ASTM A403 WP304 Stainless Steel 90° Elbow Fitting B16.9

ASTM A403 WP304 Stainless Steel Fitting 90° Short Range 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.

ASTM A403 WP304 Stainless Steel Chemical Composition

What is the difference between WP304 and WP304L?

The core difference between WP304 and WP304L materials is the Carbon Content. The upper limit of carbon content of WP304 is 0.08%, which is the standard carbon content, while the upper limit of carbon content of WP304L is strictly limited to 0.030%. The "L" stands for Low Carbon and it is an ultra-low carbon version of 304 stainless steel.

The difference in carbon content primarily affects the intergranular corrosion resistance and weldability of WP304 and WP304L. Intergranular corrosion refers to the situation where, when 304 stainless steel is exposed to the sensitive temperature range of 425°C-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 a "chromium depletion." This preferentially corrodes these depleted areas in the corrosive medium, leading to cracking along the grain boundaries.

This makes WP304 highly carbon-sensitive. When exposed to the sensitive temperature range after welding or hot working, chromium carbide precipitation and chromium depletion are highly likely to occur. Therefore, WP304 stainless steel pipe fittings require post-weld solution treatment. If a full post-weld solution annealing is not performed to restore the microstructure, the intergranular corrosion resistance of the heat-affected zone (HAZ) will be significantly reduced in the post-weld state. Therefore, WP304 stainless steel pipe fittings are not recommended for use in corrosive environments where post-weld heat treatment is not possible or where exposure to the sensitive temperature range is possible.

The ultra-low carbon design of WP304L can fundamentally and significantly reduce the amount of chromium carbide precipitation. At the same time, without heat treatment after welding, WP304L can still maintain excellent resistance to intergranular corrosion, thus eliminating the need for post-weld heat treatment and significantly saving cost and time.

ASTM A403 WP304 Stainless Steel Fitting Heat Treatment

ASTM A403 WP304 Stainless Steel Fitting Tensile Requirements

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