NITROGEN PURGING
Nitrogen purging plays an important role in the safety and functioning of various plants that are susceptible to fire hazards. In fire and explosion protection engineering, an inert (i.e, non-flammable) purge gas (like nitrogen, helium, argon, etc) is introduced into an enclosed system (e.g, a container or process vessel) to prevent the formation of a fuming flammable atmosphere. This inert gas helps to mitigate the risk by overriding hazardous fire/explosion-forming agents like oxygen.
Nitrogen purging is the process of introducing nitrogen into closed vessels, pipelines, containers, etc to displace undesirable hazardous atmosphere and to clean the inner walls. Nitrogen in the nitrogen purging process pushes out oxygen and moisture and creates a stable non-combustible environment, thus reducing the potential hazard.
Major industrial applications of the nitrogen purging process are:
- Transformers and other volatile electrical environments enhance safety by using the N2 purging procedure.
- Nitrogen purging in the brewery industry extends the shelf life of beer.
- Ships and tankers use nitrogen blanketing to remove potentially combustible environments.
- Organic compounds generating chemical and petrochemical industries widely use the nitrogen purging processes to eliminate toxic gases from process chambers.
- Atmosphere Packaging and Food industries apply the nitrogen purging process to remove moisture, oxygen, and other gaseous impurities.
- Nitrogen purging is widely used in oil and gas pipeline projects for drying, cleaning, and limiting oxygen concentrations.
- To eliminate compounds affecting weld quality, metal fabrication industries use N2 purging systems
There are four main industrial nitrogen purging procedures that are widely used. They are:
- Displacement purging (Plug effect)
- Dilution Purging
- Pressure swing Purging, and
- Vacuum purging
PIPELINE DRYING AND DEWATERING AFTER HYDROTESTING AND NEW CONSTRUCTION
Pipeline construction and pipeline repairs are major projects that require detailed steps before a pipeline can be put into service. One step that can be overlooked until late in the project is pipeline drying.
Hydrostatic Testing companies can help operators verify the safety and suitability of their pipeline network for the intended products. However, the process will leave residual water within the tested channels.
Water retained within pipelines after hydrotesting will cause rapid corrosion as well as alter the purity of fluid channelled through them. Consequently, all operators must invest in pipeline drying after hydrotesting to ensure their pipelines function as efficiently as possible.
Contact us at Zeagle Energy Limited if you need any pipeline cleaning services.
Outlined below are five effective methods of achieving pipeline dewatering and drying.
Read through the specifications of each technique to determine which options suits your operation.
1. Pipeline Drying with Nitrogen
Gaseous nitrogen possesses suitable chemical properties that make it suitable for pipeline drying including its inert, non-reactive nature which makes it very stable. As a result, pipelines primed with nitrogen gas are less likely to have explosive accidents. Further nitrogen gas will displace oxygen, water vapor, and other impurities that can erode the pipelines or alter the quality of their contents.
The nitrogen purging process typically involves feeding nitrogen gas into a selected pipeline at one end. The propulsive force and chemical nature of the gaseous nitrogen are sufficient to push residual water and impurities through the pipeline’s length and expel them through an exit port at the other end.
The drying process is deemed complete when a difference of at least 10°F between the feed gas dewpoint and outlet gas dewpoint is obtained.
2. Hot Air Pipeline Drying
The procedure for hot air conduit drying is like pipeline dewatering using nitrogen. The major difference is the use of heated air supplied by an Industrial air compressor. Introducing heated air into a wet pipeline will cause rapid water vapor formation.
This evaporated moisture can then be conducted to the opposite end of the pipeline where an exit port is located. Hot air pipeline tests can be monitored using hygrometers or transmitters that automatically detect differences between the inlet and outlet air dewpoints.
3. Chilled Air Drying
Another effective technique for eliminating moisture from pipelines following hydrostatic testing is the use of very dry chilled air. Highly powerful ventilators can be used to drive a stream of very dry cold air through a pipeline to eliminate residual water.
