Vertical-Pipe Phase Interface Detection Using Spiral Fiber Optics

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Solution Overview

Problem

Existing methods for measuring phase interface levels in multiphase fluids in vertical pipes, such as gravity separators, rely on radioactive gamma ray sensors, ultrasonic sensors, and capacitance-based systems, which are costly, complex, and lack precision, posing environmental and safety risks.

Innovation Solution

A method using a distributed fiber optic sensor spirally wound around the pipe, coupled with a DAS interrogator, determines phase interface levels by analyzing power spectral density over a frequency band, providing precise, real-time, and non-intrusive monitoring.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If gamma ray level sensors are used to measure phase interface level, then measurement capability is provided, but the system becomes complex, costly, and unreliable with radioactive hazards

Engineering Contradiction:

Improvephase interface level measurementVSAvoidsensor system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/electrical gamma ray sensor system with an optical fiber-based sensing system. The optical fiber sensor detects phase interface levels through optical property changes (refractive index, light absorption) rather than radioactive radiation, eliminating the need for complex radioactive sources and detectors while maintaining measurement capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes changes in optical parameters (light intensity, refractive index, absorption characteristics) as the phase interface level changes. By monitoring these optical parameter variations along the fiber length, the system determines phase interface positions without requiring complex radioactive sensing mechanisms.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If ultrasonic sensors are used for level measurement, then non-radioactive measurement is achieved, but measurement precision and reliability are insufficient

Engineering Contradiction:

Improveradioactive environmental impactVSAvoidphase interface level measurement accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent substitutes ultrasonic acoustic sensing with optical fiber sensing. The optical fiber detects phase interfaces through changes in optical properties (refractive index, light absorption) at the phase boundaries, providing superior precision and reliability compared to ultrasonic methods while maintaining the non-radioactive advantage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If capacitance-based level measurement is used, then a non-intrusive method is provided, but measurement precision and reliability are inadequate

Engineering Contradiction:

Improvenon-intrusive measurementVSAvoidphase interface level measurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent replaces capacitance-based electrical sensing with optical fiber sensing. The optical fiber, being dielectric and non-conductive, maintains the non-intrusive characteristic while detecting phase interfaces through optical property changes, thereby achieving both ease of operation and high measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables accurate, real-time detection of phase interfaces with high precision, allowing for continuous monitoring of fluid parameters like pressure and turbulence, and visualization of fluid distribution, without maintenance, using a non-intrusive and easy-to-install optical fiber system.

Implementation Method 1

a distributed fiber optic sensor comprising a fiber optic cable spirally wound around the pipe and optically coupled to a DAS interrogator

Methodology Applied

Scientific EffectAcoustic sensing through fiber optic detection: Acoustic Emission

Implementation Method 2

from the data acquired by the DAS interrogator, determining the power spectral density over a predetermined duration and for each point of a discretized length of the fiber optic cable

Methodology Applied

Scientific EffectDistributed acoustic sensing:

Data Source

PatentEP4204773B1Method and system for determining over time a level of a phase interface of a multiphase fluid present in a vertical pipe

Publication Date: 2025.10.22 SAIPEM SA

Figure 1
Figure 2A~2C

AI summary

The invention relates to a method and a system for determining, over time, a level of a phase interface of a multiphase fluid present in a vertical pipe (2), comprising: placing a fibre-optic distributed sensor comprising a fibre-optic cable (8) wound in a spiral around the pipe and optically coupled to a DAS interrogator (10); determining, on the basis of data acquired by the DAS interrogator, the power spectral density over a predetermined duration and for each point of a discretised length of the fibre-optic cable; interrogating the power spectral density over a predefined frequency band for each point of the discretised length of the fibre-optic cable; and setting the results of the power spectral density interrogation in matrix form, in order to determine at least one level of the interface of the multiphase fluid.