Use of Microwave in Automated Pipeline System Reduces Costs, Increases Efficiency
Authors: Messersmith I.D. , Pool J.L. 
Published: December 2007

Use of microwave as the communications link in the automation and central control of a pipeline has proven to be an outstanding success. This article describes the centralized dispatching group that maintains control and supervision over the entire pipeline system; the design of pump stations and equipment involved; and the supervisory maintenance program used in training company personnel.

Introduction

The dispatching and control of Magnolia Pipe Line Co.'s crude and LPG pipelines from Midland, Tex., to Mobil Oil Co.'s refinery in Beaumont, Tex. are under the direct control and complete supervision of a centralized dispatching group headquartered in Dallas (Fig. 1). In all, 11 stations are under remote supervision and control over a company-owned microwave system serving as the communications link. Eight stations are controlled by solid-state, continuous scan supervisory equipment, and three stations are controlled by relay type quiescent or up-set type supervisory equipment.

Microwave System

The company-owned microwave system is a 6 KMC tube type, hot-standby system consisting of 23 repeaters and three terminals. All locations are equipped with emergency power systems incorporating automatic power switch-over capabilities in case of commercial power failure.

Multiplex and Supervisory Tone Equipment

A separate multiplex channel is used on the microwave baseband to each pump station for the supervisory system communications link between each master and slave. This affords a maximum amount of security and circuit continuity from a systems viewpoint. i.e., a failure in one multiplex channel results in the loss of supervision and control of only one pump station. A routine check of tone levels on the microwave and in the multiplex equipment has proved helpful in preventing serious or catastrophic failures. The supervisory master and slave equipment communicate via frequency-shift keyed (FSK) tone equipment. This tone equipment is completely transistorized and is deigned as an integral part of the supervisory equipment. To provide maximum security against false operation of the supervisory gear, different frequencies were selected for master-slave and slave-master transmission. The tones are in the 0 to 3 kc frequency range and have a band width of 170 cycles.

Station Design Criteria

The crude oil system from Midland to Corsicana traverses several areas of production. Crude is injected into the system at four locations. The injection pumps are controlled from the Dallas console along with the main line pumps. Injections are metered and stored locally, and total accumulated flow is read out on call by the dispatcher at Dallas. There is a difference in elevation from the Midland to Corsicana stations of 2,300 ft. This potential static head, combined with the various crude injection points, results in rapid pressure changes at the main line stations. This is a critical area in the control of the system. It was decided in the initial design criteria to update all pressures as rapidly as possible with the equipment then available. Accordingly, the system was designed to update all pump units, station status and pressures at an interval not to exceed 14 sec. This has proven to be a practical time limitation for operation of the pipeline system. A permissive start feature is included in all stations except Midland and Corsicana. In the event that the system is down, the dispatcher can arm one unit at each station. He then starts the Midland pumps. As the suction pressure rises at each successive downstream station, the armed unit will start. A suction pressure rise of 100 to 160 lb mill put a mason on the line. The dispatcher may proceed with his other duties in the interim.

JPT

P. 839ˆ