Valve Magazine - Spring 2011

water. In addition, these valves offer low-depth sensitivity and have proven over time to perform well in this high-pressure, remote environment.

In midstream applications that involve transportation of oil and gas, isolation valves play an important role in pipelines. There are primarily two types of pipelines for the energy industry—those for oil and those for natural gas. Within each group are subsets that serve specific applications. For example, oil pipelines gather crude oil from a production site and transport the unrefined oil to refineries. Once refined, additional pipeline networks distribute the refined oil products throughout the world. Natural gas, on the other hand, is typically transported directly from the source to the end user; however, it also includes the cryogenic service that com-presses gas into liquid for economical transport to distant markets.

As in the upstream segment, the most common valve solutions for the midstream market include full-port gate and ball valves in materials chosen specifically for the service. For example, nozzle check valves with low-pressure drops and rapid responses to changes in the flow are a critical component to compressor stations, which energize the media for long pipelines. Some major factors when selecting a pipeline valve include the pipeline size, the media that will run through the pipelines and the environment in which the pipeline will operate. Shut-off valves must be full-

port designs, not only to minimize pressure loss, but also to accommodate pipeline inspection gauges (nicknamed “pigs”), which are used to inspect and clean the inside of pipes or to separate different media as it flows through the line. Regardless of valve style, dependability is critical. Although these valves may only rarely be cycled, they may be needed for pipeline flow diversion, shut-off or isolation performance so reliability is vital. For example, if a pipeline rupture occurred, isolation valves would play a significant role in minimizing environmental damage by shutting off the flow.

Within the downstream segment, there are many harsh environments that require a variety of design solutions. In particular, within refining, applications such as delayed coking present challenges for valve operational integrity. Delayed coking is a heat-intensive process in which heavyweight oil under-

Figure 3.

Multiturn valves

goes a thermal cracking process that produces the gas oil and petroleum coke. During this process, valves are subject to temperatures of more than 900º F (483º C). Adding to the challenge is the fact that delayed coking process valves are cycled every 12 to 16 hours (for a typical two-drum base cycle). Failure of one valve can shut the entire refinery down, which could cost untold millions of dollars in operating revenues. High-temperature applications such as delayed coking place a significant amount of thermal stress on all valve components. Added to the temperature extremes, coking fines are highly abrasive, which impacts plug/disc and body seating surfaces, as well as the gaskets and stem packing.

To support the operational integrity of this application, valves can be equipped with many special characteristics, including heat-dissipating fins, materials designed for high-temperature functionality and remotely-controlled operating systems.

SPECIFIC VALVES FOR THE
INDUSTRY

Refinery segments that use valves include atmospheric distillation, vacuum distillation, hydrotreating, catalytic reforming, fluidized catalytic cracking, alkylation, hydrocracking, delayed coking, sulfur recovery, visbreaking, gasification, lube treating and gas plants. The ideal types of valves for these applications vary widely (Figure 2); but, in general, they include multi-turn valves, HF alkylation valves, quarter-turn valves and flow reversal protection valves, to name a few.

Multi-turn valves (Figure 3), such as bolted bonnet gate and globe valves, are generally offered in materials developed to accommodate a variety of flow media. These valves feature a body cast with straight-through ports to minimize turbulence, erosion and pressure drop. Additionally, these valves can be outfitted with seat rings seal-welded to eliminate potential leak paths behind the rings. Specially developed materials are used in more erosive or higher temperature services.