Patent Description:
A Pressure Safety Valve (PSV) is used to protect a process system against overpressure. <FIG> indicates a closed PSV to the left when the process pressure is below the PSV set pressure which is normally the same as the process design pressure for the process system, and to the right a reliving PSV where the process pressure is higher than the PSV set pressure and the PSV open to allow process medium to flow out of the system.

A typical PSV is a direct spring-loaded relief valve characterized by rapid opening or pop action when subjected to an upstream pressure above the PSV set pressure.

PSVs are used in a variety of industrial application to safeguard process equipment for exposure of internal pressures exceeding the equipment design pressure. One industrial application where PSVs are used is within the oil and gas industry. Each plant may have from hundreds to thousands of installed PSVs. Consequences of a fault on any one PSV ranges from hazardous explosions and fire to releases of hydro carbon and other toxic gases to atmosphere.

Maintenance of PSVs is of major importance to the economy in the operation. In the maintenance context, it is distinguished between (Ref. NORSOK Z008 and others): "corrective maintenance" where the equipment is run to failure, "preventive maintenance" where maintenance of the equipment is performed at predefined (planned) intervals and "condition-based maintenance" where maintenance is performed based on measurements of equipment condition and performance.

PSVs are normally maintained on predefined intervals in the class of "preventive maintenance". The intervals range from <NUM> year to <NUM> years typically with an average of <NUM> years in the Norwegian oil and gas industry. Records shows that faults recorded during maintenance of PSVs are typically <NUM> to <NUM>% of tested units in the period <NUM> to <NUM>, example for <NUM> where <NUM> PSVs were tested and <NUM> reported with faults (Ref <NPL>"). Reducing the maintenance time and costs associated with maintaining PSVs can have a large impact on the plant maintenance cost.

Current approaches in monitoring PSVs with accelerometers and vibration detectors have issues with respect to effectiveness and accuracy. For example, many of the current approaches in monitoring PSVs generate nuisance alarms due to acoustic noise sources such as turbulence created from work in the area, steam whistles or ambient plant noise. Other PSV monitoring systems include continuous on-line monitoring connected to the plant monitoring system, which create huge amount of data to be analysed and evaluated, which has proved to create costly installations and require specialised personnel to maintain and extract the data for the PSV maintenance process.

A system and method relevant to the claimed subject-matter is known from <CIT>. This document however does not disclose that the system comprises a spring washer and a compression load cell sensor which detects the dynamic force applied on the valve spring washer by the spring.

The main objective of the invention is to provide a system and method to detect abnormal operating conditions which will influence functional safety for a Pressure Safety Valve (PSV).

It is further an objective of the invention to provide a method and system to reduce maintenance work and operating cost for the PSV.

It is further an objective of the invention to provide a method and system to determine when the PSV deviates from the acceptable operating specification by leaking process medium and quantify the leak rate per unit time.

It is further an objective of the invention to provide a system and method to quantify the release rate per unit time of process medium when the PSV open to process pressure exceeding the PSV set pressure and check if the flowrate deviates from acceptable design operating process variable envelope.

It is further an objective of the invention to provide a method to determine when the valve dynamic movement envelope is changed due to corrosion, deposits, wear and tear of the mechanical parts of the PSV.

It is further an objective of the invention to provide a system and method to determine when the inlet process pressure acting on the PSV disc is higher than the PSV set pressure without a correct PSV pop action.

It is further an objective of the invention to generate and store defined abnormal condition messages in real time in the local Predictor microcontroller and transmit the messages wireless as required by external operational data systems.

These objectives are achieved with the method and system of the present invention as set forth in the appended claims.

The invention will now be described in reference to the appended drawings, in which:.

At least one embodiment of the present invention is described below in reference to the operation of a Pressure Safety Valve (PSV <NUM>) within an oil and gas production plant. However, it should be apparent to those skilled in the art and guided by the teaching herein that the present invention is likewise applicable to any industrial facility that may employ PSVs. A non-exhaustive listing of possible industrial facilities that employ PSVs and have a need to monitor such valves includes power generation plants, chemical facilities and electrical facilities. Those skilled in the art will further recognize that the teaching herein are suited to other applications in addition to industrial settings such as for example military, commercial and residential applications.

