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The quick, accurate, and inexpensive measurement of Trihalomethanes (THMs) creates numerous opportunities to improve the water treatment process. THM levels can be lowered throughout the distribution system and chemical usage can be optimized to save money. What’s more, quick process adjustments can be made to control THM formation when surface water Total Organic Carbon (TOC) characteristics alter due to seasonal or unusual weather conditions. Where before you might have had limited THM data, you can now greatly expand the sampling frequency and monitoring locations to help you better understand the THM formation characteristics of your water source, treatment process, and distribution system.
Both human activities and seasonal changes can affect source water, altering the mineral characteristics of the water as well as the reactivity of its dissolved organic carbon. A water plant may observe no significant changes in the quantity of TOC due to seasonal events, but they may find their THM level has changed. Frequent measurements of THM can help operators better understand the reactivity changes of their source water.
A successful coagulation process depends on identifying the correct coagulant type and optimum dosage under suitable environmental conditions of pH and alkalinity such that the coagulant will remove the maximum TOC, UV254, and turbidity, and form easily settleable floc. However, without the ability to measure THM concentration of the finished water in real time, the plant operator will not know if the coagulation process has been optimized to also remove the maximum amount of THM precursors. With the ability to easily measure THM concentration in finished water, the plant operator can adjust the coagulation process to achieve minimal THM formation potential. Additionally, this allows the treatment plant to supply safe drinking water with the required level of disinfectant concentration while also maintaining lower DBP levels throughout the entire distribution system.
Trihalomethane formation in water distribution systems is a function of water travel time, temperature, and physiochemical and biological characteristics of pipe deposits within the distribution system. The real-time monitoring of THM at different sampling locations will help water distribution operators to identify problematic inorganic/organic pipe deposits that cause increased levels of THM formation.
Hydraulic modeling of a water distribution system is an important tool for water quality management. In addition to basic hydraulic characteristics, modeling identifies water aging and predicts disinfectant decay and DBP formation. Incorporating new data from frequent THM analysis in combination with disinfectant level data will help plant operators build an improved hydraulic model for water quality trend analysis, providing critical information for more targeted and efficient water plant operation.
Water quality levels throughout the distribution system are maintained by systematic flushing programs designed to reduce stationary water in dead end lines and increase flow volume to minimize water age. The distance of water from the water plant, dead ends in the pipe, and low water usage may cause water quality deterioration. Lower residual disinfectant levels indicate the need to flush, which can cause a significant water loss. By measuring THM concentration in addition to disinfectant levels, operators can better decide on the location and length of flushing to minimize treated water loss.
Water age is emerging as an important issue due to increased THM formation in water distribution systems. Excessive contact time caused by dampened peak-hour demands, distribution piping configurations, areas of reduced water requirements, and fire protection storage can result in elevated THM concentration. Identifying and then reducing dead spaces and stagnation in water storage tanks and looping pipe configurations in water distribution systems will reduce water age. These actions can be triggered appropriately by monitoring THM levels in storage tanks and key locations in the distribution system.
Parker’s On-Line THM Analyzer and benchtop THM Analyzer are easy to operate, integrated Purge-and-Trap Gas Chromatographs (GC) that measure THM concentration at ppb levels in less than 30 minutes right at your own facility without tedious sample preparation.
This integrated system is a powerful tool that can help operators optimize water treatment at the plant and evaluate water age in the distribution system for improved control over the formation of THMs.
Pic. 1. Parker's On-Line THM Analyzer.
Download Parker On-Line THM analyzer bulletin.
Pic. 2. Parker's benchtop THM Analyzer.
Download Parker benchtop THM analyzer product catalog.
Article contributed by Kazi Hassan - technology development manager (water) at Parker Hannifin, Instrumentation Products Division.
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How Parker's THM Analyzer Helps to Improve Safety of Drinking Water
Since the NACE (National Association of Corrosion Engineers) MR0175 standard was updated to ISO status in December 2003, there has been an air of confusion on what and how products conform to NACE. Some manufacturers simply buried their heads and try to ignore the standard, some simply decided that they would not pursue NACE product related business, some only certify to old, out of date versions of the standard, and others simply used the wording of certain clauses within the standard as a way of supplying product from materials that do not actually meet the requirements of NACE MR0175.
