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Specifying ASME Standards for cryogenic pipe projects

Note: Information in this article is subject to changes as ASME Standards and Codes are “living documents” and are constantly reviewed and revised. For current information on the standards and codes, visit: www.asme.org.

Some customers request that their equipment meet ASME code or standards, but what does that really mean?

The American Society of Mechanical Engineers (ASME) is a not-for-profit organization that promotes interdisciplinary engineering “collaboration, knowledge sharing, career enrichment, and skills development” with the “goal of helping the global engineering community develop solutions to benefit lives and livelihoods.” It serves this community by offering “quality programs in continuing education, training and professional development, research, conferences and publications, government relations and development of codes and standards.”

ASME is renowned for defining standards as a set of “technical definitions and guidelines” that can become the instructions for constructing products or buildings. Specifically in the cryogenic delivery industry, the ASME code outlines engineering requirements deemed for safe design and construction of the vacuum jacketed piping used in cryogenic applications. The Code is not an engineering design manual or handbook. Standards outlined are considered voluntary and are not mandated by law per se.  However, if a standard or group of standards is adopted by a government entity such as city, county, state or province, it can be considered code and incorporated into the standards according to ASME. Many companies or firms, as well as states and provinces, specify ASME codes as a requirement in purchase and installation of cryogenic systems.

States in which ASME Code is mandatory:

Colorado

Connecticut

Kentucky

Ohio

Washington

Provinces in which ASME Code is required:

Washington D.C.

Prince Edward Island

Alberta

British Colombia

Manitoba

Newfoundland

Nova Scotia

Ontario

Code requirements and laws change. It is wise to check your state and local requirements when considering a cryogenic pipe project and installation. 

Common ASME Codes for cryogenic projects:

Two of the most familiar codes used in cryogenic equipment applications are the ASME Boiler and Pressure Vessel Code (BPVC Section VIII) and the Pressure (process) Piping Code (ASME B31.3). Some industries that may require B31.3 pipe include food and beverage, pharmaceutical, biological research, chemical, refineries, steel, offshore offloading, electronics and semiconductor.

“The ASME BPVC Certification Program establishes rules governing the design, fabrication, assembly, and inspection of boiler and pressure vessel components during construction.” Certification stamps are available for some standards like BPVC. They indicate compliance and verify an acceptable maintenance program to ensure the quality. For other codes, like ASME B31.3, certification stamps are not used and code compliance becomes more complex and more self-regulated.

The standards are very long (BPVC is over 700 pages and B31 over 450 pages) and following the process correctly can be arduous. The Code is not an engineering design manual or handbook. Its purpose is to establish engineering requirements for the safe design and fabrication of pipe systems. The code does not address operation, maintenance, or repair of in service vacuum jacketed pipe systems.

Per ASME B31.3 code, the owner has the overall responsibility for code compliance even though tasks for a cryogenic delivery system project may be distributed among several companies. For example, a designer specifies the piping requirements, the manufacturer fabricates the pipe, and the mechanical contractor installs the system; the ultimate adherence responsibility resides with the owner. Note: The pipe manufacturer may fabricate in accordance with the standards for the pipe in a system, but if the sections of pipe are welded together onsite, then, those joints and welds also need to be to be made to ASME standards. It is the owner’s duty to ensure that they hire reputable companies. The owner’s responsibility consists of the design, construction, examination, inspection and testing of the entire fluid delivery or process installation including the pipe. A simplification of the advantages of code compliance is listed below. For additional information, visit https://www.asme.org/products/codes-standards/b313-2016-process-piping.

By complying with ASME B31.3, the owner/buyer is assured of the following:

  1. Designer qualifications: The Designer is the person in charge of the engineering of the piping system. He must hold an accredited engineering degree, or be a P.E., hold a 2-year engineering technician’s degree plus 10 years of relevant experience, or have 15 years of design experience that includes pressure calculations, load calculations, and pipe flexibility calculations.
  2. Material traceability all the way back to the mill.
  3. Certified welders with appropriate documentation.
  4. Certified weld procedures for every ASME weld.
  5. Inspected welds examined to the customer’s pre-determine requirements, including optional procedures such as visual, radiographic or penetrant examination.
  6. All examinations performed by a Level II Weld Inspector or Certified Weld Inspector (CWI)
  7. All components, including valves, meet the requirements of B31.3 or referenced codes and are plainly labeled as such.
  8. Functional pressure testing with written certification.
  9. Piping designed to meet the owner’s thermal cyclic requirements.
  10. Code compliant written certifications for file.
  11. Copies of all calculations including MAWP and the pipe support system stresses.

