Floating head exchangers are the go-to choice when you need to pull the bundle for cleaning. That's their superpower. Add corrosion-resistant materials, and you've got a unit that can handle both fouling and aggressive fluids.
But they're not the right answer for every corrosive service. And they're certainly not cheap. We've specified, installed, and repaired enough of them to know where they make sense-and where they don't.
What a Floating Head Exchanger Actually Is (and Isn't)
In a fixed tube sheet exchanger, both tube sheets are welded to the shell. You can't remove the bundle. In a floating head design, one tube sheet is fixed, and the other-the floating head-can move freely inside the shell. The bundle pulls out from the front end.
What this gives you:
- The bundle comes out for cleaning, inspection, or retubing
- Thermal expansion is accommodated without stress on the tube joints
- You can clean the shell side mechanically
What this costs you:
- Higher upfront cost (more parts, more machining)
- More leak paths (the floating head joint is a potential leak point)
- Larger shell diameter (the floating head takes up space)
Our rule: use floating head when you need to clean the shell side or when thermal expansion is a concern. If neither of those applies, a fixed tube sheet exchanger is simpler and cheaper.
When Corrosion Resistance Matters Most
- Corrosion-resistant materials are expensive. You don't use them everywhere. Here's where we've found them to be essential:
- High chloride environments – seawater, brackish water, or cooling water with high chloride content. 316L is the minimum. Duplex or titanium for aggressive conditions.
- Acidic service – sulfuric, hydrochloric, or phosphoric acid. Material depends on concentration and temperature.
- Caustic service – high pH environments that attack carbon steel and even some stainless grades.
- Process-side contamination – if the fluid contains trace contaminants that form corrosive species, even if the main fluid is mild.
Our experience: we've seen plants overspecify corrosion-resistant materials for clean services. And we've seen plants underspecify for dirty services. The underspecified ones cost more in the long run-replacing a corroded floating head bundle is expensive.
The Materials We Actually Use
Based on our field experience:
316L stainless steel
Our baseline for anything with chlorides up to about 200 ppm at moderate temperatures
Good general corrosion resistance
About 1.5x the cost of carbon steel
Service life: 10–15 years in most services
Duplex 2205
PREN 32–35 (vs. 24–26 for 316L)
Handles chlorides up to 1,000 ppm in some conditions
Higher strength than 316L
About 2–2.5x the cost of 316L
Service life: 15–20+ years in aggressive chloride services
Titanium Grade 2
Nearly immune to chloride pitting
PREN > 40
Lightweight (60% of steel's density)
About 3–4x the cost of 316L
Service life: 20+ years in seawater
Alloy 20 / Hastelloy C-276
For highly acidic or mixed acid services
Cost: 5–8x 316L
Only used when nothing else works
The Floating Head Joint: The Weak Point
The floating head joint is where the floating tube sheet seals against the shell. In a corrosion-resistant design, this joint is made from the same material as the tube sheet-or a compatible alloy.
The problem: the joint is a crevice. Fluids can get trapped between the floating head and the shell. This is where we've seen corrosion start, even with high-alloy materials.
Our prevention measures:
- Use a large-radius fillet weld on the joint-sharp corners are crevice starters
- Specify a higher alloy grade for the floating head than the tubes if crevice corrosion is a risk
- Install a flush line to eliminate stagnant fluid zones
- Inspect the floating head joint annually
Cleaning: The Real Advantage
The main reason to choose floating head over fixed tube sheet is cleaning access.
What you can do with a floating head that you can't do with fixed tube sheet:
- Pull the bundle for mechanical cleaning
- High-pressure water lance the shell side
- Visually inspect all external surfaces
- Replace individual damaged tubes
Our cleaning schedule recommendation:
- Fouling service (moderate): inspect every 12 months, clean as needed
- Heavy fouling service: inspect every 3–6 months
- Clean service: inspect every 2 years
We had a refinery client whose fixed tube sheet exchanger was cleaning every 3 months with chemical cleaning. They switched to a floating head exchanger and now pull the bundle for mechanical cleaning every 8 months. The cleaning cost per year is about 30% lower, and the heat transfer performance is better.
Selection Checklist for Corrosion Resistant Floating Head Exchangers
Before specifying:
- Need for cleaning – do you need to pull the bundle? If not, fixed tube sheet is cheaper.
- Thermal expansion – is ΔT between shell and tubes high? Floating head handles expansion.
- Corrosion risk – what are the actual chlorides, pH, and temperature? Get current fluid analysis.
- Material selection – match to worst-case conditions, but don't overspecify for clean services.
- Crevice risk – the floating head joint is the weak point. Consider higher alloy for the head.
- Cost-benefit – run lifecycle cost, not just purchase price. Include downtime cost.
- Space constraints – floating head exchangers are larger in shell diameter. Check clearance.
- Vendor experience – not every manufacturer builds floating head exchangers well. Ask for references.