Pressure Measurement:
Gauges, Innovation, and Why It Matters

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Anyone who’s opened a can of soda after shaking it knows firsthand the conceptual impact of pressure. But how many of us have ever actually considered the importance of pressure measurement in modern industry? We suspect not many have, which is why we do: Pressure management is our business.

In April 2010, the Deepwater Horizon oilrig disaster poignantly demonstrated the importance of accurately monitoring and measuring pressure. Before the explosion and during a negative pressure test on the Macondo well, two pressure gauges delivered two very different results: one indicated “no pressure” while another indicated pressure building. Amidst disagreement on the results, the test was redone; by 8 p.m., the crew and BP representatives aboard agreed that the well was stable. As they sealed the well, working quickly, Joseph Keith recalls feeling uneasy. His role, to monitor gauges that detect blowouts, is a crucial one. No leaking was noticed. But from 8:50 p.m. on, oil and gas were leaking into the well, and pressure built. At 9:47, the first explosion rocked the rig, the beginning of what would become known as the U.S.’s greatest oil disaster.

From upstream oil & gas extraction to downstream processing, from balancing reactor temperatures with precise pressure application in chemical plants to maximizing cogeneration opportunity through high-pressure boilers in water treatment facilities—pressure measurement is a vital component in successful industrial operations.

Pressure: What It Is & How We Measure It

Pressure is simply the force acting upon a unit of area. But the force on any solid surface does not apply to a single point on that surface, but rather is spread equally across the entire surface. This means the pressure depends not only on the level of compression of the media, but also on the surface-area size.

There are three kinds of pressure: fluid, absolute, and gauge. Fluid pressure is the measure of force per unit area exerted by a fluid (gas or liquid). Absolute pressure is the absolute value of the force per unit area exerted on a surface by a fluid, meaning that it is the difference between the pressure at a point in a fluid and the absolute zero of pressure (a complete vacuum). Gauge pressure is the measure of the difference between absolute pressure and atmospheric pressure, which varies based on altitude, weather, and ambient temperature; pressure gauges read differently at different levels of elevation. While a normal pressure gauge reads zero (45psi) at a certain elevation, it will read 14.5psi at sea level. This can make for a complex process of analysis when dealing with massive systems that cover multiple elevations, or several thousand feet of piping.

When we talk about pressure measurement, it’s important to also talk about what reference the pressure is related to. In the U.S., we specify pressure in terms of pounds/square inch absolute (psia) or pounds/square inch gauge (psig). Negative gauge pressure is a vacuum, the measurement of the amount by which the local atmospheric pressure exceeds the absolute pressure; a perfect vacuum equals zero absolute pressure. Differential pressure, a common measurement in industrial applications, is the difference between two unknown pressures.

The Evolution of Measurement

Modern tools for measuring pressure emerged in the mid-19th century with the introduction of the Bourdon tube, still widely employed today to determine static pressure. The mechanism has not changed dramatically: the tool generally contains a curved tube, open to pressure input on one end and coupled to an indicator needle on the other.

Technologies have evolved to meet the needs of specific applications; today’s gauges can be specialized with all-welded, stainless steel construction for corrosive media; transmitters for hybrid gauge-data collection applications; diaphragm seals to provide longer lives for pressure gauges in harsh environments; sub-sea construction that allows for deep-sea (10,000 feet) applications; and highly accurate test gauges for laboratory uses. These integrated technologies allow users to take better readings, collect more thorough data, and operate more safely and efficiently in their target-specific environments.

While the basic technology has changed little since its inception, industry leaders continue to refine, rethink, and reinvent the modern pressure gauge and its offshoots. WIKA Instrument Corporation, an innovator in gauge technology for more than 60 years, makes gauges more robust, reliable, and smart to meet ever-evolving industrial needs.

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