---
title: "Stainless Steel Flanges For Desalination Plants: Grade Selection And Chloride Corrosion Challenges"
date: 2026-06-09T03:37:54Z
modified: 2026-06-26T01:07:08Z
permalink: "https://www.longanflange.com/blog/stainless-steel-flanges-desalination-corrosion/"
type: post
status: publish
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wpid: 3706
categories:
  - Blog
featured_image: "https://www.longanflange.com/wp-content/uploads/2026/06/图片8-1.webp"
featured_image_alt: Stainless Steel Flanges For Desalination Plants
timestamp: 2026-06-26T01:07:08Z
tags:
  - Blog
---

A corrosion flange problem in a desalination plant usually starts with the wrong grade choice. Many buyers think 316L is enough because it is stainless steel. In some areas, it can work. In other areas, it can fail too early.

Desalination is not one simple water line. The chloride level, temperature, and pressure change from one section to another. Raw seawater, RO high-pressure lines, and brine discharge lines should not always use the same flange grade.

So the better question is not “What grade of stainless steel is corrosion resistant?” The better question is “Where will this flange be installed, and what chloride level will it face?”

For desalination buyers, stainless steel flange material selection should be checked by process stage, not by a general rule.

## **Why Desalination Is One Of The Toughest Environments For Stainless Steel Flanges**

Desalination plants are hard on stainless steel because they combine salt, heat, and moisture. Seawater has about 19,000 ppm chloride ions. In hot areas like the Middle East, inlet water can reach 35°C or higher.

That mix can cause pitting and crevice corrosion.

Pitting looks small at first. It may only show as tiny holes on the flange face. But those holes can grow deeper over time.

Crevice corrosion is more hidden. It happens in tight spaces where water sits, and oxygen cannot move freely. Flange joints have many of these spaces.

The risky areas are easy to picture: the flange face under the gasket, bolt holes, and small gaps around the joint. If the grade is too weak for the service, the flange can become the weak point of the whole line.

In real projects, the pipe body may still look fine after years of service, while the flange sealing face already shows corrosion marks.

![Understanding The Desalination Process](https://www.longanflange.com/wp-content/uploads/2026/06/图片9-1-1024x512.webp)

## **Understanding The Desalination Process — Where Flanges Are Used**

Flanges are used in several parts of a desalination plant. The two common systems are SWRO, or seawater reverse osmosis, and MSF/MED, which are thermal desalination processes.

In an SWRO plant, flanges may appear in the raw seawater intake line, pretreatment system, high-pressure pump area, membrane module connection, brine discharge line, and product water line.

Each area has a different level of risk.

The raw seawater intake line handles normal seawater, so the chloride level is already high. The pretreatment line is similar, but the pressure is usually lower.

The RO high-pressure section is more demanding. It has seawater, pressure, and often a higher temperature.

The brine discharge line is usually the harshest section. After water is removed, the chloride level may rise to about 38,000 to 70,000 ppm.

Product water is different. It has much lower chloride, often below 500 ppm, so the corrosion risk is much lower.

This is why one stainless grade cannot cover the whole plant safely.

## **Grade Selection By Process Stage — A Practical Guide**

The flange grade should follow the actual service area. A grade that works in product water may not last in brine discharge.



| **Process Stage** | **Chloride Level** | **Temperature** | **Suggested Grade** | **Practical Note** |
| --- | --- | --- | --- | --- |
| Raw seawater intake | ~19,000 ppm | Ambient | 316L / Duplex 2205 | 316L may work, but service life may be shorter |
| Pretreatment system | ~19,000 ppm | Ambient | 316L | Often acceptable because pressure is lower |
| RO high-pressure stage | ~19,000 ppm | 25–40°C | Duplex 2205 / Super Duplex 2507 | 316L is risky in many cases |
| Brine discharge line | 38,000–70,000 ppm | 30–45°C | Super Duplex 2507 / 904L | This is one of the toughest sections |
| Product water line | <500 ppm | ambient 304l>