Parker has taken NACE compliance very seriously and invested a lot of time to ensure that not only did we understand the consequences of the standard but what we actually put out to our customers in the market place was accurate and met the criteria of what the standard is advising the Oil and Gas Industry.
Engineers from Instrumentation Products Division Europe attended a conference organized by the authors of the NACE MR0175/ ISO 15156 document and arranged for one of the authors to visit our manufacturing facility at Barnstaple to discuss its implications and how we as a manufacturer of saleable goods should be certifying the materials we use for NACE compliant products.
Beyond Stainless Steel: Corrosion Resistant Alloys in the Oil and Gas Industry
Metallurgy Makes or Breaks Tube Fittings
Mixing Materials in Corrosive Environments
Article contributed by Clara Moyano, Innovation Engineer - Material Science at Instrumentation Products Division, Europe
Managing emissions is a major challenge for many companies. In Europe alone, a typical refinery can lose between 600 and 10,000 tonnes of fugitive emissions every year; and the majority of those losses are estimated to be caused by plant equipment, such as process to instrument valves and small bore fluid system technologies.
Valve leakage is believed to account for around 50 per cent of emissions within the chemical and petrochemical industries. That can place a major financial burden on companies - not just due to potential plant inefficiency, but also the potential costs of repairing leaks, wasting energy and environmental fines.
Reducing emissions can help businesses to protect the environment, reduce waste and save valuable time and money in the process. Engineering, Procurement and Construction (EPC) and end users involved in commissioning may find it helpful to follow a series of checks - alongside any existing processes - to determine prospective supplier capability.
International standard ISO 15848 sets a requirement for zero emissions for processes involving hazardous fluids and volatile air pollutants. The standard is split into two parts:
ISO 15848 defines three leakage classifications that specify maximum leakage rates, with Class A being the most stringent.
Parker products have been compliant with ISO 15848 for some years now.
Pic.1. Lloyd’s Register verification for the Pro-Bloc® 15mm process to instrument valves dates back as far as July 2007.
Typical industry procurement practices require certificates of approval or third-party verifications as a condition of supply. Reputable valve manufacturers, including Parker, can provide signed and witnessed certificates - along with verification from industry-leading organisations and technical advisors such as Lloyds, TUV and DNV.
If verifications are provided by an unknown third party, engineers and procurement specialists may want to satisfy themselves with the quality and level of certification offered - ensuring that any named verifiers are trusted experts in their field. And it’s important that suppliers can provide access to any stated certification, as proof of capability and to ensure practices are up-to-date.
Experience supporting major companies and being on approved vendor lists can also be a useful indicator of supply quality. Manufacturers of process to instrument valves who are working with oil majors typically have to pass stringent pre-qualification checks and approval systems. For example, Shell’s robust enterprise framework agreement requires suppliers to:
Passing these tests is a strong indicator of supplier credentials. Parker is proud to have recently secured a five-year extension to its framework agreement with Shell following a recent factory audit and witness-tested Type Approval Test. The extension was secured due to Shell being satisfied with Parker products and service over the previous five years.
Pic.2. Parker’s MESC compliant Double Block and Bleed valve.
In offshore applications, the implications of insufficient expertise or training can carry significant risk. It’s therefore imperative that any suppliers demonstrate their understanding of the business environment and relevant operations.
Asking suppliers for details of their testing practices and procedures, familiarity with legislation and adherence to industry standards will help to build a clear picture of suppliers’ relative experience and credentials.
EPC contract engineers and procurers commissioning process to instrument valves may find it helpful to consider the following areas when considering potential suppliers:
To find out more about Parker’s fugitive emission credentials and high-quality process to instrument valves, please visit Parker Instrumentation Products Division website.
Article contributed by Jim Breeze - Flange Products Product Manager at Parker Hannifin, Instrumentation Products Division Europe.
NORSOK M650 Compliance – An Essential Prerequisite for the Offshore Industry
10 Steps to Cost Effective & Safe Installation of Instrumentation Tube and Fittings Systems. Part 1
Why Standardisation Matters in the Oil and Gas Industry
How to Avoid H2S Embrittlement in Instrumentation Connections
There are many reasons why bolts should be included in material specification, particularly in the oil & gas and petrochemical industry. In this latest blog from the Process Control team, we present an overview on items for consideration that may not always be considered for a commodity part.
