C4 steel<\/a> materials
\nC4 steel is ultra-low carbon high silicon austenitic stainless steel, core composition: C\u22640.03%, Si 3.54.5%, Cr1315%, Ni1315%. In the strong oxidizing environment of concentrated nitric acid, a dense silicon dioxide passivation film is formed on the surface of the material, blocking the medium from further corroding the matrix, and the corrosion resistance is far better than that of conventional austenitic stainless steel. The cast grade ZG00Cr14Ni14Si4 is used for valve body and ball casting; the forged grade 00Cr14Ni14Si4 is used for valve stem and small size ball forging processing. C4 steel ball valve design standard GB\/T12237.<\/p>\n2.2 Applicable working condition boundaries (selection core)
\nRecommended for:<\/p>\n
Nitric acid concentration \u226585%, priority is given to concentrated nitric acid and fuming nitric acid above 98%; the corrosion performance is best below 50\u2103, and the corrosion rate is <0.1mm\/a.
\nStrong oxidizing system of nitric and sulfur mixed acid below 50\u2103.
\nConcentrated nitric acid device, nitric acid tank truck delivery pipeline, storage tank cut-off ball valve. C4 steel ball valve tank truck for nitric acid transportation.
\nConditions of use: The maximum medium temperature does not exceed 80\u00b0C. The corrosion rate will increase rapidly as the temperature increases.<\/p>\n
Selection boundaries are prohibited:<\/p>\n
Dilute nitric acid, reducing acid, and chloride ion-containing media will damage the passivation film and sharply intensify corrosion.
\nIt is not recommended to use C4 steel ball valves when the long-term temperature is >80\u00b0C, and the 2507 duplex steel and nickel-based alloy solutions should be re-evaluated.
\nThe medium contains solid particles for abrasive conditions, and the C4 steel body alone is not enough to resist erosion and wear.
\n2.3 Principles of material matching of parts and components
\nValve body, ball, valve stem, valve cover: all made of C4 steel (casting\/forging), the mixed selection of valve body C4 and ball 304 is not allowed. Galvanic corrosion will quickly damage the ball.
\nFasteners: C4 steel is also used to avoid galvanic corrosion caused by contact between dissimilar metals.
\nSealing pair: Mainstream PTFE and filled PTFE are used for soft seals; PEEK is used for high temperature and high pressure conditions; hard seals are made of C4 body surfacing carbide.
\nGasket packing: Concentrated nitric acid prohibits ordinary flexible graphite, giving priority to PTFE gaskets and PTFE braided packing. C4 steel ball valve failure and leakage treatment.
\n2.4 Comparison with other material selections
\n310S: Good high-temperature performance, but the corrosion resistance of concentrated nitric acid at room temperature is weaker than that of C4 steel, and the cost is higher. 2507 dual-phase steel: excellent pitting corrosion resistance, but in a strong oxidizing environment with high concentration of concentrated nitric acid, the stability of the passive film is not as good as that of C4 steel. High-purity aluminum: only suitable for nitric acid above 98% at normal temperature. Corrosion will accelerate as the temperature rises slightly, and the mechanical strength is poor. High-silicon cast iron: good acid resistance, but brittle and prone to bursting due to sudden temperature changes. It cannot be used to make moving parts such as ball valve balls.
\nSelection summary: For medium-low temperature and high-concentration concentrated nitric acid, C4 steel ball valves are preferred; if the temperature exceeds the standard and contains chloride ions, abandon C4 steel and replace it with other corrosion-resistant materials.<\/p>\n
3 C4 steel ball valve welding risk analysis and control measures
\nThe biggest shortcomings of C4 steel are poor welding performance and high silicon content. The welding molten pool easily generates low melting point silicate eutectic, which is prone to thermal cracks under the action of welding tensile stress. It is the main source of failure in C4 steel valve manufacturing and on-site repair welding. Ball valve body casting repair welding, flange butt welding, and ball repair welding are all high-risk welding parts.<\/p>\n
3.1 Main welding risks
\nWelding hot cracks (solidification cracks): Si, S, and P impurities segregate to form a low-melting interlayer. Intergranular cracks are generated due to welding residual stress during the cooling process. The cracks are subtle and hidden. The hydrostatic test may not detect them. After being put into concentrated nitric acid medium, the cracks expand and leak.
