JUL-AUG 2018

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FAST FORWARD l There are different level measurement options for inventory tank gauging. Cost, schedule, and other challenges affect the final technology selection. l GWR technology was tested in Saudi Aramco for inventory tank gauging with successful results. l The Saudi Aramco Riyadh Refinery revised the project scope for implementing inventory tank gauging on 42 tanks, and ended up with a simple, cost-effective, and fast project implementation. 34 INTECH JULY/AUGUST 2018 WWW.ISA.ORG Guided wave radar for inventory tank gauging Cut the cost, simplify the project, and expedite implementation By Fawaz AlSahan, CAP T here are two internationally recognized standards covering tank gauging in atmo - spheric tanks. From the American Petro- leum Institute, there is API MPMS chapter 3.1B and API MPMS chapter 7, and from the Inter - national Organization for Standardization, ISO 4266-1, ISO 4266-4, and ISO 11223. This article is based on API MPMS chapter 3.1B and API MPMS chapter 7, because these two documents provide detailed requirements for inventory applications. API MPMS chapter 3.1B mandates the following requirement for automatic tank gauges (ATGs): The reading of an ATG to be used for an in- ventory application should agree with a certi- fied measurement instrument within ±3 mm over the entire range of the ATG. l The certified measurement instrument should be traceable to the national or inter- national standards and should be provided with a calibration correction table. l The overall accuracy of an ATG in inventory control service should be within ±25 mm. l ATGs should provide security to prevent un authorized adjustment or tampering. l The level resolution of the transmitted signal is typically 1 mm. Conventional tank gauging solutions There are five common automatic tank gauging solutions widely used for both inventory and custody applications. Manual gauging This solution is the reference for all other solu- tions, and it utilizes a dip tape. Manual gauging uses either the innage (from the top flange to the bottom of the tank) or ullage (from the top flange to the top liquid layer) method to mea- sure the total liquid level inside the tank. API MPMS chapter 3.1A covers the procedure and requirement for manual gauging, which is nor- mally three consecutive readings with a differ- ence not exceeding ±3 mm. Float and tape gauge This solution uses a float attached to a spring via a perforated tape. The spring provides con- stant tension, which balances the float on the liquid level. The perforated tape is connected to a mechanical counter assembly. Servo gauge The servo gauge uses the displacement mea- surement principle. A small displacer (weight) Figure 1. Manual dip tape

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