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Fabrication Services — Vessel Fabrication

3-Phase Separators

Horizontal three-phase separators engineered to split well effluent into oil, gas, and water streams — with weir and interface-level control internals sized for stable oil-water disengagement.

Overview

Splitting three phases means controlling one boundary the whole time

A 3-phase separator does everything a 2-phase separator does — inlet momentum reduction, gravity settling, and mist elimination — then adds a second liquid-liquid separation stage to split the oil and water phases from each other. That second stage lives or dies on one thing: stable control of the oil-water interface level. A weir, bucket-and-weir, or interface-level controller keeps that boundary where the design intends it, so oil doesn't carry into the water leg and water doesn't carry into the oil outlet.

Fintelius engineers every 3-phase separator around the full retention-time picture — gas residence, oil residence, and water residence sized independently — then selects weir geometry and interface instrumentation to hold a stable boundary across the full range of expected water cut.

  • Horizontal configuration, sized for simultaneous oil, water & gas disengagement
  • Inlet diverter, coalescing internals, weir or bucket-and-weir oil-water control
  • Interface level control (displacer or capacitance) driving automated dump valves
  • Corrosion-resistant, H₂S-safe construction for sour, high-water-cut production streams
3-phase separator vessel — shop fabrication
How It Works

From process data to a commissioned three-phase vessel

Every separator follows the same disciplined path through the shop, whatever its weir configuration.

1

Process Sizing

Gas, oil & water rates and expected water cut are used to size gas capacity and independent oil/water retention time.

2

Weir Configuration Selection

Weir, bucket-and-weir, or interface-controller design is selected to match expected water cut variability and turndown.

3

Shell & Internals Fabrication

Shell is rolled and fitted with the inlet diverter, weir plates, coalescing internals, and mist eliminator.

4

Welding, NDE & PWHT

Welds are radiographed and ultrasonically tested; thick-walled sections undergo post-weld heat treatment.

5

Hydrostatic Testing & Dispatch

The complete vessel is hydrostatically tested, coated, and prepared for shipment as a skid or standalone unit.

Weir & Interface Control Types

How the oil-water boundary is held in place

WR

Weir-Type Separator

Oil spills over a fixed overflow weir once it reaches a set level, while water is drawn from beneath — simple and robust for stable, low-variability water cuts.

BW

Bucket-and-Weir Separator

Adds an oil bucket ahead of the weir to buffer surges and protect against slugs of water carrying into the oil outlet — preferred where water cut fluctuates.

IL

Interface-Level-Controlled Separator

A displacer or capacitance-type interface level controller signals automated dump valves directly — no fixed weir, so the boundary can be actively held across a wide water-cut range.

Separation Internals

Four stages, from bulk momentum to a controlled liquid-liquid boundary

Each internal component does one job in the sequence — skipping a stage compromises everything downstream of it.

01

Inlet Diverter

Breaks incoming fluid momentum and initiates gas release by disrupting surface tension at the point of entry.

02

Gravity Settling & Coalescing Section

Provides residence time and, where fitted, coalescing plates to accelerate oil droplet growth and water settling.

03

Weir Plate / Oil Bucket

Physically separates the oil and water compartments, holding a controlled interface level between the two liquid phases.

04

Interface Level Instrumentation

Displacer or capacitance-type instruments continuously monitor the oil-water boundary and signal dump valves to maintain it.

05

Mist Eliminator

Wire mesh or vane-pack demister removes entrained liquid from the gas phase before it exits the vessel.

06

Straight-Run Inlet Piping

Adequate upstream straight-run piping allows flow to develop uniformly before entering the separator, reducing turbulence-driven upsets.

Core Equipment & Mechanical Design

What stable three-phase separation demands

01

Shell & Head Fabrication

Plate rolling and head forming to the design diameter, length, and wall thickness set by combined gas and dual-liquid retention sizing.

02

Weir & Baffle Installation

Weir plates, oil buckets, and splash baffles fitted and leveled inside the shell to the process design elevation.

03

Nozzle & Instrumentation Fabrication

Inlet, gas outlet, oil outlet, water outlet, relief, drain, and instrumentation nozzles with reinforcement pads.

04

Automated Dump Valve Integration

Level-controlled dump valves on both oil and water outlets, tied to interface and level instrumentation.

05

Sour Service & CRA Construction

Corrosion-resistant alloy cladding and H₂S-safe design for sour, high-water-cut production streams.

06

Post-Weld Heat Treatment

Stress-relief heat treatment for thick-walled shell and head sections per code requirements.

07

Radiography & Ultrasonic NDE

Weld integrity verification across all shell and nozzle welds before hydrostatic test.

08

Adjustable Flow Metering & Sampling

Adjustable metering across variable flow rates and surface sampling points for produced-fluid quality checks.

09

Skid Mounting & Portability

Skid-mounted, field-portable configurations for well testing and frac flowback service.

Design Specifications

Capability at a glance

Configuration
Horizontal, three-phase (oil / gas / water)
Sizing Basis
API 12J & GPSA — gas capacity, oil retention & water retention sized independently
Governing Code
ASME Section VIII
Interface Control Types
Fixed weir, bucket-and-weir & interface-level-controlled (displacer/capacitance)
Horizontal L/D Ratio
Typically 4:1 to 5:1 for extended oil-water settling
Oil Retention Time
Typically 3–5 minutes
Water Retention Time
Typically 3–5 minutes
Gas Residence
Typically 30–60 seconds
Materials
Carbon steel standard; corrosion-resistant alloys for sour (H₂S) service
Instrumentation
Interface level control, high/low level switches & automated dump valves
Testing
Radiography, ultrasonic testing & full hydrostatic test
Delivery Format
Skid-mounted, field-portable or fixed-installation vessel
Applications

Where our 3-phase separators go to work

PD

Oil & Gas Production

Primary separation of wellhead effluent into sales-quality oil, gas, and produced water streams.

WT

Well Testing

Portable three-phase separators supporting well-test measurement of oil, gas & water rates for reservoir evaluation.

FF

Frac Flowback

Handling variable, high-water-cut flowback streams following hydraulic fracturing operations.

GC

Gathering & Central Processing

Bulk separation at central gathering facilities ahead of oil treating, water disposal & gas processing.

SG

Sour Service Production

H₂S-safe construction protecting personnel and equipment in corrosive, sour-service production streams.

EC

Environmental Compliance

Controlled produced-water separation supporting environmental discharge and disposal requirements.

Need a 3-phase separator sized for your well stream's water cut?

Send us your oil, gas, and water rates and expected water-cut range for a fabrication proposal.

Request a Proposal