Chapter 2: Materials

Why is ductile iron preferred over gray cast iron for many pressure-retaining valves?

Ductile iron is preferred over gray cast iron for many pressure-retaining valves because it has a chemical composition similar to gray iron, but special treatment during casting process enhances it metallurgical graphite structure to yield higher mechanical properties and improved ductility • Gray iron may still appear in lower-pressure or legacy flange standards. Category: 02 Materials Tags: #DuctileIron #CastIron #Metals

Why would an engineer specify 316 stainless instead of 304 stainless?

• 316 stainless has better chloride and pitting resistance. • It is more suitable for coastal, wastewater, and more corrosive environments. • Tradeoff: it costs more and may be unnecessary for normal potable water. Category: 02 Materials Tags: #StainlessSteel #316 #304

Why is 304 stainless still common in waterworks valves?

• More economical than 316 stainless. • Often adequate for stems, hardware, and trim when chlorides/corrosion risk are moderate. (18% chromium, 8% nickel) 304 SS is still common in waterworks valves because it can its .08 max carbon content reduces intergranular corrosion usually associated w/ carbide precipitation during welding. Has a wide resistance to a wide range of corrosives. Category: 02 Materials Tags: #StainlessSteel #304

Why is EPDM commonly used in potable-water valve seats and seals?

(-50 - 250F) NSF61 • Excellent compatibility with water and many municipal applications. • Good ozone and weathering / resistance to water disinfectants with chloramines (why it has increased use in municipal) • Often available with potable-water approvals. • Watch out: poor petroleum/oil compatibility. Category: 02 Materials Tags: #EPDM #Elastomer #PotableWater

When would Buna-N/Nitrile be selected instead of EPDM?

Buna-N (-50-200F) • Better resistance to petroleum oils, fuels, and hydraulic fluids. • Good abrasion resistance. • Tradeoff: generally weaker for ozone/weathering and not the default for potable hot-water service. Category: 02 Materials Tags: #BunaN #Nitrile #Elastomer

Why is FKM/Viton used in more severe elastomer applications?

FKM/Viton is used in more sever elastomer applications due to its high temperature range is can withstand (up to 400F). stronger chemical resistance including petroleum, oils, and acids. superior chloramine resistance as well. good in high-pressure applications Tradeoff: higher cost and not always needed for municipal water. Category: 02 Materials Tags: #FKM #Viton #Elastomer

Why is PTFE used for seats, liners, or seals?

PTFE: synthetic fluoropolymer, non-stick properties, high heat resistance (-328 - 500F). near-universal chemical inertness • Very low friction. Tradeoff: less elastic than rubber, so sealing design/loading matters. Category: 02 Materials Tags: #PTFE #Plastic #Seats

Why might Noryl be used for a Dual Disc Check Valve disc?

Noryl discs are prized in the valve industry for being lightweight, corrosion-resistant, and having a very low inertia, allowing the valve to open with minimal pressure and close quickly to prevent slamming• Tradeoff: lower strength/temperature limits than metal options. Category: 02 Materials Tags: #Noryl #CheckValve #Disc

Why is bronze or aluminum bronze used for valve trim?

bronze or aluminum bronze is used for a valve trim because its easy to cast, easy to solder or braze, very resistant to pitting corrosion, general resistance to chemicals. aluminum bronze is the most widely accepted disc material used in valves for liquid service; heat treatable w/ strength of steel, very corrosion resistant • Often used for seats, bushings, or trim where sliding contact occurs. Category: 02 Materials Tags: #Bronze #AluminumBronze #Trim

What is the purpose of fusion-bonded epoxy coating?

(FBE) Protects clean water (typically NSF61 cert.) prevents rust, stops chemicals from damaging the metal, and creates a smooth surface that helps water or other fluids flow easily without wearing down the valve • Common on waterworks valves, fittings, and pipe components. Category: 02 Materials Tags: #FBE #Coatings #Corrosion

Why can coating damage become a corrosion problem?

• A coating is a barrier system. • Holidays, chips, or poor surface prep expose the metal substrate. • Localized exposure can become an active corrosion site. Category: 02 Materials Tags: #Coatings #Corrosion #Inspection

What is galvanic corrosion?

galvanic corrosion is when two dissimilar metals are in electrical contact while immersed in conductive liquid like water. the more active metal (anode) corrodes much faster than is would alone while the less active metal (cathode) is protected. • Important when mixing stainless, carbon steel, ductile iron, bronze, and fasteners. Category: 02 Materials Tags: #GalvanicCorrosion #Metals

What is pitting corrosion?

• Localized corrosion that forms small pits rather than uniform metal loss. • Dangerous because deep pits can penetrate components while the surface looks mostly intact. • Common concern with stainless in chloride environments, stainless is highly resistant to rusting, but chloride ions (like salt and bleach) actively destroy its protective shield. Category: 02 Materials Tags: #Pitting #Corrosion #StainlessSteel

Why does cavitation create material damage instead of just hydraulic noise?

• Vapor bubbles collapse near metal surfaces. • Collapse creates tiny high-energy impacts. • Repeated impacts pit trim, seats, discs, and bodies. Category: 02 Materials Tags: #Cavitation #Erosion #FailureMode

What is erosion-corrosion?

• Material loss caused by both chemical corrosion and high-velocity mechanical wear. • Often worsened by grit, turbulence, cavitation, or throttling. • Material selection and velocity control both matter. Category: 02 Materials Tags: #ErosionCorrosion #Materials

Why should elastomer compatibility be checked before quoting a valve?

• Elastomers can swell, harden, crack, or lose sealing ability in incompatible fluids. • Water service does not automatically mean every chemical or wastewater condition is safe. • Seat/seal failure can become leakage or torque problems. Category: 02 Materials Tags: #Elastomers #ChemicalCompatibility

Why is material selection a sales-engineering issue, not just a design issue?

• Wrong materials cause leaks, corrosion, premature wear, or rejected submittals. • Correct materials depend on fluid, pressure, temperature, environment, approvals, and specification. • A good quote asks enough questions to avoid misapplication. Category: 02 Materials Tags: #MaterialSelection #SalesEngineering

Why might stainless hardware be specified on municipal valves?

316SS • Chemically similar to 304SS except w addition of molybdenum; provides better corrosion and pitting resistance + higher strength at elevated temps / better ductility for valve stem, body, and ball materials as well as bolts, nuts, pins, and small exposed components. • Helpful in buried, vault, wastewater, coastal, or humid environments. • Still must consider galling and compatibility with mating materials. Category: 02 Materials Tags: #StainlessSteel #Hardware

Why should material grades like ASTM A536 matter in a specification?

• They identify the material standard for the casting/part. • They help verify that the valve body or fitting material meets required mechanical properties. • They are different from the valve standard or flange drilling standard. Category: 02 Materials Tags: #ASTM #Materials #Specifications

What is the key tradeoff between plastic and metal valve components?

• Plastics can reduce weight, corrosion, and inertia. • Metals usually provide higher strength, temperature capability, and mechanical robustness. • Selection depends on service severity, pressure, temperature, and failure consequence. Category: 02 Materials Tags: #Plastic #Metals #Tradeoff