Ops teams get trained to hunt gasketed plate packs when a PHE weeps. That habit fails on a fully welded bloc. There is no elastomer between corrugated plates. The pack is laser- or TIG-welded into a cassette. When you see drips at the frame, the first place to look is usually the cover seal — the gasket (or metal seal) that sits between the removable side cover and the welded pack face — not a mythical plate gasket that never existed.
This checklist is for shift leads, reliability engineers, and mechanical techs who inherit a Compabloc-style welded unit (BlocWave-class alternative included) and need a leak walkdown that matches the hardware.
Why the mental model breaks
On a gasketed plate-and-frame exchanger, every channel edge is an elastomer. Leak → open frame → find the bad gasket → replace. On a Compabloc-style welded bloc:
- Plate-to-plate joints are welded. Channel-to-channel cross leaks go through weld defects or corrosion, not rubber.
- External process leaks at the cover face go through cover seals, nozzle gaskets, and sometimes packing around studs or instrument taps.
- Utility-side and process-side covers can each have their own seal geometry and material.
If your CMMS still codes every PHE leak as “plate gasket,” you will order the wrong kit and waste a turnaround window.
Walkdown order when you see a drip
Work from outside in. Photograph before you wipe.
- Cover face perimeter. Trace the seal land between cover plate and pack. Note which corner weeps first — gravity and stud tension often show a pattern.
- Nozzle flanges on the cover. Separate those from the cover seal itself. A flanged nozzle can drip while the cover seal is dry.
- Stud / nut seating. Look for washout stains under nuts, elongated stud holes, or painted-over previous leaks.
- Instrument and drain taps. Small NPT or flanged bosses get forgotten; they soak insulation and look like a cover leak from ten meters away.
- Only then consider internal pack issues (cross-contamination between circuits, unexplained duty loss with dry exteriors). Those need chemistry samples or pressure tests, not a cover-seal kit guess.
Cover seal types you will actually meet
Vendors differ, but field units usually fall into a few buckets:
- Elastomer O-rings or flat gaskets in a machined groove on the cover or pack face. Common on lower-temperature liquid duties. Compounds vary (EPDM, FKM, FFKM, etc.) — match fluid and temperature from the seal datasheet, not from a plate-gasket catalog.
- Graphite or composite flat seals for hotter or chemically aggressive service where rubber is marginal.
- Metal seals / specialized profiles on some high-duty designs. Do not substitute an elastomer “because it fits the groove.”
Never assume the seal on the hot-side cover is the same compound as the cold-side cover. Plants reuse whatever was in the storeroom once; the second leak is often a material mismatch, not a torque problem.
For BlocWave cover and service concepts (without inventing ratings here), start from the product page and pull the unit’s own GA and seal BOM: BlocWave welded plate heat exchanger.
Torque, sequence, and the “we snugged it” failure
Cover leaks after CIP or a nozzle swap are often assembly errors: uneven stud load (star/cross sequence — one corner crushed, opposite under-compressed), reused crushed seals, dirty seal land (spatter, remnant, paint), or warped covers after thermal cycling or impact. Record as-found torque or nut position marks before you strip anything. “We tightened it more” without a baseline is how you stretch studs.
Distinguishing cover weep from pack cross-leak
| Symptom | Points toward cover / external | Points toward pack / internal |
|---|---|---|
| Visible drip at cover land | Yes | Unlikely alone |
| Insulation wet only at perimeter | Yes | Check nozzles too |
| Two process streams mixing in sample points | No | Yes — weld/corrosion path |
| Duty collapse, exteriors dry | Maybe fouling | Cross-leak or severe fouling |
| One circuit pressurizes the other at shutdown | No | Internal communication |
Do not hydrotest one side against the other with people standing at the cover face and no relief path. Follow the site pressure-test procedure and the OEM/alternative supplier limits for that serial number.
Spares and CMMS hygiene
Stock cover seal kits by unit serial / drawing revision, not by “Compabloc-style generic.” Groove dimensions and compounds are not interchangeable across brands or generations. Tag CMMS codes separately: cover seal leak, nozzle gasket leak, pack cross-contamination (suspected), stud/hardware — so reliability gets a real Pareto instead of a fake “gasket” mountain.
Quick ops checklist (print this)
- [ ] Photo of leak location before wipe-down
- [ ] Which cover (process A / process B / utility)
- [ ] Seal compound called out on GA vs what was last installed
- [ ] Stud sequence and target from procedure
- [ ] New seal kit issued against serial number
- [ ] Land cleaned and inspected; cover flatness checked if repeat leak
- [ ] Post-assembly soap or tracer check at low pressure before insulation
- [ ] CMMS code is cover seal — not plate gasket
Welded blocs earn their keep by deleting plate-pack elastomers. They do not delete sealing discipline. Treat the cover seal as a first-class wear item, and most “mysterious” external leaks stop being mysterious.
— Sean Woo, ShineHeat Tech, Shanghai
