What Happens During a Heat Exchanger Workshop Service

Most plant engineers who send a heat exchanger to a workshop for service have limited visibility of what actually happens between the unit leaving their site and returning. The exchanger goes in, some time passes, and it comes back with a job sheet and a test certificate. What happens in between, how decisions are made about repair scope, and how the quality of the work is controlled are questions that are less often asked and less often answered in detail.

Understanding the heat exchanger workshop service process matters because the decisions made during that process have consequences for the performance and integrity of the unit when it is returned to service. This article describes what a complete heat exchanger workshop service involves, from intake and condition documentation through cleaning, inspection, repair, reassembly, and testing, to the documentation package that should accompany the returned unit. Call +61 3 9761 7766 to discuss workshop service requirements for your equipment.

Intake, Condition Documentation, and Scope Agreement

Receiving the Unit and Establishing Baseline Condition

When a heat exchanger arrives at the workshop, it is received, tagged with a unique job reference, and photographed in its as-found condition before any work begins. The as-found condition photographs document the state of the unit at intake and provide a reference point for comparing the condition before and after service. An initial visual inspection notes obvious defects, damage, fouling, and any safety-relevant conditions such as residual process fluid in the tube side or shell side.

The client’s instructions for the service are reviewed at this point and a preliminary scope of work is discussed. This preliminary scope is based on the service history, the client’s description of the performance issue or reason for service, and the findings from the initial visual inspection. It is not the confirmed scope, because the confirmed scope can only be established after cleaning and detailed inspection are complete.

Why Scope Must Be Confirmed After Cleaning

Heat exchanger cleaning is a prerequisite for meaningful inspection, not a step that follows the inspection. Fouling, scale, and process deposits on tube surfaces, tube sheets, and shell internals conceal defects including pitting, cracking, and thinning that are not visible before the surfaces are cleaned. A commitment to a fixed repair scope before cleaning is complete carries a risk of underestimating the work required.

Service and refurbishment at our AS 9001 accredited workshop in Bayswater North, Victoria, follows a documented intake and scope confirmation process that separates the initial scope discussion from the confirmed scope. The client is informed of any scope changes found during cleaning and inspection before additional work proceeds, giving them the information needed to make the repair-or-replace decision if the confirmed scope changes significantly.

Workshop Heat Exchanger Cleaning Methods

Hydroblasting and High-Pressure Water Jetting

Hydroblasting is the primary mechanical cleaning method for removing fouling, scale, and deposits from tube bores, tube sheets, shell internals, and external fin surfaces. High-pressure water delivered at the appropriate pressure for the deposit type and the tube material cuts through most industrial fouling without chemical treatment. Tube-side cleaning is carried out using lances inserted through each tube, traversing the full tube length to remove internal deposits. Shell-side cleaning removes deposits from baffle spaces, tube outer surfaces, and shell internals.

The operating pressure for hydroblasting is selected based on the nature of the deposit and the wall thickness of the component being cleaned. Higher pressures are used for hard mineral scale. Lower pressures are used for softer deposits or for thin-walled components where tube damage from excessive pressure is a concern.

Chemical Cleaning in the Workshop

Chemical cleaning is used for deposits that hydroblasting alone cannot remove effectively, including tightly adherent mineral scale, oxide layers, biological growth, and certain polymer or resin deposits. Acid-based cleaning solutions dissolve carbonate scale and iron oxides. Alkaline solutions remove oil-based deposits and some biological matter. Solvent-based treatments are used for resinous or waxy deposits that are not soluble in water-based solutions.

The cleaning chemical must be compatible with the metallurgy of the equipment. An acid solution appropriate for carbon steel components may be damaging to copper alloy or titanium tubes. Chemical selection is part of the cleaning specification for each job, not a default procedure applied uniformly.

Steam Cleaning and Other Methods

Steam cleaning is used for softer organic deposits and for decontaminating equipment that has been in hydrocarbon service before workshop entry. The heat exchanger repair process for units from certain process services requires decontamination as a safety step before mechanical work can proceed, and steam is a standard method for this purpose.

Inspection After Cleaning

Eddy Current and Non-Destructive Testing of Tubes

Eddy current testing is the standard method for assessing tube wall condition in non-ferrous tube bundles after cleaning. An eddy current probe is passed through each tube, measuring the response of the electrical field at the tube wall to detect variations in wall thickness. Pitting, thinning from corrosion, and cracks produce characteristic signal responses that the operator interprets against acceptance criteria to determine which tubes are within the minimum wall thickness and which require plugging or replacement.

Shell and tube heat exchanger repair projects use eddy current tube data to define the plugging and retubing scope precisely. The test results, reported as a wall loss percentage at each measurement point along each tube, are documented as part of the inspection record and retained in the job file.

Visual Inspection and Dimensional Assessment

After cleaning, visual inspection of all accessible surfaces covers tube ends for pitting and erosion at the tube-to-tube-sheet joint, tube sheet face condition including groove depth and surface finish, header box interior surfaces for corrosion and cracking, nozzle weld condition, and shell internals for baffle damage and shell wall condition.

Dimensional assessment checks tube sheet flatness, nozzle face finish and alignment, and gasket seating surface condition. Tube sheets that are pitted or eroded at the gasket seating surface require machining before new gaskets can provide an effective seal. This is a common finding in heat exchanger workshop service that adds scope but is necessary for reliable reassembly.

