How are heat exchanger tubes expanded and rolled into tube sheets

In a shell-and-tube heat exchanger, the tube-to-tubesheet joint does the real work. It has to hold pressure on one side, transfer heat across the wall, and survive thousands of thermal cycles without leaking. The way that joint is made is by expanding and rolling the tube into the tubesheet hole — a cold-working operation that sounds simple but actually controls whether the exchanger runs for thirty years or fails in three. This guide walks through how the process works, what tools are used, and what separates a sound joint from a leaking one.

What "Expanding and Rolling" Actually Means

Tube expansion is a cold-working process. The tube is pushed into the tubesheet hole with a small clearance, and a tool is then used to push the tube wall outward until it plastically deforms and presses hard against the hole wall. The plastic flow creates a friction-based mechanical joint that is also leak-tight.

"Rolling" is the most common way to drive that plastic deformation. A tube expander — a tapered mandrel inside a cage of three to five hardened steel rolls — is pushed into the tube end. As the mandrel advances, it forces the rolls outward against the tube's inner wall, which in turn presses the tube's outer wall into the tubesheet hole. The result is a permanent, gas-tight interference fit.

The two standards every rolled joint has to meet are leak tightness and pull-out strength. Leak tightness is achieved when the residual contact stress between the tube and the tubesheet exceeds the internal pressure of the service. Pull-out strength is the axial load needed to drag the tube back out of the hole, and it depends on how much the tube was expanded, the surface finish in the hole, and the tube material's work-hardening behaviour.

The Tube Expander: How the Tool Works

A tube expander has three working parts: a tapered mandrel, a roll cage, and three, four, or five rolls. The mandrel is driven by a torque-controlled motor (electric, pneumatic, or hydraulic). As it rotates and feeds forward, the taper pushes the rolls outward. The rolls ride against the tube's inner wall, applying radial pressure that exceeds the tube's yield strength so the wall flows.

There are two main geometries, and the choice matters:

Parallel (straight) roll expansion uses rolls with a constant diameter along the working length. It produces uniform expansion across the tubesheet thickness and is the most common method for clean, controlled joints in process service.
Tapered roll expansion uses rolls whose diameter grows from the front of the tool to the back. It produces a tapered interference fit that resists axial pull-out exceptionally well and is often used in higher-pressure fire-tube boilers and thicker tubesheets.

In practice, the choice comes down to joint design. For most heat efficiency tubes in shell-and-tube exchangers, parallel rolling is the default because it gives predictable wall thinning and clean leak-test results.

Step-by-Step: How a Tube Is Expanded and Rolled

A proper rolling job follows a controlled sequence. Skipping steps or rushing the cycle is the fastest way to produce a joint that either leaks at the pressure test or cracks the tubesheet ligament during service.

Prepare the tube end. Cut the tube square, deburr both ends, and clean the outside surface. Any score mark or burr becomes a leak path after rolling.
Check the tubesheet hole. Measure hole diameter and roundness. The standard clearance between the tube OD and the hole is typically 0.4 mm to 0.8 mm (about 0.015" to 0.030") depending on tube size and material.
Lubricate lightly. A thin film of light oil on the tube OD and the rolls reduces tool friction and gives a more uniform expansion. Heavy grease is wrong — it traps in the joint and blocks leak testing.
Set the expander. Choose the right tool for the tube OD, the wall thickness, and the tubesheet depth. Adjust the roll length so the rolls cover the full tubesheet thickness plus 3 to 6 mm, but do not extend into the tube's free span.
Position the expander. ｉｎｓｅｒｔ the tool into the tube end. The front of the rolls should sit about 3 to 6 mm below the back face of the tubesheet so the rolling action runs through the full joint.
Roll to target expansion. Drive the mandrel under torque control. The target is usually 1% to 1.5% expansion of the tube OD for carbon steel, or 0.8% to 1.2% for austenitic stainless steel. The exact number depends on the design code — TEMA, ASME Section VIII, EN 13445, or PED 2014/68/EU.
Stop, do not over-roll. Once the target torque or expansion is reached, stop the motor immediately. Over-rolling causes excess wall thinning, work hardening, and possible tube-end cracking — especially in stainless and copper alloys.
Retract the tool cleanly. Reverse the mandrel so the rolls return inward, then withdraw the expander straight out without side-loading the tube.
Measure and document. Check tube OD growth, measure wall thinning if required, and record the torque and cycle count. For critical service, perform a helium leak test or hydrostatic test on the joint.

