Nitrogen Purging

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Nitrogen Purging

Nitrogen has a number of effective uses in the oil and gas, onshore and offshore pipeline industries due to its unique properties. In hazardous situations and environments, dry and inert nitrogen creates a safe working environment for carrying out a number of maintenance works ahead of shutdown and start-up operations.

Guru Industries are the nitrogen specialists. We have one of the largest and most versatile fleets of mobile, self-contained nitrogen pumping and vaporization equipment available. We offer a number of reliable, flexible and cost-effective nitrogen solutions that will ensure safety and success for any ongoing project.

 

PURGING SERVICES - INERTING/PURGING OPERATIONS

There are four common methods for adding inert gas: A) Vacuum purging, B) Pressure purging, C) Siphon purging, and D) Sweep-through purging

    • Vacuum Purging

If the vessel to be inerted is designed to withstand vacuum pressure, an inert atmosphere can be created by repeatedly drawing a vacuum on the vessel and filling with inert gas. The three states of interest for the vacuum purging process are:

    • Pressure Purging

If the vessel to be inerted is designed to withstand elevated pressure, an inert atmosphere can be created by repeatedly pressurizing the vessel by filling with inert gas, allowing the purge and residual gases to mix, and then relieving the pressure. The three states of interest for the pressure purging process are:

    • Siphon Purging

There are two steps in the siphon purging process: 1) displacement of gas in the vessel by filling with a liquid and 2) displacement of the liquid in the vessel with purge gas. The states of interest for the siphon purging process are shown here:

    • Sweep-Through Purging

The purge gas is allowed to flow continuously through the vessel in sweep-through purging. The residual gas in the vessel can be displaced by the purge gas and/or mix with the purge gas. If the inlet and outlet ports for the purge gas are not placed properly, the purge gas may not displace and/or mix thoroughly with the residual gas in the vessel.

Displacement effects are generally neglected in sweep-through purging. Displacement is most effective if the flow within the vessel is laminar. Mixing, on the other hand, is most effective when there is a lot of turbulence in the flow within the vessel. When non-ideal mixing occurs, the purge gas is said to bypass or short-circuit (simply flow from the inlet to the outlet). Portions of the residual gas in the vessel (particularly that in corners or indentations in the vessel) will not be displaced from the vessel nor will the composition be diluted by the purge gas. For sweep-through purging to be effective, it is important for the purge gas to flow throughout the entire volume of the vessel (no dead volumes or eddies).

Summary

Sweep-through purging is a simple process that can be accomplished at atmospheric pressure (the vessel to be purged does not have to be designed for vacuum or pressure conditions). However, mixing effectiveness is an important consideration in purge gas cost and time. Vessels to be sweep-through purged should be designed to achieve good mixing.

Pneumatic Testing

Testing Beyond The Limits

Strength testing is a technique used in the oil and gas industry to prove the mechanical strength and integrity of pressure containing components in a system. The purpose of pneumatic strength testing is to verify that a system may be safely subjected to its maximum operating pressure by testing it beyond its designed pressure limit. The pneumatic strength test uses air, or an inert gas medium such as nitrogen, to pressurize the system to 110% of its designed pressure limit. A holding period is then applied for a fixed amount of time and the results monitored to determine the safety and integrity of the system.

Benefits of pneumatic testing

 » Accurate test results mean confidence in the integrity of the system
 » No need to dry or clean the system after testing
 » Will not lead to contamination of pipelines or systems
 » Certified test with full records and charts provided

In circumstances when hydrostatic testing is not possible, for instance, the weight of hydro test water is too high for the pipe support system (e.g. gas service piping) and when the introduction of water to the piping may be detrimental to the process (e.g. catalyst or reactor contamination, cryogenic service system), then the components or system can be tested with nitrogen.

Since the test medium is gaseous, it has the ability to compress and contain a large amount of stored energy (typically 200 times greater than a hydrostatic test at the same free volume and pressure condition). Extreme caution is required when using this technique. However, the specialized team at Guru Industries Industrial Services will ensure design specifications are reviewed and a detailed risk analysis completed before testing with a compressible medium.

Drying

Stability, Flexibility, Reliability

Air, nitrogen and vacuum drying techniques will thoroughly remove moisture and water from your system prior to start-up. We achieve your optimal dew point level so that you can be sure of the integrity of your product and the ongoing performance of your system.

Prior to commissioning and start-up, it can be essential to carry out a drying procedure to thoroughly remove water and moisture from the system. This procedure will help to maintain the purity of the product to be transported through the system, minimize corrosion (growth) and optimize efficiency and safety.

Guru Industries Industrial Services offers flexible solutions for completely drying your system ahead of start-up. This is necessary following a pressure or leak/tightness test during pre-commissioning in order to achieve the required dew point levels. Our personnel have the knowledge and expertise to assess your particular situation and advise the safest, most reliable and most cost-effective solution.