Automatic Line Break Systems

The “Automatic Line Break Control” module is designed  to automatically close main pipeline valves in the case of a major leak or break. By quickly and reliably closing the main pipeline block valves, gas loss can be minimized to prevent fires and other catastrophic losses.

The “Automatic Linebreak Control” module senses a pipeline break or major leak through a unique “Rate-of-Drop” circuit. This “Rate of Drop” circuit consists of a differential pilot valve, which senses pipeline pressure and compares it with the gas in a reference tank at the normal pipeline pressure. When the pressure in the pipeline decreases, the pressure in the reference tank also decreases, but at a rate dictated by a calibrated orifice. This establishes a differential pressure between the reference tank and the pilot connected directly to the pipeline. The rate of pressure differential drop is indicative of the severity of pipeline gas loss. The differential pilot valve, set at a calibrated setpoint, senses this “Rate of Drop”. When the pilot valve trips, the actuator is activated to close the main pipeline valve. This “Rate of Drop” circuit eliminates inadvertent shutdowns on short duration pressure bumps. A manual reset feature is normally included for safety purposes. Utilizing the pipeline gas itself, for both the pilot gas and power media, makes the “Automatic Line Break Control” system independent of regulator and other power media failure.

The  setting and calibration on the control module is done with the “Rate of Drop” (R.O.D.) Test Kit, which monitors the pressure levels in the pipeline, the reference tank and the differential pressure across the orifice. This kit also includes the valves required to simulate create an line break to allow testing and calibration of the control unit.

The Advantage

• Hi-pressure construction – no regulator, relief valve, or mechanical switching valve.
• Differential pilot valve utilizes a stainless steel diaphragm for accuracy and repeatability.
• Marine-grade, hard-anodized aluminum body for both poppet and differential pilot valve.
• Easily adjusted differential trip setpoint (1.5 psi to 14.5 psi).
• No mechanical linkages, which are subject to environmental failure.
• Limit valve ensures complete opening of bypass valve.
• Single unit design – Diaphragm unit and directional control valve are a single unit resulting with a shorter diaphragm stroke and lower hysterisis.

Case Study: Excess Flow Control

ATI shipped fifteen hydraulic double acting actuators with newly designed control systems on each of the units. A Houston-based valve automation center approached ATI to design a system to actuate and control the valves on a hydrogen pipeline. The control system is designed to sense a change of 7 psi differential pressure in a pipeline operating at 915 psi which would cause the actuator to shut the valve.

This is important because such an increase in differential pressure would indicate an increase in flow which may mean a leak downstream. Fast speed and fast response were critical in the design of these units.