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Quotes - Engineering - SalesBundle Renewal
Renewing a Tube Bundle
The bundle is the part of a heat exchanger that wears out; the shell usually is not. Tubes carry the seawater, take the erosion at the inlet ends, collect the scale, and are the thin metal in the whole assembly. A shell is a plain pressure vessel with nothing flowing fast through it and, on a unit whose anodes were maintained, it is routinely in good order when the bundle has reached the end of its life.
A replacement bundle is a complete assembly: tubesheet, tubes, baffles and tie rods, built to the frame's geometry so it slides into the existing shell and seals against the existing bonnets. Because nothing else changes, the pipework, the mountings, the connection positions and the bracket all carry over. On a boat that means the outage is measured in a day or two rather than a week of repiping.
To quote a bundle we need the frame number, the tube count, diameter and length, the pass arrangement and the tubesheet bolt pattern. Photograph the tubesheet face and the old bundle laid out, and note how many tubes were already plugged.
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What a Bundle Renewal Involves
Isolate and drain both circuits, remove both bonnets, unbolt the tubesheet from the shell flange and withdraw the bundle along the axis of the shell. Inspect the shell interior while it is open, because that is a view nobody otherwise gets. Then slide the new bundle in, fit new gaskets, refit the bonnets with new anodes, and pressure test both sides before returning to service.
The one thing that cannot be improvised is the clearance. Withdrawal needs at least the tube length in clear space in line with the shell, plus room to handle the bundle and set it down. Confirm that before the outage. It is the most commonly forgotten layout item and the most expensive to discover with the vessel out of service.
Reading the Bundle That Comes Out
Lay the old bundle out and look at it before it goes in the skip. Thinning concentrated in the first inch or two of the tubes is inlet erosion and points at velocity, a throttled connection or a pass arrangement that was too aggressive. Deep isolated pits away from the ends point at chloride attack under deposits and a material that was not up to the water.
Even wall loss along the whole length points at anodes that were absent or exhausted. Heavy scale on sound tube walls points at low flow and is not a material problem at all. Each of those calls for a different specification on the replacement, and only one of them is answered by ordering the same part again.
Upgrading Material at Renewal
On the standard frames the bundle carries the tube material, so an upgrade is a bundle decision. Copper-nickel replaces copper wherever raw seawater is involved, and titanium replaces copper-nickel where the water is chlorinated, warm, polluted or fast. The shell, bonnets, connections and mountings all stay as they are.
Titanium brings one consequence worth planning: it is noble, so the rest of the wetted assembly becomes more anodic and the anode arrangement should be revised rather than copied. Tell us what the surrounding seawater circuit is made from. There is more on the trade-off in Titanium vs Copper-Nickel.
When a New Unit Is the Better Buy
If the shell has lost wall from the outside through years of damp lagging, if the bonnet flange faces are pitted past sealing, or if the withdrawal clearance no longer exists because machinery went in around the cooler, a bundle is not the economical answer. On the smallest frames the price difference between a bundle and a complete unit also narrows to the point where a new cooler wins.
We will price both when the frame makes it a genuine question, and say which we would choose. What we will not do is sell a bundle into a shell that will not give another decade of service, because that puts the whole outage back on the calendar in two years.
Read the Old Bundle
A bundle coming out of a shell is the best diagnostic document on the vessel, and it is usually thrown in a skip before anyone looks at it properly.
Common FAQs
On the larger frames it is a substantial saving, and the bigger gain is often time: the shell, mountings and pipework all stay, so the outage is short. On the smallest frames the difference narrows and a complete unit can be the better buy. Send the frame number and we will price both.
Frame number from the plate if it is legible, then tube count, tube outside diameter and tube length, the pass arrangement, and the tubesheet bolt pattern and diameter. Photograph the tubesheet face and the bundle laid out, and note how many tubes were already plugged. That set is enough to quote from.
On the standard frames, usually yes, since the tube material is a bundle property. What has to be checked is the tubesheet material and joint method and whether the bonnets sit happily alongside titanium galvanically. The anode arrangement also needs revising because titanium is noble. Send the frame number and the circuit materials.
At least the tube length in clear space in line with the shell, plus room to handle the bundle and set it down. Check it before the outage, not during. If machinery has been installed around the cooler since it was fitted, the clearance may no longer exist, and that changes the plan entirely.
Only if the old bundle failed for reasons unrelated to material. Inlet thinning and mid-tube pitting are material and velocity failures, and repeating the specification repeats the failure. Even wall loss means the anodes were neglected, and heavy scale on sound tubes means the flow was low. Read the bundle first.
