These notes are extracts from documents by US department of Energy and EPA. Very tight emission standards are driving this innovation in pump seal monitoring. Many US based refineries have incorporated the state and federal guidelines as in-house policy and have very stringent operating and inspection regimes written around the emission regulations. The Bently SLD system shown here has evolved from a collaboration between ourselves and major refinery operators in US.
Typical installation of the SLD pressure sensor on a single stage seal. Only mounting hardware required are standard NPT pipe fittings. The exit orifice must be small enough to maintain some back pressure In earlier trial installations (Exxon Mobil Beaumont Refinery) the seal vent line was connected to a flare line with many other machines also connected. Pressure surges in the flare line actually damaged the prototype transducers. The new design of transducer have a mechanical support behind the diaphragm, providing burst strength of 13 times operating range – ie: approx 2.6 Mpa !
A single Trendmaster wire between machines is all that is required to connect to the DSMs, which can connect to the monitoring computer via optic fibre or copper wire LAN. The system is versatile, enabling a vast number of other plant parameters to be introduced through the Trendmaster interface, including vibration and temperature. The DSM now even has relay contacts for hard-wired machine protection…. Visual inspections should be conducted on a weekly basis. A portable data collector can be seamlessly integrated into the system to take operator status information, or vibration and temperature measurements. Alternatively a Windows CE based PDA can be used for the operators to complete their inspection log – uploading directly into System 1 once complete.
The proposed solution is based on the System 1 front-end. Key points are: accessibility to data and plant information, timeliness of reporting, expandability, actionable information (via software upgrade), Integration of other plant information systems
Key points: Trendmaster / TrendmasterPro compatible Static measurement only Burst pressure is best-in-class diaphragm deflection is measured by an 8mm XL prox probe – reliable proven, immune to noise and extremely stable….
Single-stage pump seal This drawing was provided by FPC refinery personnel The seal illustrated uses packing, although a standard mechanical seal is also an option with this pump. The seal flush line may be a good location for fitting the SLD, provided the line can bleed into a flare line. (otherwise it may raise close to discharge pressure even with a very minor seal leak. A seal leak will pressurize the gear casing, venting through the breather. Mounting an SLD pressure sensor at the seal end of the bearing housing may be an option. A third alternative being trialed by some refinery customers is to mount a temperature sensor close to the end of the seal on a single-stage shaft seal. See the following slides for further information.
Two stage shaft seal This drawing is the two stage seal diagram provided by FPC personnel. The flushing fluid is tapped off pump discharge and injected on the outside of the seal face to generate a flow away from the seal (preventing abrasive debris from entering the seal) The barrier fluid is often water and provides cooling to the second stage of the seal. This is typically the easiest and most reliable arrangement to instrument, however in this case an additional tapping may be needed if no vent line is included. Most tandem seal pumps have a vented stuffing box (seal chamber).The vent line is typically run to a common flare line, so only requitement is to install a standard NPT tee pipe fitting. If the barrier fluid runs at a constant pressure, we can monitor pressure (or temperature) at barrier fluid outlet as an alternative approach Actual seal arrangement at FPC Kao-Shiung
This case study was supplied by a Bently customer using standard RTDs integrated into their Trendmaster infrastructure. The installation was designed and implemented entirely in-house at the Exxon Mobil refinery in Melbourne, Australia
The seal failure occurred over the course of only a few hours in January 2003. As the working fluid is LPG, the leaking fluid flashes off, causing a dramatic drop in temperature. For other fluids, the temperature change may be quite different. In this case, the customer is exporting data into their site historian for trending, however they are also in the process of implementing System 1 across the site.
Note the Trendmaster cabling in the background.
Details of the RTD mounting arrangement. The end of the RTD (in this case) is approximately 5mm from the seal and shaft – measuring the air temperature in the immediate vicinity of the seal. The pipework visible here is the seal flushing line, re-injecting high pressure LPG to the seal face to force debris away from the seal.
Bently Nevada Seal Leak Detection
Bently NevadaThe Plant Asset Management Company SM System 1™ and Seal Leak Detection Machinery Asset Management for Optimal Business Performance
Air quality regulations are driving this.Typical wording:How are equipment leaks defined?• Compressors: A leak occurs when a design-specific sensor indicates a failure ofseal or barrier fluid systems•Pumps in light liquid service: emissions of 10,000 ppm (or more) organiccompounds, or there are indications of liquids dripping from the pump seal.How must equipment leaks be monitored?•Weekly: visual inspection of pump seals. Whenever liquid leaks are observed, thevolatile organic compound concentration shall be monitored immediately.•Quarterly: compressor seals, pipeline valves and pressure relief valves•Annually: pump seals, pipeline valves in liquid service, and process drains.How are repair schedules and procedures defined?• Attempts at repair must be made within five days of detection of a leak, and must becompleted within 15 days of leak detection.
Typical installation Single stage mechanical seal SLD pressure transducer fitted to standard NPT tee Vent line with existing Exit orifice isolating valve (to flare line) Seal chamber Flush line Throttle bushing (auxiliary sealing Throat device)bushing Rotating seal stationary seal member member Cross-section of single-stage shaft seal
Simple system architecture Control Room Field mounted DSM units System 1 Host To Plant ComputerInformation Optic fibre Network LAN Portable data collector for TIM Line or wireless manual inspection routes connection Direct Input Transducers
System 1 intuitive interface Ideal platform to build plant-wide asset management program
Seal Pressure Sensor andflexiTIM™ Module Features• Division 1, 2 approved & designed to IP66• Sensor may be exposed to H2S, H2SO4, Naphthenic acids, caustics, standard hydrocarbons• Pressure rating -Operating - 30 psig (gage) -Proof Pressure - 300 psig -Burst Pressure - 400 psig
Single stage shaft seal alternative strategies 3. Thermocouple at end of shaft seal 2. SLD sensor on brg housing O/B sump drain 1. SLD sensor on seal drain line
Two stage shaft seal example Potential pressure Barrier Fluid outlet Sensor locations Seal Flush Line Barrier Fluid inlet
Typical Parameters• Steady-state vent line pressure: 0 to 10 psi (up to 70 kPa)• Operators set alarms at 20 psi (140 kPa)• Full Range of transducer is 30 psi (207 kPa)• Seal temperature may change by + /- 10 to 20 degC withseal failure (depending of working fluid)
Bently NevadaThe Plant Asset Management Company SM Seal Leak Detection Case Study End-User Refinery Australia Trendmaster Pump seal temperature sensor example
EHM Case Study – TM2000 Seal leak detection ppm