A rolled joint that follows this sequence typically achieves 4–10% wall thinning in the expanded zone, well within TEMA and ASME guidelines. Hydraulic expansion produces a more uniform 2–5% wall reduction and is preferred for thick tubesheets, thin-wall tubes, and sour-service applications under NACE MR0175.

Mechanical Rolling vs. Hydraulic Expansion

The two methods produce similar joints but use very different tools.

Mechanical roller expansion uses the tapered-mandrel expander described above. It is fast, economical, and the standard choice for most shell-and-tube units. It works well for tubesheet thicknesses up to about 50 mm in routine service. The trade-off is that wall thinning varies along the joint, and residual stresses are higher than in a hydraulically expanded joint.

Hydraulic expansion uses a sealed elastomeric or metal-to-metal mandrel inflated with high-pressure water, typically 5,000 to 100,000 psi (35 to 700 MPa). The pressure pushes the tube wall outward uniformly along the entire tubesheet thickness. The result is lower residual stress, more uniform contact pressure, and less work hardening — useful for stainless steel, titanium, and nickel alloy heat exchanger tube materials in cyclic service.

For most projects, the choice is governed by the design code, the tube material, the tubesheet thickness, and the service fluid. Many exchangers use a combination: a mechanical roll for the bulk of the joint, then a seal weld at the tubesheet face to handle thermal cycling at the tube mouth.

Common Tube and Tubesheet Materials

Tube-to-tubesheet joints are only as good as the materials on either side of the hole. For a heat exchanger running in refining, petrochemical, power, or marine service, the most common combinations are:

Carbon steel tubes rolled into carbon steel tubesheets — typical for low- and medium-pressure air, water, and steam service. Standards include ASTM A179, A192, A210, and A334.
Austenitic stainless tubes rolled into stainless or clad tubesheets — used in chemical, food, and pharmaceutical service. Standards include ASTM A213 TP304/L, TP316/L, TP321, and TP347.
Copper-nickel tubes rolled into copper-nickel or naval brass tubesheets — standard for seawater cooling and marine heat exchangers per EEMUA 234, BS 2871, and ASTM B111.
Nickel alloy tubes rolled into nickel-clad tubesheets — used in sour service, acid, and high-temperature process duty. Standards include ASTM B163, B407, B466, and B165.
Titanium tubes rolled into titanium-clad tubesheets — used in seawater, chlor-alkali, and high-purity applications.

A frequent mistake is mixing tube and tubesheet materials with very different thermal expansion coefficients. Under thermal cycling, the tube can work loose from the hole. The fix is to choose material pairs with similar expansion rates, or to use a seal weld at the tube face to take the thermal load.

Common Defects in Rolled Joints and How to Avoid Them

Most rolled-joint problems trace back to one of a handful of process errors. Knowing them up front is the cheapest way to avoid rework in the field.

Over-rolling. The tube wall thins too much, the ligament between holes is overstressed, and the tube may crack at the back face of the tubesheet. Fix: use torque control, not feel, and stop at the target expansion value.
Under-rolling. The joint leaks under pressure test or shortly after start-up. Fix: re-roll the joint with the proper tool, or ｒｅｐｌａｃｅ the tube and start over.
Diametral over-growth. The tube ID grows too much, weakening the tube in the ligaments and in the tube sheet grooves. Fix: calculate target expansion from the tube OD, wall thickness, and material — do not just keep rolling until the joint feels tight.
Tube-end cracking. Common in austenitic stainless and nickel alloys after heavy rolling or seal welding. Fix: keep expansion in the 0.8–1.2% range, anneal the tube end if required, and use low heat-input seal welding.
Tool marks on the bore. Caused by worn or damaged rolls. Fix: inspect rolls before each shift, ｒｅｐｌａｃｅ any with chipping or wear, and re-calibrate the expander against a sample tube.
Misalignment between tube and hole. Causes uneven expansion and local over-rolling. Fix: check tube squareness before rolling, and ream the tubesheet hole if it is bell-mouthed.

