- Published on Monday, 07 November 2011 10:46
- Written by Greg Johnson
This nation is crisscrossed by hundreds of thousands of miles of crucial pipelines that transport vital feedstock from sources to the places where it’s transformed into fuel and products. For the valve industry, that translates into millions of dollars of business.
According to Hart Data and Mapping Services, the United States has over 700,000 miles of crude oil and natural gas pipelines—about 100,000 miles of crude onshore pipelines and over 600,000 miles of onshore gas pipelines. This number stands to greatly increase as drilling in the various shale plays across the continent occurs. These seemingly endless strings of pipe have one thing in common: They all contain large numbers of valves optimized for pipeline operating conditions.
WHAT’S IN A PIPELINE?
Both quarter-turn and multi-turn block valves as well as check valves are used in pipeline service. Those built for gas or crude oil pipeline service are designed and tested in accordance with the American Petroleum Institute (API) specification 6D “Pipeline Valves.” The document, which is also published by the International Organization for Standardization as ISO 14313, includes requirements for gate, ball, check and plug type valves. Prior to the mid-1950s, the choice of valve for use in pipeline blocking applications was easy—gate valves were used because the pipeline ball valve had not been invented yet. Some plug valves also were used back then, but the majority of the designs for these valves were reduced-port type that were not piggable.
The term “piggable” has nothing to do with breakfast meat choices. Rather, it means being “pig-capable”—in other words, the devices designed to clean or inspect the interior of the pipeline (the “pigs”) also may be passed through the bore of the valve without catching on a reduced bore or other interior projection in the valve. A requirement in API 6D gate valves is that their inside bore dimensions are precisely specified to allow this passage of pigs.
With the advent of quality pipeline ball valves over the past few decades, sales of pipeline gate valves have fallen. Meanwhile, pipeline ball valves, which are trunnion style, are now making inroads in all types of pipeline service, particularly in natural gas. Still, holdouts exist.
“Some companies are staunchly entrenched in the gate valve,” according to David Fehrenkamp, a senior sales engineer with Cameron. He also adds that “in many natural gas pipeline operations, quarter-turn has taken over 100%.”
So why do many pipeline owners favor the gate valve for pipeline service? Product pipelines that carry fluids such as gasoline, distillates, diesel fuel and other finished petroleum products are a popular place for the rough and ready gate valve. “We use slab gate valves for most of our main line valves, but we do use expanding gate valves on our product line from Texas City to Pasadena,” says Billy Daigle, maintenance services specialist for Marathon Pipe Line LLC (MPL). “We use expanding gate valves for station isolation valves and pig launchers. Pig launcher and receiver service is harder on valves because of the debris from the pigging operation, so we choose expanding gates because of their toughness,” he adds.
The quarter-turn vs. gate valve debate gets hotter when cost becomes the prime factor for selection. The quarter-turn trunnion pipeline ball valve is much cheaper to make than the jumbo-sized gate valves, with their large and expensive body castings. Another factor that tips the pendulum toward quarter-turn pipeline valves is the availability and delivery of quarter-turn products. Because drilling in the shale plays across the country is exploding in terms of how fast it’s occurring, Fehrenkamp says the requests from customers for delivery time is “rush, rush, rush, I need it now!” A domestically produced trunnion pipeline ball valve can be built in roughly four weeks, which is about the time needed to get a good gate valve casting under the luckiest of circumstances. An additional four to six weeks might then be required to complete the gate valve machining, assembly and testing.