The RHP™ Zero-Leakage Solution

CCI has developed a revolutionary new type of controlvalve seat that delivers Repeatable Zero Leakage™ for shutoff pressures up to 10,000 psi.

This design evolved out of a project CCI completed for DuPont Sabine River Works in Texas . The specification was for special valves known as Y-Conduit valves, which are the opposite of a DRAG® valve in that they are near zero resistance trim. Y-Conduit valves are reciprocating valves that operate as full ported ball valves for ethylene vent applications inplastic manufacturing processes. If there is a temperature control problem in the hydrogen reactor, it has to be vented quickly in order to recover the temperature.

CCI’s RHP provides repeatable zero leakage up to10,000 psi.

For at least 15 years the vent valves used for this service had to be refurbished after every cycle. This involved shutting down the reactor, removing the valve from the line, installing a new valve, purging the system with nitrogen, and re-starting the process. The reason for valve removal is that the soft seat would blow out every time it was operated. Typically it took two to four days before the plant could start making plastic again. This lag in productivity created a strong desire to achieve a bubble-tight, absolutely zero-leakage valve that would be able to open and shut repeatedly.

CCI went through an extensive redesign of the Y-Conduit valve to greatly simplify the design. In order to achieve the repeatable, bubble-tight shutoff, a completely new valve seating system was developed. The result was a revolutionary high-pressure valve seat called the RHP. The RHP design was an extension of a special “no-load” soft seat developed earlier for pipeline surge relief valves for Saudi Aramco. This is a special seal located under the normal hard seat of the valve and is actually the first of two redundant seats. In DuPont’s case there were two pressures: 7500 psi and 2000 psi. Later, it was found that this same technology could be beneficial to traditional DRAG® valves.

The first such application was on compressor recycle and vent valves for MW Kellogg’s Uzbekneftgas project in Uzbekistan . The client (Uzbekneftgas) insisted that the control valves meet seat leakage criteria per API 6A, which is far more stringent than the seat leakage criteria normally applied to control valves.

Control valves are typically held to ANSI/FCIS70.2 Class III, Class IV, Class V or Class VI shutoff; API6A requires zero leakage at the rated pressure of the valve, typically 10,000 psi. The valve must be able to openunder that pressure, reseat, open, andreseatseal again.

The test duration is three or 15 minutes per cycle, depending on the product specification level. With ANSI, there is always leakage allowed and the test duration is only one minute and often at much less than the rated pressure of the valve. CCI product engineers determined that the RHP technology from the Y-Conduit valves would be able to be transferred to control valves.

RHP valve seating technology is now more broadly applied, but is particularly useful in compressor recycle. Zero leakage enhances compressor efficiency, as well as venting applications, where any leakage across the valve is lost product up the stack.

Today, the RHP seat has been adapted for control valve use worldwide, with major installations in Asia , the Middle East and North America. The RHP is capable of meeting virtually any shutoff requirement, including the daunting requirements of API 6A, PSL 2, 3, or 4, which is zero leakage at full rated pressure. It is rated up to 10,000 psi and is available in plug sizes 1-1/2 inches to five inches (38millimeters to 127millimeters). These are nominally two inch to eight inch (51 millimeter to 203 millimeter) valve sizes.

Substantial benefits are realized in applications such as blowdown and vent-to-flare valves where any valve leakage is “money up the stack.” Compressor efficiency is augmented where recycle and hot gas bypass valves are equipped with RHP zero leakage seats.

Conventional soft seats do not compare well with the RHP’s ability to achieve dead tight shutoff at high pressure (a Class VI seat is tested at only 50 psi). Nor are conventional soft seats able to maintain their shutoff capability cycle after cycle (soft seats can blow out after one cycle at pressures as low as 600 psi). The RHP is the only guaranteed zero leakage solution above 600 psi.

The RHP delivers shutoff performance that is unmatched in the control valve industry. ACCI DRAG® control valve equipped with RHP seating technology establishes a higher standard of value for critical gas applications.

Published in SOLUTIONS Summer 2000