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Industrial gases are used in various manufacturing processes across many industries. These gases include oxygen, nitrogen, hydrogen, argon, carbon dioxide and others. Several of these gases are also used in healthcare facilities. Typically, the tanks are provided as rentals from an outside supplier who often remotely monitors the content level in the tank and refills it using portable tanks owned by the suppliers. In certain cases, the level monitors can be located on the tank and connected to an internal plant monitoring system with level alarms. The maintenance, filling safety, testing of safety relief valves and overpressure protection systems are the responsibility of the suppliers/owners of the tank. The tanks are commonly installed in a fenced area with restricted access. They fall within the unfired pressure vessels category of most state jurisdictional codes, thus requiring jurisdictional safety inspections. Most of these inspections are completed externally, often from a distance.

The industrial gases storage tanks discussed below are nitrogen, oxygen, argon, propane and carbon dioxide (CO2).

All tanks are constructed based on the codes and standards listed below:

ASME BPVC Section VIII, Division 1 and Division 2
ASME B31.3 (Process Piping Code)
American Petroleum Institute (API) Standards
API 625 – Tank Systems for Refrigerated Liquefied Gas Storage
NFPA 59A – Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG)
NFPA 55 – Compressed Gases and Cryogenic Fluids Code

Cryogenic tanks — such as those for liquid oxygen, nitrogen or argon — are constructed as double-walled, vacuum-jacketed, and super-insulated to reduce product losses and compensate for varying outside temperatures.

Industrial propane storage tanks are generally not double-walled. Instead, they are typically constructed with a single-walled design made from thick, high-strength carbon steel, designed to safely contain propane under pressure.

During external jurisdictional inspections, if a safety relief valve is found hissing, it may not necessarily indicate a defective valve. Other overpressure-causing symptoms can be attributed to each type of gas storage tank. However, it is an indication that the relief valve is operable. The cause of overpressure in the tank and the relief valve lifting should be investigated. Replacing the relief valve may not necessarily mitigate the problem. Overpressure in combustible gas storage tanks is serious; a sudden release of gas can cause a vapor cloud explosion and extensive damage. An ignition source could be nearby electrical equipment or weather conditions such as lightning.

The installation of a pressure controller should be seriously considered to prevent overpressure in the tanks.

There are several manufacturers of pressure controllers for tanks.

The controller is called PID (Proportional-Integral-Derivative) controller. The function of PID is to continuously protect the vessel from pressure buildup. All the control valves, including the vent valve, should ideally communicate continuously with the controller.

Pressure Sensors – Continuously measure the measure inside the tank and communicate with the controller

Control Valves – Should be actuated based on a signal from the controller. The actuation can be pneumatic, hydraulic or electric.

The controller receives signals from the pressure sensors. If the pressure exceeds the setpoint, the controller signals the control valve to open, allowing fluid to escape and reducing pressure, and if the if pressure drops below the desired level, the controller signals the valve to close or open an inflow valve to increase pressure.

Causes of Overpressure

Propane Storage Tanks: Overpressure in industrial propane storage tanks can occur due to several factors:

Temperature Increase: Higher outside temperatures can cause propane inside the tank to expand, increasing pressure. This can happen due to external heat sources or inadequate insulation.
Overfilling: Overfilling a tank can lead to pressure build-up, as there is insufficient space for vapor expansion. An Overfill Prevention Device (OPD) could be defective.
Faulty Safety Devices: Issues such as valve malfunctions, pressure relief valve failures, or other equipment failures can prevent proper pressure regulation.
Chemical Reactions: While propane is generally stable, contamination with reactive substances could theoretically cause pressure changes.
Blocked Venting Systems: If the venting system is blocked or restricted, it can prevent pressure from equalizing, leading to overpressure.

interior view of parts and fittings in a propane tank

Industrial propane storage tanks are equipped with various fittings that serve specific purposes for safety, functionality, and maintenance. Some of the key fittings include:

Liquid Withdrawal Valves: Used to draw liquid propane from the tank for distribution or use.
Vapor Withdrawal Valves: Allow for the extraction of propane gas (vapor) from the tank, often used in applications where gas is needed rather than liquid.
Filling Valves: Used to fill the tank with propane and typically equipped with safety features to prevent overfilling.
Pressure Relief Valves (PRVs): Automatically release gas to prevent overpressure in the tank, which is crucial for safety.
Emergency Venting Devices: Designed to release gas during emergencies, such as rapid pressure increases.
Gauge Fittings: Allow for the installation of pressure and liquid level gauges to monitor the tank’s contents and internal pressure.
Safety Shutoff Valves: Automatically close in case of a leak or emergency, preventing the release of propane.
Grounding Fittings: Used to prevent static electricity buildup, which could ignite propane vapors.

