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Inspection & service
Testing a gasketed plate heat exchanger: a photo guide
A point-by-point guide to plate inspection, dye-penetrant testing and documented verification. For single-plate gasketed designs only, not semi-welded units.
Use this guide to understand and plan an inspection with a qualified service team. Dye-penetrant (DP) inspection looks for surface-breaking indications on accessible individual plates. It is not a pressure test, and an absence of visible indications does not by itself prove complete leak-tightness or fitness for service.
01. Confirm scope and prepare safely
- Record the model, serial number, plate arrangement, process fluids and service history.
- Agree the inspection coverage, acceptance criteria and test procedure with the responsible engineering team.
- Arrange isolation, depressurisation, draining and cooling under the site permit system. Qualified personnel must confirm safe access before work begins.
- Review chemical safety data, compatible consumables, ventilation, protective equipment and waste handling.
02. Plan any preliminary leak check
- Treat an assembled-unit leak or hydrostatic check as a separate, controlled activity from DP inspection.
- Use only the manufacturer-approved test medium, pressure, differential-pressure limit, duration and connection arrangement for the particular unit.
- Record observations for comparison with the individual-plate inspection. Do not infer a safe test pressure from this article or the operating pressure alone.
03. Open, identify and visually inspect
- The service team opens the unit following its specified sequence and handling instructions.
- Maintain plate identification and original order so every finding can be traced to a plate position.
- Record fouling, deformation, corrosion and gasket condition; identify suspect plates without losing their original position.
04. Clean and dry the inspection surface
- Remove contamination using the approved cleaning method so it does not mask an indication.
- Allow the surface to dry as required by the selected penetrant system.
- Do not treat the reference photo's consumable as mandatory for every plate material or application.
05. Apply penetrant and control dwell time
- Apply the approved visible penetrant to the inspection area under the written test procedure.
- Record the application time and maintain the required dwell conditions.
- The supplied references show different dwell-time examples. The approved procedure and consumable instructions determine the actual timing, not a universal value from this guide.
06. Remove excess surface penetrant
- After the specified dwell, remove excess penetrant using the method approved for that penetrant system.
- Avoid a removal process that washes penetrant out of discontinuities and reduces detection sensitivity.
- Check surface condition before proceeding to the developer stage.
07. Apply developer and allow development
- Apply developer in the manner and coating thickness required by the approved inspection procedure.
- Allow the specified development time before evaluation.
- Control viewing conditions and timing; an overly heavy coating can make interpretation more difficult.
08. Evaluate and photograph indications
- A qualified inspector evaluates indications against the agreed acceptance criteria.
- Record plate position, indication location, observations and clear photographs. Distinguish relevant indications from background or non-relevant marks.
- Red bleed-out requires evaluation; it is not automatically proof of a crack. No visible indication is not a guarantee that all possible leakage paths have been ruled out.
09. Clean, assess gaskets and reassemble
- Complete post-test cleaning and drying appropriate to the process, including hygiene requirements before returning product-contact surfaces to use.
- Inspect gasket condition, grooves, frame, guide bars and tightening components; agree replacement needs.
- Reassemble only accepted components in the approved plate sequence and close to the unit-specific dimension. Do not substitute a generic torque or closing value.
10. Verify and document the outcome
- Carry out the agreed final leak or hydrostatic verification under the approved unit-specific test plan.
- Compile the inspection scope, procedure, consumables, timings, plate identification, photographs, results and limitations.
- Record repairs or replacements, recommendations and the responsible team's return-to-service approval.
- Send DFT your equipment details and intended shutdown window to discuss an inspection scope; this article does not promise certification or a fixed completion time.
Prepared from DFT's supplied DP Test Procedure and project inspection proposal. Photos are reference illustrations, not a record of testing the reader's equipment. Customer-specific identifiers and commercial estimates have been omitted. This educational overview is not an approved work instruction, certification or substitute for the applicable equipment manual.
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