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Safety Relief Valve FAQs

Safety Relief Valve FAQs

Companies that repair, test, maintain or...

An Update on U.S. Valve-Related Standards

An Update on U.S. Valve-Related Standards

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Diagnostics for Commissioning and Startup

Diagnostics for Commissioning and Startup

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Industry Headlines

Natural Gas-Fired Electricity Conversion Efficiency Grows, Coal Stable

Monday, 21 August 2017  |  Chris Guy

From 2006 to 2015, annual average heat rates of natural gas-fired electricity generators decreased 7% as heat rates of coal-fired electricity generato...

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Safety Relief Valve FAQs

Safety Relief Valve FAQs

Monday, 14 August 2017  |  Lyndon Garrick

Companies that repair, test, maintain or supply valves routinely receive inquiries from end users about safety-relief valves. Here are a few questions...

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Industry Headlines

Rotork Contracted to Supply UAE Oil Field

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Awarded by Hyundai Heavy Industri...

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Natural Gas-Fired Electricity Conversion Efficiency Grows, Coal Stable

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From 2006 to 2015, annual average heat rates of natural gas-fired electricity generators decreased 7% as heat rates of coal-fired electricity generators remained stable, increasing only 1%. Heat rates are calculated based on the amount of energy (measured in British thermal units) reported to the U....

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Executive Order to Speed Up Infrastructure Project Approval

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President Trump signed an executive order intended to roll back “rules regarding environmental reviews and restrictions on government-funded building projects in flood-prone areas as part of his proposal to spend $1 trillion to fix aging U.S. infrastructure,” Reuters reports .

“Trump's...

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U.S. Factory Output Declined in July

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Manufacturing output edged down 0.1% in July. The index for durables decreased 0.5%. Among durable manufacturing industries, with the indexes for primary metals and for furniture and related products each dropped more than 1%. The index for other manufacturing (publishing and logging) moved down 0.4%....

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Empire State Manufacturing Index Highest in Nearly Three Years

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Business activity grew strongly in New York State, according to firms responding to the August 2017 Empire State Manufacturing Survey. The headline general business conditions index climbed fifteen points to 25.2, its highest level since September 2014. The new orders index rose seven points to 20.6 a...

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Less Expensive Stainless Steels

materials_q_and_a_graphicQ: High metal prices, especially for nickel and molybdenum, have our procurement people looking at less expensive stainless steels like the 200 series. Are these as good as 304 and 316 stainless steels?

A: Before answering this question, let’s look at the history and differences between the 200 and 300 series stainless steels. The original 200 series stainless steels were first developed in the 1930s by using manganese to replace some of the nickel in the 300 series austenitic stainless steels. Certain elements used in stainless steels either promote the formation of the austenitic or ferritic atomic structure, and the austenitic stainless steels are the more corrosion resistant. The austenitic-forming elements are nickel, manganese, nitrogen, copper and carbon. The primary ferrite-forming element is chromium.

Since a stainless steel needs 10-12% minimum chromium to be considered “stainless,” it then takes about 8-10% nickel to offset the ferritic-forming tendency of chromium to make a stainless-steel austenitic more corrosion resistant. Historically, manganese has always been a lower cost element than nickel. So whenever there is a scarcity of nickel (as there was in the 1970s) or when nickel prices are high, such as they are now, people look to the 200 series stainless steels as lower cost alternatives.

But before deciding to use a 200 series stainless steel, there are issues to be considered. To further complicate the matter, there has been an increase in newer chrome-manganese grades developed and produced in Southeast Asia and China. The 200 series now represent 34% of China’s production of stainless steels.

Facts About the 200 Series

There are two categories of the 200 series stainless steels—those that only replace some of the nickel with manganese, such as the original 201 or 202 grades, and those that replace most of the nickel, such as the newer grades now being seen in Asia. These newer low-nickel grades also tend to have lower chromium, which further decreases their corrosion resistance.

To date there are no international standards for the use of these newer grades. To add additional confusion, users of stainless equipment, such as valves, know that magnetism—or more correctly, the lack of magnetism—is a way of verifying they have received the superior 300 series stainless steels. Since 200 series grades are non-magnetic, this could cause a buyer to mistakenly believe they have the correct and more corrosion-resistant 300 series stainless steel. In fact, there have been a few instances of deliberate mislabeling of 200 series grades as being 304 stainless. Some scrap dealers also still rely on magnetism to sort the 300 series grades from the magnetic and less corrosion-resistant 400 series stainless steels. Thus, the proliferation of the non-magnetic 200 series grades could lead to some serious scrap contamination issues if recyclers are not careful.

The first indication as to whether these grades are equivalent to 304 and 316 is they receive little attention until nickel either becomes scarce or when nickel prices are high. The primary reason they do not see greater use is simply because they are not as corrosion resistant as 304 and 316 stainless steels. However, the 200 series grades do have several beneficial uses, including cookware, railcars, lighting columns, washing machines and most mildly corrosive applications.

Problems with Corrosion

While the 200 series alloys do have good atmospheric corrosion resistance, they do not have good resistance to most corrosive chemicals. In addition, because most of the 200 series alloys tend to have a higher carbon content to help promote the austenitic structure, it makes them more susceptible to intergranular corrosion. Other characteristics that make the 200 series less attractive include their tendency to be more work hardenable and their potential to have slightly inferior surface finish.

So if you really need to lower your cost, you need to be very careful in the application of these 200 series stainless steels. A better choice would be to look at some of the duplex stainless steels such as S31803. The duplexes have about half the nickel of the 300 series so at the higher nickel prices they may be less expensive than the 300 series while providing comparable corrosion resistance. There are also some new lean (lower nickel) duplex grades on the market that may be even more cost effective. In any case, be sure to deal with reputable and knowledgeable suppliers who can assist you with the proper material selection.


Thomas Spence is director of materials engineering of Flowserve Corporation (www.flowserve.com). Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it.. The author wishes to acknowledge the assistance of Don Bush, materials engineer, Emerson Process Management-Fisher Division (www.emersonprocess.com).

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