Recommended Specifications of Ball Valves Designing in Gas Pipeline System

Recommended Specifications of Ball Valves Designing in Gas Pipeline System

Abstract:

Ball valve has been utilized in the gas pipelines system that contains sour gas and sweet gas services due to several Characteristics including A quarter-turn valves, double block and bleed, full bore with a spherical closing element held between two seats and a quick opening with good shut-off .Moreover, larger valves with heavier balls have trunnions to help support the ball and prevent damage to soft internals. In addition to that, ball valves cover all requirements international standards including API 6D, API 608, API STD 598, ASME B16.34 and NACE MR0175.

Different types of the body design have been utilized in gas pipelines system application, including one piece, top entry, two pieces, fully welded or sealed type. Top and bottom entry valves are expensive choses but allow on line maintenance tool. However, most of the top entries valves where never been repaired on line simply because either the operator has no capability to repair or most probably because there is no window to repair the valve on line. As replacing, the valve is most cost effective chose. The third common type is the fully welded ball valves. Usually it is used in a hazards application or buried pipeline. However, it is limited

The soft- metal seats feature has been also used in the gas pipeline system in order to eliminate the seat sealing failure. the metal seat is used in the upstream seat with the single piston feature (Self-relieving) to release of any overpressure in the body cavity when the valve is in the fully open or fully closed position. The downstream seat is used a soft seat type with a  double piston effect to provide a soft seating action in addition to the metal to metal seating between the ball and the seat rings for more sealing.

The objective of this paper is not to provide specifications for ball valves as it is in the international standards, instead the paper objective is to provide a general recommendation practice for the service based on field experience.