Using carbon steel bolts on a stainless steel flange is generally not recommended unless special precautions are taken. Here's why and what you need to consider:
⚠️ Why It Can Be a Problem:
Galvanic Corrosion
When carbon steel bolts (anodic) are in contact with stainless steel flanges (cathodic) in the presence of moisture or an electrolyte, galvanic corrosion can occur. This causes the carbon steel bolts to corrode faster.
Differential Durability
Stainless steel flanges are corrosion-resistant, while carbon steel bolts are not, leading to mismatched longevity and potential bolt failure.
Appearance and Maintenance
Corroded bolts can stain the stainless steel and require more frequent replacement.
✅ Best Practices:
Use stainless steel bolts (e.g., A193 B8 for 304 or B8M for 316) to match the flange material.
If carbon steel bolts must be used:
Apply isolation kits (non-conductive washers and sleeves).
Use coated bolts (e.g., zinc-plated, hot-dip galvanized).
Ensure dry or sealed environment to minimize corrosion.
🔩 Recommended Bolt Materials by Application:
| Flange Material | Recommended Bolt |
|---|---|
| 304 SS | A193 B8 (304 SS bolts) |
| 316 SS | A193 B8M (316 SS bolts) |
| Duplex SS | Alloy 625 / Duplex bolts |
| Carbon Steel | A193 B7 (Carbon steel bolts) |