Because the high chloride environments where the instrumentation is used, including seawater and bleach plants, are extremely corrosive, therefore it is a good idea if Corrosion Resistant Alloys (CRA) are specified by engineers for all parts in these applications. Super austenitic stainless steel 6Mo is a high-performance alloy renowned for its corrosion resistant properties.
It can be a false economy if inferior materials are chosen for the bolts, rather than corrosion resistant alloys. In highly exposed environments, 6Mo is often specified by engineers for instrumentation systems, including tubing, manifold, gauge and fittings. However, bolts may seem like the last piece of the jigsaw - a tiny part of an overall system - but if the wrong material is specified, this could lead to the whole system’s downfall. Corrosion of the bolts in a hook up could lead to stress corrosion and cracking, causing them to snap, which results in catastrophic failure and the potential for accident and injury.
The third reason is that inferior material specification can cause maintenance issues too. Corrosion to the bolts can be so rapid that by the time it is noticed, the bolts simply cannot be replaced. Instead, they have to be sawn off, potentially causing expensive damage to the instrument tubing system.
Similarly, if tubing clamps are not manufactured from corrosion resistant alloys, this could lead to stress cracking and fatigue, resulting in equipment failure.
Specifying a Corrosion Resistant Alloy, such as 6Mo, throughout the instrumentation tubing system, including all component parts, gives complete peace of mind. Specifiers and customers can, therefore, be reassured that all components, including bolts, will ensure durability and long-term performance of their instrumentation system.
Learn more about corrosion and materials selection for corrosion control.
Deborah Pollard is business development leader capital projects, Instrumentation Products Division, Europe of Parker Hannifin.
Learn the Anti-corrosion Code - alloy selection and measurement of relative corrosion resistance. White Paper
Understanding Corrosion in Challenging Offshore Applications
Choosing the Right Tube Clamps for High Temperature Environments
One Smart Solution For Preventing Corrosion Between Tubing
Condensate pots play a key role in maximising the accuracy of differential pressure flow measurement on steam or vapour applications. When installed correctly, these simple devices can significantly improve flow measurement accuracy in differential pressure measurement systems by providing an interface between the vapour and liquid phases.
Condensate pots also prevent flashing of liquid in the impulse line, which can occur if there is a sudden change in the temperature of the steam.
As a result, condensate pots are widely used in applications such as refineries, power plants, chemical and petrochemical, steel plants and other process industries as they provide an interface between the vapour phase and the condensed phase in the impulse lines. They also facilitate the minimisation of gauge line error caused by pressure differences in pairs of impulse lines.
Parker’s condensate pots are suitable for use either on vertical or horizontal lines, between the primary (Flow Meter) and the secondary (transmitter/gauge) to act as a barrier to the line fluid, allowing direct sensing of the flow conditions.
The correct installation of condensate pots, however is really important to ensure long service life and maximum efficiency.
Make sure you evaluate the number of connections required on the condensate pot before ordering (for example, inlets, outlets, fill port, drain port, gas vent port.) This ensures that the Condensate pot meets your specific application requirements.
Carefully define the condensate pot volume in litres, system pressure and temperature requirements. This is important as the size of the pot needs to relate to volume of steam passing through the steam pipeline.
It may be necessary to trace heat and insulate all impulse lines. This ensures that the vapour phase is maintained in the tube lines between the pipeline and the condensate pot. It may also be required to prevent freezing in the liquid lines between the condensate pot and the transmitter.
Consider adding an anti-freeze media, such a glycol, to the water lines. This may be essential in climates where below freezing temperatures are reached.
Keep vapour impulse lines as short as practicably possible. This ensures that the steam can remain in this state and requires minimal or no heating.
Ensure both condensate pots are mounted at the same level, minimising possible error that could arise due to unequal head of fluid in the connecting pressure lines. This should take into account both vertical and horizontal steam pipelines. The higher connection point should be the reference.
The differential pressure measuring device (DP) should be mounted below both the condensate pots and the steam pipe line.
It is recommended that both impulse lines from the condensate pot to the DP include the facility for ‘blow down’. Blowing down these lines periodically prevents the collection of debris, which could impact on measurement accuracy.
