How to Prevent Stainless Steel Fastener Galling in Segmented Tower Internals

Segmented tower internals are often assembled using stainless-steel:

• bolts;
• nuts;
• washers;
• threaded rods;
• clamps.

Stainless fasteners provide corrosion resistance and are convenient for internal assembly.

They can also experience a frustrating installation problem:

galling.

A bolt begins tightening normally.

Then the nut suddenly becomes difficult to turn.

Within another fraction of a turn, the threads seize completely.

The fastener may then need to be cut off.

Inside a tower during shutdown, this is more than an inconvenience.

It can delay installation.

1. What Is Galling?

Galling is a form of severe adhesive wear that can occur when metal surfaces slide against each other under pressure.

Stainless-steel threaded fasteners are particularly associated with this risk because mating thread surfaces can locally adhere.

As tightening continues, material can transfer and the threads can seize.

The result may be:

• locked nut;
• damaged threads;
• broken bolt;
• field replacement.

2. Galling Is Not the Same as Corrosion

A new stainless bolt can gall during its first installation.

The failure may occur before corrosion has had time to develop.

Therefore seeing a seized SS316L fastener does not automatically mean:

the bolt corroded.

The failure mechanism may be mechanical adhesion during tightening.

3. High Installation Speed Can Increase Risk

Rapid tightening creates more:

• friction;
• localized heating.

Power tools can therefore increase galling risk if used without suitable control.

For sensitive stainless fasteners, slower assembly may be more reliable than aggressively driving the nut to final position.

4. Dirty Threads Increase Problems

Threads contaminated with:

• metal particles;
• dirt;
• damaged packaging debris;
• fabrication dust

can increase friction.

Fasteners should be stored and handled so the thread surfaces remain reasonably clean before assembly.

5. Damaged Threads Should Not Be Forced

If a bolt has:

• dented threads;
• bent shaft;
• deformed start thread,

forcing the nut can increase the chance of seizure.

The better solution is normally to replace the damaged fastener.

Small spare quantities can save significant shutdown time.

6. Lubrication May Be Appropriate—but Must Match the Service

Suitable anti-galling compounds or lubricants can reduce friction in some applications.

However, the selected product must be compatible with:

• process cleanliness;
• temperature;
• chemical service;
• project specifications.

Do not apply an arbitrary workshop grease to every tower internal.

Some projects may prohibit particular lubricants or contaminants.

7. Fastener Material Pairing Can Matter

Using identical stainless materials for both bolt and nut can contribute to galling susceptibility under some conditions.

Alternative fastener combinations may be considered where appropriate.

However, material selection must still account for:

• corrosion;
• galvanic interaction;
• strength;
• process requirements.

Do not change bolt material solely to solve galling without engineering review.

8. Overtightening Creates Additional Risk

Tower internals are not all structural pressure-vessel joints.

A segmented:

• distributor;
• hold-down grid;
• demister frame

may require secure assembly without extreme bolt preload.

Uncontrolled overtightening can:

• gall threads;
• deform thin components;
• damage washers;
• distort panels.

The required tightening method should match the joint function.

9. Torque Values Cannot Be Invented Universally

A common question is:

What torque should be used for this stainless bolt?

The correct answer depends on:

• fastener diameter;
• thread;
• material;
• lubrication condition;
• required preload;
• joint design.

A torque value copied from an unrelated carbon-steel fastener table may be inappropriate.

If controlled preload is important, the engineering documentation should define the method.

10. Many Tower Internal Bolts Are Positioning or Assembly Fasteners

Some bolts primarily:

• connect segments;
• maintain alignment;
• prevent movement.

They may not require the same preload philosophy as a highly loaded structural flange joint.

The design should make the required fastener function clear.

11. Washers Can Protect Thin Components

Where a bolt clamps thin sheet, a suitable washer can help distribute load.

Without adequate bearing area, tightening may:

• deform the sheet;
• elongate a hole;
• damage the panel.

Galling control should therefore be considered together with the complete bolted joint.

12. Accessibility Matters

A joint may be easy to tighten in the workshop but difficult inside a tower.

Check:

• wrench access;
• hand clearance;
• bolt orientation;
• nearby shell;
• support beams.

If a galling fastener must be cut inside a confined location, poor accessibility makes the delay much worse.

13. Trial Assembly Can Expose Fastener Problems

For complex segmented internals, shop trial assembly can identify:

• poor hole alignment;
• wrong bolt length;
• inaccessible nuts;
• thread damage;
• galling tendency.

Problems can then be corrected before shipment.

14. Keep Spare Fasteners

For field-assembled internals, a small spare quantity is normally prudent where permitted by the project.

Spare sets should match:

• size;
• grade;
• washer configuration.

Do not assume locally available hardware will match the project material requirement.

15. Protect Fasteners During Shipment

Small fasteners should be:

• bagged;
• labeled;
• associated with the correct internal.

They should not be left loose inside a crate where threads can become damaged.

For multiple assemblies, package bolts by:

• tower;
• internal;
• segment group.

16. What If Galling Occurs During Installation?

If the joint seizes:

Do not keep applying unlimited torque.

Possible consequences include:

• bolt fracture;
• panel deformation;
• damaged mounting point.

Remove the seized fastener using an appropriate site method and inspect the joint.

Before installing the replacement, determine whether the cause involved:

• thread damage;
• contamination;
• excessive tightening speed;
• unsuitable assembly method.

17. Final Inspection After Bolting

After assembly, verify:

• all required bolts installed;
• nuts secure;
• washers present where specified;
• no visibly distorted thin sheet;
• segments aligned.

A fully tightened fastener does not guarantee the assembly is correct.

Engineering Takeaway

Stainless fastener reliability in tower internals depends on more than alloy grade.

Control:

**Clean Threads

• Undamaged Fasteners
• Appropriate Assembly Speed
• Compatible Lubrication Where Approved
• Correct Joint Loading
• Good Access
• Spare Hardware**

The objective is not simply to make the bolt as tight as possible.

It is to create a secure, serviceable bolted connection without seizing the threads or deforming the internal.