Metal Trunnion Mounted Ball Valve – Wear Resistant Carbide Coated

Description

A metal three piece trunnion mounted ball valve is a heavy‑duty shut‑off device engineered for large‑bore high‑pressure piping and process streams carrying solid‑particle contaminants. Its assembly consists of three discrete bolt‑tightened components: left flanged body, central body and right flanged body. The ball is anchored at the valve cavity centre by upper and lower support bearings under trunnion mounted construction and remains unaffected by process‑media pressure. Axial thrust generated by fluid pressure is absorbed by the bearings instead of being transferred onto valve seats, delivering stable, predictable operating torque across high differential‑pressure conditions.

Seats fitted within this trunnion mounted ball valve are all‑metal, overlaid with Stellite cobalt‑base alloy or coated with tungsten carbide, replacing conventional polymeric seats such as PTFE or PEEK. This enables the valve to withstand operating temperatures up to 400 ℃ and resist erosive wear induced by entrained solid particulates. This metal seated ball valve delivers far extended service life compared with soft‑seat alternatives when handling abrasive media including mineral slurry, oil slurry and black water.

Thanks to its three‑piece layout, technicians can extract the central cartridge on‑site for replacement of metal seats and sealing assemblies without disconnecting flange joints, eliminating complex lifting and full‑valve removal operations for large‑size units. The metal three‑piece trunnion mounted ball valve is specified for service conditions with DN ≥ 200 and Class ≥ 900, representing the standard selection for large‑bore pipeline isolation under harsh media environments.

Material and Technical Specifications

Parameter Item	Specification Range
Valve Body Material	WCB Carbon Steel / CF8M (316 Stainless Steel) / Duplex Stainless Steel 2205 / Alloy 20
Ball Material	316L / Duplex stainless steel / Surface overlay with Stellite or tungsten‑carbide coating
Stem Material	316L / 17‑4PH / Inconel 718
Support Bearing Material	Hard alloy / Stainless‑steel‑PTFE composite bearing / Bronze alloy
Seat Material	Tungsten‑carbide coating (HRC 70+) / Stellite 6/12 overlay (HRC 45‑50), corresponding to metal seated ball valve configuration
Nominal Size	DN200 ~ DN600 (8″ ~ 24″) and larger
Pressure Class	Class 900 / 1500 / 2500
Applicable Temperature Range	‑46 ℃ ~ 400 ℃ (metal seat)
End Connection	Flanged (ASME B16.5) / Butt‑weld (ASME B16.25)
Body Structure	Trunnion mounted, i.e. three piece flanged trunnion ball valve body design
Face‑to‑Face Standard	ASME B16.10 / API 6D
Fire‑Safe Design	API 607 / ISO 10497 (optional)
Anti‑Static Design	Standard provision (between stem and ball)
Operation Method	Worm‑gear gearbox / Pneumatic actuator / Electric actuator
Applicable Standards	API 6D / ASME B16.34 / ISO 17292
Material Certificate	EN 10204 3.1 / 3.2 (available upon request)
Non‑Destructive Testing	PT / RT / UT examinations performed in accordance with ASME Section V

Structural Highlights: Wear and Erosion Resistance

Superior wear performance of the metal three‑piece trunnion mounted ball valve stems from the combined merits of high‑hardness metallic seat alloys, trunnion‑supported ball geometry and service‑friendly three‑piece architecture.

‑ Tungsten‑carbide / cobalt‑alloy seats against particle‑driven erosion: Conventional polymer seats (PTFE/PEEK) suffer rapid degradation in streams loaded with hard contaminants such as quartz, catalyst fines and coal ash. Solid particles get pressed or cut into polymer surfaces, carving erosive grooves within weeks or months of runtime. This metal seated ball valve features hard‑alloy overlay or coating deposited onto seat sealing surfaces. Tungsten‑carbide coatings achieve hardness above HRC 70, exceeding the indentation hardness of quartz (Mohs 7). Stellite 6/12 cobalt‑base alloy reaches HRC 45‑50 and suits media carrying moderately hard particles. Such high‑hardness metallic layers resist gouging under particle impingement and preserve the geometric integrity of sealing surfaces.

