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Safety Valves for Oil & Gas

Pressure relief and safety valves are the last line of defence against overpressure in oil & gas facilities — from wellhead separators and slug catchers to refinery process columns and LPG storage bullets. Vajra Industrial Solutions supplies API 526 flanged safety relief valves (SRVs) sized to API 520, in carbon steel, stainless steel, and exotic alloys for upstream, midstream, and refinery service — including pilot-operated relief valves (PORV) for superimposed backpressure applications and balanced-bellows designs for variable backpressure.

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Key Applications — Safety Valves in Oil & Gas

Wellhead Separator and Slug Catcher

Conventional spring-loaded safety relief valves for wellhead separators, slug catchers, and production headers. Sized to API 520 for fire case and blocked outlet scenarios. CS (WCB) body for sweet crude; SS 316 or duplex for sour or CO₂-containing produced fluids. Inlet pressure drop must not exceed 3% of set pressure (API 520 requirement).

Inlet DN25–DN100, Outlet DN40–DN150, Class 150–600, WCB / CF8M, API 526, API 520

Gas Compressor Station — Suction/Discharge Protection

Safety relief valves on gas compressor suction scrubbers and discharge pulsation bottles. Set pressure per ASME VIII MAWP of the protected vessel. Anti-chatter design for gas service — gas SRVs must not chatter at low-accumulation conditions. Balanced-bellows or pilot-operated design where backpressure on the relief system is significant.

Inlet DN25–DN100, Class 300–600, WCB / LF2, API 526, anti-chatter trim, API 520

Refinery Process Column and Vessel Protection

API 526 safety valves for atmospheric crude distillation columns, vacuum towers, hydrotreater reactors, and refinery pressure vessels. High-temperature alloy (WC6/WC9) for furnace outlet and reactor effluent. Pilot-operated relief valves (PORV) for columns with significant superimposed backpressure or tight operating margin above set pressure.

Inlet DN25–DN150, Class 150–900, WC6 / WC9 / CF8M, API 526, pilot-operated option

LPG and NGL Storage and Loading

Safety valves for LPG bullets, NGL spheres, and storage tank pressure relief. Sized for fire case (API 520 Appendix D) and vapour generation. Low-temperature carbon steel (LF2) or SS 316 for LPG (-40°C bubble point). Open-bonnet design for clean LPG vapour; closed-bonnet balanced-bellows for heavier hydrocarbon liquids.

Inlet DN25–DN100, Class 150–300, A350 LF2 / CF8M, API 526, fire case sizing

Required Certifications

API 526 — Flanged Steel Pressure Relief Valves (design standard)API 520 Part I & II — Sizing, Selection, and InstallationASME Section VIII Div. 1 — Pressure Vessel Code (UV stamp where required)NACE MR0175 — Sour service trim and body complianceAPI 598 — Valve TestingEN 10204 3.1 MTCs — Material traceabilityATEX (actuated pilot valves in Zone 1/2 hazardous areas)

Recommended Materials

A216 WCB (carbon steel) — sweet crude oil, gas, and general hydrocarbon service
A351 CF8M (SS 316 cast) — sour gas, CO₂-containing, and corrosive refinery service
A350 LF2 (low-temp CS) — LPG, NGL, and cold-climate gas relief
A182 F316 (SS 316 forged) — small bore nozzle and disc for corrosive trim
Hastelloy C-276 trim — highly corrosive H₂S and acid gas service
Inconel 718 spring — high-temperature, corrosive spring environment

Selection Factors

Type: Conventional SRV (backpressure <10% set pressure); balanced-bellows (variable backpressure up to 50% set); pilot-operated (tight blowdown, high backpressure, or large capacity)
Sizing: API 520 governs — calculate required orifice area for blocked outlet AND fire case, select the larger
Set pressure: Must not exceed vessel MAWP; typically set at 95–100% of MAWP
Inlet pressure drop: Must not exceed 3% of set pressure at relieving flow (API 520 requirement)
NACE: Sour service requires MR0175 compliant disc, nozzle, spring, and body
Installation: SRV inlet connected directly to vessel nozzle (no block valve between, or with locked-open block valve)
Testing: Proof test interval typically 2–5 years for oil & gas service per site risk assessment

Technical FAQs

What is the difference between API 526 and ASME UV-stamped safety valves?
API 526 defines the design, materials, pressure-temperature ratings, and dimensions for flanged steel safety relief valves used in oil & gas and petrochemical service. It is a procurement standard specifying interchangeable dimensions and trim options. ASME UV stamp (from ASME Section VIII Div. 1) is a manufacturing quality certification — a UV-stamped valve is certified by ASME for use as a pressure relief device on ASME-coded pressure vessels. Many oil & gas SRVs are both API 526 and UV stamped.
When should a pilot-operated relief valve (PORV) be used instead of a conventional SRV?
PORVs are preferred when: (1) the operating pressure is within 90–95% of set pressure, making conventional SRV chatter a risk; (2) backpressure on the relief system exceeds 50% of set pressure; (3) the valve requires large orifice capacity with a relatively small inlet pipe; or (4) remote actuation capability is required. PORVs maintain tight shut-off up to set pressure and open fully and rapidly at set pressure without chatter. They are widely used on refinery columns, compressor discharge vessels, and gas storage bullets.
How is a safety valve sized for fire case in oil & gas?
Fire case sizing per API 520 Appendix D calculates the heat input from a pool fire engulfing the vessel, converting this to a vapour generation rate, and sizing the SRV orifice to vent that vapour at 121% of set pressure. The formula uses vessel wetted surface area (or all-surface area for vapour vessels), a heat absorption factor F (0.045 for bare steel), and the latent heat of vaporisation of the fluid. The required orifice area is then matched to the next larger standard API 526 orifice designation (D, E, F, G, H, J, K, L, M, N, P, Q, R, T).

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Safety Valves for Oil & Gas

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