12182017Mon
Last updateMon, 18 Dec 2017 3pm

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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

3 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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Empire State Manufacturing Grew at Slower Pace in December

-1 DAYS AGO

Business activity continued to grow at a solid clip in New York State, according to firms responding to the December 2017 Empire State Manufacturing Survey . The headline general business conditions index, at 18.0, remained close to last month’s level. The new orders index and the shipments inde...

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U.S. Industrial Production Up 0.2% in November

-1 DAYS AGO

Industrial production moved up 0.2% in November after posting an upwardly revised increase of 1.2% in October. Manufacturing production also rose 0.2% in November, its third consecutive monthly gain, and was 2.4% above its year-earlier level.

The increase in November reflected a gain of 0.4% for durabl...

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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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