Another ASME standard used in the cryogenic piping industry is B16.34.

https://www.asme.org/products/codes-standards/b1634-2013-valves-flanged-threaded-welding-end

ASME B16.34 is a standard that covers detailed requirements on design, manufacture, and testing of valves. The standard outlines procedures for rating valves, material compliance, and test validation. Like the codes above, this code promotes safety by minimizing risk through design principles and construction of valves used in cryogenic temperatures.

The ASME Codes promote conformity through standards publication, manufacturer accreditation, and product validation.  Standard fabrication processes vary from manufacturer to manufacturer. Reputable manufacturers incorporate ASME guidelines into the normal product design as well as the production of the vacuum jacketed pipe and cryogenic components, fabrication processes, quality procedures and final inspection. However, this does not mean that the products are ASME certified. No marks or labels are required by ASME to identify adherence on vacuum jacketed pipe and accessories. Conversely, valves require identification. Only a Certificate of Authorization issued to the manufacturer from ASME ensures conformance to the safety and performance established.

To find out more about the American Society of Mechanical Engineers and the standards and codes, visit www.asme.org.

The author wishes to thank Philip Redenbarger P.E. for his hard work and collaboration on this article.

Frequently Asked Questions

For over 25 years, we have been asked many questions about vacuum jacketed pipe (VJP).  The following article answers the most frequently asked questions about VJP and cryogenic equipment.

What is the different between foam insulated pipe and vacuum jacketed pipe (VJP)?

Foam insulated pipe is usually constructed using a copper pipe and foam insulation covered by a protective polyvinyl chloride layer. The foam insulation is inexpensive and works well when new. However, it degrades substantially over time making the foam ineffective and the pipe inefficient. The reason is that during manufacture, the foam typically bonds to the inner pipe. As the foam becomes cold during cool down, it shrinks, forming small cracks and pulling away from the pipe. This situation allows water vapor to fill the void and increases the insulation’s thermal conductivity causing attrition in efficiency. Over time the expansion and contraction cycle causes the foam to crumble. After about five years, the foam has deteriorated to the point where it loses all effectiveness.

VJP - Frequently Asked Questions

Vacuum jacketed pipe is a conduit in conduit fabrication with a vacuum annual space. The inner pipe transfers the liquid cryogen at temperatures of -3201 and below, while the outer pipe remains at ambient temperature, safe to touch. VJP is designed to reduce all three forms of heat transfer, convection, conduction, and radiation, into the liquid cryogen as it travels from the tank to the end use point. VJP uses multi-layer insulation to deter radiation and convention transfer. Due to the low heat leak, VJP is highly efficient about 40 times better than foam insulated pipe. In many applications, VJP has a product life of greater than 20 years.

Rigid versus Bendable vacuum jacketed pipe, which is better? 

Both types of pipe have advantages and many projects require a combination to enable installation and delivery of the cryogen to the end use point.  They may be interconnected using close fit bayonets which reduce the heat leak into the system and allow for future reconfiguration if required. Vacuum jacketed pipe may be used with all cryogens in industries such as aerospace, semiconductor, pharmaceutical, food and beverage packaging, biological research and storage, rubber deflashing as well as original equipment manufacturers applications. ASME B31.3 Certification is available from many manufacturers.

Bendable Pipe

Rigid pipe is available in tube and pipe options. Vacuum jacketed tube is applied when low flow and quick cool down are required.  Vacuum jacketed pipe (VJP) is used for larger flow applications beginning at ½” IPS up to 10” IPS diameter in some system designs. The advantages of rigid VJP include the lowest heat leak, highest efficiency, longest life cycle and easiest maintenance.

