Valve M A G A Z I N E | F a l l 2 0 0 6

CASTING BASICSA cast valve is produced by pouringliquid metal into a mold, whichdefines the casting’s outer surface.One or more cores define the inter-nal passages and may also defineexternal pockets of a complex cast-ing. A valve family productionpackage may consist of multiple,interchangeable core and moldpieces, producing multiple varia-tions of the same basic valve body.CAD, solid modeling and solidifica-tion modeling permit rapid itera-tions of the initial design, resultingin: reduced lead times; lighter, moreefficient valves; and superior, “fitfor purpose” casting quality. Final,digitized designs are rapidly con-verted into patterns and coreboxesready for production.Optimized valve design, con-

verted into good molds and cores,is the starting point for high-qual-ity cast valves. Metal selection andquality are equally, if not more,important. The casting processoffers almost unlimited metalchoice, enabling valve manufactur-ers to tailor metal performance tothe valve application requirements.Additionally, small batch sizes,spectrographic analysis and cost-and property-focused charge calcu-

lation programs result in flexibility, economy and metal chemistries that gobeyond specifications to meet unique valve performance needs.At the machine shop, castings offer further advantages. Cast-to-shape internal cav-

ities, reduced draft and the ability to cast rather than machine valve changes, all addup to significant reductions in machining costs. The modern foundry’s casting advan-tage? Short lead times, flexibility, reduced economic lot sizes, reduced machiningcosts, and quality and chemistry to optimize lifecycle costs.

The“casting or forging”question,which regularly confronts valve industry purchasing staff, does nothave a simple answer.Over the years, industry experts have published detailed comparisons of the twoprocesses (see Resources, page 46).A review of the available literature reveals that both the castingand forging industries are more than capable of making excellent valve bodies, resulting in a win-winsituation for buyers.Ultimately, there will be situations in which castings are the optimum cost andperformance solution,and other cases where forgings are the best choice.To help industry newcomersunderstand the differences, here’s a quick overview of the casting and forging processes and industries.

CASTINGSBY DICKWARDA,PHD.

A two-stage API 610 pump case:The internal cavitycoring of a mold shows the complexity offered by thecasting process.This photo was taken at HighlandFoundry’s plant in Surrey,BC.

© 2006 Valve Manufacturers Association. Reprinted with permission.

AS SEEN IN THE FALL 2006 ISSUE OF...

Metal PerformanceIncreasingly challenging operating envi-ronments and the demand for more effi-cient and reliable valves place a greateremphasis on material selection. Experi-enced end users often go beyond specifi-cations in defining their projectrequirements. The casting process offersthe quality and flexibility to meet thesenew requirements. Cast valves currentlymeet or exceed ASTM, ASME, API,AWS, NORSOK and additional cus-tomer specifications for both mechani-cal properties and corrosion resistance.The casting process eliminates direc-tionality of properties, thus avoidingissues of transverse vs. longitudinalproperties. Reduced, near-net sectionsizes provide greater assurance thatheat treatments of heavy-section castvalves will provide consistent through-wall properties.Because foundries control their own

metal composition, they are well placedto meet special customer requirementsnot covered in the broad standard speci-fications. Want a CF8M valve withguaranteed cryogenic performance?Can do! Need a super duplex valve with248 max BHN, PREN over 41 and 40-45% ferrite that is super tough? Noproblem! And you get the certified testresults to prove it.

Cast Valve QualityForgings and castings are each vulnera-ble to specific types of defects, but thegood news is that, for both processes,the described defects are possible butpreventable. Defect types and theirseverity are defined in many NDE qual-ity specifications, such as the MSS-SPseries. The valve manufacturer shouldselect acceptance levels that satisfy thevalve performance and cost criteria.Good basic foundry practices, wide-

spread use of solidification modeling,and continuous improvements in mold

and coremaking processes have com-bined to eliminate most casting defects.When required, castings may beupgraded using weld repair proceduresthat comply with ASME and ASTMcodes, thus ensuring that the upgradedvalve meets the most stringent perform-ance standards. VM

RESOURCES“Steel Castings vs. Forgings—A Realistic Evalua-tion,” CASTEEL, V17, No.1, Summer 1984.Steel Founders’ Society of America.

“The Niche for Steel Castings,” Advanced

Materials & Processes, 8/94. American Soci-ety for Metals.

“Castings vs. Forgings: A Realistic Evaluation,”Malcolm Blair and Raymond W. Monroe,Modern Casting, November 1995. AmericanFoundrymens’ Society.

“Forgings vs. Castings,” Felicia Miller Day, ValveMagazine, Winter 1994. Valve Manufactur-ers Association of America.

DICKWARDA,PHD., isVice President ofTechnologyand Metallurgy for Highland Foundry, Ltd.(www.highlandfoundry.com), a stainless-steelfoundry specializing in duplex and nickel-basedcastings.The company is located in Surrey, BritishColumbia.

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THE ABC…D’S OF BUYING THE BEST VALVE BODY

� Define the total operational environment, including risk analysis. Investingin the front end of valve body procurement can pay off hugely during theproduction and life cycles of the end product.

� Determine the required corrosion resistance and mechanical properties.Corrosion testing can rank and confirm the corrosion resistance of candi-date materials. Mechanical property requirements are intimately relatedto valve design. Good foundries have the capability and flexibility to reactto these needs through custom alloys. Design changes suggested toimprove castability and casting quality often have the added benefit ofreduced operating stresses.

� Due Diligence should be performed in evaluating the capabilities and trackrecords of the candidate foundries and forge shops. Good suppliers wel-come and benefit from technical audits.

� Dispel the myths about the two processes. Castings and forgings fail for thesame reasons—deficient designs or deficient processes. Good valve bodiesare the result of high standards and the constant attention to criticaldetails, from design to delivery.

� Dialogue with the chosen supplier is essential to optimize the performanceand cost of the valve body. Information exchange at the quote stage givesboth parties the opportunity to clarify requirements and improve both theprocess and the product.

� Digitized solid model information should be an integral part of the infor-mation dialogue.The modern foundry can add significant value to the castvalve body through detailed modifications that can reduce weight, improveefficiency, and enhance castability and final quality.

� Develop partnerships with your best suppliers. Like the natural world,mutually beneficial relationships improve the survivability of both parties.

C A S T I N G S

© 2006 Valve Manufacturers Association. Reprinted with permission.