Ensure both the high pressure (HP) and low pressure (LP) impulse lines are the same length, which should eliminate pressure head errors. The theory of operation for condensate pots is that between the process taping and the pot is steam vapour. Between the pot and the differential pressure transmitter is water (liquid) thus eliminating any measurement errors due a liquid / vapour mix at the measurement device.
It is advisable to select condensate pots as part of a complete Parker instrumentation solution. We can supply all associated valves, manifolds, tubing and fittings alongside condensate pots, ensuring that all components work together and providing added reassurance about accuracy and safety. This also includes providing tubeline heating and insulation to ensure performance is maximised.
Parker condensate pot pressure ratings are for temperatures up to 100°C. We can also supply condensate pots to meet other pressures and temperatures. The most commonly used materials to manufacture condensate pots are steel, 316, 304, 6MO stainless steel and monel.”
For more details visit our website or view our condensate pot brochure.
Article contributed by Graham Johnson, Small Bore Product Marketing Manager - EMEA, Instrumentation Products Division Europe.
Reducing Lost and Unaccounted Natural Gas
Smarter Instrument Mounting Using Close-Coupling Techniques
Condensate Pot Brochure
Traditional coal ash sampling and analysis using a laboratory facility can take a few hours if there is an on site lab or days if the samples are sent away for analysis. Using the Parker Bretby Gammatech portable Ash Probe, the results are available in a few minutes by probing the coal pile with no special training required by the operator. All the data is collected during the shift and can be downloaded onto a memory stick or direct USB cable to a PC in CSV format for analysis and reporting. The unit comes with the Parker Bretby Gammatech utility software for ease of download. This white paper describes the journey the Parker team made in producing the new AshGraffix controller for the Ash Probe.
Download white paper as pdf.
During the latter part of 2012, we were advised by our supplier that the micro processor used in the Ash Probe system was being made obsolete; this gave us two choices:
1. Incorporate the new processor and modify the software for the existing display unit.
2. Develop a new design display unit based on our customers feedback using the latest processor.
Fig 1. Old QWERTY keyboard display unit with LCD display in English only.
To support sales of the Ash Probe while we developed the completely new unit, we chose to write the new software code for the existing display unit as the old processors were getting harder to obtain; this was essential so we did not leave customers waiting for the upgraded version of the display unit and gave us the opportunity to upgrade older units coming back for repair.
Our customers gave us some important clues as to what features they would find useful in a new unit:
During 2014 we set out to design the new product and software called AshGraffix with the customer needs in mind. The project time frame was 12 months from concept so we would be able to demonstrate the first unit at mining shows in 2015. The design for hardware, electronics and software was all done in house by the Parker team. Support from our local suppliers was critical as we went through several iterations of the printed circuit board design as this was the first time we had used surface mount components and touch screens. Finding low power components was key to the end result as the unit needed to work a full shift in some very harsh conditions from the heat and humidity of India and Vietnam to the low temperatures and dry conditions in Mongolia and Siberia.
Neil Jenkinson, our mechanical Engineer, selected an aluminium extrusion for the outer case that was rugged and could hold the printed circuit board and touchscreen. He found a superb membrane protector product that would sit on top of the touchscreen preventing scratching and potential failure if sharp items hit the screen by accident or in duality use, e.g a pen tip to tap the screen. The industrial cable connectors were retained as they had given good service over 20 years and readily available for after market sales. Different types of of battery packs were tested for durability and full function duration with industry standard Metal Halide rechargeable cells coupled with an intelligent charger selected as the best all round option for the AshGraffix.
As Human Machine Interfaces (HMI) have become more prevalent in the industrial world and availability for colour touchscreens has increased, we had a good choice of suppliers knocking on our door to show us their ranges. In the end a choice was made and the quality has remained high during the last two years of sales.
The multi-layered printed circuit board was the most difficult item to develop as we wanted all the electronic components and connections to the outside world on a single board only slightly larger than the touchscreen. This task did not phase Chris Knight, our electronics engineer, who put in many hours working on the pcb design software to get the SMT components and tracks right on the multi layered design before it went out to prototype manufacture. The end result was a triumph for the design team.
Fig 2. New AshGraffix multi-layered single printed circuit board with new processor and using many surface mount components (SMT).
