05262016Thu
Last updateThu, 26 May 2016 2pm

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Industry and Regulatory Changes in Offshore Operations

Industry and Regulatory Changes in Offshore Operations

On May 13, 2016, the offshore oil and ga...

Strategies for Successful SIS Valve Diagnostic Implementation

Strategies for Successful SIS Valve Diagnostic Implementation

End users and contractors alike strive t...

Stop Check Valves

Stop Check Valves

Stop check valves are vital to several i...

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Industry Headlines

Why $50/Barrel Oil Means Stability to U.S. Producers

-1 DAYS AGO  |  Chris Guy

The rise to $50-per-barrel oil means a return to stability, particularly for domestic shale producers, according to Dan K. Eberhart, CEO, Canary, LLC....

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Industry Headlines

ValvTechnologies Names Garcia, Mermelstein to New Positions

17 HOURS AGO
ValvTechnologies Names Garcia, Mermelstein to New Positions

ValvTechnologies, Inc. has named David Garcia director of manufacturing and Steve Mermelstein as regional director, Americas and director, channel management.

Previously, West Point graduate Garcia served as director of operations for Merla Wellhead Solutions and held plant manager positions at Hallib...

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Emerson Automating UK Waste-to-Energy Plant

18 HOURS AGO

Emerson will provide control systems and project services for a new waste-to-energy power plant near Knaresborough Allerton, North Yorkshire, UK. Construction is expected to be completed in 2017, with the plant fully operational in 2018.

The plant , which will also incorporate biogas and recycling faci...

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Why $50/Barrel Oil Means Stability to U.S. Producers

-1 DAYS AGO

The rise to $50-per-barrel oil means a return to stability, particularly for domestic shale producers, according to Dan K. Eberhart, CEO, Canary, LLC. At this level , companies that saw the value of their product drop more than 75% in less than two years might have the confidence to resume drilling ac...

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Oil Industry Expects Cuts for Record Third Straight Year

13 HOURS AGO

According to Statoil ASA, “[g]lobal crude supplies will start to dwindle in as little as two years, boosting prices, as the industry cuts investment to weather the worst market collapse in a generation,” Bloomberg reports .

“Despite signs the supply glut is easing, companies are prepar...

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Durable Goods Orders Surge 3.4%, But Demand Soft

-1 DAYS AGO

New orders for manufactured durable goods in April increased $7.7 billion or 3.4% to $235.9 billion, the U.S. Census Bureau announced today. This increase, up three of the last four months, followed a 1.9% March increase. Excluding transportation, new orders increased 0.4%. Excluding defense, new or...

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Markit PMI Shows U.S. Manufacturers Stagnating in May

1 DAY AGO

The U.S. manufacturing sector crept closer to stagnation in May, with the seasonally adjusted Markit Flash U.S. Manufacturing Purchasing Managers’ Index (PMI) registering only slightly above the neutral 50.0 mark at 50.5. This was down from 50.8 in April and signaled only a marginal improvement...

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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.

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