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2008 API AST Conference

Introduction

This presentation describes a sensor system for 

monitoring of floating roofs in ASTs for conditions 

leading to: 

 Roof capsizing as a result from liquid buildup on 

the roof.

 Fire due to volatile hydrocarbon accumulation on 

the roof. 

 Roof failure due to misalignment. 
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2008 API AST Conference

The problem

Illustration reprinted courtesy of Tank Industry Consultants TIC

Floating roof related AST accidents have significant 

consequences:

 Loss of life.

 Financial damages. 

 Expensive collateral damage.

 Environmental damages and related fines.

 Tightening of government regulations.

 Negative publicity.

Orion Refinery June 7, 2001: Sunken roof & fire due to Tropical Storm Allison

Source: SP Swedish National Testing and Research Institute 
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Source: Large Atmospheric Storage Tank Fires (LASTFIRE) study, 2006 

Accident Causes

Common causes of accidents include:

 Fire or explosion due to hydrocarbon accumulation on the roof.

[LASTFIRE, BP] 

 Roof sinking due to rain water accumulation. [TCI Tank industry Consultants]

 Overfilling. [LASTFIRE, BP] 

 Leaky pontoon or punctured deck. [TCI Tank industry Consultants]

 Roof misalignment due to various causes. [BP NineSigma]
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What can be done?

Monitoring the status of floating roofs with 

permanent sensors is an effective approach... 

...however, aside from overfill detection, 

currently there are no sensor systems 

dedicated to monitoring the floating roofs in 

ASTs.
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A wireless sensor system can alert the tank 

operators when one of the following conditions is 

detected on a petroleum storage tank’s floating roof:

 Excessive water accumulation. 

 Liquid hydrocarbons.

 Volatile Organic Compounds (VOC).

 Roof misalignment.

Note: Overfill warning techniques are already implemented reliably by the petroleum industry.

Proposed System
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System Requirements 

Technical requirements for creating a practical floating 

roof sensor monitoring system:

 Completely Wireless System.

 Low Power Consumption.

 Proven Sensor Technologies.

 Immunity to False Alarms.
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Completely Wireless System

Wire Pros:

 Provide power. 

 Bring communications.

 Reliability.

Wire Cons: 

 Practical issues; roof constantly moving. 

 Installation costs.

 Electrical loops.

Solution: Autonomous wireless devices that harvest 

energy from the environment.
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Low Power Consumption

Battery powered device. Low power consumption 

equals:

 Long maintenance free operation.

 Small size solar panel.

 Small footprint.

 Low heat dissipation.

 Lower cost.

Solution: Integration of low-power microelectronics 

& IEEE 802.15.4 radios. 
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Proven Sensor Technologies

In this system the most critical components are the 

sensor transducers. Issues to consider:

 Reliability. 

 Susceptibility to calibration drifts.

 Self calibration.

 Self diagnostics.

 Track record.

Solution: Combine proven technologies 

with modern advancements. 
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Immunity to False Alarms

False alarms:

 Unnecessary deployment of resources.

 Cannot sacrifice reliability.

 Must be minimized.

Solution: Distributed sensor network.

Multiple sensors reduce false alarms.
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Sensor System Components

The AST floating roof monitoring system consists of 

wireless sensor pods and a base station:

Wireless Sensor Pod

Base Station
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Wireless Sensor Pod

2.4 GHz RF 

Module

Communication to 

base station

Solar Panel

Energy autonomy

Status LED

Visual alarm and status

GPS Antenna

Location & quick deployment

Clear Potted Dome

Explosion proof & durable

Gas/Liquid Sensor intakes

Protection of the internal sensors Magnetic Base

Rapid deployment on steel 

structures 

Hard Plastic Body

UV & chemical resistance,

intrinsically safe, explosion 

proof 
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NDIR Sensor

NDIR Gas Sensor: 0 – 100% LFL (0 – 100% vol. 

conc.) for detecting hydrocarbon gasses on the 

floating roof.

Nondispersive Infrared Sensors (NDIR) measure the 

wavelength absorption of gasses:

 Accurate.