Referring to the drawings <FIG> is a schematic illustration of a PSV <NUM> with monitoring system for abnormal situation detection depicting the communication as a generic symbol, achieved either over a Wi-Fi network, Bluetooth protocol, SMS protocol (a Cloud, dedicated Application or a Handheld Device), or any other applicable method according to one embodiment of the present invention. The PSVs with sensors and the Predictor is adapted to communicate with different recipients.

<FIG> is a sectional view through a PSV equipped with sensors according to the present invention. The PSV as such includes a housing with an inlet and outlet. The fluid flow between the inlet and outlet is controlled by and normally closed by a disc <NUM>. The disc <NUM> is connected to an elongated stem or spindle <NUM>. The spring <NUM> is connected to the stem <NUM> by a spring washer <NUM>, the disc <NUM> onto a valve seat closing the inlet, and with an adjustable screw <NUM> allowing the position of the spring washer <NUM> on the stem <NUM> to be adjusted, thus controlling the closure force acting on the disc <NUM>. The PSV further includes a predictor <NUM> interfacing the sensors of the PSV to the communication means, here a wireless interface <NUM>. The predictor <NUM> also includes a microcontroller <NUM> connected to a shock sensor <NUM> and an external sensor interface <NUM>. The microcontroller <NUM> is powered by a battery <NUM>.

<FIG> shows the details where at least one predictor <NUM>, fixed on top of PSV <NUM> monitor and record if the PSV <NUM> sticks in closed position or is worn by wear and tear and/or leaks and/or open or pop at a calibrated inlet pressure set, where at least one position detector <NUM> measures the disc <NUM> position transferred through the stem <NUM> and at least one compression load cell <NUM> measures the dynamic force applied on the valve spring washer <NUM> by the spring <NUM> and at least one piezoelectric sensor <NUM> measures the dynamic pressure in the inlet process piping <NUM> and the vibrations in the disc <NUM> and/or at least one pressure transmitter <NUM> also measures the said pressure in the inlet process piping <NUM>, where the sensors <NUM>, <NUM>, <NUM>, and <NUM> are wired <NUM> into the external sensor interface <NUM> which is controlled by the microcontroller <NUM> and measure the disc position <NUM>, and the spring dynamic force <NUM>, and the inlet pressure and/or disc vibrations <NUM>, and/or the inlet pressure <NUM>, which together is the Dynamic Movement Data Set (DMDS) <NUM> for PSV <NUM>.

<FIG>, shows the illustration of the program steps for the said microcontroller <NUM>, where Start <NUM> is the initial sleep mode state of the microcontroller <NUM>, when vibrations generated by process flow through the PSV <NUM> generate sufficient vibrations to activate at least one shock sensor <NUM> installed in the Predictor <NUM> and/or at least one compression load cell <NUM> and/or at least one piezoelectric pressure sensor <NUM> which will generate an electric activation signal <NUM> and wake up the microcontroller (step <NUM> wake up). The system also includes a wake-up timer that is adapted to initiate a wake-up routine (step <NUM>) at even selectable intervals.

When awake, the microcontroller <NUM> read sensor data, step <NUM>, from the sensors <NUM>, <NUM>, <NUM>, and initiate a procedure <NUM> where the inlet pressure <NUM> is compared with the set pressure for the PSV <NUM>. If the pressure in the inlet process piping <NUM> is in excess of the set pressure the PSV is stuck, whereby the microcontroller <NUM> generates a PSV <NUM> Stuck alarm message. This message is communicated to external operational data systems and stored with real time in the microcontroller <NUM>, and the microcontroller <NUM> goes back to sleep mode <NUM> and return to Start <NUM>.