The next task that faced Kevin Corcoran, our intrepid software engineer, was to incorporate all our ideas into code. After many discussions and updates during 2014 (usually accompanied with tea and some form of cake - this was before the Great British Bake Off was aired to the nation, as we found this was the best way to inspire creativity), we designed the home screen, menus and navigation through the system with the question to the operator:
What do you want to do today?
The concept was to give the operator access to commence ash sampling with two taps from power up screen and standard icons used for configuration and saving files to the unit itself or to USB output.
Fig 3. Ash Probe and AshGraffix complete system.
During the first half of 2015 we were happy with the final design; software bugs had been eliminated and some test users had put the unit through its paces; only then did we go to the mining shows and offer the unit to the market.
Gary Wain is Product Manager, Parker Hannifin Manufacturing Ltd, Bretby Gammatech, Instrumentation Products Division, Europe
Handling Data in Coal Quality Monitoring
Ash Probe and AshGraffix Installation Guide and Product Overview
Innovations in the design of primary isolation valves and manifolds for mounting pressure instrumentation can deliver enormous pressure control advantages to both instrument and piping engineers, ranging from significantly enhanced measurement accuracy, to simpler installation and reduced maintenance. Parker Hannifin has created a comprehensive range of instrument manifold mounting solutions for the main types of pressure instrumentation, employing close-coupling techniques which eliminate impulse lines and tube fittings to improve overall instrument performance and reliability.
There is no formal definition for close-coupling, but it has come to mean any instrument mounting system that enables a user to connect an instrument directly on to the process line, and primary flow control isolation valve. The overriding objective of this is to optimise the accuracy of measurement, by eliminating the long runs of tubing, tube fittings and bends and joints between process pipe and instrument that can cause pressure drops, and gauge/ impulse line errors.
Transmitter ‘hook-ups’ are often configured individually for each application, and can be large, heavy and difficult to install. By replacing such arrangements with purpose-designed close-coupled manifold/mounting solutions, users are able to optimise accuracy and reap a whole range of additional benefits such as...
‘Hook-ups’ for pressure transmitters often involve the custom configuration of complex arrangements of tubing, with multiple connections and valves. Measurement errors can be introduced as a result of long length impulse lines. These errors are frequently compounded by the use of different tube, fitting and valve components whose diameters may vary throughout an instrument installation.
Inaccuracies can distort the pressure impulse signal, causing errors of up to 15% (on flow measurements).
This traditional solution uses two sets of valve assemblies to create the double block and bleed valves, which are connected with impulse lines and connectors to the instrument manifold. It involves numerous discrete components, with all the associated costs and assembly time, and introduces bends that cause attenuation and turbulence that can affect measurement accuracy. If not carefully specified, other measurement accuracy problems can arise from differences in bore diameters of the various components, and unequal lengths of tubing.
View the Parker Close-Coupled Instrument Mounting System here.
Jim Breeze is Product Manager, Instrumentation Connections and Process Valves, Parker Hannifin, Instrumentation Products Division, Europe.
Brochure - CCIMS - Close Coupled Instrument Mounting Solutions
Manifold Connector Technology – Why Settle for Second-best?
Equipment Winterization Techniques
Choosing the Right Connector, Tubing and Accessories for Your Application - Part 1
There are many different industries that work with pressures over 10,000 psi, ranging from the oil and gas industry to laboratories and waterjet applications. With such high pressures and often elevated temperatures involved, safety is critical and choosing robust, tested and certified tubing and cone and thread fittings is essential. In fact, engineers and specifiers should always start by identifying compatible tubing and cone and thread fittings that can withstand these severe conditions. Taking this approach not only ensures the safety and reliability of the process but ensures that buyers have a clear specification that enables like-for-like comparison.
Parker Autoclave Engineers
When our company was established some 70 years ago, one of our major markets was laboratories. Today our pressure vessels can be found in laboratories all over the world and are renowned for their ability to withstand extremely high pressures and temperatures. The parameters we work within are between -423oF to 1200oF and full vacuum to 150,000 psi using over 40 different metals to-date.
Over the past seven decades, Parker Autoclave Engineers technology has been used in an extensive range of applications from providing tubing and cone and thread fittings for fueling rockets for the space industry to supplying the same for use on oil & gas wells in the deepest oceans.
