Heat Exchanger Tube-to-Tubesheet Joints From China That Leak at Startup
Quote from chief_editor on April 22, 2026, 2:50 amProcess plant operators buy Chinese shell-and-tube heat exchangers with pressure test certification. Tube-to-tubesheet joint integrity — the most common field failure point — depends on expansion process quality that pressure tests do not fully verify.
A refinery expansion project in India received 12 shell-and-tube heat exchangers from a Nanjing manufacturer — AES type, carbon steel shell, admiralty brass tubes, design pressure 2.5 MPa. All 12 units had pressure test certificates showing successful shell-side and tube-side hydrostatic testing at 1.5 times design pressure. Fourteen passed pre-commissioning checks without incident. Two leaked at startup, from the tube-to-tubesheet junction on the floating head end.
The tube-to-tubesheet joint in a shell-and-tube heat exchanger is made by expanding the tube into a grooved hole in the tubesheet — a mechanical compression joint that seals by the interference fit between the expanded tube and the groove walls. The quality of this joint depends on the expansion ratio — how much the tube has been expanded relative to its original OD — and on the consistency of the expansion tool calibration across all tube positions.
The Nanjing manufacturer's tube expansion procedure specified a 5 to 8% wall reduction during expansion — a range that produces adequate joint integrity for the design conditions. The two leaking units had been expanded at the lower end of the range at the tubesheet grooves, producing joints that held at ambient temperature during the hydrostatic test but relaxed slightly when the exchanger reached operating temperature and the differential thermal expansion between the tube and tubesheet created additional stress on the joint.
A Hydrostatic Test at Ambient Temperature Does Not Replicate Operating Thermal Loading
The tube-to-tubesheet joint failure mode — leakage at operating temperature that does not appear at ambient-temperature hydrostatic test pressure — is thermally driven. The expansion joint that is tight at 20°C may have insufficient interference when the exchanger reaches 140°C operating temperature due to differential thermal expansion between the tube material and the tubesheet material. In a carbon steel tubesheet with admiralty brass tubes, the brass tube expands more than the steel tubesheet at elevated temperature, which reduces the interference of the expansion joint.
The hydrostatic test at 1.5 times design pressure demonstrates joint integrity under static hydraulic load at ambient temperature. It does not demonstrate joint integrity under the combined thermal and pressure loading of the actual operating condition. For tube-to-tubesheet joints in exchangers with significant differential thermal expansion — which includes most non-ferrous tube / ferrous tubesheet combinations — thermal qualification testing or mandatory expanded tube pull-out testing during fabrication provides better assurance of field integrity.
Two Exchangers Repaired, Two Weeks Lost
The two leaking exchangers were repaired in-situ by roller re-expansion of the affected tubes at the floating head tubesheet — a standard repair technique that increases the expansion ratio and tightens the mechanical joint. The repair took four days per exchanger, conducted sequentially during a period when the refinery's hot oil circuit was operating on partial capacity through alternative exchangers.
The production throughput reduction during the 10-day repair period — both exchangers out plus the changeover periods — cost $1.8 million in reduced refinery margin. The repair itself cost $85,000 in labor.
The Nanjing manufacturer's quality procedure included an expansion ratio measurement requirement. The measurement records for the two failed units showed tube expansion values at the lower specification limit — technically compliant, insufficient for the thermal application. The buyer's factory witness had not reviewed the expansion measurement records during the FAT because the FAT scope covered pressure test witnessing, not fabrication process parameter verification.
A heat exchanger pressure test certifies the joint under the test conditions. The joint sees different conditions in service.
Keywords: China heat exchanger tube tubesheet joint quality | shell tube heat exchanger China, Chinese heat exchanger manufacturer, heat exchanger tube expansion China, TEMA heat exchanger procurement China
Words: 576 | Source: Documented tube-to-tubesheet failure — refinery heat exchangers, Nanjing manufacturer, India, 2023. Pressure test records, expansion ratio measurement data, in-situ repair records and cost. | Created: 2025-02-01T09:20:00Z
Process plant operators buy Chinese shell-and-tube heat exchangers with pressure test certification. Tube-to-tubesheet joint integrity — the most common field failure point — depends on expansion process quality that pressure tests do not fully verify.