Liquid Oxygen Tank – A cryogenic liquid oxygen storage tank is an insulated vessel consisting of a carbon steel outer shell and a stainless-steel inner vessel, with an insulating vacuum space between the layers.

Causes of Overpressure: Overpressure in industrial liquid oxygen storage tanks can arise from several factors:

Temperature Increase: Liquid oxygen can vaporize when temperatures rise, resulting in a rise in internal pressure. This could happen during high surrounding temperatures or loss of insulating medium between the double walls.
Faulty Vent/Line: When liquid oxygen is drawn from the tank, the remaining liquid can rapidly vaporize. If not vented, this will raise the internal pressure.
Overfilling: A faulty OPD system resulting in overfilling a tank can lead to insufficient space for vapor expansion, causing pressure to rise.
Mechanical Failures: Failures in valves, pressure relief devices or other components can prevent pressure regulation.
Chemical Reactions: Although liquid oxygen is stable, contamination with organic materials or other reactive substances can lead to dangerous reactions that produce heat and pressure.
Cooling System Failure: This could lead to increased vaporization of liquid oxygen within the tank.

Industrial liquid oxygen storage tanks have several specialized fittings designed to ensure safe operation, proper handling, and effective monitoring. Key fittings include:

Filling Valves: Used to fill the tank with liquid oxygen, equipped with safety features to prevent overfilling.
Liquid Withdrawal Valves: Allow for the extraction of liquid oxygen for various applications.
Vapor Withdrawal Valves: Enable the extraction of gaseous oxygen from the tank, often for immediate use or distribution.
Pressure Relief Valves (PRVs): Automatically vent excess pressure to prevent overpressure conditions in the tank.
Emergency Venting Devices: Designed to release gas during emergencies, such as rapid pressure increases, ensuring safety.
Level Gauges: Fittings for monitoring the liquid level in the tank that are essential for managing inventory and preventing overfilling.
Pressure Gauges: Provide real-time readings of the internal pressure, helping operators monitor tank conditions.
Thermal Relief Valves: Protect against pressure build-up due to thermal expansion of the liquid oxygen.
Grounding Fittings: Prevent static electricity buildup, which could ignite oxygen-rich atmospheres.
Isolation Valves: Allow for safe isolation of the tank from piping systems for maintenance or emergencies.

Nitrogen: Overpressure in industrial nitrogen storage tanks can result from several causes. Key causes include:

Defective Overfilling Device (OPD): Overfilling a nitrogen storage tank beyond its design capacity can cause pressure to exceed safe limits, leading to overpressure.
Thermal Expansion: Nitrogen is stored as a cryogenic liquid at extremely low temperatures. If the liquid nitrogen warms up, even slightly, it will expand significantly, generating higher pressure. Insufficient venting or temperature control could lead to overpressure.
Malfunctioning Pressure Relief Valve (PRV): PRVs are designed to release gas if pressure exceeds a certain threshold. If these valves malfunction, are blocked or are improperly sized, pressure may build up beyond safe limits.
Rapid Temperature Changes: Sudden changes in temperature, such as rapid heating of the tank’s environment, could cause nitrogen inside the tank to expand and generate pressure faster than the venting system can manage.
Faulty Gauges or Instrumentation: If pressure sensors or gauges fail to provide accurate readings, operators may be unaware of rising pressure levels, leading to overpressure conditions.
External Heat Sources: Exposure to external heat sources, such as hot weather conditions or fires, can increase the temperature of nitrogen inside the tank, resulting in overpressure.
Blockage in Venting System: Nitrogen storage tanks have venting systems to safely release gas and maintain appropriate pressure. Any blockage or malfunction in this system can prevent proper venting, causing pressure buildup.

accessories and parts for liquid nitrogen tanks, labeled

Fittings on industrial nitrogen tanks are designed to safely handle and control the storage, flow and transfer of nitrogen:

Pressure Relief Valve: Automatically releases gas in the event of overpressure.
Rupture Disc: Sometimes installed to rupture in the event of overpressure.
Shut-Off Valve: Manually opens or closes the gas flow.
Pressure Regulator: Reduces high-pressure nitrogen from the cylinder to a usable lower pressure.
Pressure Gauges: Allow for monitoring of internal pressure.