Quality Control After Rolling

The rolled joint is not finished until it has been measured and tested. A typical quality control sequence includes:

OD measurement. Measure the expanded tube OD with a bore gauge or micrometer at the front face, mid-thickness, and back face of the tubesheet. The growth should fall within the design code's allowable range.
Wall-thinning check. For critical service, measure the residual wall thickness in the expanded zone using ultrasonic testing. Wall reduction should be in the 4–10% range for mechanical rolling or 2–5% for hydraulic expansion.
Leak test. Hydrostatic test the joint at 1.3 to 1.5 times the design pressure, or perform a helium mass-spectrometer leak test for higher-integrity service. ASME Section VIII and TEMA specify the test method and hold time.
Pull-out test. For new tooling or new tube-tubesheet combinations, perform a destructive pull-out test on a sample joint to confirm the design's assumed pull-out strength.
Documentation. Record the tool serial number, torque, expansion value, and operator for every joint. This data is required for ASME U-stamp and PED 2014/68/EU CE-marked exchangers.

How Tube Material Choice Affects the Rolling Process

Not all tubes roll the same way. A few practical rules of thumb based on the materials used in real heat exchangers:

Carbon steel (A179, A192, A210) rolls easily, tolerates a wide expansion range, and gives consistent joint strength. The default choice for boiler and condenser tube service.
Austenitic stainless (TP304, TP316) work-hardens quickly. Keep expansion low (around 1%) and avoid re-rolling the same joint. If the joint leaks, ｒｅｐｌａｃｅ the tube.
Copper-nickel (90/10, 70/30) is soft and rolls easily, but the joint can loosen under thermal cycling. Use a seal weld or a light mechanical expansion followed by light hydro-expansion.
Nickel alloys (Monel, Inconel, Incoloy) are tough and work-harden severely. Hydraulic expansion is preferred for thick tubesheets, with a target expansion in the 1.0–1.5% range.
Titanium is gummy and tends to gall against the tubesheet. Use sharp, polished rolls, a small amount of lubricant, and avoid re-rolling the same joint.

These differences are exactly why the same rolling parameters cannot be used across the whole exchanger. A good fabricator sets the rolling schedule per material and verifies the first few joints before starting production rolling.

Standards Governing the Rolled Joint

The rolled joint is not just a workshop detail — it is covered by major design and manufacturing standards. The most commonly referenced documents are:

ASME Boiler and Pressure Vessel Code, Section VIII — Division 1 covers most shell-and-tube exchangers, with rules for tube-to-tubesheet joint design, expansion limits, and testing. Division 2 is used for higher-stress designs.
TEMA (Tubular Exchanger Manufacturers Association) — Classes R, C, and B define joint tightness, expansion ranges, and testing requirements for the most common process exchangers.
EN 13445 — the European standard for unfired pressure vessels, with its own rules on tube expansion and joint design.
PED 2014/68/EU — the European Pressure Equipment Directive. CE-marked exchangers must show joint design, expansion limits, and test results in the technical file.
HEI (Heat Exchange Institute) — standards for surface condensers and feedwater heaters, including rolled-joint requirements.
NACE MR0175 / ISO 15156 — sour-service rules that often force the use of hydraulic expansion or special tube materials to avoid sulphide stress cracking.

A rolled joint that meets these standards is accepted worldwide for refinery, petrochemical, power, and marine service.

Practical Tips From the Shop Floor

A few habits separate a reliable rolled joint from one that fails in service:

Always use a fresh, sharp set of rolls for stainless and nickel-alloy tubes. Worn rolls work-harden the inner surface and lead to cracking at the tube end.
Mark the expander depth on the tool with tape so the operator can see at a glance that the rolls are positioned correctly in the tube.
Roll a sample joint, section it, and measure wall thinning before starting production. The numbers you get from a sample joint are the ones you should use to set the production parameters — not the numbers in a textbook.
Document every joint. When a leak shows up three years later, the records are the only way to know whether the problem is at the tube, the tubesheet, or the rolling process.
None of these steps are exotic. They are simply the discipline that turns a hand operation into a controlled manufacturing process.

Summary

Tube expanding and rolling is the cold-working process that turns a loose-fitting tube into a leak-tight, high-strength joint with the tubesheet. It works by forcing a tapered mandrel through a cage of hardened rolls inside the tube, plastically deforming the tube wall until it presses hard against the tubesheet hole. Done right, the joint is gas-tight, mechanically strong, and durable enough to survive decades of thermal cycling. Done wrong, it leaks at the pressure test or fails in service.

The keys to a good rolled joint are simple: choose the right expander for the tube size, material, and tubesheet thickness; control expansion to the value allowed by the design code; stop on target rather than on feel; measure the joint and leak-test it before sign-off; and document everything. Whether the joint is rolled mechanically or expanded hydraulically, those rules do not change. They are the difference between a heat exchanger that runs for thirty years and one that fails in three.