Stainless Steel Standard Parts Locked-Up Condition and Solutions

Stainless steel fasteners (such as bolts and nuts) are prone to seizing. This phenomenon essentially involves “cold welding” or “adhesion” occurring at metal contact surfaces due to pressure, friction, and chemical reactions, rendering the components impossible to disassemble or even completely locked in place. To resolve this issue, it is essential to first identify the core causes of seizing and then implement targeted preventive and remedial measures.

1. When using stainless steel standard fasteners, do you always tighten the nuts at a fixed torque?

If you are new to using stainless steel standard fasteners or unfamiliar with their manufacturing processes, consult your supplier regarding the relevant properties of stainless steel. Generally, slowing down the tightening speed can significantly reduce the likelihood of seizing. Since heat is often generated during tightening, the probability of seizing increases as heat accumulates. When using stainless steel fasteners, tighten them at a slower rate than you would carbon steel fasteners.

2. Do you lubricate the screws or nuts before locking them?

If the answer is “no,” it is recommended to lubricate the internal and external threads with substances such as butter, molybdenum disulfide, graphite, mica, or talcum powder to reduce the occurrence of seizing. Coating is also an effective lubrication method; nuts treated with coating will function as if an additional lubricating film exists between the nut and bolt.

3. Are screws and nuts of the same material grade selected?

If the answer is yes, it is recommended to use screws and nuts of different grades together, such as pairing 304 with 316. However, note that the selected stainless steel grade must still meet your specific requirements for rust resistance and corrosion resistance.

Additionally, locking the flange is the most common cause of seizing. Assuming you have already taken note of and followed all the key points mentioned above—including using washers, coating nuts, tightening nuts in a diagonal sequence, slowly tightening them sequentially to the appropriate torque, etc.—and the issue still persists, the final solution is to temporarily use carbon steel nuts when pre-locking the flange assembly. Then, when performing the final, permanent lock, switch to stainless steel nuts. This approach strikes a balance between aesthetic appeal, rust resistance, and preventing locking.