Nickel Tubes for Heat Exchangers: What Should Buyers Check?

Start at the Tube Sheet, Not With the Tube List

Many enquiries begin with a simple size line:

• 19.05 mm OD × 1.2 mm wall × 3000 mm length

That is enough to identify the nominal tube, but not enough to confirm that it will fit the exchanger.

The workshop needs to know how the Nickel Tube will meet the tube sheet. Some tubes are mechanically expanded. Others are welded. Certain designs use both methods.

The supplied wall thickness and end condition must leave enough material for the selected joint.

A wall chosen only from the heat-transfer calculation may be too light for aggressive expansion. A heavier wall may make the joint easier to produce, but it also changes:

• Tube weight
• Expansion force
• Material consumption
• Heat-transfer performance
• Finished joint geometry

The tube-sheet drawing is therefore more useful than a worn sample tube.

An old tube has already been expanded, heated, cleaned, and possibly corroded. Its measured diameter near the end may no longer represent the original supplied size.

The controlled drawing should show:

• Tube-sheet hole diameter
• Tube projection
• Expanded length
• Weld detail
• End preparation
• Any machined or trimmed section

ASTM B163 is commonly specified for seamless nickel and nickel-alloy condenser and heat-exchanger tubes.

The order should also state whether the tube is controlled by average wall or minimum wall. These descriptions should not be treated as the same requirement.

Length needs workshop margin as well.

A tube cut exactly to the final installed length may become unusable if one end is damaged during transport or needs additional preparation before welding. Where the fabricator plans to trim the bundle after assembly, the raw tube length should include that allowance.

Does the Exchanger Need Nickel 200 Tube or Nickel 201 Tube?

Most commercially pure nickel heat-exchanger enquiries begin with Nickel 200 Tube.

Nickel 200 is UNS N02200. Nickel 201 is UNS N02201. Nickel 201 has a lower carbon limit and deserves review where commercially pure nickel remains at elevated temperature for an extended period.

The important value is the tube-wall temperature, not simply the temperature shown for the process liquid.

A liquid may enter the exchanger at 250°C while the tube near a hot-gas inlet or heating zone operates at a different local temperature. Uneven flow may also leave one area hotter than the rest of the bundle.

Time at temperature matters as well.

A short rise during start-up does not create the same material condition as continuous operation. A monthly hot cleaning cycle is also different from a tube that remains at elevated temperature for many hours every day.

When sustained service approaches or exceeds roughly 315°C, Nickel 201 Tube deserves closer consideration because of its lower carbon content.

That does not mean every exchanger touching this temperature automatically requires Nickel 201.

The buyer should review:

• Hottest tube location
• Maximum tube-wall temperature
• Normal operating temperature
• Duration of the hot stage
• Start-up and shutdown cycles
• Cleaning temperature
• Later fabrication or heat treatment

Nickel 201 should not be treated as a general upgrade in corrosion resistance.

The process medium must first be suitable for commercially pure nickel. Temperature and exposure time then help determine whether Nickel 200 or Nickel 201 is the more appropriate grade.

A normal exchanger operating well below the prolonged high-temperature concern range may gain no practical benefit from changing a Ni200 Nickel Tube order to Nickel 201.

Both Sides of the Tube Need a Process Review

The tube-side fluid is usually written clearly on the exchanger data sheet. The shell-side condition is more often overlooked.

A Pure Nickel Tube may carry an alkaline process liquid inside while steam, condensate, cooling water, or another chemical contacts the outside.

Both surfaces need to remain suitable throughout the operating cycle.

The tube ends may experience an even more complicated environment.

Near the tube sheet:

• Deposits may collect around the joint
• Small crevices may retain liquid
• One area may remain wet after shutdown
• Another area may dry while still hot
• Cleaning chemicals may concentrate locally

Cleaning introduces another service condition.

A Nickel 200 Tube may be suitable for the production medium but face a stronger oxidizing cleaner, hot rinse, or descaling solution during maintenance.

The cleaning procedure therefore belongs in the material review rather than being considered after the bundle is built.

A useful process description normally includes:

• Tube-side fluid
• Shell-side fluid
• Concentration range
• Normal temperature
• Maximum temperature
• Known impurities
• Flow condition
• Solids or deposits
• Cleaning chemicals
• Cleaning temperature

General descriptions such as "chemical service" or "alkali exchanger" leave too much open.

Deposits and suspended solids can also change local conditions. They may restrict flow, hold chemicals against the surface, and make one section of the Nickel Tube behave differently from a clean central area.

When the exchanger is replacing a failed bundle, the location of previous damage can be especially useful.

Repeated failure near the inlet, outlet, support plate, or tube sheet often reveals more than a broad corrosion description.

What Usually Causes Problems After Delivery?

Straightness is one of the first practical checks.

A short tube with a slight bow may still be easy to handle. A long Nickel Tube must often pass through several support plates and reach the opposite tube sheet without being forced into position.

Excessive bow can:

• Slow bundle assembly
• Scratch the tube surface
• Increase insertion force
• Damage the tube end
• Create alignment problems at the second tube sheet

End roundness is equally important.

A tube may meet the average OD requirement along most of its length but become oval near the cut end. That can interfere with insertion, expansion tooling, and weld fit-up.

The cut should normally be square, and the ends should be free from heavy burrs unless another preparation has been agreed.

Buyers requiring machined ends, controlled OD near the tube sheet, or weld preparation should show the required length of that area on the drawing.

Surface condition

Surface requirements need to identify which surface matters.

A normal mill or drawn surface may be acceptable for a general exchanger. A process sensitive to deposits or contamination may require closer control of the inside surface and cleaning condition.

Asking only for "polished Nickel Tube" does not state whether the OD, ID, or both surfaces need treatment.

The enquiry should define:

• OD surface requirement
• ID surface requirement
• Permitted scratches or marks
• Cleaning condition
• Oil or residue restrictions
• Any polishing or roughness requirement

Inspection

Inspection should match the exchanger risk.

Dimensional checks may include:

• OD
• Wall thickness
• Length
• Straightness
• Ovality
• End condition

Depending on the project, the buyer may also require:

• Hydrostatic testing
• Eddy-current examination
• Ultrasonic testing
• Pneumatic testing
• Another agreed nondestructive examination

The actual method should be named.

"100% tested" does not explain what was done.

Packing

Packing is part of the final condition.

Long, thin-wall tubes need enough support to prevent bending inside the case. Tube ends should be protected against impact, while clean bores may need caps or another barrier against moisture and packing debris.

A correct material certificate cannot prevent transport damage.

What Should Buyers Confirm Before Ordering?

A practical Nickel Tube enquiry should connect the material specification with the exchanger drawing and fabrication route.

Nickel 200 Tube is often the practical starting choice for pure nickel heat exchangers operating outside prolonged high-temperature conditions. Nickel 201 Tube becomes relevant when the actual tube wall remains hot long enough for the lower-carbon grade to provide a real benefit.

The best order is not simply the one with the correct OD and wall thickness.

It is the one that reaches the fabricator straight, clean, properly identified, and ready for the actual tube-sheet joint.

Related Reading

Nickel 200 vs Nickel 201: Which One Should Buyers Use?