Argon Storage Tank: The causes of overpressure in industrial argon storage tanks can include:

Temperature Increases: As temperature rises, the gas expands, increasing pressure within the tank. This can happen due to ambient temperature changes or heat from nearby equipment.
Overfilling: Filling the tank beyond its rated capacity can lead to excessive pressure, especially if the gas expands due to temperature changes.
Gas Compression: During gas transfer or due to operational issues, compression can occur, leading to increased pressure in the tank.
Equipment Malfunctions: Failure of pressure relief valves, gauges or other safety devices can prevent proper pressure regulation.
Chemical Reactions: Although argon is inert, if mixed with other substances, unexpected reactions can occur that may generate additional gas or heat.
Blockages: Obstructions in the piping or venting systems can trap gas and prevent proper pressure relief.
Poor Ventilation: Inadequate ventilation can lead to localized pressure increases, particularly if gas is released into a confined space.
Leaking Systems: If there are leaks in the system, pressure differentials can cause issues that may lead to overpressure.

Cryo-Tank-PFT-Digram

Industrial argon storage tanks typically have several key fittings to ensure safe and efficient operation. Here are the main fittings you might find:

Inlet/Outlet Valves: Used to fill and discharge argon from the tank and usually equipped with a safety valve to prevent overpressure.
Pressure Relief Valve: Critical safety feature that releases excess pressure to prevent tank rupture.
Level Indicators: Allow operators to monitor the liquid level inside the tank, often using float gauges or ultrasonic sensors.
Thermowells: Used for temperature measurement, thermowells protect sensors from the process environment.
Sampling Ports: Allow for the collection of gas samples for analysis, ensuring quality control.
Vapor Return Lines: In some setups, vapor return lines recycle vaporized argon back into the system.
Safety Relief Devices: Additional safety measures, such as burst discs, may be installed to handle emergencies.
Grounding and Bonding Connections: Essential for preventing static electricity buildup during filling and discharging.
Drain Valves: Used to remove any liquid contaminants or condensation that may accumulate.

Conclusion

From the above-stated causes of overpressure in industrial storage tanks, a regular maintenance program should be instituted that includes checking and testing all the fittings and relief valves (RV) on the tanks. The RV should be replaced according to the codes and standards, which typically range from five to ten years depending on the gases stored. The most important factor is not to overfill the tanks. There are several methods of filling the tanks, some of which involve human error. The most common methods are stated below.

Stationary tanks are filled by mobile tankers. Detecting when the maximum level of liquid is reached in the tank is done by various methods, such as observing when liquid flows from a try-cock, by weight or by measurement of flow.

Single Hose Filling by Pump: It is common to fill a transport tank using a pumping system via a single filling hose, except for cryogenic gases, which are commonly filled with a dual hose (liquid feed and vapor return). To obtain sufficient flow rates, the pump may have a maximum discharge pressure exceeding the receiving vessel’s MAWP. The standard single hose filling procedure requires the operator to continuously monitor and control the receiving vessel pressure by adjusting the top and bottom fill valves. Keeping the pressure below the MAWP is critical to safety.
Automatic Filling Systems: This procedure uses flow meters or weighing scales. Filling is complete when the intended amount of liquid is transferred or the maximum fill level is reached. If the operator fails to end the filling process when the maximum filling level is reached or fails to control the tank pressure during filling, the pressure in the transport tank may increase, potentially reaching the MAWP, and causing the relief devices to open.
Filling with Pressure Balance: This method involves an additional hose connection between the gas phase of the receiving vessel (transport tank) and the storage tank. The differential pressure requirement of the transfer system is reduced as the pressures of the transport tank and the storage tank are equalized before or during filling. This method may also be used to reduce the loss of gaseous product from the gas phase of the transport tank. The product may be transferred by a pump or by the liquid head of the storage tank. The filling procedure is normally controlled by an operator, who may be supported by automatic systems. Any potential over-pressurization of the receiving vessel can be reduced when using this two-hose transfer method, as the pressure can balance.
Pressure Transfer: This method is a technique used to move gas from a tanker to a storage tank using the pressure difference between the two systems. The tanker is equipped with a pressurized gas system, while the storage tank is designed to receive gas under pressure. Gas is transferred by opening the valves, allowing the higher-pressure gas from the tanker to flow into the lower-pressure storage tank. Throughout the transfer, pressure and flow rate are monitored to ensure safety and efficiency. This helps prevent over-pressurization and ensures that the gas is transferred safely. This method is efficient and often used for liquefied gases, ensuring a safe and effective transfer process.