\nEmbrittlement of the heat-affected zone: excessive heat input results in coarse grains, reduced toughness, and simultaneous sensitization, inducing intergranular corrosion. Although C4 is ultra-low carbon and has no knife edge corrosion after welding, hot crack defects will become corrosion breakthroughs.
\nResidual stress induced stress corrosion cracking: forced assembly, large misalignment, welding residual stress superimposed on concentrated nitric acid corrosion, stress corrosion cracking at the weld, and weld leakage after the ball valve is operated.
\nImproper use of welding materials: Direct use of ordinary 308 and 316 welding materials will result in insufficient silicon elements in the weld, and the weld will fail to resist corrosion by concentrated nitric acid.
\n3.2 Engineering welding control strategies
\nThe welding materials must match: Use special HC4 welding wire for C4 steel and special welding rod for AC4. It is strictly prohibited to substitute ordinary stainless steel welding materials; the welding rod is baked and kept at 250-350\u2103 for 12 hours, and the insulation cylinder is ready for use.
\nControl the welding heat input: use low current, short arc, and fast welding; give priority to argon arc welding to reduce heat input; high current surfacing welding is strictly prohibited; the interlayer temperature is strictly controlled to \u22645060\u00b0C, and the next welding pass is welded after cooling to the appropriate position.
\nForced alignment is prohibited during assembly: valve body repair welding and flange welding must not be forcibly corrected to reduce assembly stress; the amount of misalignment is strictly controlled to avoid additional stress.
\nGroove cleaning: Use acetone to clean oil dirt and oxide scale on the groove and the surrounding 10mm range to prevent S and P impurities from being brought into the weld.
\nPost-treatment of repair welding of castings: After repair welding of important pressure-bearing castings, solution treatment should be performed according to the process to ensure the corrosion resistance of the weld; after the repair welding is completed, penetrant PT testing should be performed to check for micro-cracks. Hydrostatic testing should not be performed instead of non-destructive testing. C4 steel ball valve welding process.
\nKey points for manufacturing supervision: When repairing welding of C4 steel ball valve castings, welding material records, interlayer temperature records, and PT flaw detection reports must be checked. The water pressure of hot cracks often does not leak, and the medium will not be used until it fails.<\/p>\n
4 Main reasons and solutions for seal failure of C4 steel ball valve
\nIn addition to the corrosion of the body weld, a large number of failures of C4 steel ball valves come from the failure of the sealing system, which is divided into internal leakage of the soft seal, external leakage of the valve stem packing, and corrosion and scratches on the surface of the ball under some working conditions, causing damage to the seal pair.<\/p>\n
4.1 Soft seal (PTFE) failure mode
\nPTFE cold flow creep: PTFE undergoes plastic cold flow deformation under continuous medium pressure, and the valve seat is completely deformed. After closing, the ball and the valve seat are not tightly fitted, resulting in internal leakage; the higher the pressure and the higher the temperature, the more obvious the creep.
\nThermal cycle damage: The temperature fluctuates when the device starts and stops, the PTFE thermally expands and contracts repeatedly, micro-cracks occur inside the valve seat, and the sealing performance deteriorates. The recommended temperature for pure PTFE is \u2264180\u00b0C, and the recommended temperature for C4 steel nitric acid working conditions is \u226450\u00b0C.
\nMedium crystallization and solid particle erosion and scratching: Concentrated nitric acid medium crystallization particles get stuck on the sealing surface of the ball valve seat, and scratch the valve seat and ball when opening and closing, forming a sealing groove and causing continuous internal leakage.
\nWrong selection: pure PTFE is still used under high temperature conditions, and the filled PTFE or PEEK valve seat should be upgraded.
\n4.2 Failure of metal seal pair
\nThe surface of the C4 steel ball has casting defects, repair welding micro-cracks, pitting corrosion in concentrated nitric acid medium, pitting on the sealing surface, and the hard seal cannot be closed tightly.
\nThe media particles erode and wear the ball sealing ring.
\n4.3 Valve stem packing leakage and failure
\nConcentrated nitric acid strongly oxidizes, and ordinary graphite packing is oxidized and pulverized; the packing pre-tightening force is too large, the valve stem gets stuck, and the pre-tightening force is insufficient, the medium escapes, and the valve stem part becomes sour.<\/p>\n
4.4 Countermeasures to prevent seal failure
\nValve seat selection: For conventional \u226450\u2103 concentrated nitric acid, use filled modified PTFE valve seat to reduce creep; for high temperature and high pressure conditions, use PEEK valve seat.
