05202018Sun
Last updateFri, 18 May 2018 4pm

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The Past, Present and Future of Fire Testing

The Past, Present and Future of Fire Testing

Because so many of the applications wher...

Advancements in Blue Laser Scanning

Advancements in Blue Laser Scanning

As the industrial world continues to exp...

Cavitation in Globe Valves—and Proposed Solutions

Cavitation in Globe Valves—and Proposed Solutions

Straight pattern globe valves are widely...

The VMA Knowledge Forum, Part Two: The Human Factor

The VMA Knowledge Forum, Part Two: The Human Factor

Finding and retaining the right talent i...

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Industry Headlines

Emerson Agrees to Buy Aventics

Friday, 18 May 2018  |  Chris Guy

Emerson has agreed on terms to acquire Aventics from Triton for a cash purchase price of $620 million. Aventics deals in smart pneumatics technologies...

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Industry Headlines

Emerson Agrees to Buy Aventics

2 DAYS AGO

Emerson has agreed on terms to acquire Aventics from Triton for a cash purchase price of $620 million. Aventics deals in smart pneumatics technologies that power machine and factory automation applications. Aventics significantly expands Emerson’s reach in a growing $13 billion market.

With cen...

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Conval Names Brian White Refining & Chemical Industry Manager

3 DAYS AGO

Conval has appointed Brian E. White as refining & chemical industry manager serving the petrochemical industry in the Gulf states and elsewhere as opportunities and needs arise.

Based in Houston, White has over 20 years of experience selling instrumentation and capital equipment to the oil & ga...

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Outside of U.S., Natural Gas Outlook Diminishing

3 DAYS AGO

The mood in the natural gas industry, at least outside the U.S., is not as optimistic as it once was. According to the International Energy Agency (IEA), demand has slowed considerably for most of the period since 2011, from an average of 2.8% per year between 2000 and 2010, to 1.4% per year from 2011...

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ExxonMobil, BASF Form Gas Treating Alliance

3 DAYS AGO

ExxonMobil Catalysts and Licensing LLC and BASF Corporation have signed an alliance agreement to jointly develop new gas treating solvents and process technologies for use in natural gas processing and petroleum refining. Under this new agreement , BASF will market and license technologies developed f...

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Leading Economic Indicators Up 0.4% in April

2 DAYS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 0.4% in April to 109.4, following a 0.4% increase in March, and a 0.7% increase in February.

April’s increase and continued uptrend in the U.S. LEI suggest solid growth should continue in the second half of 2018. How...

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U.S. Factory Output Rose in April

3 DAYS AGO

Industrial production rose 0.7% in April for its third consecutive monthly increase. The rates of change for industrial production for previous months were revised downward, on net; for the first quarter, output is now reported to have advanced 2.3% at an annual rate.

Manufacturing output moved up 0.5...

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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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