Heat Exchanger Problems Often Begin at the Tube Ends
Most of the tube stays straight inside a conventional exchanger. The difficult area is usually where it meets the tubesheet.
The tube must enter the drilled hole without excessive clearance, remain reasonably round, and respond consistently during expansion. A slightly oval end may pass a normal dimensional check yet behave badly when the expansion tool is inserted. Wall variation can create the same problem. One side grips early while the other side has not made proper contact.
That is why heat-exchanger tubing should not be purchased from nominal dimensions alone.
The plant fluid also needs a proper description. Cooling water may mean seawater at one site and treated closed-loop water at another. Their effect on the tube is not identical. Temperature, deposits, cleaning chemicals, flow velocity, and periods of stagnant service can alter the result even when the normal operating data looks harmless.
Grade 2 titanium tube is often considered for industrial heat-transfer equipment because it can be fabricated and welded without the higher strength of Grade 5. Still, the grade does not decide the service by itself. A change in temperature or contamination may matter more than the difference between two tube specifications.
For replacement bundles, an old sample can help with diameter and surface comparison. It does not always reveal the original tolerance, heat-treatment condition, or reason the first bundle failed.
Pressure Cannot Be Confirmed From Wall Thickness Alone
Buyers sometimes ask, "Can this titanium tube hold 10 bar?" There is no reliable answer from the wall thickness alone.
The tube outside diameter, minimum remaining wall, operating temperature, material condition, joint design, and applicable equipment code all affect the calculation. A straight length may be adequate while the bend, branch, welded connection, or transition becomes the limiting point.
The distinction between tube and pipe also becomes important here. In ordinary sales conversations, the words are often exchanged. In an engineering order, they may refer to different dimensional systems, manufacturing standards, tolerances, and end connections.
This detail affects more than the document title. A tube ordered by actual outside diameter and wall thickness may not match fittings selected from a nominal pipe system. The mismatch often appears during assembly, when the material has already been cut.
Testing has limits too. A hydrostatic test can show that the supplied tube held the agreed test pressure without visible leakage. It does not certify the complete piping system, confirm every field weld, or replace the pressure design calculation.
For pressure-related work, the operating pressure is only one number. The buyer also needs to consider design pressure, temperature range, thermal cycling, fluid condition, connection type, and what happens during startup or shutdown.
The Straight Section Is Usually the Easy Part
Custom fabrication changes the tube before it reaches service. Bending, flaring, machining, welding, and attaching fittings can all reduce the margin built into the original straight tube.
Take a bent coil as an example. The tube may arrive with the correct wall and diameter, but the finished bend can show thinning on the outside and flattening across the bend. A tight radius makes this more difficult. The result also depends on tooling, material condition, lubrication, and whether a welded seam must be positioned in a controlled direction.
The drawing should therefore show the finished centerline radius and dimensional tolerance, not only the straight tube size.
End details deserve the same attention. A machined groove may require more wall than the process engineer first expected. A welded flange changes the cleaning and shielding requirements. A titanium-to-steel connection cannot usually be handled like an ordinary same-metal weld.
This is where many custom inquiries become delayed. The tube itself is available, but the end connection has not been decided.
Titanium welding must also be planned around cleanliness. Contamination from steel tools, dirty work surfaces, or inadequate shielding can damage the weld area while the base tube still looks acceptable. Better raw material cannot correct a poor fabrication route.
Seamless or Welded Depends on the Work After Delivery
Seamless tube is often requested automatically. Sometimes that is justified. Sometimes it only increases cost without solving the real issue.
A seamless tube may be preferred for heavier walls, smaller production quantities, demanding bends, or a specification that expressly requires a seamless product. Welded titanium tube can be practical for many straight heat-exchanger applications when the weld condition, dimensions, heat treatment, and inspection are suitable.
The decision becomes clearer when the next process is known.
A long straight exchanger tube that will be expanded into a tubesheet has different needs from a short tube that will be bent twice, welded to a flange, and pressure tested as an assembly. The second part may require closer discussion of ovality, bend thinning, weld position, and final inspection than the first.
Surface requirements also follow the application. A clean internal surface may matter where deposits, product purity, or cleaning access are concerns. A cosmetic outside finish may add little value when the tube will be enclosed inside equipment. Asking for every surface to be polished can raise cost while leaving the important internal condition undefined.
An industrial titanium tube should be selected around the point where fabrication or service is most likely to create trouble. In a heat exchanger, that may be the tubesheet joint. In pressure work, it may be the connection or minimum wall after forming. In a custom assembly, it is often the bend or welded end.
Once that point is identified, the grade, tolerance, test route, and manufacturing method become much easier to specify.
Related Reading