Pressure Testing Before and After Repair

A pressure test before repair begins confirms the as-found integrity of pressure-containing joints and identifies any leaks not apparent from the initial visual inspection. This pre-repair test provides a clear baseline for comparing with the post-repair test and documents the initial condition of the unit. Post-repair hydrostatic testing at the test pressure specified by the applicable pressure vessel standard confirms that all repaired and reassembled joints are leak-tight before the unit is returned to service.

Repair Work Carried Out in the Workshop

Tube Plugging and Partial Retubing

Tubes found to be below the minimum acceptable wall thickness during eddy current testing are plugged at both ends using tapered plugs or threaded plugs, depending on the tube material and the joint type. Plugging isolates the failed tube from service without removing it from the bundle. A small number of plugged tubes in a large bundle has a minor effect on the total heat transfer area. As the number of plugged tubes increases, the impact on heat duty becomes significant and full retubing is required to restore performance.

Air cooled units with finned tube bundles follow the same plugging and retubing decision framework. The finned tube version of this process involves removing the fin tube assembly from the header box and replacing it as a unit rather than plugging an individual tube in a shell, but the decision logic of when plugging is adequate and when full replacement is required is the same.

Full Bundle Retubing

Full retubing requires removing all tubes from the tube sheet, inspecting and preparing the tube sheet for new tube installation, installing new tubes to the specified material and dimensional standard, rolling or welding the tube-to-tube-sheet joint, and verifying joint integrity before reassembly. The tube material for the new bundle may match the original specification or may be upgraded based on the service history and the client’s instruction.

Tube-to-tube-sheet joint verification includes visual inspection of the expanded joint profile and, where the specification requires welded joints, dimensional and visual inspection of each weld. Weld procedure qualification records are provided as part of the documentation package for jobs involving pressure weld repairs.

Weld Repairs to Pressure Components

Weld defects identified during inspection of shell seams, nozzle attachment welds, and header box structural welds are repaired by removing the defective weld material and depositing new weld metal to an approved weld procedure. All weld repairs to pressure-containing components require a qualified weld procedure and a qualified welder, and the completed repair is subject to non-destructive examination as specified by the applicable pressure vessel standard.

Our engineering team manages the weld procedure qualification records, welder qualifications, and NDE documentation for pressure weld repairs carried out at the workshop, ensuring that the completed repair meets the requirements of AS 1210, ASME VIII, or the applicable code as specified in the original design documentation.

Reassembly and Final Testing

Gasket Replacement and Header Box Reassembly

All flanged connections are reassembled with new gaskets of the specified material and dimensions. Gasket material is selected to match the original specification, confirmed against the process fluid and temperature conditions, and installed on properly prepared gasket seating surfaces. Header boxes are assembled and bolted to the specified torque using calibrated torque equipment.

Hydrostatic Testing and Acceptance

Hydrostatic testing fills the pressure-containing spaces with water and pressurises to the test pressure specified by the applicable standard. The unit is held at test pressure for the specified duration while all joints, welds, and connections are inspected for leaks. A unit that passes the hydrostatic test without visible leakage is accepted and drained before return to service.

The test pressure, hold duration, and acceptance criteria are determined by the applicable pressure vessel design standard. These parameters are documented in the test record and included in the documentation package returned with the unit.

Documentation Package Returned with the Unit

The completed job documentation includes the intake condition report and photographs, eddy current or NDE tube inspection results, confirmed repair scope and work carried out, material certificates for any new tubes or pressure component materials, weld procedure qualification records where applicable, and the hydrostatic test certificate. This documentation provides the client with a complete record of the service for asset management, regulatory compliance, and future maintenance planning purposes.

Heavy-duty industrial radiators serviced at the workshop receive the same documentation package: intake condition record, cleaning and inspection findings, repair scope, and test certificate. The workshop heat exchanger service process applies consistently across equipment types.

The Role of AS 9001 Accreditation in Workshop Service

Documented Procedures and Quality Control

AS 9001 accreditation requires that the workshop operates to documented procedures for each step of the service process: intake, cleaning, heat exchanger inspection, repair, reassembly, testing, and documentation. Heat exchanger inspection records generated at each step, including eddy current tube data, wall thickness measurements, and visual findings, are part of the documented evidence that work was carried out to specified acceptance criteria. Inspection equipment must be calibrated and calibration records maintained. Welders must hold current qualifications and weld procedure documents must be available at the point of use.

The accreditation framework provides the client with assurance that the workshop heat exchanger service has been carried out to a consistent, documented standard. Tube bundle repair and other pressure equipment work is supported by documented weld procedures, material traceability, and test records. The heat exchanger repair process under AS 9001 is verifiable: every significant step is documented, and that documentation is returned to the client with the unit.

Fan systems serviced at the workshop, including fan assembly overhaul, blade replacement, and balance verification, are subject to the same documented procedure and quality record requirements as heat exchanger service work carried out within the AS 9001 accreditation scope.

Conclusion

A heat exchanger workshop service involves a defined sequence of steps from intake to documentation: condition recording, cleaning, inspection, scope confirmation, repair work, reassembly, pressure testing, and documentation. Each step produces information used in the next, and none can be skipped without affecting the reliability of the outcome.

Tube bundle repair documentation and heat exchanger inspection records are not administrative formalities. It is the record that confirms what condition the unit was in, what work was done, and how the completed unit performed against the acceptance criteria. For pressure equipment returned to service in an industrial facility, this record is part of the plant’s safety and regulatory obligations.

Call +61 3 9761 7766 to discuss workshop service requirements for your heat exchanger.