Bendable pipe is manufactured in sizes ¼” through 2” ID. These systems simplify the VJP layout and reduce the need for precise system measurements. The pipe is easier to layout and install than rigid, less costly to buy and lighter, which reduces the packaging and shipping expenses.

Are there different types of bayonets?

In general, the industry supports three types of bayonets.  The Linde style or tip seal bayonet has become an industry standard for use in liquid helium transfer especially when filling MRI machines.  The other two styles are prevalent in the industry but are usually proprietary to the manufacturer. These are the close fit and nose seal bayonets.  The most efficient bayonet design is the close fit type because it relies on small, precise tolerances between the male and female to prevent a leak path. This design offers the lowest heat leak meaning the least amount of vapor generation. Because each manufacturer has a proprietary designed bayonet pair, competitors’ bayonets do not normally connect to each other.

Why does vacuum jacketed pipe take so long to make?

Vacuum jacketed pipe (VJP) is complex to manufacture and special fabrication procedures are required to ensure a reliable and hhigh-qualityproduct.  The VJP design is pipe-in-pipe with a vacuum in between. To begin with, the incoming materials are inspected for adherence to quality specifications.  Then, two sets of pipe are fabricated for each line, an inner and outer. The inner and outer pipes are cleaned to remove contaminants, which helps with creating vacuum integrity and preventing long term off-gassing in the annual space where the vacuum is maintained.  Both must be welded and each are leaked checked. Before assembling the two pipes, the inner is wrapped with multilayer insulation. The next step is to assemble pipes to create the spool. The spools are leaked check and the vacuum process begins. The vacuum process includes heating the spool and pumping the annular space. This process alone may take up to several days. To insure the spools maintain vacuum integrity, they are allowed to sit prior to final inspection.  The spools are then flowed with liquid nitrogen and inspected to rigid quality standards.

Because not all manufacturers have the same quality standards, we recommend asking questions about your supplier’s fabrication processes, quality procedures and inspections.

Gas Vent
Gas Vent

What is the difference between a gas vent, cryovent, vapor vent, keep full, and keep cold?

The answer is simple. They are different names for the same device.    All provide the same function. The purpose of a gas vent is to release gas boil off generated in your cryogenic delivery system as the system sits idle while maintaining liquid in the system to satisfy immediate equipment demands.

Where are SRV’s needed?

A safety relief valve (SRV) is required anywhere in a liquid cryogen delivery system where liquid has the potential to be trapped. The reason for relief valves is clear, liquid cryogens expand at a very high rate. For example, liquid nitrogen expands at a rate of 700 to 1

A safety relief valve (SRV) is required anywhere in a liquid cryogen delivery system where liquid has the potential to be trapped. The reason for relief valves is clear, liquid cryogens expand at a very high rate. For example, liquid nitrogen expands at a rate of 700 to 11.  If a safety relief valve is not used where liquid cryogen is trapped, it will expand and rupture its container.

To further illustrate this point, standard practice includes a safety relief valve between any two shut off valves located in a VJP system. If both valves are closed, the normal heat leak into the pipe will cause the liquid to vaporize and raise the line pressure until the pipe ruptures. Including the required safety relief valve in the line prevents damage to the spool, vents the excess gas to the atmosphere, and maintains a safe system pressure.

Note:  The cracking pressure of the relief valves must not exceed the rated Maximum Allowable Working Pressure (MAWP) of the pipe. Operating the system at a pressure greater than the MAWP is dangerous and with most manufacturers will void the equipment warranty. Standard practice dictates that at least one relief valve is required in a transfer system and that it must be set at or below the MAWP.

Where is the serial number? 

Serial number placement varies with the manufacturer. Technifab Cryogenic’s serial numbers are located on the nameplate under the evacuation port. The number usually begins with a “T” such as T011887.

What is the metal cap on each section of pipe?

The metal cap is a cover for an evacuation port. The port is sealed with a vacuum plug. The evacuation port should never be tampered with and only accessed by a trained technician.

Metal Cap

What is the price per foot?

