Controlling corrosion in Saudi Arabia’s desalination plants

As Head of Corrosion Department 

He elaborates: “Desalination is not 

Another important task which falls 

is split into various fields such as chemistry, marine biology & environment, corrosion, thermal process engineering, reverse osmosis engineering, etc. As a corrosion department, we investigate plant failures and provide recommendations, and test new materials and chemicals that could affect the integrity of equipment in desalination plants. 

Our activity is mainly focused on applied research, studying existing technology and finding its limitations, how we can use and adapt it to the needs of our customers. It’s a very practical, application-focused approach. However, we also carry out

some fundamental research through collaborations with universities or companies which are working on the development of new solutions for the desalination sector.”

Desalination technologies

The main desalination technologies used in the Middle East are thermal and membrane. Each method differs in terms of working principle, energy consumption, cost and reliability for seawater treatment. The most common desalination technologies in the region are:

“The various thermal and membrane desalination processes each present their own set of corrosion, materials and environmental challenges, requiring wide-ranging areas of research,” continues Dr. Meroufel. “These include corrosion occurring in hot vapour environments, aerated and nonaerated seawater, potable water, soil for water transmission pipelines, as well as in storage tanks and boilers. Troubleshooting investigations and failure analysis are important tasks for our team. Any equipment that suffers corrosion-related failures or environmentally assisted cracking is investigated to determine the root causes and provide recommendations to avoid repetition.”

Current projects

Apart from his ongoing research, Dr. Meroufel is currently involved in two large-scale projects. “We are involved in a worldwide project managed by the French Corrosion Institute to investigate crevice corrosion of stainless steels and nickel-based alloys. The objective is to examine various grades of stainless steels that have been exposed to natural seawater at locations around the world. This will provide very valuable information. For example, we will see how biofilm – which is different in the North Sea compared to the Gulf Sea – impacts on the initiation and propagation of crevice corrosion.

We are also looking at the impact of seawater temperatures which vary greatly around the planet. Crevice geometry is another factor we are studying. Initial results were presented during the European Desalination Society conference in 2016 and further results will be presented soon.” “This project has an impact on reverse osmosis membrane desalination in particular. Since we use a large amount of corrosion-resistant alloys (CRA) we are very satisfied with this project as the result will provide us with a clear picture when combined with information from the field and feedback from our desalination plants. We are now trying to make a correlation between the findings of the study and the experiences of our colleagues at the desalination plants.”

Localized corrosion & biofouling

Aged thermal desalination plants face more corrosion issues than the newer RO technology, Dr. Meroufel explains: “Existing plants in Saudi Arabia were mostly constructed in the late 1970s/ early 1980s. At that time the industry wasn’t aware of some problems that could occur during operation. It’s difficult to modify the design during operation, so the reality is that we need to find ways to treat the seawater going into the unit to avoid corrosion. One of the main problems is the continuous operation of the plants. Water demand is growing rapidly with the population and this puts enormous pressure on the plants, making it difficult to respect the interval between periodic inspections that are needed. We are forced to wait for longer intervals and this creates specific problems. One major challenge for the CRAs we use in the high temperatures and more severe conditions in plants today is localized corrosion. There is no way to monitor or detect this corrosion unless we stop the unit and open it up for inspection. Monitoring localized corrosion is a major challenge.”

“Another significant challenge is the problem of biofouling, a normal phenomenon that cannot be avoided even with chemical treatment. It plays a specific role especially within our RO desalination plants. In thermal MSF and MED plants biofouling doesn’t cause a lot of problems, but in RO plants it creates problems both for the membranes and for metallic materials like super austenitics, duplex and super duplex.”

Material evolutions

As desalination technology has matured the materials specified have also been modified. “In the early days, seawater desalination plants utilized a lot of Ni-Resist alloy, an austenitic cast iron in seawater or brine handling pumps. However, in response to the problem of stress corrosion cracking, we recommended to plant maintenance engineers that this material be replaced with duplex 2205. Based on feedback, there have been no problems using this material. Today we largely use a combination of two materials: stainless steel 316L and duplex 2205. In RO plants, super austenitics are the most commonly used materials, especially for high-pressure piping and pumps.

In some cases plants are also using super duplex 2750.” An innovation at the Ras al Khair MSF plant on the eastern coast, which was commissioned in 2015, was the use of duplex 2205 as the evaporator shell material. “Previously the materials specified were carbon steel for the low-temperature stages and carbon steel clad with 316L for the hightemperature stages. However for this new construction it was decided to use solid duplex for the entire evaporator shell.” “Materials used for tubing inside the heat exchangers are also evolving. In situations where the operating conditions are very aggressive titanium grade 2 is specified, otherwise copper nickel 90/10 or modified 70/30 are the two main materials most often specified.”

“Most of the corrosion solutions we propose are related to CRAs when our studies show that new materials in the market could be suitable solutions depending on the situation. Another emerging possibility, however, is the shift from metallic material to composites, particularly for heat exchangers. The implementation of reinforced polymers in this application is a solution that we are exploring for the future. Composites can be a viable option in terms of cost, corrosion performance and degradation. The degradation characteristics of composite materials need further study and comparison to the degradation of metallic materials. However we already know that reinforced polymer composites can offer a good compromise between mechanical and heat transfer properties.”