Over the years, new markets have emerged that Parker Autoclave Engineers has been able to service, for example, the plastics industry has grown significantly in the last 30 years manufacturing producing LDPE (low density polythene) plastic being produced by the petrochemical industry to make food wrap, grocery and refuse bags. The raw LDPE plastic is made at very high pressures which we help to control.
The waterjet industry is another growing market where our expertise in producing high pressure tubing and fittings is used. Waterjets are employed for a huge variety of applications today from cutting lettuce in a farmers field, to slicing cake, chicken, meat or fish, to cutting gaskets, carpet, marble and even steel up to 10” thick. Often the waterjet industry requires pressures of over 60,000 psi and our team at Parker Autoclave Engineers are continually developing new technologies that can address these ever more challenging requirements.
A closely related industry to waterjet is waterblast. This involves wide high pressure or rotating streams of water, which are supported by our tubing and fitting systems. Waterblast products are used in a variety of applications from removing paint from the hull of a ship and immediately ready for repainting, to cleaning rubber off aviation runways. And in even higher pressure applications it can be used to break up concrete on a highway, without damaging the rebar, ready for repair.
There are many good environmental reasons to use this technology, which has resulted in its ongoing growth and importance in the marine, aviation, construction, civil engineering and quarrying industries. New uses are continually being identified, opening it up for a number of other sectors.
In most cases, we supply directly to the OEMs (Original Equipment Manufacturers) who recognise the fact that we have extensive capabilities and offer high quality products, with more connection choices available than any other manufacturer globally. This has led to us becoming a market leader in all our key markets. As part of our service, we provide a consultative and technical supporting role for our customers, ensuring their staff are fully trained in the use of high and medium pressure tubing and cone and thread fittings when operating at high temperatures and high pressures for a wide variety of applications.
The variety of uses for high and medium pressure tubing and cone and thread fittings is just about endless and you will find Parker Autoclave Engineers components in an extensive range of applications globally, where safety and performance are essential. View the Parker Autoclave product range here.
Michael O’Keane – Product Marketing Manager for Parker Autoclave Engineers.
Choosing the Right Connector, Tubing and Accessories for Your Application - Part 1
NORSOK M650 Compliance – An Essential Prerequisite for the Offshore Industry
Medium Pressure Safety - All Tubing is Not Created Equal
For over forty years, Parker has the lead the development of the chemical hardening process ideal for ferrules designed to grip and seal stainless steel tubing. The process is called Suparcase. This article reviews the importance of metallurgy and how Parker has utilized Suparcase technology. The best compression tube fittings balance hardness, strength, and corrosion resistance. Parker's Suparcase ferrule-hardening process does not require the high temperatures and long duration of more-conventional case-hardening procedures that, in turn, lower stainless steel's corrosion resistance.
Stainless-steel compression tube fittings make it easy to install and maintain measurement and control instruments used in chemical processing, petrochemical plants, and many other industrial settings. They seal a broad range of aggressive fluids and chemicals, and resist internal and external corrosion. The fittings grip and seal by compressing the nose of a ferrule into the tubing OD. High-quality compression fittings hold internal pressure without leaks or failure until the tubing fractures. And users can repeatedly disassemble and reassemble them with no loss of sealing integrity.
Today, compression tube fittings are available from many fluid system technology suppliers, and they tend to look the same although they may vary slightly in design details and manufacturing processes - but looks are deceiving.
The ferrule, perhaps the most-critical component in compression tube fittings, appears rather simple. Yet it is highly engineered and, to function properly, requires considerable design, metallurgy, and production expertise. Not all products on the market meet these stringent requirements. For instance, the ferrule must precisely deform elastically and plastically during fitting assembly to properly grip and seal the tubing. Its front edge must be harder than the tubing to grip and seal through surface scratches and defects, but if the entire ferrule is too hard, it may not deform properly. Therefore, only the gripping edge of the ferrule is hardened while the rest has different, tightly controlled mechanical properties. Also, the hardening process must not compromise stainless steel's corrosion resistance. And finally, production processes must consistently turn out defect-free ferrules that hold tight tolerances and maintain metallurgical specifications.