Maintenance and Testing of Relief Valves: Pressure relief valves are critical to the safe operation of bulk gas storage tanks. They are closely regulated in most states and subject to both National Board Inspection Code (NBIC) and NFPA requirements, which call for testing and replacement at regular intervals.

During inspections, it should be verified that an appropriate device is installed on tanks, in addition to rigorous testing to confirm their proper working condition in accordance with the NBIC and NFPA 58 recommendations, including:

Pressure relief valve testing and certification should be completed every five years.
Inspections must be performed by a certified pressure relief valve testing contractor to ensure compliance.
At the owner’s discretion, pressure relief valve replacement is an acceptable alternative to testing.

Meet Melanie Rogers: a hard-working woman, a loving mom to her two sons and an amazing grandmother to her three sweet “grandgirls”. We’ve gotten to know her pretty well over the past 10 years of her time at BPC, and she has been a tremendous asset to our team.

Before BPC, Melanie was a stay-at-home mom for 15 years and worked at her former church as a ministry assistant for 6 years. It was there she met Brandon Loveridge, BPC’s CFO, who introduced her to the job opportunity for BPC’s administrative assistant.

Melanie confidently handles the behind-the-scenes of our work here at BPC, spending her days working on inspection reports, jurisdictional inspection reports and RISK assessment reports. She is the only one on our team who takes charge of processing for two of our largest customers! She also diligently answers phone calls, serving as the smiling voice of BPC.

All of that paperwork could become overwhelming for most, but Melanie truly enjoys it! However, she enjoys her coworkers at BPC even more.

“I definitely want to thank the Lord for providing the job opportunity and for having Brandon [BPC’s CFO] as my boss. I feel like I have been appreciated over the years, and that helps for sure to boost my confidence!” Melanie said.

As Melanie is the one taking phone calls, she often hears what BPC’s clients have to say about the company. One comment she hears over and over again? The overall quality of attention that is shown to customers.

“We have competitors that do similar work to what we do, but we are frequently told by our customers that we do some things differently,” she said. “We provide detailed letters that other insurance companies don’t do.

“The way we try to provide the best information for our customers is helpful. We get complimented on how quickly we respond to questions and things that our customers ask or request.”

Melanie works on the front lines to provide quick and easy information for our clients. Plus, around 50 inspectors work with BPC, and she’s there for all of them.

“I enjoy when I have the opportunity to talk to our inspectors,” she said. “I get to meet people from all over [the US]!”

Thank you, Melanie, for all of your hard work! You’ve been a true asset to our company for the past 10 years, and we feel lucky to have you as a part of our family.

Congratulations! Long-time inspector and fishing enthusiast Mike Scott was awarded the President’s Award in July.

His long history in the industry has been an asset to BPC for several years.

“I retired from the state of Washington after 30 years and joined BPC a few years ago in the Washington, Alaska and Oregon region,” Mike said. “I inspect everything from high pressure boilers to low pressure boilers, hot water heating boilers, air compressor tanks, hot water heaters, CO2 bulk oxygen, nitrogen — a myriad of all the jurisdictional pressure vessels.”

BPC President Venus Newton had some input regarding Mike’s work ethic and determination.

“Mike has been on a roll, starting back in June when he made a trip to Alaska that resulted in getting stuck on an island in the Aleutian Island Chain for three days with no internet, cell phone or TV due to heavy winds,” Venus said. “This threw his schedule into chaos, but Mike still managed to knock out 55 site visits across the state.

“Then in July, back in his regular territory, Mike worked with the Chief Boiler Inspector for the City of Seattle. They worked together to create a plan to address the overdue external inspections for a large school system that had all their high-pressure boilers open and due for internals. As a result, Mike completed 117 site visits in July. By working with the jurisdiction, he found a solution to a difficult dilemma and displayed flexibility and creativity in meeting our customer’s jurisdictional inspection needs.”

