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Last updateMon, 20 Nov 2017 4pm

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Where Valves Are Used: Everywhere!

Where Valves Are Used: Everywhere!

Valves can be found just about anywhere ...

Oxygen Cleaning: A Validated Process is Critical for Safety

Oxygen Cleaning: A Validated Process is Critical for Safety

From time to time, we re-publish well-re...

Inspiration and Automation: Keys to Best-in-Class Operations

Inspiration and Automation: Keys to Best-in-Class Operations

For the last several years, at industry ...

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Industry Headlines

VanAire Celebrates Manufacturing with ‘Industry After Hours’

-1 DAYS AGO
VanAire Celebrates Manufacturing with ‘Industry After Hours’

On Nov. 8, Delta County, MI K-12 students and parents attended Industry After Hours at VanAire to learn more about the high tech, high skilled manufacturing jobs that are available. Over 276 participants were treated to a fun, entertaining and informative event that exceeded expectations and inspired ...

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Emerson Opens Solutions Center in Singapore

2 DAYS AGO

As part of its drive to make Singapore a hub for the delivery of Industrial Internet of Things (IoT) technologies and services for customers across Asia Pacific, Emerson opened a customer-focused Solutions Center at the regional headquarters of its Automation Solutions business in Singapore. To mark...

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Energy Outlook Shows a World in Transformation

5 DAYS AGO

The resurgence in oil and gas production from the United States, deep declines in the cost of renewables and growing electrification are changing the face of the global energy system and upending traditional ways of meeting energy demand, according to the World Energy Outlook 2017 . A cleaner and more...

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U.S. Shale Output Expected to Rise Again in December

5 DAYS AGO

“U.S. shale production for December is expected to rise for a 12th consecutive month,” according to the Energy Information Administration (EIA), “as oil prices remain near their mid-2015 highs.”

Reuters reports that “projected gas output would increase in each of the major...

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U.S. Industrial Output Up 0.9% in October

2 DAYS AGO

Industrial production rose 0.9% in October, and manufacturing increased 1.3%. The index for utilities rose 2.0%, but mining output fell 1.3%, as Hurricane Nate caused a sharp but short-lived decline in oil and gas drilling and extraction. Even so, industrial activity was boosted in October by a return...

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Empire State Manufacturing Survey Shows Continued Growth

3 DAYS AGO

Business activity continued to grow strongly in New York State, according to firms responding to the November 2017 Empire State Manufacturing Survey. Though the headline general business conditions index fell eleven points from the multiyear high it reached last month, it remained firmly in positive ...

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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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