Valve Magazine

Wed04162014

Last updateTue, 15 Apr 2014 3pm

The Expanding Network of Valves

The Expanding Network of Valves

As industry itself reaches into more and more area...

Valve Packing & Gasket Research and Development Devices

Valve Packing & Gasket Research and Development Devices

The continuous improvement of valve packing techno...

Fire Protection Solutions

Fire Protection Solutions

Because of the potential harm and damage to people...

Understanding Functional Safety Standards

Understanding Functional Safety Standards

While many people might recognize the term “functi...

VALVE Magazine Print & Digital

Subscribe

Read
the latest digital edition


Subscribe to the digital edition

Subscribe to the print edition

  • VMA Links

  • Gallery of Valves

Ball Valve Butterfly Valve Check Valve Control Valve Diaphragm Valve Gate Valve Globe Valve Needle Valve Pinch Valve Plug Valve Relief Valve
BUYERS GUIDE 300x80

Sponsored Products

  • ja-news-1
  • ja-news-2
  • ja-news-3
Advertisement

Web Only

Magazine

The Expanding Network of Valves

The Expanding Network of Valves

As industry itself reaches into more and more areas of the world, getting the eq...

The Expanding Reach of Plastic Valves

The Expanding Reach of Plastic Valves

Although plastic valves are sometimes seen as a specialty product—a top choice o...

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).

 

Valve Magazine Digital Edition

14 wnt cover 160x214Inside the Winter 2014 issue…

• Compression Packing Friction
• Wireless Technology
• Purchasing Standards
• New EPA Concerns

CLICK HERE TO REQUEST YOUR
DIGITAL EDITION PREVIEW EMAIL