Due to the complexity of fabricating a vacuum jacketed pipe system, cryogenic delivery systems are usually priced per the project, not per foot.  The price of a foot of VJP may vary significantly depending on the pipe type and number of components.  To illustrate, a single 100 foot run of rigid pipe delivering liquid cryogen from a bulk tank to a machine will be a certain price per foot. However, a 100-foot rigid run that has several drops delivering cryogen to multiple machines will cost more per foot. This is because building vacuum jacketed tees into a system is more time consuming to fabricate. The extra time and materials increase the manufacturing costs and cause the price per foot to increase. Consequently, the industry usually prices VJP project on a system basis.

What is a phase separator?

A phase separator’s purpose is to supply high-quality liquid to a use point while, at the same time, delivering a customer specified pressure and flow required by the downstream equipment. Another less frequent application is using the phase separator as an accumulator in systems where the flow requirements are high for short durations, but still need quality liquids.

Some phase separators offer adjustable liquid level limits and pressure settings. Liquid level limits must be considered with regard to the application. Settings where the high and low liquid levels are close together result in rapid pressure fluctuations of low amplitude. Conversely, settings with wider limits result in pressure fluctuations less frequently but of higher amplitude. Narrow level settings are best for controlling pressure closely, while settings that are farther apart offer longer phase separator component life and quieter operation.

To ensure the most efficient use of the phase separator, place it upstream and as close to the end use point as is practical.  This minimizes pressure drop, heat leak, and cool down losses, all of which degrade the liquid quality.

 

1http://www.airproducts.com/~/media/Files/PDF/company/safetygram-7.pdf

Save Money By Selecting Quality VJP Pipe

Whether you are making ice cream, manufacturing semiconductor wafers, storing biological samples, freezing food or cooling MRI machines, the most effective way to save money on liquid cryogen is by selecting quality vacuum jacketed pipe (VJP) and cryogenic components.

A well-designed VJP system reduces operating expenses by delivering more liquid to the end use point while vaporizing less liquid cryogen. This is accomplished through carefully engineered vacuum jacketed products that are imagedesigned to reduce overall heat leak, lessen gas generation and minimize two-phase liquid cryogen flow which improves the performance of the system and uses less liquid cryogen. In contrast, the performance of a foam insulated pipe system worsens with time. After about five years, the foam has deteriorated to the point where it is no longer effective1. VJP is generally cost competitive with foam insulated pipe when all the expenses are considered. Although the initial capital investment for a copper foam-insulated pipe system is commonly less, the pipe installation is labor intensive and the equipment performance deteriorates rapidly with time. The outcome is a long-term investment more costly than anticipated.  Whereas with VJP, the first capital outlay may be more but the system assembly is easier with pre-engineered sections requiring less installation time. The higher efficiency and performance stability of the VJP results in lower operation expenses. Over the long term, a VJP system results in a better payback than the copper foam insulated pipe (in many cases, less than 14 months) and justifies the initial investment.

But buyers beware because not all vacuum jacketed pipe and components are created equal.

Making consistent, high-quality vacuum jacketed pipe is challenging. With a little research and some manufacturing experience, it is possible for someone to make their own vacuum insulated pipe. However, making quality, high-performance vacuum jacketed pipe that lasts for many years, with little or no maintenance, requires a thorough understanding of cryogenic and vacuum engineering, highly skilled technicians and fabricators, and years of experience.

Variations in the VJP design and manufacture may significantly change the longevity and performance of the pipe, which directly affects your cryogen consumption, overall operating expenses, and profitability.

Because there are always performance/cost trade-offs inherent in any design/fabrication equation, VJ pipe and cryogenic components should be engineered and manufactured with predetermined quality requirements in mind. Whether it is directly stated or not, each manufacturer has a design/ fabrication philosophy that determines the efficiency and longevity of their pipe1. Design decisions about the material, manufacturing processes, in-process inspection and final testing establish the quality and life cycle of the product. Poor designs offer greater opportunities for higher heat leak, increased gas production and two-phase liquid in the pipe and overall delivery system. “Disadvantages of two-phase flows include higher pressure drop when flowing through pipes and other components, flow instabilities may develop that result in pressure surges and vibrations”2 both cause less cooling capacity at the use point, variable cool-down time and inconsistent liquid delivery. All hinder the performance of your delivery system, increase cryogen use and add to your operating expenses, which reduces your profits.

