Water Treatment / Desalination

Mega-Scale SWRO Desalination Plant — Duplex 2205 Piping System

UAE, Gulf Cooperation Council85+ tons (pipe + fittings)2205 Duplex Stainless Steel Welded Pipe & Butt Weld Fittings

Project Background

A mega-scale seawater reverse osmosis (SWRO) desalination plant in the Gulf region, with a daily capacity exceeding 900,000 m³, supplies drinking water to 2 million residents. High-pressure brine piping (70 bar operating pressure), seawater intake lines, and chemical dosing systems are exposed to 65,000+ ppm TDS high-chloride environment with a 25-year design life. Conventional 316L material in this service achieves less than 3 years of service life.

Technical Specifications

Grade	UNS S32205 (2205) Duplex Stainless Steel
Size Range	DN50 – DN900 (2" – 36") welded pipe + butt weld fittings
Standards	ASTM A790, ASTM A815, NORSOK M-650
Key Metrics	PREN ≥ 35, Ferrite 40–60%, ASTM A923 Method C Pass

The Challenge

Desalination main process lines face severe pitting and crevice corrosion risks in concentrated seawater. 316L (PREN ~25) offers insufficient protection at chloride concentrations above 65,000 ppm, with critical pitting temperature well below operating conditions.

TOKO TECH Solution

TOKO TECH supplied 2205 (S32205) duplex stainless steel welded pipes with PREN ≥ 35, providing more than double the pitting resistance of 316L. The critical pitting temperature exceeds 50°C in 65,000 ppm Cl⁻ environment. All fittings underwent solution annealing + quenching to ensure optimal phase balance (40-60% ferrite) and uniform microstructure.

Search Keywords

duplex stainless steel pipeSWRO desalination2205 pipehigh chloride pipingseawater corrosion resistant pipe

Frequently Asked Questions

Why use duplex 2205 instead of 316L for desalination?

2205 duplex stainless steel provides a PREN (Pitting Resistance Equivalent Number) of 35+ compared to 316L's PREN of ~25. This means 2205 can withstand chloride concentrations above 50,000 ppm at elevated temperatures where 316L would rapidly fail from pitting corrosion. Additionally, 2205's yield strength (450 MPa) is double that of 316L (170 MPa), allowing thinner wall pipe and reduced weight.

What is PREN and why does it matter for desalination piping?

PREN = %Cr + 3.3 × %Mo + 16 × %N measures a stainless steel's resistance to pitting corrosion. For SWRO desalination plants operating with TDS above 50,000 ppm, a minimum PREN of 35 is recommended. 2205 achieves this through its balanced chromium (22%), molybdenum (3%), and nitrogen (0.15%) content.

What standards apply to duplex pipe for desalination plants?

ASTM A790 governs seamless and welded duplex stainless steel pipe. NORSOK M-650 is often specified for offshore/desalination applications requiring additional qualification testing. ASTM A923 tests for the absence of detrimental intermetallic phases in duplex stainless steels.

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