 Cannot be poisoned.

 Self calibration.

 Self diagnostics.

 Repeatability.

 Ruggedness.

 Temperature compensation.

Source: iBall Instruments LLC, 2007 

IR600 Series NDIR by e2v UK 
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Inclinometer

Roof inclination measurement. Dual-axis 

Tilt/Accelerometer Sensor - 0.025° resolution. Micro 

Electro-Mechanical Systems (MEMS): 

 High Precision.

 Unaffected by temperature.

 Low power.

 Repeatability.

 Self testing.

 Ruggedness.

 Miniature.

MEMS inclinometer relative size MEMS micro motor, Source: SFU IMMR
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2008 API AST Conference Acoustic Liquid Sensor

Measuring water and liquid hydrocarbons levels on the 

roof using acoustic TDR (Time-Domain 

Reflectrometry):

 Commercial use for more than 60 years. 

 Competitively priced.

 Inherently rugged.

 Very sensitive.

 Reliable.

Fluid-tracTM: accurate at ±0.125”, resolution of 0.07” inches

Acoustic level sensor: Principle of operation
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2008 API AST Conference Optional Sensors

Other sensors that may be added:

 Fire/flame detection.

 GPS.

 Temperature.

 Pressure.

 Snow/hail accumulation.

 Overfill.

Fire Sentry: Model FS24XTM QuadBandTM triple IR fire and flame detector

Locosys: Model AC-1513 GPS module
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2008 API AST Conference System Deployment

 Sensors are dropped 

on the floating roof.

~ AC Power

 Modbus RTU/Modbus TCP. 

 Firmware upgrades enable future protocol 

upgrades.

 Relay outputs interlocks to DCS/Alarm 

system.

Shown: Emerson DeltaV Control System

DCS

EIA-485/Ethernet/Relay Interconnect
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Distributed Sensor System

Representation of the overall environment is achieved 

by simultaneously analyzing data from individual 

sensors monitoring adjacent areas:

 Reliability.

 Accuracy.

 Less False Alarms.

 Self testing. Distributed wireless sensors deployed on an AST floating roof

Inclinometers

5°

5°

5°

0° 0° 5°

Inclinometers

a: correct sensor readings across the roof b: a single faulty sensor reading
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Sensor Operation

Example of sensor operation:

Detection of liquid on the floating roof of AST

Detection of hydrocarbon vapors at LFL on the roof

Detection of roof inclination

Detection of snow cover on the roof (optional sensor)
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Alarm Annunciation

Alarm conditions and system alerts will be annunciated 

to the tank farm’s DCS. The alarm types and system 

alerts are:

 Liquid flooding detected (hydrocarbon/water).

 Hydrocarbon gas alarm (LFL).

 Misalignment/tilt alarm.

 Loss of communications.

 Malfunctioning sensor.
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Product Roadmap

Product evolution into covered floating roof ASTs. 

Emissions measurement and seal gap inspection 

vehicle could become standard procedure. 

LEXID is a promising technology for seal inspection.

Wireless sensors deployed on a covered tank roof Remote-control seal inspection vehicle
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Seal Inspection with LEXID 

LEXID “Lobster-Eye X-ray Inspection Device.

LEXID does not require a detector (film, sensor) 

behind the object.

LEXID could be used in a remote controlled seal 

gap inspection system that would not require tank 

decommissioning.

Source POC: LEXID inspection through a car door

Source POC: LEXID Operation Concept
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2008 API AST Conference Conclusion: System Benefits

The tank monitoring sensor system will:

 Reduce the risk of catastrophic floating roof failure.

 Save operational costs by potentially reducing the 

need for manual tank monitoring. 

 Inexpensive - low upfront cost, low deployment 

cost, and minimal maintenance cost.
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Q & A Session

Thank you!

For questions and comments please contact:

Nick Tzonev, CEO

Syscor Controls & Automation Inc.

Suite 201 – 60 Bastion Square

Victoria, British Columbia, V8W 1J2, Canada

Telephone: +1.250.361.1681 ext 621

Email: ntzonev@syscor.com