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PUMPS, VALVES & ACTUATORS
Various factors influence the
effectiveness of a grab sampling system in enhancing employee safety and preventing undetected leaks, says Matt Dixon, Application Commercialisation Manager, Swagelok Company
Also referred to as field sampling, spot sampling, or simply sampling, the process allows operators to make sure systems are functioning as intended. Upstream sampling also offers valuable insights into the consistency of the final product. Sampling methods differ depending on what process fluid is involved. For gases and volatile liquids, technicians use sample cylinders specifically designed to prevent dangerous gas or liquid releases. For nonvolatile liquids, operators can opt for the less-expensive bottle sampling method (Figure 1).
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Safe and effective sampling is important for providing operators with accurate data, and specific techniques can simplify the process. While challenges may occasionally arise, using the correct sampling system design typically enhances operations and performance, leading to greater efficiency and profitability for the facility over time. The goal of grab sampling is to obtain representative fluid samples from pipelines, tanks, or systems for external laboratory testing to ensure the composition meets the necessary standards. Typically, technicians will use a sampling panel and valve to ensure safe fluid sampling and consistent control over sample volume and efficiency. The grab sampling process (Figure 2) follows these steps:
• The bottle is inserted into the shroud of the grab sampling valve.
• As the bottle is inserted, the rubber septum is pierced with two needles—one fills the liquid and the other allows air to escape. • The operator opens the grab sampling valve, allowing liquid to fill the bottle. • When the bottle is filled to the appropriate
24 SEPTEMBER 2024 | PROCESS & CONTROL
rab sampling is crucial to the safe operation of chemical plants, refineries, and oil and gas facilities.
assemblies simplifies maintenance, it also presents challenges. The rubber O-rings in these assemblies can harden or become damaged, increasing the risk of leaks. If the process fluid is toxic, leaks can pose risks to operators and the environment, and they can delay routine system maintenance—assuming the leak is detected in time.
Many suppliers have engineered specific valves for liquid grab sampling, which often enhance employee safety and reduce the maintenance required to keep them functioning properly. Additionally, these specialised valves reduce the possibility of introducing human error into the sampling process.
Figure 3
Images © 2024 Swagelok Company
During grab sampling system design, the components matter. Identifying the essential features in advance ensures the system operates at peak performance. For example, a replaceable needle assembly connected to
OVERCOMING POTENTIAL BOTTLE SAMPLING OBSTACLES
level, the valve is closed, and the sample bottle is removed.
Over time, bottle grab sampling valves can clog, bend, or break, necessitating maintenance by technicians (Figure 3). Facilities should consider using grab sampling valves with easily replaceable needle assemblies to improve efficiency and minimise system downtime. This practical approach enables technicians to remove and service the needle assembly
without needing to replace the entire valve. Although using replaceable needle
Figure 2
the valve body using a tube fitting offers several advantages over grab sampling valves that rely on rubber O-rings. A tube fitting connection swages the needle assembly to the valve body, creating a leak- tight, metal-to-metal seal at two points. This design can endure harsher operating conditions compared to valves with O-rings, which are prone to deterioration when exposed to certain chemicals and temperatures. A leak-tight connection also protects employees from accidental exposure to caustic or toxic process fluids. Other features to look for might include: • Intentional needle design. Most grab sampling valves use a lancet-point needle, which can core the bottle septum, leading to clogged needles or leaking sample bottles. A pencil-point needle design, however, can pierce the septum without coring it, reducing the risk of clogs or leaks. • Customisable shrouds. Various shroud options are available to accommodate a facility’s existing sample bottles. For non- standard bottles, manufacturers can provide custom shrouds tailored to specific needs. • Spring-return handles. Specifying a grab sampling valve with a spring-return handle ensures the valve automatically returns to the closed position when the handle is released. • Elastomer-free design. Eliminating rubber O-rings can help reduce a facility’s maintenance parts inventory and minimise the potential for system leaks.
Finding grab sampling systems with these features will improve the overall performance and enhance the process. Design engineers should consult with suppliers to identify the best grab sampling system for their specific needs.
Figure 1
Swagelok Company
www.swagelok.com/en
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