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Portable Alloy Verification Devices

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Industry Headlines

PA Town Approves $6B Shell Ethane Cracker Plant

Monday, 16 January 2017  |  Chris Guy

Potter Township in western Pennsylvania has granted a conditional use permit for a $6 billion petrochemical plant to be built by Shell Chemicals. The ...

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Industry Headlines

David Paradis Named President of Weir Flow Control Division

3 DAYS AGO

The Weir Group PLC has appointed David Paradis to its group executive as president of the Weir Flow Control Division. He will take up this new role on January 23, 2017. Paradis succeeds John Heasley who was appointed Weir Group CFO in October 2016.

Paradis is currently president of Weir Oil & Gas&r...

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GE, Transocean Announce Performance-Based Service Agreement

5 DAYS AGO

GE Oil & Gas has secured a new contractual service agreement (CSA), valued at approximately $180 million, with Transocean. Under the agreement , GE will provide condition-based monitoring and maintenance services for pressure control equipment on seven of Transocean’s rigs over the next 10 t...

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PA Town Approves $6B Shell Ethane Cracker Plant

16 HOURS AGO

Potter Township in western Pennsylvania has granted a conditional use permit for a $6 billion petrochemical plant to be built by Shell Chemicals. The location was chosen because more than 70% of North American polyethylene customers are within a 700-mile radius of Pittsburgh, PA. More state and fede...

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$4.17B Canadian Trans Mountain Pipeline Expansion Approved

4 DAYS AGO

Kinder Morgan’s Trans Mountain Expansion Project has received its environmental certificate from British Columbia, Canada. The proposed $4.17 billion Trans Mountain Expansion Project would increase the capacity of the pipeline to 890,000 barrels per day. The current capacity of the pipeline is 3...

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Texas Economy Poised to Shift into ‘Second Gear’ in 2017

17 HOURS AGO

Texas job growth should increase slightly from 1.6% in 2016 to about 2% in 2017, says Federal Reserve Bank of Dallas assistant vice president and senior economist Keith Phillips.

“Job growth picked up in the second half of 2016 due to a stabilization of the energy sector,” Phillips said. ...

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World Bank: U.S. Could Boost Global Economy in 2017

4 DAYS AGO

Global growth for 2017 is projected at 2.7%, 0.1% lower than the June 2016 forecast, and 0.4% higher than the estimate for 2016. Going forward, according to the World Bank, global growth is projected to pick up modestly, reaching 2.9% by 2018.

Downside risks to global growth include increasing policy u...

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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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