This article focuses on single-ferrule compression fittings, but many of the principles also apply to two-ferrule compression fittings. Ferrules were originally machined from cold-drawn stainless-steel bar stock. Cold drawing strain hardens the metal and imparts mechanical strength throughout the ferrule. But the ferrule's front edge was often still not hard enough to seal against tube surface defects such as scratches, weld seams, ovality, and hardness
One solution was to plate ferrules with a soft metal (such as silver) for a better seal when dealing with high-pressure gas. This improved resistance to impulse pressures, temperature swings, and vibration. Many ultra high vacuum and high-pressure seals deform hard edges into soft metal gaskets. Deforming the soft component with a hard one provides intimate metal-to-metal contact over the contact surfaces and overcomes surface irregularities. (A good source of detailed information is Industrial Sealing Technology, H. Hugo Buchter, John Wiley and Sons, 1979.) Manufacturers applied this concept to tube fittings by case hardening ferrules, which substantially increases surface hardness and lets them shear through surface defects and compensate for tubing variations.
Conventional gas nitriding case hardens the inner surface to a depth of approximately 0.004 in. During assembly, the ferrule front edge shears into the tube. If disassembled, the ferrule remains tightly locked to the tubing, allowing remakes with consistent sealing integrity. The fitting handles internal pressures, impulse pressures, temperature changes, and vibrations until the tubing fractures or fails in fatigue. However, gas nitriding (as well as carburization and carbonitriding) substantially lowers stainless steel's corrosion resistance. Process refinements let manufacturers harden only a band approximately 0.050 in. from the ferrule nose — sometimes termed a "limited nitrided" ferrule. This reduces the likelihood of corrosion, as the nitrided band is buried in the tubing surface. But it still poses a potential corrosion problem if, due to improper make up or surface defects, chemicals contact the band. Also, uninstalled fittings stored in corrosive environments, such as salt air, sometimes rust on the nitrided band.
Conventional nitriding and carburizing require high temperatures for the hardening constituents, nitrogen and carbon, to penetrate the passive oxide layer that makes stainless steel corrosion resistant. The high temperatures permit chromium, an anticorrosion alloying element, to diffuse through the metal and form chemically stable nitrides and carbides. These compounds give the surface layer most of its hardness, but in this chemically combined form chromium no longer resists corrosion, and the nitrided or carburized layer corrodes in many environments, including seawater and even moist air.
In addition, nitriding and carburizing can "sensitize" austenitic stainless steel exposed to high temperatures for an extended time. Carbon, which has low solubility in stainless steel, precipitates as chromium carbides in the grain boundaries, depleting regions adjacent to the grain boundaries of the chromium necessary for corrosion resistance. This process is known as sensitization.
A new hardening process that was introduced by Parker Hannifin in the late 1980s does not reduce the corrosion resistance of stainless steel. More recently, some other fittings manufacturers have introduced ferrule-hardening processes with similar advantages.
These new processes do not require the high temperatures and long durations that permit chromium diffusion. This keeps chromium in solid solution as a corrosion-resistant alloying element. The hardened layer is continuous, free of defects and voids, as the process tends to fill surface inclusions and substantially reduce end-grain corrosion effects.
The new processes also do not affect the bulk metal. There is no sensitization or change in mechanical strength beneath the hardened layer. The ductile layer deforms with the ferrule during assembly without cracking or spalling.
In these processes, carbon supersaturates the hardened layer. Carbon atoms occupy interstitial sites in austenitic stainless steel's face-centered, cubic crystal lattice, strengthening the hardened layer. The hard crystal-lattice structure would like to expand to accommodate the carbon atoms, but is constrained by the unhardened substrate. As a consequence, high compressive stress further enhances hardness. Compressive stress has the added benefits of substantially increasing a ferrule's fatigue and stress-corrosion resistance.
In general terms, the process removes the passive oxide layer from the steel surface, letting carbon atoms diffuse directly into the metal lattice without traversing the passive layer barrier. The carbon atoms diffuse at lower temperatures than other alloying elements, thus avoiding problems caused by formation of carbides and nitrides.
A balance of metallurgical properties is critical to a ferrule's mechanical action during fitting assembly. For instance, the front edge of Parker Hannifin's CPI single-ferrule fitting shears down into the tubing, while the body arcs and clasps the tubing at the trailing edge. The front-edge grip prevents blow-out under pressure.
