06222017Thu
Last updateWed, 21 Jun 2017 6pm
Why Air Valves are Needed in Water Applications

Why Air Valves are Needed in Water Applications

Air valves are hydromechanical devices d...

Achieving Profitability Through Maintenance Management

Achieving Profitability Through Maintenance Management

One of the distinctions between maintena...

Control Valve Positioner Performance Diagnostics

Control Valve Positioner Performance Diagnostics

There has been discussion for some years...

Are Your Safety Instrumented Systems Proof Tests Effective?

Are Your Safety Instrumented Systems Proof Tests Effective?

Many people assume that a proof test of ...

Subscribe vmspr17

FREE SUBSCRIPTION*

•  Print magazine
•  Digital magazine
•  VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Smart Technology Transforming Oil & Gas Industry

Wednesday, 21 June 2017  |  Chris Guy

“A new cadre of services companies, trying to sell the energy industry on the promise of a more efficient digital age, is fighting to get smart ...

Readmore

Loading...
Advertisement
i

Industry Headlines

Chesterton Expands Environmental Consulting Expertise

1 DAY AGO

A.W. Chesterton Company  is expanding its global environmental solutions expertise with the addition of two highly experienced industrial emissions specialists, Bronson Pate and Beau Stander. Both will be joining FluidEfficiency, a Chesterton business group. Pate and Stander will serve in the ro...

Readmore

VMA Members Take Home 2016 Plant Engineering Awards

1 DAY AGO

Plant Engineering celebrated its 29th anniversary of the Product of the Year award program this year. The winners were honored at the annual Engineering Awards in Manufacturing dinner on April 3, 2017, in Chicago, hosted by CFE Media.

Emerson Automation Solutions took home a Bronze Award in the Asset Ma...

Readmore

Smart Technology Transforming Oil & Gas Industry

12 HOURS AGO

“A new cadre of services companies, trying to sell the energy industry on the promise of a more efficient digital age, is fighting to get smart technology onto pipes, tanks, platforms and drills, in some cases deeply discounting prices to gain market share,” the Houston Chronicle reports .

C...

Readmore

U.S. Refineries Running at Record-High Levels

1 DAY AGO

Gross inputs to U.S. petroleum refineries, also referred to as refinery runs, averaged a record high 17.7 million barrels per day (b/d) for the week ending May 26, before dropping slightly to 17.5 million b/d for the week ending June 2 and 17.6 million b/d for the week ending June 9. According to th...

Readmore

U.S. Economic Picture for First Half of 2017 Changes Little

15 HOURS AGO

Economic indicators released in May and June point to continued moderate growth and a mostly unchanged outlook for the U.S. The economy is approaching full employment, long-term inflation expectations remain anchored despite a recent dip in inflation, and real GDP is projected to grow at a moderate ra...

Readmore

Global Spending on Robots to Hit $87 Billion by 2025

16 HOURS AGO

The global market for robotics is growing far faster than expected and is projected to reach $87 billion by 2025, according to new research by The Boston Consulting Group (BCG). Updating its previous estimate of $67 billion from three years ago, the BCG recently revised its forecast sharply higher, mo...

Readmore

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.

  • 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