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Quotes - Engineering - Sales| PRODUCT | STYLE | TEMA TYPE | BUNDLE |
| U-Tube Heat Exchanger | U-Tube, single tubesheet | BEU / AEU / BKU | Removable |
Corrosion-Resistant U-Tube Heat Exchangers
Selecting Alloy by Attacking Species
Naming a bulk fluid rarely settles a material question. What matters is what concentrates at the surface, at what temperature, and whether the surface is wetted continuously or intermittently. A stream that is benign in the pipe can be aggressive in the exchanger.
Chlorides. The classic limitation on 300-series stainless is chloride stress-corrosion cracking, and it depends on chloride concentration, temperature and tensile stress together. Duplex grades resist it markedly better. Titanium is effectively immune in most chloride service and is the standard answer for seawater and hypochlorite.
Acids. Sulfuric, phosphoric and organic acids each have their own map. Alloy 20 was developed for sulfuric service; Hastelloy C-276 handles a broad range of oxidizing and reducing conditions; AL-6XN sits between the duplex grades and the nickel alloys on both performance and price.
Sour service. The U-bend is a residual stress concentration because cold bending work-hardens the outside of the bend. NACE MR0175 limits hardness there, which in practice means post-bend stress relief of the bend zone, a documented procedure and hardness testing. It is routine work, and it adds cost and lead time, so it needs to be on the table at enquiry.
Typical Construction
- 304L / 316L stainless: General service; limited by chloride stress-corrosion cracking
- Duplex 2205: Higher chloride tolerance and strength; work hardens in the bend
- Super duplex: Severe chloride and strength duty
- Alloy 20: Sulfuric acid and mixed acid service
- Hastelloy C-276: Broad oxidizing and reducing chemical resistance
- AL-6XN: High chloride and seawater duty, between duplex and nickel alloys
- Monel: Hydrofluoric acid and some reducing conditions
- Titanium Grade 2: Seawater, brine, hypochlorite; effectively immune to chlorides
- Copper-nickel 90/10 and 70/30: Seawater with velocity limits observed
- Sour service: NACE MR0175 hardness control and post-bend stress relief
Corrosion-Resistant U-Tube Heat Exchangers
U-TUBE • CONSTRUCTION
High-Pressure U-Tube
High-pressure U-tube heat exchangers. Why the U-tube wins above the range of a floating head seal, D-type front heads, heavy tubesheets and hydrostati
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U-TUBE • CONSTRUCTION
High-Temperature U-Tube
High-temperature U-tube heat exchangers for thermal fluid and hot oil service. Unlimited differential expansion with no expansion joint, and design fo
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U-TUBE • CONSTRUCTION
Sanitary U-Tube
Sanitary U-tube heat exchangers in 316L with tri-clamp connections, drainable geometry and removable bundles. Built for 3-A duty and CIP circuits.
+ Learn MoreCorrosion-Resistant U-Tube Heat Exchangers
Bending Changes What the Alloy Can Do
This is the part of alloy selection that is specific to U-tube construction. Cold bending work-hardens the outside of the bend and leaves residual tensile stress there. Duplex grades work-harden noticeably. High-strength alloys can approach their formability limit at tight radii.
The consequences are practical: a larger minimum bend radius on some alloys, a heavier tube gauge to compensate for wall thinning, and stress relief where the service or the code demands it. All of that is manageable, but it means the tube alloy and the bend radius have to be decided together rather than in sequence.
Mixed Construction Is Often the Right Answer
It is common and entirely correct to build the shell in one material and the bundle in another. Carbon steel shells with stainless or high-alloy bundles are routine where the shell-side fluid is benign and the tube side is not.
The detail to watch is galvanic pairing at the tubesheet and any wetted joint, and differential thermal expansion between dissimilar materials. Both are straightforward to design around once they are acknowledged.