This method involves the use of industrial chillers to cool the air to sub-zero temperatures before use to facilitate efficient moisture removal. As with other drying procedures, dewpoint monitoring is conducted to determine the completeness of the drying cycle.
4. Vacuum Drying
In vacuum drying, the selected pipelines are completely sealed off at both ends with a single port connected to a vacuum device. The attached vacuum system is used to remove air and residual water from the pipelines after a stable vacuum pressure is achieved.
Operators can monitor variations in dew points during the drying process to accurately determine completion. For example, the dewpoint readings will initially stabilize as water is being removed from the system, then drop once all the moisture has been vacuumed out. Additionally, automated devices can also provide accurate data on the drying process.
5. Pigging and Swabbing
Pipeline pigging and swabbing is a mechanical method of pipeline drying. The swabbing process is conducted using a device called a pig which is made of foam or other suitable polymer materials.
A pig is introduced at one end of the pipeline to be dried and driven along the entire length of the channel to the other end. Pigs’ devices are usually manufactured to fit the internal diameter of the pipelines they dry with a larger contact area between them and the inner walls of the pipelines.
Pigging/swabbing is very effective at removing residual moisture from hydrotesting as well as any particulate impurities present. If you’re searching for experienced pipeline maintenance companies, contact Zeagle Energy Limited about our services today.
GENERAL PIPELINE PRE-COMMISSIONING
Before the commencement of full-scale operations, newly constructed pipelines are subjected to a series of checks which determine their suitability for their intended functions. These procedures include pipeline pre-commissioning and commissioning checks which are carried out one after the other.
Pre-commissioning is primarily done to ensure that all pipeline construction was satisfactory and meets the standard safety specifications. Commissioning activities can only be carried out after pipelines have been duly pre-commissioned and determined to be safe for initial testing.
Depending on the intended content a pipeline is meant to conduct, these pre-testing procedures may vary slightly.
PIPELINE PRE-COMMISSIONING PROCEDURE
Pretesting natural gas lines follows an ordered set of steps which allow for satisfactory performance analysis. Highlighted below are the key components of pipeline pre-commissioning and commissioning carried out by Zeagle Energy Limited team of professionals.
Pipeline Flushing/Cleaning
A significant majority of newly constructed pipelines will require initial cleaning before they can be cleared to deliver their intended payloads. Pipeline cleaning services can be carried out both at the pre-commissioning and commissioning phases of final testing.
Flushing out natural gas lines can be done with the help of mechanical devices (pigging) or chemically by forcing chemical compounds through the pipeline channels.
Pigging
During a pigging operation, a device called a pig is driven through the interior of the pipeline system to clean it and flush out retained impurities. Pig devices can be used in new as well as in-service pipelines to help remove debris and halt the onset of corrosion.
Hydrostatic Pretesting
Hydrostatic testing involves passing a liquid through the newly constructed pipelines to detect areas of leakage. Water containing a dye is the typical medium utilized in this test. This type of screening test is the most used method of checking for pipeline integrity.
Additionally, altering the pressure of the fluid during the hydrostatic testing procedure for pipelines can help determine unusual pressure bleeding. A modified form of hydrostatic pressure testing can be done at intervals to ensure sustained flow line integrity.
Pipeline Dewatering
Hydrostatic testing processes leave moisture within the pipelines they check. The presence of vaporized water within the lumen of pipelines constitutes a potential impurity for fluids that are transported through them.
Pipeline drying services will remove the retained moisture from within the pipes and ensure the quality of the products transmitted through them.
Pipeline Purging
A vital aspect of natural gas pipeline commissioning procedures is the purging of flow lines. Atmospheric air present within newly forged pipelines will alter the quality of their intended gaseous or liquid cargo as it contains suspended impurities.
Pipeline purging is done as part of commissioning procedures, and it involves using an inert gas (usually nitrogen) to replace the air contained within the flow line lumen. Nitrogen purging is an effective and cost-efficient method and can be carried out using on-site nitrogen generators.
