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Process Instrumentation in Oil and Gas

Process Instrumentation in Oil and Gas

Process instrumentation is an integral p...

Check Valves in LNG Cryogenic Service

Check Valves in LNG Cryogenic Service

Because natural gas is currently conside...

Will Smart Machines Obsolete Human Resources?

Will Smart Machines Obsolete Human Resources?

Is artificial intelligence (AI) going to...

Is Valve Live Loading an Option?

Is Valve Live Loading an Option?

Valves leak. There’s no getting ar...

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Construction and Mining: Is 2018 The Year for Growth?

Construction and Mining: Is 2018 The Year for Growth?

Tuesday, 12 December 2017  |  Kate Kunkel

While there is a degree of optimism in the mining industry that hasn’t been seen for some years, much uncertainty still exists in this sector. A...

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Industry Headlines

United Valve Names Jim Nelson Engineering and Production Manager

2 DAYS AGO

United Valve LP has promoted Jim Nelson to production and engineering manager. Nelson will be responsible for overseeing all production and engineering activities at United Valve.

“Jim Nelson has demonstrated consummate professionalism and shown his strong leadership skills, earning the respect ...

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Setpoint I.S. Honored by Baton Rouge Business Report

3 DAYS AGO

Setpoint Integrated Solutions (Setpoint I.S.) was honored this fall at the Baton Rouge Business Report’s Top 100 Private Companies Luncheon. Celebrating its 35th Anniversary this year, the Baton Rouge Business Report hosts many events in the community.

At the most recent event , the Top 100 Private C...

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EIA Forecasts Record U.S. Oil Output in 2018

2 DAYS AGO

The U.S. Energy Information Administration (EIA) estimates that U.S. crude oil production averaged 9.7 million barrels per day (b/d) in November, up 360,000 b/d from the October level. Most of the increase was in the Gulf of Mexico, where production was 290,000 b/d higher than in October. Higher pro...

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Chemical Industry Growth Rate Surpasses 20-Year Average

4 DAYS AGO

The U.S. chemical industry is riding a global wave of growth as the world’s major economies experience an upswing for the first time in a decade. Increased output and accelerating growth rates that surpass the previous twenty-year average will help cement the business of American chemistry as ...

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U.S. Manufacturing Technology Orders Up 6.3%

4 DAYS AGO

Orders for manufacturing technology kept their momentum in October 2017, gaining 6.3% over September to a total value of $428.32 million, according to the latest U.S. Manufacturing Technology Orders Report from The Association for Manufacturing Technology (AMT). Year to date, orders are up 7.6% comp...

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NAM Survey: Manufacturers’ Optimism Reaches Record High

5 DAYS AGO

The National Association of Manufacturers (NAM) released the results of the Manufacturers’ Outlook Survey for the fourth quarter of 2017, showing manufacturers’ optimism has risen to unprecedented heights amid the legislative progress made on tax reform. With 94.6% of respondents saying ...

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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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