The ferrule must also work equally well across the tubing diameter tolerance range, typically ±0.005 in., and handle surface defects such as scratches that may be several thousandths of an inch deep. The arcing action turns the ferrule into a spring of sorts, letting it maintain tension against the tubing and the proper seat angle to seal despite vibration, mechanical shock, and thermal expansion. The back of the ferrule also loosely grips the tubing, damping vibrations that would otherwise transmit to the sealing interface.
Mechanical properties such as yield strength and hardness must be precisely controlled to effect this action. An extremely hard ferrule will be too stiff during assembly and will not bow and properly grip the tubing. But if it is too soft, the underlying material will not support the case-hardened surface. The result is an eggshell effect: the gripping front edge collapses during assembly and cannot hold the tubing under pressure. It also reduces the arcing spring effect.
Cold working is the only way to increase hardness and strength of Type 316 austenitic stainless steel after annealing. However, work-hardening rates change with the steel's composition, and constituent percentages can vary within an allowable range. Cold working can also reduce corrosion resistance. Thus, manufacturers must precisely control composition to maintain consistent mechanical properties and retain the austenitic structure, and case hardening must not uncontrollably change these.
Stainless-steel parts that rub together under high pressure have a strong tendency to cold weld and seize. And to form high-integrity, leak-free tubing connections, ferrules must only slide forward during assembly and not rotate with the nut. To prevent seizing and ensure only linear ferrule movement, engineers must precisely control surface conditions and lubrication at the nut/ferrule and nut/body interfaces.
All mating surfaces must be smooth and free of defects, which exacerbate seizing. A bonded molybdenum-disulfide coating is the recommended lubricant for many compression fittings. Solid molybdenum disulfide readily adheres to surfaces, is noted for its lubrication and anti-seizing properties, and the solid does not squeeze out like liquid or soft, waxy lubricants under extreme pressure. The result is low assembly torque and consistent performance, even with repeated remakes.
Article contributed by Jim Breeze, product manager, Instrumentation Connections and Process Valves, Instrumentation Products Division Europe.
Counting the Cost of Cutting Corners in the Oil and Gas Industry
Mixing Materials in Corrosive Environments
In industrial applications where high pressures (over 6,000 psi) are used, safety is of paramount importance. Even well below these pressures, precautions are needed to ensure a safe working environment. Tubing from different manufacturers may look the same on first glance – and, indeed, it may be certified to meet minimum requirements, but is it going to perform correctly, do the job and ultimately, not risk the safety of plant and personnel?
Because of the risks with connection leaks, there is a real need to make sure it is has undergone all necessary tests, is specified alongside appropriate fittings and will, therefore, optimise safety and performance.
To reassure customers that our tubing is certified over and above current requirements, we introduced our own AES 222 (Autoclave Engineers Specification). This covers an extensive range of additional requirements for which the tubing is tested, including bore finishes, milled sections, and non-destructive testing. The bore examination that we carry out, for example, involves the tubing being cut and then sectioned to allow microscopic examination of the bore finish.
View the Parker Autoclave Engineers' Fitting and Tubing Guide here.
Another important consideration with tubing is its ovality and wall thickness. If this is not rigorously tested, then uncertified, untested tubing will have different dimensions. This could lead to leakage and unnecessary safety risks.
It is therefore important to ensure that outside dimensions are specified, to ensure a correct fit of tubing. If the manufacturer operates to tight tolerances on tubing wall thickness and run-out it will ensure a more uniform wall thickness. This provides an even wall at the sealing point and leads to higher calculated design pressures.
These rigorous tests ensure that when the tubing is installed for the first time, risks are much reduced. Leakage is the biggest worry with any tubing system and our tests ensure that risks are kept to a minimum
What is sometimes overlooked is the fact that warranties for fittings are often not valid if the associated tubing is not specified from the same manufacturer. The reason for this is that another manufacturer’s tubing may compromise the safety of the fitting, as Parker Autoclave Engineers’ tubing and fittings are designed to work as a complete system. Our AES specifies and controls both material and critical dimensions and tolerances to meet the conditions for which they are designed.
So it can clearly be seen why safety should be a major concern when specifying tubing for industrial, high-pressure applications. By selecting tubing that has been rigorously tested, there is much less risk of tube leakage or failure, which compromises the safety of the whole system.
View Parker Instrumentation Products Division products here.
Franck Grignola is product manager, Autoclave Engineers, Parker Hannifin manufacturing, Instrumentation Products Division Europe.
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