Paper FOS Pcs Lone RG Rev2.pdf

7/23/2019 Paper FOS Pcs Lone RG Rev2.pdf

1/5

InvitedPaper

REAL TIME PIPING / PIPELINE INTEGRITY

SOLUTION

WALL THICKNESS, DEFECT AND STRESS EVALUATION USING

DISTRIBUTED FIBER OPTIC SENSORS (FOS) TO ANALYSE STRUCTURAL

INTEGRITY AND CORROSION

The future of Asset Integrity and Health Monitoring Systems (HMS)

Ryan [email protected]

ABSTRACT

This paper will explore the use of l on g gage-length and spiral FT fiber optic sensors (FOS) for in - s er vice, r eal -tim e m on it or in g of p l a n t a n d pipeline integrity. Key areas of concentration are wall thickness reduction,rate of corrosion, known defect monitoring, external structural stress as a result of soil displacement, Hoop Stress andBend Stress in pipelines, data analysis, interpretation and modeling.

The above technology will be evaluated with a view of adding value to conventional inspection and maintenanceprograms as applicable to the Oil and Gas / Energy sector.


2/5

1. INTRODUCTION

Corrosion is a major problem that affects the integrity of p r o c e s s p i p i n g a n d pipelines within the oil andgas / energy sector.. In order to reduce the r isk of structural failure, operators need to demonstrate that the corrosion ratewith regards to wall thickness loss is monitored and does not exceed a set rate of deterioration per year, to resolve all ofthe above and provide a system that meets industry requirements we need to provide a solution that monitors the

structural integrity of the asset, with an emphasis on corrosion mapping, leak detection and stress analysis (Hoop andBend)

There is currently a system used in the oil and gas industry that monitors the security of assets by way of detectingdisturbances, third party interference, geo-hazards and leaks using fiber optics. However, industry is in need of anadvanced corrosion mapping system that is both equal by way of technological advancement and flexibility, a REALTIME integrity solution that can replace costly manual NDT inspection, such a system would be a feasiblereplacement for conventional NDT in specific circumstances that will allow clients to realize considerable cost savingsas a result of implementation.

Historically, both basic and advanced NDT is extremely time intensive, requires additional technically trained personnel,is susceptible to human error, requires access to process piping and pipelines in inaccessible areas and in some casesdisrupts operations. These methods are also utilized at great expensive due to periodic survey requirements and the

need to mobilize third party equipment and personnel. A permanent corrosion mapping system is required, a systemthat can be monitored and analyzed by current control room staff, one that models corrosion rates and pipe wallthickness in real time by way of graphical user interface (GUI). A system that is non intrusive, requires no servicedisruption and requires minimal maintenance.

2. SOLUTION DISTRIBUTED FIBER OPTIC SENSORS (FOS)

The fundamental principle behind the FT sensor is the interference of low coherence light. The sensor system, asmodelled in Figure 1, is comprised of two optical paths one through the sensor and one through the reference arm with a light source and a detector. Each of the optical paths has a reflective surface at the end, so that any light travellingdown that path is reflected back. Initially, with no load on the sensor, the two optical path lengths are exactly equal, sothat LS = LR and _LS = _LR = 0. In this instance, the light signals arrive in phase at the detector at the same time. Thisresults in constructive interference and a peak in the magnitude of the optical signal occurs as the detector.


3/5

When the sensor is under load, it is elongated or compressed and resulting in a change in the optical path length. Thischange means that the two signals at the detector are no longer in phase and the signal at the detector is extinguished. Ifthe length of the r eference path is changed, then the two signals are brought into phase again and the interference peak isseen by the detector. Because the light source has a low coherence length, the interference peak only occurs when the

path lengths are matched to within approximately 25 m (microns). This narrow range means that the change in length ofsensors from 10 cm to over 100 m long can be accurately measured to better than 5 m (0.5 microstrain for a 10 mgage length sensor). The high accuracy is crucial in the detection of the small strain change associated with wall thinningdue to corrosion or bending deformations.

The FT sensor system measures total displacement over the sensor gage length, and average strains are calculated bydividing this measurement by the gage length. A plot of the sensitivity of the sensor in terms of the change in wallthickness ratio (wall thickness/original wall thickness) is shown in Figure 2. The standard sensor itself is made fromsingle-mode optical fiber, which has a diameter of 250 m. The load displacement response of the sensor is linear up toelongations of 3% (30,000 microstrain). The small diameter flexible fiber allows the sensor to be packaged intoconfigurations, such as the coil sensor that are suitable for monitoring almost any type of local or large area defect or

problem.