If the pressure in the inlet process piping does not exceed the set PSV pressure, the microprocessor will continue to step <NUM> and compute the Dynamic Movement Data Set, which is time series of frequency spectrum with amplitude generated from the said signals from the disc position <NUM>, and the spring dynamic force <NUM>, and the inlet pressure disc vibrations <NUM> and the inlet pressure <NUM> for a defined time interval for PSV <NUM> to check for stiction, friction, wear and tear by comparing the Dynamic Movement Data Set <NUM> with the PSV <NUM> Condition Data Set <NUM> (CDS) defined as acceptable stiction, friction, and movement characteristic for the PSV <NUM> to be in good working condition or not, stored in the microcontroller <NUM>.

If the recorded Dynamic Movement Data Set <NUM> is outside the acceptance range of the Condition Data Set <NUM> a message Check Movement <NUM> and Movement Alarm <NUM> is generated, communicated to external operational data systems and stored with real time in the microcontroller <NUM>, and the microcontroller <NUM> goes back to sleep mode <NUM>,
but if the recorded Dynamic Movement Data Set <NUM> conform with the Condition Data Set <NUM>, the PSV <NUM> is in good working condition, and the microcontroller <NUM> check the recorded Dynamic Movement Data Set <NUM> against the PSV <NUM> pop algorithm, step <NUM>, which define the fast opening and discharge flow characteristic for PSV <NUM>, were the pop action can be the cause of the generated wake up <NUM> (check for pop), of the PSV <NUM>, and if the PSV <NUM> has popped and the movement data set <NUM> conform to the stored pop algorithm <NUM>, the microcontroller <NUM> log the pop movement <NUM>, estimate the flow volume <NUM>, communicate to external operational data systems and store the said data <NUM> with time information, and the microcontroller <NUM> goes back to sleep mode <NUM>; and/or.

if the recorded Dynamic Movement Data Set <NUM> is outside the defined range of the pop algorithm <NUM>, the PSV <NUM> has not popped, and the microcontroller <NUM> check the recorded Dynamic Movement Data Set <NUM> against the PSV <NUM> leak algorithm, step <NUM>, which define the characteristic of a small leak flow for PSV <NUM>, were the leak <NUM> action can be the cause of the generated wake up <NUM>, of the PSV <NUM>, (check for leak) and if the dynamic movement data set <NUM> conform to the stored leak <NUM> algorithm the PSV <NUM> leaks, and the microcontroller <NUM> log the leak <NUM>, estimate the leak flow volume <NUM>, and store the data <NUM> with real time information, and the microcontroller <NUM> goes back to sleep mode <NUM>; and/or.

if the recorded Dynamic Movement Data Set <NUM> is outside the defined range of the Leak <NUM> algorithm, the PSV <NUM> is not leaking and go back to sleep <NUM>, and wait for the above cyclus from <NUM> to <NUM> is repeated by either the action of the shock sensor <NUM> or the wake up timer <NUM> where the wake up timer <NUM> is set by operational procedures to typically between <NUM> hour to <NUM> hours.

Claim 1:
A system for detecting safe operating conditions and maintained integrity in a Pressure Safety Valve (PSV) (<NUM>), the system comprising a valve (<NUM>) with an inlet (<NUM>), an outlet (<NUM>), a valve disc (<NUM>) controlling fluid flow between the inlet and outlet, a stem (<NUM>) connected to the valve disc (<NUM>), a spring washer (<NUM>), and a spring (<NUM>) in communication with the valve disc (<NUM>) and the spring washer (<NUM>),
a position sensor (<NUM>) which detects the position of the valve disc (<NUM>) transferred through the stem (<NUM>),
a vibration sensor (<NUM>) which detects vibration in the valve disc (<NUM>), an inlet pressure sensor (<NUM>) which detects the static pressure in the inlet (<NUM>),
a microcontroller (<NUM>) which is controlling said sensors (<NUM>, <NUM>, <NUM>), and further including a compression load cell sensor (<NUM>) which detects the dynamic force applied on the valve spring washer (<NUM>) by the spring (<NUM>).