Welker Flow Limiting Nozzles will allow turbine meters to flow at designed capacities while at the same time providing them with the over-range protection required without significant pressure loss to the flowing system.

David J. Fish, Senior Vice President, Welker, Inc., USA, provides an overview of LNG sampling systems and their streamlined evolution over recent years.

LNG is natural gas that has been cooled to a liquid state (liquefied) at approximately -260˚F, for shipping and storage. The volume of natural gas in its liquid state is approximately 600 times smaller than its volume in its gaseous state in a natural gas pipeline. LNG = liquefied natural gas. Hugely important to note, it is natural gas in liquid form. It is not a mysterious or unique hydrocarbon. It is natural gas that has been produced in the traditional manner and that has been processed and liquefied for transportation purposes, with the expectation of being vaporised and returned to natural gas for commercial consumption. At -260˚F it is at approximately 600 to 1 in volume. 1 ft3 of LNG is equal to 600 ft3 of natural gas. This makes marine transport feasible and profitable. Hence, when it is vaporised, it will be natural gas again.

In the oil and gas industry, there are generally two ways that we take measurements of product. The first is by volume. As fluid flows through a pipeline or sits in a tank, the industry has developed many ways by which we can capture that fluid and calculate “how much” of a particular product we have. These methods are calculated and refined to the point that we can determine these volumes down to the lowest possible unit. The second method by which we measure fluid is a quality measurement. Quality measurement has been well refined over the years to include new technologies not seen in the past. Electronic devices are very commonly used to provide real time analyzation of product as it flows through a custody transfer system. Although there have been many advances in the electronic quality measurement realm, another of the most common and widely accepted method of quality measurement is the composite sampling system. These systems incorporate the use of mechanical devices that capture small bites of the flowing product to compile a composite sample that is representative of the flowing batch. In crude oil sampling, these devices are used almost religiously to provide a primary source of measurement, or even a redundancy to an electronic system. In either scenario, there are certain considerations one should entertain in order to ensure that the composite sampling system is set up for success.

The purpose of this paper is to discuss in depth systems we use as a standard to sample natural gas liquids, or NGL’s. Before we discuss the systems and methods used to sample these products, we must first clearly define what NGL’s are. NGL’s can be a combination of any fluid in liquid form that is taken from the pipeline under pressure. Typically, “NGL” refers mainly to ethane, propane, butanes, natural “gasolines” (pentanes) and condensates. Because of the broad range of products that can be claimed as NGL’s, there are many different approaches to the methods by which we sample them. The common thread among all NGL’s is that these products, in order to be maintained and properly sampled, require the use of specific sampling techniques unique to light liquid and NGL sampling.