\nA filter is added upstream to intercept the crystallized particles of the medium and protect the sealing surface of the ball and valve seat.
\nThe packing gaskets are all made of PTFE series, ordinary graphite is prohibited; the packing gland bolts are moderately pre-tightened and equipped with load gaskets to avoid over-tightening the valve.
\nRegular maintenance: The soft seal of the C4 steel ball valve is a wearing part. Replace the valve seat regularly according to the device maintenance cycle. Do not wait for leakage before dealing with it.
\nThe procurement technical agreement is clear: the sphere shall undergo penetrant inspection, and repair welding in the sealing zone area shall not be allowed. C4 steel ball valve sealing material is PTFE\/PEEK.
\n5 Comprehensive project suggestions
\nSelection stage: Strictly calculate the medium concentration and temperature. Don\u2019t just look at whether the medium is concentrated nitric acid and ignore the temperature boundary; the technical agreement clarifies that all C4 materials of the valve body, ball and stem are specified, welding materials and flaw detection requirements are clarified, and low-priced non-standard mixed material valves are rejected. ZG00Cr14Ni14Si4 cast steel ball valve.
\nManufacturing supervision: focus on the repair welding process of castings. Repair welding of C4 steel requires PT penetration testing and cannot rely solely on hydraulic test acceptance. C4 steel floating ball valve.
\nInstallation stage: When welding flanges, it is strictly forbidden to force the joints, pipelines should be filtered, and the valve should be installed after pipeline purging is completed to prevent welding slag particles from scratching the sealing surface. C4 steel hard seal ball valve Q41Y16C4.
\nOperation and maintenance stage: record the temperature fluctuations of the medium and prohibit over-temperature operation; conduct regular inspections for internal and external leaks; the soft-sealing ball valve is included in the list of regular replacement seals. C4 steel floating ball valve.
\n6 Conclusion
\nC4 steel ball valve is an ideal valve for medium and low temperature concentrated nitric acid working conditions, but the material has two major pain points: sensitivity to welding hot cracks and creep failure of seals. Selection cannot be as simple as “choose C4 steel if the medium is concentrated nitric acid”. The boundaries of temperature and concentration working conditions must be kept; the welding process and non-destructive testing must be strictly controlled in the manufacturing process; and seal loss management must be paid attention to during operation. Only by controlling the entire chain of model selection, manufacturing, installation, operation and maintenance can we avoid premature failure of the C4 steel ball valve and ensure the safe and stable operation of the concentrated nitric acid plant. Electric C4 Steel Ball Valve Q941F16C4.<\/p>\n
References (standard for technical articles) [1] 00Cr14Ni14Si4 High Silicon Austenitic Stainless Steel Technical Conditions [2] GB\/T12237 Steel ball valves for petroleum, petrochemical and related industries [3] C4 Steel Welding Process Evaluation Chemical Equipment Anti-Corrosion Manual<\/p>\n","protected":false},"excerpt":{"rendered":"
1 Introduction Concentrated nitric acid production, tank truck transportation, and storage tank pipelines are working conditions with strong oxidative corrosion. Ordinary 304 and 316L stainless steel have high corrosion rates. High-silicon cast iron is brittle and cannot withstand temperature shock. The use temperature of high-purity aluminum is limited. The procurement cost of nickel-based alloys is […]<\/p>\n","protected":false},"author":1,"featured_media":18715,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"jetpack_seo_schema_type":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[791,790,792,795,794,793],"class_list":["post-18714","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry-news","tag-00cr14ni14si4","tag-c4-steel-ball-valve","tag-concentrated-nitric-acid","tag-material-selection","tag-sealing-failure","tag-weld-hot-cracking"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/oudianvalve.com\/wp-content\/uploads\/2026\/09\/C4-BALL-VALVE.png","_links":{"self":[{"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/posts\/18714","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/comments?post=18714"}],"version-history":[{"count":2,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/posts\/18714\/revisions"}],"predecessor-version":[{"id":18719,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/posts\/18714\/revisions\/18719"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/media\/18715"}],"wp:attachment":[{"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/media?parent=18714"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/categories?post=18714"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/oudianvalve.com\/it\/wp-json\/wp\/v2\/tags?post=18714"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}