In the Oil & Gas sector, operating conditions are among the most demanding in industry: high pressures, extreme temperatures, corrosive fluids and stringent safety requirements. The ball valve is the most widely used isolation component in this sector. But choosing the wrong one can cost far more than the initial saving.

Floating vs trunnion: which design to choose

Oil & Gas ball valves are divided into two main categories based on how the ball is supported:

Floating ball valves

The ball is supported only by the seats and "floats" under differential pressure. This design provides excellent sealing at low to medium pressures, but as diameter and pressure increase, seat loading grows and limits application.

Classes: typically 150–600 lbs
Sizes: up to 8"–10" (above that, switch to trunnion)
Construction: 1-piece, 2-piece, 3-piece
Applications: service lines, utilities, branch connections

Trunnion ball valves

The ball is supported by upper and lower pins ("trunnions") that prevent axial movement. This results in lower operating torque and the ability to handle much higher pressures and larger diameters.

Classes: 150–2500 lbs
Sizes: from 2" up to 60" and beyond
Features: Double Block & Bleed (DBB), spring-loaded seats, metal-to-metal seats
Applications: pipelines, compressor stations, offshore platforms, refineries

Rule of thumb

For sizes ≤ 6" and classes ≤ 300 lbs in non-critical services, a floating valve is adequate. For any other combination in Oil & Gas, consider a trunnion.

Materials: steel, special alloys and when you need them

Material selection depends on the fluid, temperature and presence of corrosive agents (H₂S, CO₂, chlorides).

Material	Designation	When to use
Carbon steel	A105, WCB, LF2	Standard services, non-corrosive hydrocarbons, -46°C to +425°C
Stainless 316	A182 F316, CF8M	Moderate corrosion, process water, utilities
Duplex	A182 F51 (2205)	Chlorides, seawater, offshore platforms
Super-duplex	A182 F53 (2507)	High pitting resistance, severe offshore environments
Inconel 625	N06625	High temperature + high corrosion, deep wells
Monel 400	N04400	Hydrofluoric acid (HF), reducing environments
Hastelloy C-276	N10276	Maximum chemical resistance, mixed acids

For sour service (with H₂S), materials must comply with NACE MR0175 / ISO 15156: body hardness ≤ 22 HRC, specific heat treatments, qualified welding.

ANSI/ASME pressure classes

In Oil & Gas, ANSI classes (ASME B16.34) are used instead of European PN ratings. The class indicates the maximum allowable pressure at ambient temperature:

ANSI Class	Pressure at 38°C (bar)	Typical applications
150	19.6	Utilities, low pressure, distribution
300	51.1	Medium pressure process, natural gas
600	102.1	Gas pipeline, platforms
900	153.2	High pressure, downstream
1500	255.3	Wellhead
2500	425.5	Ultra-high pressure, deep wells

Note: allowable pressure decreases with temperature. A Class 300 in carbon steel handles 51 bar at 38°C but only 34 bar at 300°C. Always check the pressure-temperature tables from ASME B16.34.

Essential Oil & Gas certifications

In Oil & Gas, certifications are not optional. Here are the key ones:

API 6D — Pipeline Valves

The reference standard for pipeline valves: design, manufacture, inspection and testing. Covers ball, gate, check and plug valves. API monogram is mandatory for major oil companies.

API 6A — Wellhead Equipment

For wellhead valves and Christmas trees. Product Specification Level (PSL) from 1 to 4 with increasing test and documentation requirements.

API 607 — Fire-Safe

Fire resistance test: the valve must maintain sealing after 30 minutes of flame exposure. Essential in refineries and platforms.

NACE MR0175 / ISO 15156

Material requirements for H₂S contact (sour service). Hardness, heat treatments, welding. Indispensable for production and extraction.

SIL (Safety Integrity Level)

For valves in Safety Instrumented Systems (SIS). SIL 2 and SIL 3 are the most requested levels in Oil & Gas. Requires reliability calculations and third-party certification.

PED 2014/68/EU

European Pressure Equipment Directive. Mandatory for sales in the EU. Categories I–IV based on pressure, volume and fluid group.

Upstream, midstream, downstream: different requirements

Upstream (extraction)

Most severe conditions: high pressures (classes 1500–2500), fluids containing H₂S and CO₂, temperatures from -46°C to +200°C. Trunnion valves with metal-to-metal seats, NACE-compliant materials, API 6A certification. FAT (Factory Acceptance Test) mandatory for major oil companies.

Midstream (transportation and storage)

Pipelines spanning hundreds of kilometres. Trunnion valves with Double Block & Bleed function, classes 300–600, carbon or low-alloy steel. API 6D certification. Pneumatic or electro-hydraulic actuators for remote operation. Automatic block valves (ESD) with SIL certification.

Downstream (refining and distribution)

Variety of services: hydrocarbons, steam, acids, utilities. Mix of floating and trunnion, classes 150–600. Fire-safe API 607 in process areas. Plug valves for viscous fluid services. ATEX for classified zones in explosive atmospheres.

Quick selection checklist

Define the service: fluid, pressure, temperature, flow rate
Check for H₂S/CO₂: if yes → NACE MR0175 materials
Choose the design: floating for classes ≤ 300 and DN ≤ 6"; trunnion for the rest
Select the material: carbon for standard, duplex for offshore, Inconel/Hastelloy for high corrosion
Determine the class: 150–2500 lbs based on design pressure
Verify required certifications: API 6D/6A, fire-safe, NACE, SIL, PED
Request FAT: mandatory for majors, recommended for critical services
Evaluate actuation: manual, pneumatic, electric, electro-hydraulic

Common mistakes to avoid

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Using floating where trunnion is needed — At high pressures, seat loading increases enormously, causing premature wear and loss of sealing.

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Ignoring NACE certification — In sour service without compliant materials, you risk brittle failure from Stress Corrosion Cracking (SCC). A catastrophic failure.

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Sizing by class alone — Allowable pressure drops with temperature. A Class 150 at 400°C handles only 9 bar.

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Skipping fire-safe certification — In a refinery, a fire can spread in seconds. API 607 certification isn't a cost — it's insurance.

Conclusion

Selecting ball valves for Oil & Gas requires specific expertise: it's not enough to choose a size and a class. Materials, certifications, floating/trunnion design and service conditions are interconnected variables that determine the safety, reliability and lifespan of the plant.

Roffia srl distributes Oil & Gas ball valves from Valpres (Bonomi Group) — floating and trunnion, in steel and special alloys, with all API, NACE and fire-safe certifications. We can also supply Valbia actuators for complete assemblies. Contact us for sizing and selection.

Ball valves for Oil & Gas: materials, pressure classes and certifications