As such a hard-working and creative problem solver, it’s easy to see why Mike was selected for the month’s $1,000 award.

“It’s an honor to be recognized. Among all the other inspectors within the company, it’s kind of cool to be singled out,” Mike said. “I really couldn’t have done it without the other inspectors in our region, like Robert, Aaron and Greg who filled in when I was up in Alaska. They kept my territory in check and helped out there. It was kind of a team effort, and without them, I think I would’ve been behind and just playing catch up.”

“This type of attention to detail, dedication and execution is what sets us apart from our competition and why Mike has been awarded the $1,000 President’s Award for July,” Venus said. “Fantastic job, Mike!”

Importance of Overspeed Testing Prime Movers

Overspeed trip devices are provided to protect prime movers such as steam turbines, gas turbines, hydroelectric turbines, wind turbines and internal combustion engines from overspeeding in the event of load rejection coincident with failure of the speed controller. Severe overspeed conditions result in catastrophic destruction of the prime mover resulting in extensive property damage and business interruption loss. To prevent such an event, it is vital that overspeed trip devices are tested to original equipment manufacturer (OEM) specifications annually, for base-loaded units and at pre-startup of standby units.

All prime movers have overspeed protection systems that detect when operating speed is exceeded by the designated OEM specified percentage. In this scenario, prime movers will initiate the closure of valves to isolate all potential energy sources, steam for steam turbines, gas for combustion turbines, wicket gates for hydroelectric turbines and fuel supply valves for internal combustion engines. For wind turbines, an electric control system to change the blade pitch, and yaw control supplemented with mechanical brakes is utilized.

Overspeed occurs in three circumstances:

Loss of load
Failure of the control system (Governor)
Failure of the overspeed protection system

There are two primary types of overspeed protection systems: Mechanical/Hydraulic and Electronic.

Mechanical overspeed trip protection has a spring-loaded bolt that is held in a recessed position attached to the rotating shaft of the turbine. As the turbine shaft spins, centrifugal force is asserted on the bolt. The spring-loaded bolt is designed to stay in place at the designed revolutions per minute (rpm) of the turbine shaft. If the turbine shaft exceeds the predetermined designed overspeed, the centrifugal force on the bolt exceeds the mechanical force maintained by the spring, causing the latch to tilt the pivot and shut down the energy source to the turbine. Mechanical trip devices have been in use for decades and largely phased out by Electronic systems.

Mechanical trip systems are subject to wear and are not always accurate, with a variance below or above the 108% to 112% overspeed generally recommended by OEM. Therefore, Mechanical systems must be diligently maintained and tested. Mechanical overspeed trip is tested by removing the load from the prime mover. In the case of a driven generator, the generator breaker is opened. For some drives, the drive coupling must also be uncoupled. The speed of the prime mover is increased often by bypassing or changing the limits on the governor, the trip speeds are recorded and adjustments are made if required to meet OEM specifications.

Electronic systems differ by manufacturer, however, their working principles are similar.

Systems are comprised of several sensors that are mounted on a speed wheel spur gear type of wheel. The sensors measure the passage of teeth of the rotating speed wheel spur gear. The overspeed digital logic controller determines the shaft rpm based on designed ratio of the rotating spur gear. If the rpm exceeds the preset rpm of the shaft, logic controllers signal the trip relay to de-energize, and the machine goes through the trip procedure.

There are multiple methods to test electronic overspeed trip systems. This can be accomplished by changing the overspeed trip set point to achieve OEM-specified trip speed. Newer electronic overspeed trip devices are installed with control cards that permit a simulated self-test. This is most common for gas turbines.

Electronic overspeed protection supersedes the reliability of mechanical trip system accuracy and response times. Per API 670, overspeed reaction time should be less than 50 msec. Also, electronic governor and electronic overspeed protection systems must be installed in strict accordance with API 612 and API 670. Consequently, during inspections, overspeed systems should be revived. Mechanical overspeed trip systems should be replaced with electronic speed trip systems, or an Electronic system should be installed in addition to the already installed mechanical system for greater reliability and accuracy.

Protected: President’s Input – Q3 2024

Protected: Operations Update – Q3 2024

Protected: CFO Notes Q3 2024 – Who is INVO PEO?