General Design Principles of Stainless Steel Equipment
| Principles | Description |
|---|---|
| Ensure Continuous Flow | Design systems to maintain liquid flow, avoiding areas where water may stagnate or sediment can accumulate. |
| Agitation in Wastewater | Keep wastewater agitated to reduce sludge buildup |
| Optimal Flow Rates | Achieve at least 1 m/s for raw water and 0.5 m/s for treated water to minimize sediment deposits. |
| Avoid Deadlegs | Avoid pipe sections where stagnant water and air may trap deposits. For pipes with intermittent flow, slope horizontal pipes and tank bottoms to drain completely. |
| Regular Wetting | For parts of the system that can’t be fully drained, design so they can be wetted periodically, which helps prevent salt or deposit buildup. |
| Consider Acoustic Damping | For thin stainless steel pipes, account for any potential noise from pressure pulses. |
Stainless Steel Grade Selection
316 Grades with Molybdenum: These stainless steels have a higher resistance to corrosion than 304 grades, making them suitable for environments with higher levels of chloride and chlorine. 316 is commonly used in water and wastewater treatment and preferred for building water systems that may experience stagnation or have numerous fittings.
304 Grades: These grades work well in most ambient water systems with chloride levels below 200 ppm. They are suitable for areas where abrasion or erosion resistance is needed, like in screens or grids. Chlorine or other oxidizers reduce this threshold, making 304 more prone to corrosion at lower chloride levels.
316 Grades for High Chloride Levels: The 316 grades, resistant to pitting and crevice corrosion, are ideal for waters with chloride levels up to around 1000 ppm.
Impact of Oxidizing Agents: Chlorine and other oxidizing agents can increase the risk of crevice corrosion even at a given chloride level. Trials in the U.S. found 304 grades suitable for up to 2 ppm chlorine in waters with chloride levels below 23 ppm, with 316 types offering a larger safety margin.
Areas with Chlorine Vapours: In areas where moist chlorine vapours may build up, it may be necessary to improve ventilation or choose a more corrosion-resistant grade.
Low-Carbon and Stabilized Grades: For welded structures, the low-carbon “L” grades or those with a maximum of 0.05% carbon are recommended. For heavy-duty structures that involve multiple welding passes, stabilized grades may be necessary; consulting a welding engineer or steel supplier is advised.