Due to the unique way the FT sensors operate, demodulation of the optical signals requires a specialized monitoringinstrument. This system allows total sensor displacements of up to 15 mm to be monitored (1500 microstrain for a 10m gage length sensor). Remote monitoring, control, data collection, trend analysis, and alarmlevels are achievable in a local mode, or over a network.

Demodulation software combines the measurements of change in strain from the FT sensor monitor, with geometryinformation about the equipment, to convert the raw data into parameters including temperature, pressure, bending strainand pipe wall loss, the system can span over 100 km.

3. RELIABILITY

Implementation of any new sensor system is frequently driven by the requirement that the information must provide aclear cost benefit. Beyond providing some additional data on wall loss or temperature, such a system must operate withhigh reliability if the cost benefit is to be realized over time. There are many factors which affect the performance andreliability of fiber optic sensor systems.

Installation.

Planning of the installation is the key first element. Identification of the proper location for sensors, cable routing,junction boxes, conduit, and monitoring stations relating to the pipeline. Proper familiarization of the clients personnelwith the requirements and operation of the system will ensures integration of the new sensing system.

SensorIntegrity.

As with most bonded or mechanically affixed sensors, full lifetime of the installation is guaranteed with properconsideration for: configuration or sensor selection; cleanliness of surface; proper adhesive selection; full cure cycle;choice of sensor-lead connector for the temperature/chemical environment; thermal/stress fatigue life of adhesiveinterface; cable bend radius; coating defects; maximum strain limit; thermal limit of adhesive and fiber coating.

Operating Environment.

Sensor systems installed on pipelines are subject to operating environments that are significantly more severe than thetypical laboratory or office environment. Systems reliability hinges on the temperature limits of monitor; corrosivenessof the atmosphere/soil; humidity; seismic loads; vibration; probability of lightning strikes and proper groundingrequirements for cable/instrument enclosures.

Communications.

Assurance of uninterrupted data from the sensors requires a robust communication system. Considerations includerouting of lead cables; code/integrity requirements for armored cable; radius of cable bends, location of adjacent hazards(e.g. hot spots); quality of patch panel and connectors; availability of on-demand battery power for remote/wirelesstransmission; accessibility of network connection and permission to access data over a network.


4/5

Software.

No matter what type of sensor system is employed, the data is typically coupled to some software to predict trends,activate alarms, provide feedback to control systems, and to store/archive results of the measurements. Ideally, remoteaccess and control of the monitoring instrumentation is also available through such a facility. Key features that impactupon reliability include no false alarms; self-check diagnostics; security of data, and ease of use. Based on pastexperience with FT data shows that these they can survive for more than 10 years.

4. CONCLUSION

Fiber optic sensors are ideally suited for monitoring corrosion in process piping, pipelines and other equipment that require

extreme emphasis on structural integrity, such as pressure vessels. Equipment with critical or single point failure areas, and

where process controls can be used to mitigate damage when corrosion rates are immediately known will benefit greatly

from the accuracy and flexibility of this technology. Such monitoring can lead to increased safety, increased

productivity, reduced turnaround times, fewer unplanned shutdowns, and lower operating costs. The technology is highly

adaptive thus application to down hole technology with regards to oil and Gas exploration is a viable expansion project,

should portfolio expansion be an option in future. The technology can also be used for structural integrity monitoring

systems (bridges, platforms, vessels).

With the development of Pulse-Pre-Pump Optical Time Domain Analysis (PPP-BOTDA*1) a hybrid Brillouin Rayleigh

sensory system, with a strain measurement accuracy of 0.0025% this system is now very attractive and exceeds

industry requirements. This accuracy makes the technology perfect of monitoring the integrity of Oil and Gas /Petrochemical assets. The current technology cycle within the oil and gas industry is still to incorporate fiber optics with

regards to asset integrity application. Viewed globally as a key innovation in asset integrity and the future of pipeline

monitoring, a technology that will change the way we monitor structural integrity, and dominate the market in future.


5/5

5. REFERENCES

1) Long Gage length fiber optic sensors for monitoring pipeline integrity. R.C. Tennyson*, W.D. Morison2) Solving common corrosion problems, non intrusive fiber optics corrosion and process monitoring sensors. W.D.

Morison, T. Cherpillod

Documents

Paper FOS Pcs Lone RG Rev2.pdf