Patent Application
20150346159
1. Technical Field
The invention relates to corrosion monitoring in general and more specifically a permanently installed monitoring system for corrosion under insulation (PIMSCUI) and a method for performing the monitoring of said system.
2. Background Art
Pipeline and process vessel corrosion under insulation is an enormous and costly problem across northern European oil and gas installations, and similar weather related challenges are likely to face other growing markets around the world such as those in Canada and Brazil. At present CUI detection is a slow manual process requiring skilled inspectors with costly inspection tools. There are no permanent monitoring systems available suitable for CUI purposes. Enormous direct cost reductions could be achieved through better decision making enabled by permanent monitoring technology. Savings would be magnified through the reduction of indirect costs such as CUI related shutdowns.
From prior art one should refer to US patent application US20100141281 based on WO/2009/002180 by Johnsen disclosing a fibre optic based humidity measurements. The problem is that such a measurement systems lacks a mechanism to confirm that corrosion has taken place. Furthermore the system of WO/2009/002180 refers the implementation of a grid or line of discrete and spaced humidity sensors, and as such the humidity can only be measured where the discrete sensing elements exist
References should also be made to US 2012294124 A1, regarding monitoring of corrosion in a pipe.
Finally from prior art one should also refer to US 2012092960 A1, regarding a system having distributed acoustic sensors wherein an optical fibre is used for distribution of signals.
Therefore, a main objective of the present invention is to provide a permanently installed monitoring system for corrosion under insulation (PIMSCUI) and a method for performing the monitoring of said system.
In one aspect a permanently installed fibre optic technology for monitoring corrosion under insulation (CUI) continuously over large surface areas is provided. The technology revolves around discrete or continuous moisture under insulation monitoring using fibre optics, alone or in combination with direct measurements for CUI. The direct measurements can either be spot measurements or quantities averaged over any given length of the installation. The technology has extremely low installation overhead demands: minimal power cabling is required, and signal transmission is through the fibre optic sensing cable.
The objective is achieved according to the invention by a sensor system for corrosion monitoring as defined in the preamble of claim 1, having the features of the characterising portion of claim 1, and by a sensor system for corrosion monitoring as defined in the preamble of claim 1, having the features of the characterising portion of claim 1
The present invention attains the above-described objective by a fibre optic cable permanently mounted between walls of a pipeline and pipeline insulation surrounding the pipeline and placement of acoustic emitters along the length of the pipeline in mechanical contact with the optical fibre. The acoustic emitters send a pulsed acoustic signal towards the pipeline which is received by the optical fibre, the acoustic signal subsequently travels through significant depths of the pipeline wall, if desired up to the extent that said wave is reflecting from the inner diameter of the pipeline before the reflected pulse is received at the optical fibre.
A technical difference over WO/2009/002180 is the use of acoustic emitters. The effect of this is the ability to use acoustic means to probe corrosion conditions while the fibre is used to act as an acoustic signal receptor. A second technical difference is that the humidity sensing elements need not necessarily be discrete, and could give a spatially continuous measurement profiles over significant lengths.
Furthermore the chemical sensing capability of the invention described here extends to one or more of a family of corrosion related parameters comprising of humidity, liquid water, pH, conductivity, salinity and hydrogen.
These effects provide in turn several further advantageous effects:
The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an [exemplary] embodiment of the invention given with reference to the accompanying drawings.
The invention will be further described below in connection with exemplary embodiments which are schematically shown in the drawings, wherein:
The following reference numbers and signs refer to the drawings:
Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.
The invention will be further described in connection with exemplary embodiments which are schematically shown in the drawings, wherein
An optical fibre 300 is positioned between the outer wall 220 of a pipeline and the inner wall 260 of the pipeline insulation 250 surrounding the pipeline 200. A fibre comprises typically a core 310 surrounded by a cladding 320, see
At least one acoustic emitter 400 is positioned along the length of the pipeline in mechanical contact with the optical fibre. Each acoustic emitter comprises means for emitting an acoustic signal, typically a piezo element 410, a means for providing operating power, typically a battery 430 and a clamp 440 for providing mechanical attachment.
Each acoustic emitter sends an excited beam 450 of a pulsed signal towards the pipeline 200 (see
The excited signal is emitted from the acoustic unit, typically by a piezo element. The excited and reflected signal are detected by the fibre, typically a suitable optical method for converting the acoustic signals to fibre transmitted optical signals include the use of fibre Bragg gratings. Other methods for encoding the acoustic signal include, but are not limited to, the use of Distributed Acoustic Sensing (DAS, see Optasense 2012) or elements introducing microbend losses into the fibre, detectable using e.g. optical time domain reflectometry (OTDR) methods.
Pipeline wall thickness measurements could be made at various points along the pipeline with the use of multiple acoustic emitters and optical multiplexing techniques. The acoustic emitters could be user controlled through wireless communication, or operate as independent units activating at predetermined time intervals.
