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Last updateMon, 25 Sep 2017 6pm

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Carbon Capture and Storage: Why and How?

Carbon Capture and Storage: Why and How?

Carbon (CO 2 ) capture and storage (CCS) i...

Can Valves Mitigate Flooding from Severe Weather Events

Can Valves Mitigate Flooding from Severe Weather Events

Hurricanes Harvey and Irma have certainl...

Machine Learning: A Brave New World

Machine Learning: A Brave New World

Whether you embrace it as a way to more ...

The Road to Valve Knowledge

The Road to Valve Knowledge

Valve expertise is a journey, not a dest...

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Industry Headlines

Permian ‘Super Basin’ Holds Trillions in Untapped Oil

Monday, 25 September 2017  |  Chris Guy

Energy researchers at IHS Markit have completed the first, three-year phase of a massive Permian Basin research project that models and interprets the...

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Industry Headlines

Flowserve Appoints Lee Eckert as CFO

8 HOURS AGO

Flowserve has named Lee Eckert as senior vice president and chief financial officer (CFO), effective October 9, 2017. Eckert joins Flowserve from CHC Group LLC., a global commercial helicopter service provider to the offshore oil and gas industry, where he served as senior vice president and CFO since...

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Velan Announces New Sales Structure

4 DAYS AGO

Velan is re-designing its sales structure to be better aligned with customers’ market approach. This change is intended to focus Velan’s resources on maximizing impact and competitiveness in today’s challenging economy.

Paul Dion has been appointed as vice-president of sales, process ...

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Permian ‘Super Basin’ Holds Trillions in Untapped Oil

2 HOURS AGO

Energy researchers at IHS Markit have completed the first, three-year phase of a massive Permian Basin research project that models and interprets the giant basin’s key geologic characteristics to better estimate its remaining hydrocarbon potential, and initial results indicate the giant basin ...

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DowDuPont Opens New Ethylene and Plastics Plant in Texas

5 HOURS AGO

DowDuPont Materials Science announced the startup of its new integrated world-scale ethylene production facility and its new ELITE enhanced polyethylene production facility, both in Freeport, TX. Both units will continue to ramp up through the third quarter and are expected to reach full rates in the ...

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U.S. Manufacturers Seeking More Renewable Energy

4 DAYS AGO

A new report from David Gardiner and Associates finds that 83% of the largest manufacturing companies with a U.S. footprint have established greenhouse gas reduction targets and 25% of manufacturers have established renewable energy targets. The analysis also finds that enabling access to renewable en...

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Harvey Caused Steep Drop in U.S. Industrial Output

7 DAYS AGO

Industrial production declined 0.9% in August following six consecutive monthly gains. Hurricane Harvey is estimated to have reduced the rate of change in total output by roughly 0.75%. The index for manufacturing decreased 0.3%; storm-related effects appear to have reduced the rate of change in facto...

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Multi-colored Stain on Valves

materials_q_and_a_graphicQ: I am handling high purity-water and keep getting a multi-colored stain on my valves and other equipment. What is this, and how can I prevent it?

A: You are describing a phenomenon called "rouging," a term that pertains to the multi-colored stain you are seeing. Rouging is a problem that is seen primarily in high-purity water applications or steam. Though more commonly associated with the pharmaceutical and electronics industries, it can occur most anywhere. At the lower temperatures rouge is red or yellowish in appearance, but in high-temperature steam it will be dark gray or black. The FDA has not made any formal opinion about rouging, but pharmaceutical companies are concerned about contamination of their products so they go to great lengths to prevent it and to clean their systems when it occurs-incurring undesired downtime and expense.

The mechanism of rouging is still not fully understood and as a result there are some myths and misconceptions about what it is and how to prevent it. Essentially, rouge is a form of rust, i.e., iron oxide, but different than the heavy rust seen when stainless steel is not cleaned properly after heat treatment or welding. While normal rust is a result of improper cleaning during manufacture, rouge is a much thinner layer that occurs when perfectly cleaned stainless steel reacts with high-purity water environments. Rouge seems to be more prevalent at temperatures in excess or 60° C.

We know that stainless steels achieve their corrosion resistance by developing a very thin microscopic chromium oxide layer. The general consensus about rouging is that certain services, such as high purity water with very low oxygen content, dissolve this protective layer and allow the stainless steel to resume corroding. This corrosion is then responsible for the staining we call rouging. These stains have been analyzed as being various types of iron oxide as well as containing traces of chromium and nickel.

While mainly an aesthetics problem, most people still want to prevent rouge in their systems. One commonly held belief is that the ferrite phase in cast stainless steels or welds causes rouging, and purchasers of valves and other equipment frequently impose strict limits on the ferrite content of cast stainless steels. Since wrought stainless steels with no ferrite also experience rouging, it doesn't appear that ferrite is the culprit.

A study conducted by AvestaPolarit1, found that the water's gas content and a metal's surface finish were influential for rouging. Basically, water with high oxygen and low carbon dioxide content was less likely to cause rouging as were electro-polished surfaces of the metal components. This study also found no significant correlation for the different alloy grades, including duplex stainless steels with their high ferrite content.

Since most people find rouge objectionable in their systems, much attention has been given to its removal. Various acids and chelates are used to clean systems of rouge, but these can leave behind their own contaminates or films. In addition, if acid exposure is not controlled closely, the acid can etch the metal surfaces thus destroying the expensive electro-polished surfaces. Therefore, the most effective way to prevent rouge is by somehow introducing sufficient oxygen to the system, which helps maintain the protective chromium oxide layer.

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