 1.00 | 8.0-12.0 | 18.0-20.0 |
What is the difference between WP304 and WP304L?
The core difference between WP304 and WP304L lies in their carbon content. WP304 has a standard upper limit of 0.08%, while WP304L has a strictly limited upper limit of 0.030%. The "L" stands for Low Carbon, an ultra-low carbon version of 304 stainless steel. This difference in carbon content primarily affects the intergranular corrosion resistance and weldability of WP304 and WP304L.
Intergranular corrosion occurs when 304 stainless steel is exposed to the sensitive temperature range of 425°C to 850°C. Carbon combines with chromium to form chromium carbides, which precipitate at grain boundaries. This significantly reduces the chromium content near the grain boundaries, creating "chromium depletion." Corrosive media preferentially attack these depleted areas, leading to cracking along the grain boundaries.
This makes WP304 highly carbon-sensitive, while the ultra-low carbon design of WP304L can significantly reduce the amount of chromium carbide precipitation. At the same time, without the need for post-weld heat treatment, WP304L still maintains excellent intergranular corrosion resistance, thus eliminating the need for post-weld heat treatment and significantly saving cost and time.
ASTM A403 WP304 Stainless Steel Fitting Heat Treatment
| WP GRA. | Solution Anneal Temperature, min °F [°C]B | |
| WP304 | 1900 [1040] | water or other rapid cool |
ASTM A403 WP304 Stainless Steel Fitting Tensile Requirements
| WP GRA. | Yield Strength, min, ksi [MPa] | Tensile Strength, min, ksi [MPa] |
| WP304 | 30[205] | |
ASTM A403 WP304L Stainless Steel Fitting Application
- Chemical and petrochemical industries
- Food and beverage processing
- Pharmaceutical industry
- Water treatment and distribution
- Building water supply and drainage
- HVAC
- Marine industry
- General industry
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