02192017Sun
Last updateThu, 16 Feb 2017 9pm

i

Improving Valve Sealing Performance and Reliability

Improving Valve Sealing Performance and Reliability

From time to time, we are re-posting wel...

A Primer on Fugitive Emissions

A Primer on Fugitive Emissions

Fourscore and seven years ago, no one ha...

The State of Industrial Distribution in 2017

The State of Industrial Distribution in 2017

Key trends for the industrial distributi...

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

ITT Reports 2016 Fourth-Quarter, Full-Year Results

Thursday, 16 February 2017  |  Chris Guy

On a GAAP basis, ITT Corporation delivered revenue of $588 million in the fourth quarter of 2016, reflecting a 12% decline that included a 2% negative...

Readmore

Loading...

Industry Headlines

ITT Reports 2016 Fourth-Quarter, Full-Year Results

2 DAYS AGO

On a GAAP basis, ITT Corporation delivered revenue of $588 million in the fourth quarter of 2016, reflecting a 12% decline that included a 2% negative impact from foreign exchange. GAAP segment operating income decreased 12% .

In the Industrial Process segment, total revenue decreased 29% to $212 milli...

Readmore

Delta Centrifugal Rejoins VMA

3 DAYS AGO

This week VMA welcomed back associate member Delta Centrifugal Corporation of Temple, TX after a one year absence from the association.

Delta produces custom-made castings. Delta’s operations include Texas Stainless, Inc. Texas Stainless is a metals distributor and sells castings produced by Delt...

Readmore

How New U.S. Policies Will Affect the Chemical Industry

4 DAYS AGO

“In 2017, barring a recession in the U.S. and Europe or a slowdown in China, Moody’s Investor Service expects EBITDA in the chemicals industry to slip by 1 or 2% year-over-year.”

A new report from PwC predicts that the Trump administration “is likely to embrace policies that are...

Readmore

$2.2 Billion Investment Approved for Mad Dog Phase 2 Project

5 DAYS AGO

BHP Billiton has approved expenditure of $2.2 billion for its share of the development of the Mad Dog Phase 2 project in the Gulf of Mexico. During the fourth quarter of 2016, BP, which holds a 60.5% participating interest, sanctioned the Mad Dog Phase 2 project.

Mad Dog Phase 2, located in the Green...

Readmore

Philly Fed Manufacturing Conditions Continued to Improve in February

3 DAYS AGO

The index for current manufacturing activity in eastern Pennsylvania, southern New Jersey and Delaware increased from a reading of 23.6 in January to 43.3 this month and has remained positive for seven consecutive months. The share of firms reporting growth continues to increase: More than 48% of the ...

Readmore

Industrial Production Down 0.3% in January

4 DAYS AGO

Industrial production decreased 0.3% in January following a 0.6% increase in December. In January, manufacturing output moved up 0.2%, and mining output jumped 2.8%. The index for utilities fell 5.7%, largely because unseasonably warm weather reduced the demand for heating. At 104.6% of its 2012 avera...

Readmore

Wrong Alloy?

materials_q_and_a_graphicQ: My 316 stainless-steel valve is rusty and attracts a magnet. Did I get the wrong alloy?

 

A: Let's answer the second part of the question first. Forged 300-series stainless steels should be non-magnetic. However, cast versions of the 300-series stainless steels-such as CF8 (304), CF3 (304L), CF8M (316), CF3M (316L), CG8M (317), CG3M (317L), CF8C (347), etc.-are all formulated to contain some ferrite. The presence of ferrite makes the alloy less prone to cracking as the hot casting cools in the mold. Weld filler materials are also formulated to contain some ferrite for the same reason. The ferrite makes the material attract a magnet. The exact amount of ferrite, which influences the strength of magnetic attraction, is dependent on the exact chemical composition and the thermal history of the casting. In any event, CF3, CF8, CF3M, CF8M, CG3M, CG8M, and CF8C should all attract a magnet to some degree. In fact, if you have a casting in one of these alloys that doesn't attract a magnet, you should wonder whether something is wrong.

 

Now let's discuss the rusting portion of the question. While the term stainless steel implies that such an alloy is "stainless" or will not rust, the reality is that stainless-steel castings can exhibit a rusty appearance if not processed correctly. The rusty appearance is only superficial surface rust, i.e. iron oxide, and for most applications it is neither a problem nor an indication as to how the equipment will perform in service. However, there are some services where this surface rust is objectionable and special processing is necessary to make sure the stainless-steel castings are truly "stainless." Some of the industries where any rust is undesirable are food and beverage, pharmaceutical, and electronics.

Shot blasting is routinely used by foundries and forge shops to remove burned-in sand, core material, and scale that are formed during casting, forging, and/or heat-treating processes. Steel shot is normally used because it is the quickest and most economical cleaning abrasive. A slight amount of iron contamination remains on the surface of the stainless steel, and may later cause surface discoloration or rusting.

Sand blasting or grit blasting with various abrasives may also be used to clean castings and forgings. If the sand or abrasive was previously used on steel, it may contaminate the stainless-steel surface, which can result in rusting. Therefore, if sand or grit blasting is utilized, the sand or grit should either be new or only used previously for cleaning stainless-steel items.

Pickling, or the more technically correct term acid cleaning, is used to remove iron oxide that formed during the heat treatment of stainless steel or to remove free iron contamination that may have occurred from shot blasting, grit blasting, and/or grinding of stainless- steel castings or forgings. Normally, acid cleaning is only necessary for alloys that do not have sufficient chromium content to prevent oxidation of the surface during heat treatment, such as the 300-series stainless steels. The higher-chromium-content duplex stainless steels do not require acid cleaning unless they are to be used in one of the rust-sensitive industries mentioned above. Pickling is normally done as a last step before machining.

Passivation is the process by which a stainless steel will form a thin, invisible, chemically inactive surface when exposed to air or other oxygen-containing environments. At one time it was considered necessary to apply an oxidizing treatment to stainless steels in order to establish this protective oxide film. It is now accepted that this oxide film will form spontaneously in any oxygen-containing environment provided the surface has been thoroughly acid cleaned, i.e. pickled or descaled. This oxide film is the mechanism by which corrosion-resistant alloys achieve their corrosion resistance. Although a stainless steel is basically self passivating in any oxygen-containing environment, even air, some users of stainless-steel equipment still feel it is necessary to require a separate passivation treatment. If passivation is performed, it is generally done after finish machining.

Acid cleaning and passivation are covered by ASTM specifications A380 and A967. These specifications provide complete details on the acid cleaning and passivation of stainless steels as well as a variety of tests to measure the effectiveness of these processes, including simple wet-dry immersion tests to chemical testing for the detection of free iron. As with any special order requirement, there should be discussions between the manufacturer and customer up front so that everyone is in complete agreement on the processes to be used and how the results will be measured.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association