A refinery expansion project in India received 12 shell-and-tube heat exchangers from a Nanjing manufacturer — AES type, carbon steel shell, admiralty brass tubes, design pressure 2.5 MPa. All 12 units had pressure test certificates showing successful shell-side and tube-side hydrostatic testing at 1.5 times design pressure. Fourteen passed pre-commissioning checks without incident. Two leaked at startup, from the tube-to-tubesheet junction on the floating head end.
The tube-to-tubesheet joint in a shell-and-tube heat exchanger is made by expanding the tube into a grooved hole in the tubesheet — a mechanical compression joint that seals by the interference fit between the expanded tube and the groove walls. The quality of this joint depends on the expansion ratio — how much the tube has been expanded relative to its original OD — and on the consistency of the expansion tool calibration across all tube positions.
The Nanjing manufacturer's tube expansion procedure specified a 5 to 8% wall reduction during expansion — a range that produces adequate joint integrity for the design conditions. The two leaking units had been expanded at the lower end of the range at the tubesheet grooves, producing joints that held at ambient temperature during the hydrostatic test but relaxed slightly when the exchanger reached operating temperature and the differential thermal expansion between the tube and tubesheet created additional stress on the joint.
A Hydrostatic Test at Ambient Temperature Does Not Replicate Operating Thermal Loading
The tube-to-tubesheet joint failure mode — leakage at operating temperature that does not appear at ambient-temperature hydrostatic test pressure — is thermally driven. The expansion joint that is tight at 20°C may have insufficient interference when the exchanger reaches 140°C operating temperature due to differential thermal expansion between the tube material and the tubesheet material. In a carbon steel tubesheet with admiralty brass tubes, the brass tube expands more than the steel tubesheet at elevated temperature, which reduces the interference of the expansion joint.
The hydrostatic test at 1.5 times design pressure demonstrates joint integrity under static hydraulic load at ambient temperature. It does not demonstrate joint integrity under the combined thermal and pressure loading of the actual operating condition. For tube-to-tubesheet joints in exchangers with significant differential thermal expansion — which includes most non-ferrous tube / ferrous tubesheet combinations — thermal qualification testing or mandatory expanded tube pull-out testing during fabrication provides better assurance of field integrity.
Two Exchangers Repaired, Two Weeks Lost
The two leaking exchangers were repaired in-situ by roller re-expansion of the affected tubes at the floating head tubesheet — a standard repair technique that increases the expansion ratio and tightens the mechanical joint. The repair took four days per exchanger, conducted sequentially during a period when the refinery's hot oil circuit was operating on partial capacity through alternative exchangers.
The production throughput reduction during the 10-day repair period — both exchangers out plus the changeover periods — cost $1.8 million in reduced refinery margin. The repair itself cost $85,000 in labor.
The Nanjing manufacturer's quality procedure included an expansion ratio measurement requirement. The measurement records for the two failed units showed tube expansion values at the lower specification limit — technically compliant, insufficient for the thermal application. The buyer's factory witness had not reviewed the expansion measurement records during the FAT because the FAT scope covered pressure test witnessing, not fabrication process parameter verification.
A heat exchanger pressure test certifies the joint under the test conditions. The joint sees different conditions in service.
Keywords: China heat exchanger tube tubesheet joint quality | shell tube heat exchanger China, Chinese heat exchanger manufacturer, heat exchanger tube expansion China, TEMA heat exchanger procurement China
Words: 576 | Source: Documented tube-to-tubesheet failure — refinery heat exchangers, Nanjing manufacturer, India, 2023. Pressure test records, expansion ratio measurement data, in-situ repair records and cost. | Created: 2025-02-01T09:20:00Z