Industrial Process

Pressure cycling the unit was not selected for. Fast-closing solenoid valves produce water hammer, and piston or diaphragm pumps deliver flow in pulses. Each spike flexes the plates a little, and the braze joints fatigue even though the pressure never approaches the rating.

The symptom is a leak after months instead of years, with no sign of corrosion on the failed unit. Slow the valves, add a pulsation dampener or accumulator near the pump, and make sure the piping is supported so the connections carry no load. Tell us when a duty is cyclic, because that is what the fatigue-tested M class exists for.

Viscosity dominates it. Oil flows in thick, slow layers that transfer heat poorly and cost a lot of pump head, so the oil side sets the plate type and plate count while the water side has capacity to spare.

Select at the coldest oil temperture the unit will see in operation, not only at the hot running condition. Cold oil at start-up can be many times thicker, and a selection that works warm may trip the system on high differential pressure when cold. Send the oil grade or its viscosity at two temperatures. The oil cooling page goes further.

The nameplate tells us exactly what was fitted. It does not tell us wether that unit still suits the plant. A change of fluid, a higher operating temperature, a new cleaning chemical or a switch from town water to recycled water can each make the original material code wrong.

Send the nameplate and today's operating conditions together. If nothing relevant has changed, the replacement is the same designation. If something has, we keep the frame and connections where possible and change only the field that needs it, most often the material code or the plate count.

There are three, and the lowest one governs. The pressure class trades pressure against temperature: L reaches 225 C but only at up to 14 bar, while H holds 45 bar at 155 C. The braze has its own ceiling, roughly 185 C for copper, so a duty near the top of the L class is beyond a copper-brazed build and calls for nickel.

The third is the approval. The ASME envelope covers -40 C to +150 C and CRN covers -196 C to +225 C, so a hot duty can fall outside the code a site requires. Raise the code requirement at enquiry; approvals and certifications has the detail.

When the fluid carries solids, fibers or a scale that a strainer and a chemical clean cannot deal with. A brazed pack has narrow channels and cannot be opened, so anything that lodges inside stays there. Slurries, fluids that crystallize or set on cooling, and heavily scaling water all belong in an exchanger that can be taken apart.

The same holds where the process requires the heat transfer surfaces to be inspected. On clean, filtered or closed-loop fluids a brazed unit is the compact and economical choice. Name the fluid and what is in it.