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Where Valves Are Used: Everywhere, Part 2

Where Valves Are Used: Everywhere, Part 2

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Market Outlook 2018: A Sunnier Mood with a Few Caveats

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Industry Headlines

VMA Associate Members Named to Annual BIG 50 List

Monday, 23 October 2017  |  Chris Guy

MRC Global (no. 9), NOW Inc. (no. 13) and Wolseley Industrial Group (no. 16) are all on the latest BIG 50 List, Industrial Distribution's annual list of...

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Adapt and Thrive, Say Annual Meeting Speakers

Adapt and Thrive, Say Annual Meeting Speakers

Monday, 23 October 2017  |  Judy Tibbs and Kate Kunkel

The theme of adapting to change was set very early for the Valve Manufacturers Association (VMA) and Valve Repair Council (VRC) 79th Annual Meeting. O...

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Industry Headlines

VMA Associate Members Named to Annual BIG 50 List

-1 DAYS AGO

MRC Global (no. 9), NOW Inc. (no. 13) and Wolseley Industrial Group (no. 16) are all on the latest BIG 50 List, Industrial Distribution's annual list of the largest industrial distributors in the world. VMA associate member DistributionNOW is a subsidiary of NOW Inc.

All Big 50 companies are ranked accor...

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Emerson Agrees to Acquire Paradigm

5 DAYS AGO

Emerson has agreed to acquire Paradigm for a purchase price of $510 million, reflecting a multiple of 13 times expected 2017 EBITDA. Paradigm will be joined with Emerson’s existing Roxar automation software. The acquisition is expected to close within the next 60 days, subject to various regulat...

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Projects Valued at $17B Increase Sept. Construction Starts 31.5%

-1 DAYS AGO

According to ConstructConnect, September’s volume of construction starts, excluding residential activity, was $42.8 billion. The month-to-month change versus August was an outsized +31.5%. The big improvement in the latest period was thanks to go-aheads for three mega projects combining for a to...

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Crude Oil, Petroleum Product Exports Reach Record Levels

4 DAYS AGO

According to the U.S. Energy Information Administration ( EIA ), crude oil exports in the first half of 2017 increased by more than 300,000 barrels per day (b/d) from the first half of 2016, reaching a record high of 0.9 million b/d. Petroleum product exports also grew over the same period with propan...

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Philly Fed Manufacturing Index at 5-Month High

2 HOURS AGO

The index for current manufacturing activity in the Philadelphia Federal Reserve region increased 4 points to a reading of 27.9 and is now at its highest reading since May. More than 39% of the firms indicated increases in activity this month, while 11% reported decreases. Both the new orders and ship...

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Fed Reports Economy Growth in September, Early October

4 DAYS AGO

Reports from all 12 Federal Reserve Districts indicated that economic activity increased in September through early October, with the pace of growth split between modest and moderate. The Richmond, Atlanta, and Dallas Districts reported major disruptions from Hurricanes Harvey and Irma in some areas a...

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Supplemental Requirement S23 in ASTM A703

materials_q_and_a_graphicQ: A customer has asked whether we can supply carbon and alloy steel valve bodies meeting Supplemental Requirement S23 in ASTM A703. What is the purpose of this requirement?

A: The macroetch test specified in Supplemental Requirement S23 in ASTM A703 is designed to detect the occurrence of aluminum nitride embrittlement in castings.

When steel is melted, oxygen and nitrogen can be dissolved in the molten steel. When the metal is poured into the casting mold, the oxygen can come out of the solution and form gas porosity in the castings. In order to avoid castings with excessive gas porosity, the foundry may add deoxidizing elements to the melt. The presence of these elements results in the formation of oxide compounds, which mitigates the formation of oxygen gas bubbles during solidification.

One of the elements that is sometimes added as a deoxidizer is aluminum, which creates a potential for the formation of aluminum nitride. This compound tends to precipitate in the prior austenite grain boundaries and can result in castings that display loss of ductility that could result in brittle failure of the casting if it is shock-loaded in service. If fracture occurs, it has a rock-candy appearance due to fracture along the prior austenite grain boundaries. The fracture is often very shiny due to the presence of aluminum nitride platelets on the surface.

Variables That Influence Embrittlement

There are a number of variables that influence the potential for this type of embrittlement:

1) The steel must contain enough aluminum and nitrogen to support the formation of enough aluminum nitride to cause a significant embrittling effect. Most foundries have the equipment necessary to analyze and report aluminum content. However, the specifications for the common cast steels used in valve bodies do not require analysis or reporting of aluminum as a standard requirement, so some foundries do not monitor and/or report the aluminum content.

Although some foundries monitor nitrogen levels in their steel, many do not have the necessary equipment to do this. The specifications for the common cast steels used in valve bodies do not require analysis or reporting of nitrogen as a standard requirement. Therefore, the nitrogen content of the steel is often not known or reported, and it is possible that enough nitrogen is present to form aluminum nitride.

2) Other elements that inhibit the formation of aluminum nitride must be present in low enough quantities that the reaction can occur. Certain elements are known to inhibit the formationof aluminum nitride. Additionsof titanium and/or zirconium, addedeither along with or after the additionof aluminum, can inhibit the formationof aluminum nitride by forming titaniumnitride and/or zirconium nitrideinstead. It has also been found thathigher levels of phosphorus, sulfur,boron, molybdenum and copper inhibitaluminum nitride embrittlement.

3) The cooling rate in the mold must be slow enough through the critical temperature range to allow the formation of the aluminum nitride phase. The thickness of the casting (orportion of the casting) is an obviousfactor influencing whether embrittlementoccurs, since thicker casting sectionswill cool more slowly through thecritical temperature range than thinsections.

The casting configuration can also influence the cooling rate. A complex casting with relatively thin walls may experience slower cooling rates than a simple casting with the same wall thickness because the complex casting will lose heat through the mold less effectively.

The mold material can also influence the cooling rate. For example, air-set sand is known to inherently produce molds that cool slower than green-sand molds.

Reporting Aluminum Content

When Supplemental Requirement 23 in ASTM A703 is imposed on steel castings produced under ASTM A216, A217 and A352, aluminum is required to be reported. For heats with aluminum content greater than 0.08%, a macroetch must be performed on one of the following:

  • A cross-section of the heaviest section of a sacrificial casting
  • A coupon attached to the heaviest section
  • A coupon removed from directly under a riser or
  • A coupon from the same heat of material removed from a separately cast test block with a thickness representative of the heaviest section of the casting.

The resulting etched specimen is compared with 10 reference macrographs. Heats with severity levels 4 and lower are acceptable. Heats exhibiting higher levels are dispositioned by a number of means, including examination of etch structures on individual castings, fracture testing to determine the degree of “rock candy” appearance, mechanical testing, weld crack susceptibility testing and/or high-temperature solution heat treatment, as agreed upon by the supplier and purchaser.


REFERENCES:

1. ASTM A703 (latest revision), “Steel Castings, General Requirements, for Pressure-Containing Parts,” ASTM International, West Conshohocken, PA.

2. ASM Materials Information On-Line: ASM Metals Handbook - Volume 1, Properties and Selection: Irons, Steels, and High Performance Alloys -> Embrittlement of Steels -> Embrittlement in Carbon Steels and Alloy Steels.

3. SFSA SFSA Casteel Reporter, August 2006, Page 2, Steel Founders’ Society of America, Crystal Lake, IL.

4. Banks, WC, “Avoiding Aluminum Nitride Embrittlement in Steel Castings for Valve Components,” V-Rep 84-1, Flowserve, 2003, Raleigh, NC.

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