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Metal Additive Manufacturing in the Valve Industry

Metal Additive Manufacturing in the Valve Industry

Metal Additive Manufacturing (AM) is a f...

The Past, Present and Future of Fire Testing

The Past, Present and Future of Fire Testing

Because so many of the applications wher...

Advancements in Blue Laser Scanning

Advancements in Blue Laser Scanning

As the industrial world continues to exp...

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Industry Headlines

IHS: Manufacturing at Strongest Level Since Sept. 2014

Thursday, 24 May 2018  |  Chris Guy

The seasonally adjusted IHS Markit Flash U.S. Manufacturing PMI registered 56.6 in May, up fractionally from 56.5 in April, to signal the strongest im...

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Industry Headlines

Curtiss-Wright Supporting Ford-Class Aircraft Carrier Program

3 DAYS AGO

Curtiss-Wright has been awarded a contract valued in excess of $85 million to provide main propulsion steam turbines and auxiliary equipment for the U.S. Navy’s Ford-class aircraft carrier Enterprise (CVN 80). The award was received from Huntington Ingalls, Newport News Shipbuilding (HII-NNS) ...

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Crane Celebrates Opening of New Plant in India

3 DAYS AGO

Crane ChemPharma & Energy celebrated the inauguration of its newest location, an aseptic diaphragm valve factory in Satara, India. Crane invited hundreds of customers and industry stakeholders to participate in a day-long event complete with a tour of the new plant and luncheon held on May 10, 201...

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LNG, Ethanol Sellers Buoyed by China Trade Talk

2 DAYS AGO

“China's interest in reducing its trade surplus with the United States through increased energy imports could advance plans for U.S. liquefied natural gas (LNG) plants and ethanol sales, said analysts and energy executives involved in developing new LNG facilities.”

Reuters  reports th...

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Chemical Activity Up as Pace of Growth Slows

2 DAYS AGO

The Chemical Activity Barometer (CAB) from the American Chemistry Council (ACC), rose 0.1% on a three-month moving average (3MMA) basis in May to 121.9. The barometer is up 3.9% on a 3MMA compared to a year earlier. The unadjusted CAB showed a second consecutive month of gains, up 0.2% in May and also...

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IHS: Manufacturing at Strongest Level Since Sept. 2014

1 DAY AGO

The seasonally adjusted IHS Markit Flash U.S. Manufacturing PMI registered 56.6 in May, up fractionally from 56.5 in April, to signal the strongest improvement in business conditions since September 2014 . May data revealed relatively strong rises in both manufacturing production and incoming new busi...

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Philly Fed: Manufacturing Activity Up in May Survey

3 DAYS AGO

The Philadelphia Fed’s monthly survey indicate a pickup in growth for the region’s manufacturing sector. The indexes for general activity, new orders, shipments, and employment all improved from their readings last month. The indexes for prices paid and received continued to suggest price ...

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Cast or Forged?

materials_q_and_a_graphicQ: Should I be concerned whether my valve is cast or forged?

 

A: Just as in politics, everyone has an opinion on this issue.

 

The good news is that both types of valves should be able to provide you with acceptable performance, although a perception exists that forged valves are superior to cast valves. However, if cast valves are made properly, they can and have worked equally well in a variety of services and usually at a much lower cost than forged valves. Also, the belief that forged components are infallible is not true. Let’s look at an example of a 4-inch diameter wrought valve stem in N07718 (Figure 1). A crack-like defect was seen on the end of the stem, so the part was cut in half, and the large shrink cavity you see here was discovered. This shows that forged material is not without its own problems. But let’s examine how cast and forged valves are made and how we can assure we get a good valve.

What most people don’t realize is that cast and forged valves start out the same way—molten metal is poured into a mold or ingot. As a result, both types can have defects such as the shrinkage in the above mentioned N07718 bar. Other defects associated with forgings are inclusions, laps, seams, cold shuts and cracks. Defects with common castings are inclusions, porosity, misrun and hot tears. As you can see, both have their potential issues.

An issue with forgings often overlooked is that forgings and wrought products will have non-uniform mechanical properties. This is because they are worked or formed more in one direction than in another. Therefore, the grains will be elongated more in one direction than in the other, which has a direct affect on mechanical properties, particularly impact strength. As a result, the design of forgings needs to take into account these anisotropic properties whereas castings have uniform properties no matter what the orientation of the test coupons.

Another advantage of cast valves is that they can be produced in more complex designs than forged valves. Certain valve designs such as a globe valve are simply difficult or impossible to produce as forgings. This flexibility of design in cast valves allows them to be more efficient in controlling flow than a similarly forged valve.

Something else to consider with forged valves is that they usually are made in halves, particularly the larger sizes. This means there is either an additional flanged connection that can be a potential leak path or the halves are welded together. Welding, however, is another process for cast metal that can have its own set of problems.

The questionable reputation that castings have is from two sources. First, most of the ASTM cast specifications are lenient in requirements for composition, heat treatment and inspection. Second, some foundries either use this latitude to their advantage or simply do not know enough to implement tighter controls when needed on chemistry or heat treatment. This concern about castings has resulted in equipment produced to ASME Section VIII having a quality factor on castings of 80% of the allowable stress values for a wrought component. However, this quality factor can be increased to 100% if sufficient NDE (non-destructive evaluation) per Appendix 7 is performed.

Casting purchasers need to understand that in most ASTM specifications these additional NDE requirements are not mandatory. They are simply listed as supplementary requirements at the end of the product specifications and are only invoked if included in the purchase order. Specifying additional NDE-like radiography or dye penetrant inspection is one way of helping ensure the quality of valves being purchased. However, a more cost-effective way is to deal with valve suppliers who already control the quality of the products they produce and have a long and successful track record. In either case, the decision to go with cast or forged valves depends on several factors, and cost is usually the determining one.


THOMAS SPENCE is director of materials engineering for Flowserve Corp. (www.flowserve.com), Dayton, OH. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

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