Assembling shell-and-tube heat exchangers: step-by-step instructions and common mistakes 

Assembling shell-and-tube heat exchangers is not just assembling parts. This is a critical stage where 73% of failures in the first 6 months of operation are due to errors in the assembly stage rather than design or manufacturing. We, the engineers of Wuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd., annually assemble more than 180 units of ASME devices under pressure up to 25 MPa. This article contains only what works at sites in Iran, Indonesia and Italy: a step-by-step sequence without “water”, real breakdown points and how to get around them.

Step 1: Tube sheet and bundle preparation - the basis for reliability

We start not with welding, but with geometry control. Before assembly, we check three parameters: the perpendicularity of the grille surface to the casing axis (tolerance ±0.15 mm), flatness (no more than 0.2 mm per 300 mm), and the coincidence of the diameters of the holes with the pipes (gap 0.05–0.12 mm for copper alloys, 0.15–0.25 mm for stainless steel). We use composite gratings clad with a copper alloy - they eliminate galvanic corrosion upon contact with the carbon steel of the casing. If the gap exceeds the norm, the pipes will vibrate. If it is less, stress will arise due to thermal expansion. Not a single weld seam can withstand this.

Step 2: Fixing the beam - don’t “weld it and forget it”

Pipes are fixed in the grid in two ways: by flaring or welding. For high-pressure ASME models, we use combined fixation: flaring + laser spot welding around the perimeter. Why? Because flaring alone causes leakage under cyclic loads, and continuous welding causes microcracks in the heat-affected zone. In practice: 4–6 welding points evenly around the circumference, penetration depth is no more than 1.2 mm, heating temperature is controlled by thermocouples. Missing control here is a direct path to an accident in oil refining.

Step 3: Installing the partitions and attaching to the casing

• The partitions are installed strictly according to the drawing - the step between them determines the flow rate and heat transfer coefficient. A deviation of 5 mm reduces efficiency by 8–12%;

• The partitions are fastened to the casing using bolts with an anti-corrosion coating (not welding!) - this allows them to be replaced without cutting the casing;

• The gap between the partition and the pipe should be 1.5–2.5 mm. More - the growth of eddy currents and erosion. Less - pinching of pipes when heating.

Typical mistakes we see from customers

Mistake #1:Assembly without preliminary hydraulic testing of the tube bundle. We require a test of 1.5×P_slavebefore installation in the casing. In 2023, at one facility in Singapore, a crack was discovered in a U-shaped pipe after installation - replacement cost 3.2 times more than preliminary maintenance.

Mistake #2:Use of standard seals for H₂S or chloride media. Our standard is Viton® fluorine rubber with the addition of graphite for aggressive petroleum products. Rubber gaskets work here for no more than 4 months.

Mistake #3:Neglect of the thermal gap between the casing and the tube sheet. At a temperature difference of >150 °C, insufficient clearance leads to deformation of the grid and failure of the welds. We calculate it individually - according to the material, length of the device and operating mode.

How to avoid failure: our pre-launch checklist

• The composition of the lattice metal was checked with a spectrometer - compliance with ASTM B152 for copper alloys;
• Ultrasonic testing of all welded joints according to ASME BPVC Section V, Article 4;
• The thickness of the casing wall was measured at 12 points - tolerance ±0.5 mm;
• Fixed orientation of U-shaped pipes: bending radius ≥ 3×D_n, without folds or thinning;
• Test hydrotest at 1.5×P was completed_slavewithin 30 minutes - without a drop in pressure.

The assembly of shell-and-tube heat exchangers is not a mechanical operation, but an engineering process with feedback from every millimeter of gap and every second of welding. We do not sell devices “from a catalogue”. We design, manufacture and control every stage - from the selection of bimetallic finned tube to the final hydrotesting in our own laboratory. Technical regulations, test reports and examples of solutions for oil refining, energy and pharmaceuticals are available on the website ks-heatexchanger.com. Reliability doesn't start with a certificate - it starts the moment the first bolt is tightened to the correct torque.