Vacuum Drying
This process involves the use of a high-volume vacuum to manipulate the pressure within the pipeline system. At pressure levels 40 Torr or below, water deposited within the flow lines will vaporize and can then be displaced leaving the moisture content within the pipelines at minute quantities. The remaining moisture can then be eliminated by purging the lines with an inert gas.
Nitrogen Drying
The importance of properly drying pipeline networks cannot be overemphasized. Poorly dried pipelines are at a higher risk of corrosion, hydrate formation, and blockage. Utilizing nitrogen-based drying to clear out moisture will limit the onset of potentially hazardous leaks and minimize the cost of pipeline maintenance services.
NITROGEN/HELIUM LEAK TESTING
A nitrogen leak test procedure is performed to verify the integrity of the channels through which it flows. This analytic process is conducted on pipelines, storage vessels, and any other conduit through which an industrial product is conveyed. Leak detection using nitrogen can be done either before the first operational use of equipment or at intervals once during routine operation.
Leak testing allows industrial equipment operators to safely convey their products while minimizing the personnel risk exposure from hazardous chemicals being conveyed through the production channels. Examples include testing for leaks in pipelines, refrigeration systems, checking seals in food processing facilities, and ensuring the functionality of newly installed fire sprinkler systems.
How to Conduct a Nitrogen Leak Test
A nitrogen leak test follows an orderly set of steps which varies depending on the nature of the equipment to be checked. The process typically requires channelling a steady stream of gaseous nitrogen through the selected pipes, vessels, or vats under increasing amounts of pressure.
Various mechanical and automated methods can then be used to identify defects within the industrial components being analysed.
PRESSURE TESTING
Pressure testing is a critical aspect of pipeline testing before first use as it determines readiness for full operational use. During pressure testing activities, various parameters are analysed including the following:
- Maximum permissible pipeline capacity
- Leak checking
- Joint fitting stability
- Pressure ratings
- Component reliability
After careful consideration of the above-stated parameters, operators will be able to determine if their newly assembled pipeline will be able to withstand the rigors anticipated when operating at full capacity.
Several pressure tests may be required to find, and correct defects in newly assembled pipeline networks before they can be granted full operational status. Zeagle Energy Limited has a pipeline fill calculator available for easy gas volume calculations during pressure tests.
Why Use Nitrogen for Pressure Testing?
The reasons surrounding the use of nitrogen gas as a driver for pressure testing are due to the favourable physical and chemical properties. To begin with, nitrogen is an odorless, colourless, and chemically inert gas which implies non-reactivity with equipment components being subjected to pressure testing.
Further, nitrogen will not expose sensitive equipment to moisture, corrosion, and the accumulation of particulate impurities, rather, the gaseous nitrogen being used to conduct pressure testing has the added benefit of displacing oxygen, moisture, and particulate contaminants from within the equipment being tested.
Lastly, pressure testing done with nitrogen significantly reduces the risk of spontaneous combustion accidents making the test process a much safer one for all involved personnel.
If you’re in search of a company that can carry out any kind of pressure testing, look no further! Zeagle Energy Limited has the solutions you need.
How to Pressure Test with Nitrogen
The specifics of leak testing will depend on the vessel or system being tested, but there are general guidelines. To prepare a component of a system for testing, it will need to be isolated from the rest of the system that isn’t to be included in the test. This may require temporarily securing any pressure valves and closing valves that connect the pipe or vessel to upstream or downstream apparatuses.
To begin testing a component, a nitrogen tank or on-site nitrogen generator will be connected to the component. Nitrogen will be released to elevate the pressure within the test component to a low pressure while forcing any air, debris, or other substances out of the component. This will purge the system of contaminants and check for leaks.
Routine pressure testing involves two stages:
- Low-pressure testing
- High-pressure testing
Low-Pressure Testing
This low-pressure test will typically be performed at no more than 25% of the component’s rated operational pressure. The pressure will be held at this level long enough to ensure that the component can successfully hold the pressure without leaking.
