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Survey Shows Small Business Confidence Increasing

Thursday, 27 April 2017  |  Chris Guy

The second annual Allstate/ Small Business Barometer finds increasing optimism and innovation among small business owners, despite the rising cost of ...

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Industry Headlines

Metso Providing Valves for Oman Petrochemical Complex

19 HOURS AGO

Metso will supply 400 Neles emergency shutdown (ESD) valves for an ethylene cracker as part of the new Liwa Plastics Industrial Complex (LPIC) Project in Sohar, Oman. The new complex will process light ends produced in Orpic's Sohar Refinery and its aromatics plant as well as optimize natural gas li...

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Curtiss-Wright Earns Safety Award for Third Year in a Row

20 HOURS AGO

A Curtiss-Wright facility located in Chanhassen, MN, received a Governor’s Safety Award for superior performance in workplace safety and health as part of the Minnesota Governor’s Safety Awards. The Chanhassen site produces Exlar electric actuators and earned this award by reporting better...

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East Coast Refiners Eye Texas as Alternative to North Dakota

16 HOURS AGO

“Major U.S. East Coast refiners profited from railing hundreds of thousands of barrels of discounted Bakken crude to their plants daily from 2013 until 2015. But as more and more pipelines were built in North Dakota, the discount began to disappear, and so did the rail cars,” Reuters repor...

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Wind Energy Growing Nine Times Faster Than Overall Economy

1 DAY AGO

American wind power added jobs over 9 times faster than the overall economy amid robust growth for another year, according to the American Wind Energy Association (AWEA), which just released its annual report. Installing over 8,000 MW of new wind power for a second straight year, the U.S. industry inv...

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Survey Shows Small Business Confidence Increasing

-1 DAYS AGO

The second annual Allstate/ Small Business Barometer finds increasing optimism and innovation among small business owners, despite the rising cost of doing business. Nine in 10 local entrepreneurs say the benefits of owning a business outweigh the challenges. This year’s Barometer found that, ...

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Durable Goods Orders Up 0.7% in March

-1 DAYS AGO

New orders for manufactured durable goods in March increased $1.6 billion or 0.7% to $238.7 billion, the U.S. Department of Commerce announced today. Economists were anticipating an increase of 1.2%. This March increase , the third consecutive, followed a 2.3% February increase.

Excluding transportatio...

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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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