Gr7 Titanium Heat Exchanger for Seawater Desalination

Product Overview

Reviewed and maintained by the Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd.

Gr7 Titanium Heat Exchanger for Seawater Desalination | Ti-0.2Pd (R52400), ASTM B338, ASME VIII + TEMA

Meta Description: Gr7 (Ti-0.2Pd, R52400) titanium heat exchanger for seawater desalination — MSF brine heaters, MED evaporators, condensers in hot deaerated brine. Palladium 0.12–0.25% raises crevice-corrosion threshold; same strength as Gr2, no wall re-design. ASTM B338 tube / B265 tubesheet, ASME VIII + TEMA, roll+seal weld, PMI per heat, EN 10204 3.1, 3.2 TPI PO-fronted.

Gr2 Is Great — Until the Brine Gets Hot and Stagnant

Seawater desalination is not one duty. It is three:

• SWRO auxiliaries / ambient seawater coolers → Gr2 is usually correct
• MED evaporators / condensers (65–70°C) → Gr2 standard
• MSF brine heater (110–120°C, concentrated, deaerated brine) → Gr2 fails by crevice corrosion + hydrogen absorption regardless of wall thickness; Gr7 is the engineered answer

Thicker Gr2 does not raise the crevice threshold. At ~80°C+ in deaerated chloride, CP titanium can absorb hydrogen → hydride cracking in 6–12 months. That is not a wall-thickness problem; it is an alloy-potential problem.

What Palladium Actually Does (the Gr7 mechanism)

• Gr7 = commercially pure titanium + 0.12–0.25% Pd (UNS R52400, TA9)
• Pd ennobles the alloy, holds the TiO₂ passive film stable in hot deaerated chloride
• Crevice corrosion initiation temperature shifts substantially higher than Gr2 (~80°C CCT)
• Hydrogen evolution at the crevice is suppressed — no hydride embrittlement in MSF brine heater service
• Mechanicals unchanged: min tensile 345 MPa, yield 275 MPa, elongation ≥20% (annealed) — same allowable stress as Gr2, no re-rating

Translation: specify Gr7, keep the same wall, keep the same ASME calc — just close the corrosion gap.

Where Gr7 Is the Right Call in Desalination

How to Prove It Is Really Gr7 (not Gr2 with a Gr7 tag)

1. MTC EN 10204 3.1 must declare Pd 0.12–0.25% — no Pd figure = not Gr7 proof
2. Arrival PMI (OES/XRF): Pd detectable in matrix, not just surface
3. Weld filler: matching Pd-bearing wire (ERTi-7) to keep HAZ corrosion upgrade
4. Heat number cross-linked: tube tag = MTC = weld map
5. 3.2 TPI (SGS/BV/TÜV) witness on Pd chemistry when PO-fronted

Design & Fabrication Baseline

• Tube: ASTM B338 Gr7, seamless or welded-annealed; typical 0.7–1.65mm wall
• Tubesheet: ASTM B265 Gr7 (solid) or Ti-clad CS; groove + roll+seal weld
• Joint: hydraulic roll → autogenous GTAW seal weld, dual-side argon ≥99.999%
• Clearance roll-to-weld ≥3.2mm; PT non-chlorinated; weld color silvery/straw only
• Code: ASME VIII Div.1 + TEMA Class R/C/B; MSF duty calc includes thermal shock + blowdown
• Surface: pickled/passivated, ferroxyl free-iron check, no carbon-steel contact in store
• Velocity: 1.5–2.5 m/s tube-side to limit scaling/biofouling (confirm with licensor)

MSF Brine Heater — Why Gr7 Pays Back

• Gr2 in 120°C deaerated brine: hydride risk in 6–14 months, perforation possible within a season
• Gr7 with 1.2–1.65mm wall: 10–15 yr service life typical, no hydrogen-damage driver
• Pd premium vs Gr2 is recovered by avoiding one unplanned retube in a critical-path unit
• Lifecycle cost, not kg-price, is the right comparison in MSF

QC Chain (per heat, per joint)

1. B338 Gr7 MTC 3.1 — Pd chemistry explicit + tensile + ET/hydro election
2. PMI on tube body + tubesheet — Pd verified
3. Roll parameter log + seal-weld gas-shield record
4. PT (non-chlorinated) on U-bends + tubesheet welds
5. Helium leak option for critical MSF/MED duty
6. Hydro per ASME VIII; as-built + weld map in MDR
7. 3.2 TPI PO-fronted where project specifies