If the low-pressure testing is successful, the pressure will then be gradually increased to test if the system will maintain its integrity at higher pressure.
High-Pressure Testing
The pressure will eventually be increased to the rated operational pressure. The actual upper pressure necessary to complete the test will depend on the industry and regulations regarding leak testing.
To locate leaks, a soapy solution can be applied. The pressurized nitrogen escaping will cause the soapy solution to bubble, thus identifying the locations of the leaks. Once any leaks are found at a given pressure level, the component will need to be depressurized and then repaired. Once repairs have been completed, the pressure test can restart from the beginning.
After the pressure test has been completed, the pressure of the nitrogen is lowered. A smaller amount of nitrogen is usually left within the line or vessel to protect it until it is filled with the substance it is designed to hold. The nitrogen continues to protect the interior from the damage or risks that could be caused by exposure to the air.
Often leak tests must be conducted in remote facilities or field locations.
For clients performing pipeline or vessel purging less often, the best option could be the use of Zeagle Energy Limited nitrogen generator rentals. Zeagle can transport and operate the nitrogen generators whenever they are needed.
PIPELINE FREEZING FOR SECTIONAL REPLACEMENT PROCESS
Pipeline freezing is a technique used to modify and repair pipelines. Pipe freezing cools the exterior of the pipe for a period long enough for the fluid within the pipe to solidify. The frozen fluid isolates a section of the pipe so that work can be performed in a more expeditious manner.
Pipeline freezing is a useful tool when shutoff valves are not available in the pipeline that needs repair. Pipe freezing permits repairs in isolated areas. Because individual sections of a pipeline can be separated using the pipe freezing method, the entire pipeline system may not need to be shut down. Pipeline freezing is very practical for small diameter pipes, however large diameter pipes (150 mm or greater) may require special equipment and considerations.
To perform the procedure, the temperature of the pipeline must be reduced below the freezing point of the fluid it is carrying. This is accomplished with some type of refrigerant. A popular method is to apply liquid nitrogen to the pipeline, although different freezing methods may be required for different types of pipe materials and different types of fluids. After the cooling has begun, the fluid within the pipe will begin to form what is known as an ice plug. The ice plug prevents the rest of the fluid in the pipe from flowing, allowing repairs or other pipeline modifications to occur.
Trust us at Zeagle Energy Limited to carry out any of your pipeline freezing projects.
VACUUMING OF CRYOGENIC TANKS & INDUSTRIAL CHILLING UNITS
The ability of a cryogenic vessel or transfer line to maintain the liquefied gas in a liquid state is crucial. This attribute is usually referred to as its “holding time.” This means that some sort of insulation be provided to prevent warm air from contacting the actual container. The generally accepted method of insulating the container is by taking advantage of a good vacuum’s almost non-existent thermal conductivity. A double-walled container with a vacuum between the walls constitutes the concept of the Dewar flask.
If the volume between the walls is filled with gas molecules at atmospheric pressure, the heat transfer across the volume is basically by the heat being exchanged between hotter and colder molecules as they collide with one another. If the molecules are removed with a vacuum pump, the number of molecular collisions drop in proportion to the pressure which can be thought of as the molecular population per unit volume. As the gas is pumped out, the thermal conductivity between the walls will fall off quickly until a pressure corresponding to molecular flow conditions is achieved.
Molecular flow is defined as a statistical condition where a gas molecule, in normal motion, will strike a wall before it strikes another molecule. Below this pressure, usually about 10 millitorr or so, changes in thermal conductivity with lower pressure still occur due to fewer molecules, but the changes occur at a lower rate. This explains, for example, why thermal conductivity vacuum gauges such as thermocouple or Pirani gauges, have a useful limit only slightly below 1 millitorr.
At Zeagle, we offer professional vacuuming services at your beck and call.