Superior VJP integrates strategies and features components specifically designed to inhibit heat transfer from conduction, convection, and radiation. The smaller the heat leak the more cost effective the operation of the cryogenic delivery system. Good pipe design includes thermal expansion joints that minimize movement during liquid transfer.

The most critical factor in producing quality vacuum jacketed pipe is establishing and maintaining the vacuum integrity. Without vacuum integrity, the pipe will not perform well for the long term. Guaranteeing a high performing vacuum, one with integrity, begins with defining strict process standards that provide long term results. But life cycle integrity is ultimately ensured during the manufacturing of the product.

Because the manufacturing process is vital to vacuum integrity, the fabrication facility should be an air conditioned environment with low humidity. Moisture is counterproductive to creating a quality vacuum and can be a large obstacle in obtaining a long-term, reliable vacuum. Lower humidity augments the vacuum acquisition by minimizing the number of water molecules needed to be removed and reducing the bake-out time.  Bake out time is important to ensure reliability and should be designed to maximize vacuum performance. A quality VJP design will integrate a molecular sieve which improves water absorption during this process.

Another component important to long term vacuum effectiveness is the inclusion of a getter. Getter selection is significant because it helps take up gas within the pipe.  Accurate determination of the type, amount as well as location enhances and maintains the vacuum integrity throughout the product life.

A clean work space is another key requirement for production of a quality VJ product with a high vacuum reliability.  Any contaminants such as lint, metal shavings, or dirt have the potential to destroy the vacuum. Another potential hazard is finger prints. Fingerprints leave oil, which causes outgassing during pump down and can also potentially damage the vacuum. Therefore, proper handling of the components using gloves during fabrication reduces fingerprints and helps produce a quality vacuum jacketed product.

Other aspects for further design consideration include incorporating nitrogen gas back flush, instituting quality measures for in-process inspections, and establishing final testing requirements. For example, higher quality VJP manufacturers use a high vacuum leak check test at final inspection to predict long term vacuum integrity.

Buyers be wise

Providing your company with the highest return on their investment and the best cryogenic liquid for the application begins with specifying a vacuum jacketed pipe system instead of copper insulated pipe. But outlining the specifications alone does not guarantee that you are buying a high-performance VJP system. Be sure to purchase from a reputable manufacturer. The company should, first and foremost, design their products with quality in mind. Then, fabricate and inspect their products to strict standards which substantiate the quality. By investigating your supplier, you will help ensure the most efficient liquid cryogen transfer, the least costly operation of your delivery system, and best return on your capital investment.

When selecting a vendor, be wise:

  • Qualify your suppliers.
  • Know your application requirements as well as the specifications for your cryogen delivery system such as bulk tank pressure, pipe size, special machinery requirements and end use point flow rate and pressure.
  • Fully understand your needs and system parameters.
  • Ask questions about the vacuum jacketed pipe design, fabrication process and internal quality controls and product warranty.
  • Request pipe performance verification from your vendors.

Failure to investigate your vacuum jacketed pipe manufacturer may result in a less efficient operation, more liquid cryogen use, higher overall operating expenses and a longer return on your capital investment.

 

 

1Rendenbarger, P (2005). High-Efficiency Liquid Nitrogen Transfer Piping, Process Cooling & Equipment

2 Weisend, J (2016). Defining Cryogenics. Cold Facts, 32(4), 21.

 

 

Techflow Tube Series Cryogenic Vacuum Jacketed Valves

Techflow 500 Series Vacuum Jacketed Valves

Low Cryogen Losses With Minimal Space Claim

  • Vacuum-jacketed, to prevent the ice and condensation seen with non-vacuum jacketed cryogenic valves.
  • Compact design reduces the space claim, ideal for transfer hoses and smaller diameter pipe/tubing.
  • Easy grip handle provides low torque opening and closing.
  • Lower cost than pipe sized valves.
  • Wear parts are easily removed and replaced reducing down-time.
  • Made by Technifab to the same high quality standards as our vacuum jacketed pipe.

We also offer Techflow Pipe Series Vacuum Jacketed Valves in larger diameters.

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