Hard Boundaries (no overclaim)

• Gr7 does not make HF/fluoride safe — titanium excluded on fluoride contact
• Dry Cl₂ (<0.5% H₂O) excluded — moisture required for passive film
• Gr7 ≠ strength upgrade — for high-pressure thin wall use Gr9; for hot-brine strength use Gr12
• Pd value must appear on MTC; "Grade 7" text without Pd = incomplete certification
• 3.2 cannot be back-issued; TPI named at PO
• Biofouling still happens on titanium — velocity + pretreatment still required

RFQ Template (copy-paste)

Process: MSF brine heater / MED evaporator / condenser / SWRO cooler ___
Seawater or blowdown Cl⁻ ___ppm, TDS ___, dissolved O₂ ___ppb
Max tube-wall temp: ___°C (upset ___°C)
Aerated / deaerated: ___
Scaling/biofouling: yes/no, treatment chem ___
Tube: ASTM B338 Gr7, OD×wall ___mm, straight / U-bend ___
Tubesheet: B265 Gr7 solid / clad (__mm Ti) ___
Joint: roll+seal weld, argon backing ___%
NDE: ET / hydro / PT(non-Cl) / helium (__ mbar·L/s)
Cert: 3.1 (Pd declared) / 3.2 TPI (SGS/BV/TÜV ___)
Code: ASME VIII Div.1 + TEMA Class ___
Incoterm: EXW / FOB / CIF / DAP ___

FAQ — Gr7 Titanium Desalination Exchanger

Q1: Can't I just use thicker Gr2 in MSF brine heater?
A: No. Wall thickness does not stop hydrogen absorption or crevice depassivation at 110–120°C deaerated brine. Gr7 changes the electrochemical potential; thickness cannot.

Q2: Is Gr7 stronger than Gr2?
A: Mechanically identical (345/275 MPa, ≥20% elong.). Gr7 is a corrosion upgrade, not a strength upgrade.

Q3: How do I confirm genuine Gr7 on arrival?
A: MTC must list Pd 0.12–0.25%; PMI verifies Pd in the matrix. No Pd on cert = not provable Gr7.

Q4: Gr7 or Gr12 for desalination?
A: Gr7 for maximum crevice/hydrogen resistance in hot deaerated brine (MSF). Gr12 where higher strength + lower cost is needed and duty permits.

Q5: Weld filler — can I use ERGr2 wire?
A: Only if you accept losing Pd in the weld/HAZ. For full Gr7 performance use matching Pd-bearing filler (ERTi-7).

Q6: Does Gr7 need cathodic protection?
A: Usually not in aerated seawater. In stagnant/deaerated hot brine, the alloy itself is the protection — that is the point of Pd.

Q7: SWRO plant — do I need Gr7?
A: Most SWRO aux coolers run Gr2. Gr7 is specified when temps/crevices or blowdown concentration push past Gr2 limits.

Q8: Lead time vs Gr2?
A: Pd-bearing melt slot confirmed per inquiry; not "always in stock", not "months". Firm slot after PO + heat allocation.

Q9: HS code?
A: Tube vs complete exchanger differ; Broker confirms by config/destination.

Q10: Biggest EPC mistake?
A: Writing "titanium, ASME" on an MSF brine heater PO with no grade call. Gr2 gets bought, hydride cracking arrives in under a year — and the cheapest tube becomes the most expensive retube.

Request a Grade-Fit Quote

Email: sales@[yourdomain].com

Send process step + dissolved O₂ + max wall temp + Cl⁻ + duty. We return Gr2-vs-Gr7 justification (not a default Gr2 quote) with Pd-verification scope.

About: Baoji Gr7 titanium desalination exchanger desk — ASTM B338 R52400 tube bundles and shell-and-tube units for MSF brine heaters, MED evaporators and seawater condensers. Pd 0.12–0.25% declared on every 3.1 MTC, PMI-verified per heat, roll+seal-weld joints, ASME VIII + TEMA, EN 10204 3.1 default, 3.2 TPI PO-fronted. Grade chosen by dissolved oxygen, crevice temp and brine concentration — not by catalog. Heat No. = tube tag = MTC = weld map.