The clamps 440 should be located such that the inward travelling acoustic wave is effectively transmitted through the optical fibre and into the pipeline/vessel wall. The clamps should also ensure effective transmission of the reflected outwardly travelling acoustic wave into the optical fibre from the pipeline/vessel wall,
A second property of the system is that the fibre used for transmitting the acoustic signals has optomechanical properties that are a function of the humidity in the surrounding space between the pipeline and insulation. Humidity is a known precursor to the development of corrosion. Materials such as di ureasil (Correia, 2012) and PVA/COCI2 (Cho, 2011) compounds could be used to surround the fibre to give it the desired optomechanical optical properties. Using such materials the ambient humidity could be converted to a loss parameter of the fibre, probed for example using optical time domain reflectometry (OTDR) methods. In such an embodiment, the humidity sensitive material 330 would typically replace part or all of the fibre cladding 320 which would be partially removed or tapered, see
A number of variations on the above can be envisaged. For instance the person skilled in the art will see that the acoustic emitters can be operated in two modes.
In a first mode the wall thickness is measured at a single point. Here the acoustic emitter and receiver, typically the sensitive fibre element, are positioned at substantially the same point along the pipeline, with the acoustic wave propagating substantially perpendicular to the pipeline. The wall thickness is derived from the propagation time of the acoustic wave for the forward and return pass through the pipeline wall.
In a second mode an average pipeline wall thickness is measured. Here an acoustic emitter positioned at a specific point along the pipeline wall sends a guided ‘lamb wave’ through the pipeline wall to a receiver positioned further along the pipeline. The propagation time of the lamb wave is a function of the average wall thickness between the emitter and receiver. The invention also makes it possible to employ modes in the group containing longitudinal waves, transverse waves, shear wave, Rayleigh waves, Stonely Waves and Sezawa love waves, in order to assess the physical condition of the pipeline. This invention makes it also possible to measure second acoustic reflection indicating solid build-up at pipe inner wall (e.g. sand, scale, asphaltenes, waxes) cracking, pitting, density variations and other material degradation and deficiencies. The fibre can also be used for communications such as for additional instruments communicating through the fibre infrastructure including instruments for measuring salinity and temperature. The fibre can be used as part of a distributed sensing system, specifically those that measure temperature, strain, and acoustic signals. The fibre can also be used for measuring additional parameters that could act as corrosion indicators, such as the presence of liquid water, humidity, salinity, pH, conductivity and hydrogen Additional parameters could also be measured for the purpose of compensating for environmental effects on other corrosion indicator measurements.
In another embodiment, the invention monitors the wear and degradation of components internal to the pipeline/process vessel. This can be achieved by measuring the evolution in space and time of (i) acoustic signals transmitted through the pipeline wall, (ii) temperature, and (iii) the previously named parameters that act as corrosion indicators.
In a further embodiment a reference fibre is used, running parallel with the sensing fibre. The reference fibre could be used for example to compensate for the influence of temperature on the sensing fibre. The reference fibre could also be used to compensate for other environmental or system related effects on the sensing fibre.
In another embodiment the humidity and acoustic sensing elements are on separate optical fibres.
In yet another embodiment the excited and reflected acoustic signals are detected by a technology other than fibre optics, the detected signal is then encoded on the optical fibre by some means such as an amplified acoustic signal or electro optical protocols.
In a further embodiment the optical fibres are single lengths, or comprised of discrete sections that are assembled into one continuous length before, during or after the installation process. A modularised embodiment would be particularly compatible with modern insulation systems that comprise many discrete insulating units.
In a further embodiment, the acoustic emitter and received are replaced with other instrumentation that measures pipe vessel wall material degradation such as pitting, cracking and the presence of hydrogen typically. In such cases the fibre could be used as a medium to transmit data from these instruments to a remote location.
Clampon 2012, Clampon website; http://www.clampon.com/?page=2&show=7 GE 2012, GE website; http://www.ge-mcs.com/en/ultrasound/corrosion-monitoring/rightrax-automate-lt.html
Correia, S, F. H. et. al. 2012 “Optical Fiber Relative Humidity Sensor Based on a FBG with a Di-Ureasil Coating” Sensor, 12, 8847-8860.
Cho, H., et. al. 2011, “Monitoring of Corrosion Under Insulations by Acoustic Emission and Humidity measurement” J. Nondestruct. Eval. 30, 59-63 Johnsen 2010, US patent US20100141281
The invention according to the application finds use in continuous monitoring, typically for offshore applications and other places where access is hard or limited such as in nuclear reactors
| Number | Date | Country | Kind |
|---|---|---|---|
| 20121544 | Dec 2012 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO2013/050230 | 12/19/2013 | WO | 00 |
