Valves and Flow Components: Protecting Critical Infrastructure from Degradation

In the oil & gas sector, valves are the silent guardians of safety, efficiency, and profitability. They are everywhere — in upstream, midstream, downstream — and each one is a potential failure point capable of bringing an entire production to a standstill.

The numbers speak for themselves:

• A refinery shutdown costs approximately 1 million dollars per day, according to consolidated industry data
• The hourly cost of unplanned downtime in oil & gas ranges between $10,000 and $250,000 depending on the process involved
• The annual cost of plant failures can average 42 million dollars for an oil & gas company, with peaks up to 88 million in the worst cases
• 46% of the 1,700 shutdowns recorded in U.S. refineries between 2006 and 2017 were caused by mechanical failures, according to Department of Energy data

In this scenario, valves — and in particular metal seated ball valves, gate valves, and choke valves in severe service — represent one of the most significant risk factors. But they also represent one of the areas where engineering intervention produces the fastest and most measurable ROI: the protection of contact surfaces through HVOF Tungsten Carbide coatings.

In this article we analyse the specific degradation mechanisms of valves and flow components, the reasons why metal seated valves represent the fastest-growing segment of the valve market, and how HVOF Tungsten Carbide technology transforms the TCO (Total Cost of Ownership) of these critical assets.

Anatomy of degradation: what really happens to a valve in service

A valve in severe service in the oil & gas sector faces multiple degradation mechanisms simultaneously, which often act synergistically. Understanding them is the prerequisite for any effective intervention.

Galling

When two metal surfaces slide or rotate against each other under load — as occurs at the ball/seat contact of a metal seated ball valve or the wedge/seat contact of a gate valve — localised micro-welds can form between surface asperities. With each subsequent movement, these micro-welds break apart, removing material and creating progressive cratering. Galling is particularly insidious because:

• It generates leakage through the seats even with the valve "closed"
• It exponentially increases the operating torque (risk of actuator stall)
• It is self-accelerating: each new asperity generates further micro-welds

Particle erosion

Formation sand, pipe scale, corrosion products, and hydrate crystals impact valve surfaces at high velocities, removing material by micro-cutting (grazing impact) or plastic deformation (normal impact). The most affected components are:

• Choke valve in upstream production
• Control valve trim (plug, cage, seat)
• Ball and seat in multiphase flows with sand
• Gate valve wedges and seats during depressurisation

Synergistic erosion-corrosion

When particulate and a chemically aggressive environment (H₂S, CO₂, chlorides, acids) are present simultaneously, the total damage significantly exceeds the sum of the two isolated phenomena. The passive film is continuously removed by particle impact and exposed to a new cycle of corrosive attack.

Fretting wear

Micro-vibrations induced by flow pulsations, line vibrations, or actuator movements generate micro-friction between nominally "stationary" surfaces. The result is slow but constant degradation, particularly affecting secondary sealing points, stem bushings, and spring-loaded contacts.

Cavitation damage

In control valves and choke valves, significant pressure drops generate cavitation: the collapse of vapour bubbles near surfaces produces localised shock waves with peak pressures exceeding 1 GPa. The result is crater-like pitting that rapidly destroys trim surfaces.

Hydrogen embrittlement and degradation in sour service

In the presence of H₂S, traditional materials — even if initially compliant with NACE MR0175 — can suffer hydrogen embrittlement, localised pitting, and SSC in stressed zones. The result is a loss of surface mechanical properties that amplifies other wear mechanisms.

Critical flow components: where risk is concentrated

Type	Critical degradation point	Typical failure consequence
Metal seated ball valve	Ball/seat contact	Leakage on closure, rotation seizure, SIL loss
Gate valve (incl. through-conduit)	Wedge/seat, guide grooves	Leakage, jamming, stem breakage
Choke valve	Variable-position trim	Catastrophic erosion, loss of flow control
Control valve	Plug, cage, seat	Regulation inaccuracy, cavitation
Globe / angle valve	Plug and seat	Leakage, cavitation
Plug valve	Plug/body	Galling, seizure
Subsea valve (API 17D)	All dynamic contacts	Extremely costly intervention, months of lead time
ESDV (Emergency Shutdown Valve)	Ball/seat and actuator	Loss of safety function, HSE risk

 

Metal seated ball valves: the fastest-growing segment

Metal seated valves today represent the fastest-growing segment of the industrial valve industry. The reasons are clear: in all applications where temperature, pressure, abrasiveness, or chemical aggressiveness of the fluid rules out soft seals (PTFE, PEEK, elastomers), the metal seat is the only technically viable option.
A high-performance metal seated ball valve must guarantee:

• Bidirectional sealing even after thousands of cycles
• Low operating torque — critical for actuators and SIL
• Galling resistance under spring-loaded or pressure-energized loads
• Chemical compatibility with the process fluid
• Operation across a wide thermal range — from LNG cryogenics (-196 °C) to high-temperature applications (above 500 °C)

All these performances depend on a single key technological factor: the coating applied to the ball and seats.
Materials commonly used for coating sealing surfaces:

Coating	Typical hardness	Strengths	Limitations
WC-Co (Tungsten Carbide / Cobalt)	Up to 72 HRC	Excellent abrasion resistance, extreme hardness	Cobalt binder can corrode in certain environments
WC-Co-Cr (Tungsten Carbide / Cobalt-Chromium)	~1,200 HV / >65 HRC	Excellent abrasion/corrosion balance, first choice in oil & gas	Material cost
Cr3C2-NiCr (Chromium Carbide / Nickel-Chromium)	~68 HRC	Excellent at high temperature (up to 815 °C)	Lower hardness than WC, less effective in pure abrasion
Stellite (PTA)	~45-55 HRC	Good galling resistance, weldable	Lower hardness than carbides, high cost
ENP (Electroless Nickel Plating)	~65-70 HRC	Low cost	Hexavalent chromium carcinogenic (REACH), high porosity, lower performance in cavitation

 

HVOF Tungsten Carbide: the state of the art

HVOF (High Velocity Oxygen Fuel) is today the preferred deposition technology for tungsten carbide coatings on high-criticality valves and flow components.

Why it works so well

The HVOF process accelerates cermet powder particles to supersonic velocities (up to 800 m/s) while keeping the particle temperature low enough to avoid fully melting the carbides. The result is a unique microstructure:

• Very high density: typical porosity <1%
• Low decarburisation: carbides remain intact and do not decompose in the matrix
• Superior bond strength: over 12,000 psi (≈83 MPa) for carbide-based systems, compared to 5,000–7,000 psi for plasma ceramic coatings
• Compressive state: high-velocity particles impact with a shot-peening effect that places the coating in compression, increasing fatigue resistance
• Typical thickness: 200–500 µm, machinable to mirror finish (Ra < 0.1 µm)

The practical benefits on a metal seated valve

A metal seated ball valve with ball and seats coated in WC-Co-Cr applied by HVOF offers:

Characteristic	Typical value
Surface hardness	1,100–1,300 HV0.3
Operating thermal range	-196 °C ÷ +538 °C
Chemical resistance	Excellent vs. mineral acids, hydrocarbons, chlorides
Friction coefficient (lubr.)	0.10–0.15
Abrasion resistance (ASTM G65)	3–10 mm³ vs 50–100 mm³ of alloy steels
Extended service life	Up to 5–10x compared to uncoated substrate

 

Reworkability and reconditioning

An often-overlooked advantage: a valve with HVOF coating can be reconditioned at the end of its service life. The worn layer is removed, the surface is prepared, and a new HVOF layer is applied. The saving compared to full replacement can exceed 60–70% of the new cost, with a lead time often halved.

When to intervene: new, retrofit or reconditioning

HVOF Tungsten Carbide treatment is economically advantageous in three distinct scenarios:

• New valves
  The valve manufacturer integrates the HVOF coating into their trim specification. This is the ideal situation: maximum process quality, geometry designed around the coating, integrated certification.
  
• Retrofit of existing valves
  An installed valve that begins to show early signs of degradation can be recovered by dismantling the critical components (ball/seat, wedge/seat, plug/seat) and applying the HVOF coating in a specialist workshop. This intervention is particularly advantageous for:
• Valves subject to recurring failures

• Components with critical replacement lead times
• "Obsolete" valves no longer in production
  
2. Cyclic reconditioning
   A predictive maintenance programme that includes HVOF reconditioning of critical valves at every turnaround, with a full inspection history and complete traceability. This is the most mature strategy and is today adopted by leading international operators.

Reference standards and coating qualification

For oil & gas valves, HVOF coatings must be applied and qualified according to recognised standards:

• API 6A / API 6D / API 17D — Specifications for upstream and subsea valves
• API 6DSS — Subsea pipeline valves
• NACE MR0175 / ISO 15156 — H₂S service
• NACE MR0103 / ISO 17945 — Refinery service
• ASTM G65 — Abrasion resistance (reference standard for HVOF qualification on valves)
• ASTM C633 — Coating bond strength
• ASTM E384 — Vickers microhardness
• ISO 14923 — Characterisation and testing of thermally sprayed coatings

A mature technology partner is able not only to apply the coating, but to certify its performance through an in-house metallurgical laboratory with micrographic, adhesion, porosity, hardness, and service simulation testing.

Conclusion: the valve is a strategic asset

In oil & gas, every critical valve is a balance point between productivity, safety, and compliance. When it fails, the consequences extend well beyond the cost of the valve itself: they manifest as plant shutdowns, HSE performance impacts, and operational reputation damage.
The protection of contact surfaces through HVOF Tungsten Carbide coating is today the most mature technical solution, validated by decades of industrial experience and supported by a robust regulatory framework. The true competitive differentiator is no longer "whether or not" to apply a coating, but choosing the right partner to do it:

• Knowledge of the component's specific failure mode
• Correct selection of the material-substrate pair
• Mastery of HVOF process parameters
• Post-coating machining capability (grinding, lapping)
• In-house metallurgical laboratory for qualification and testing
• Global production network for competitive response times
• On-site service for non-moveable components