‑ Trunnion‑mounted design mitigates vibration‑accelerated wear: Within particle‑laden flows, floating‑type ball valves push the ball against downstream seats under fluid pressure. Trapped particulates initiate three‑body abrasive wear between ball and seat, accelerating sealing‑surface deterioration. The trunnion‑mounted setup locks the ball centrally by upper‑lower bearings, preventing ball displacement driven by fluid pressure. Fretting motion and particle entrapment between ball and seat are minimised. Axial loads are borne by bearings rather than seats; seats only carry contact force required for effective sealing.

‑ Matched‑pair lapping guarantees metal‑sealing reliability: Prior to assembly, each metal seat undergoes dedicated paired‑surface lapping with its mating ball. Lapping compound removes micro‑protrusions and creates full‑contact sealing bands across spherical and seat faces. Post‑lapping surface roughness achieves Ra ≤ 0.2 μm, delivering controlled leakage rates compliant with ISO 5208 Rate B/C for metal‑to‑metal sealing interfaces.

‑ Three‑piece benefits for abrasive‑condition maintenance: Even robust metal seats experience gradual material loss under long‑term exposure to particle‑rich fluids. The three‑piece configuration enables service crews to pull out the central body cartridge on‑site without flange disassembly, inspect ball‑and‑seat wear, replace metal seats or perform on‑site lapping refurbishment for sealing surfaces. It eliminates heavy‑lifting operations for large‑bore high‑pressure valves, proving particularly valuable for mine sites and remote installations where heavy‑duty hoisting equipment is limited.

Application Scope

The metal three piece trunnion mounted ball valve is primarily deployed for high‑temperature high‑pressure piping conveying solid‑particle‑bearing fluids:

‑ FCC slurry systems: High‑temperature oil‑slurry circuits (~350 ℃) laden with fine catalyst powders under severe particle erosion.

‑ Mineral slurry & tailings transport: Slurry pipelines carrying hard mineral particles such as quartz with intense abrasive wear.

‑ Coal‑gasification black‑water circuits: High‑pressure black‑water piping loaded with carbon black and coal‑ash particulates.

‑ Ethylene‑cracking high‑temperature gas: Hot cracked‑gas streams containing coke particles.

‑ High‑temperature‑high‑pressure steam & thermal oil: Steam and heat‑transfer‑oil loops operating at 250 ℃‑400 ℃ beyond polymer‑seat temperature limits.

‑ Syngas & coal‑chemical processes: High‑temperature syngas piping mixed with pulverised coal or ash residues.

Field Reference Case

Metal three piece trunnion mounted ball valve units serve as pipeline switching manifolds diverting tailings slurry to different tailings ponds at the mineral‑processing plant of Zijin Mining Group Co., Ltd., Zijinshan Gold‑Copper Mine (Shanghang County, Longyan City, Fujian Province). Installed sizes range DN200‑DN300 at Class 300 pressure rating. Valve bodies adopt Duplex Stainless Steel 2205; ball surfaces are overlaid with tungsten‑carbide coating (HRC 70+), and integral tungsten‑carbide alloy seats are fitted within trunnion‑mounted assemblies.

This concentrator processes over 50 000 tons of ore daily. Tailings slurry carries 30‑40 wt% solid particles dominated by quartz (SiO₂, Mohs 7) and pyrite, generating continuous abrasive impingement across valve flow‑paths and sealing interfaces.

Multiple valve concepts had previously been trialled at this location. Rubber‑lined ball valves suffered liner rupture within several weeks from coarse‑particle cutting action. Ceramic‑lined variants developed cracking and spalling triggered by thermal fluctuation and particle impact. Soft‑seat ball valves with PTFE/PEEK seats exhibited erosive grooving and severe internal leakage after weeks to months of service.

Tungsten‑carbide coated seats and ball sealing surfaces of these metal three‑piece trunnion‑mounted valves reach HRC 70+, far exceeding quartz indentation hardness. Sealing surfaces remain free of prominent erosive grooves under continuous scouring by high‑concentration quartz‑rich tailings. Trunnion bearing support stabilises ball positioning under high differential pressure and avoids extra wear caused by particle jamming typical for floating‑ball designs.

These valves achieve over 18‑month service life on the same duty, greatly outperforming former solutions. During scheduled plant shutdowns, maintenance personnel extract central cartridges directly on pipe racks to inspect ball‑and‑seat wear and reassemble after verifying intact tungsten‑carbide sealing layers. Full‑valve hoisting and flange dismounting are unnecessary. Given confined pipe‑rack space with no access for heavy lifting gear inside this concentrator, three‑piece construction resolves major on‑site servicing obstacles.