Snow and Ice loading is an environmental load and must be considered in pipe stress analysis where the climatic condition specifies the possibility of snow or ice formation. Piping projects in various cold geographical locations like Canada, Russia, the USA, Europe, etc where winter temperature falls below a certain limit that causes snow or ice formation must be designed considering the impact of snow loading. Both snow and ice loads are considered as live loads on piping.
Codes and standards stipulate that the system must be designed against snow and ice loading. They provide a lot of guidance for snow loading calculation and application for system design to safeguard them from failure for building structures. But for non-building structures like piping systems, the calculations for snow loading are too limited. In this article, we will try to explore the philosophy of snow loading in piping and pipeline systems and its application in the pipe stress analysis process.
What is Snow and Ice Loading?
Snow and ice loading is a type of sustained loading. The possibility of snow loading will be mentioned in the project environment conditions of the region. Ice and snow loading for piping systems is basically additional downward-acting forces exerted by the accumulated snow and ice. The increase in support load and system stress due to the weight of the accumulated snow and ice must be considered in the structural design.
Snow and ice loading is only significant for outdoor piping installations and is treated similar to other deadweight loads.
In general, snow and ice loading is considered in pipe stress analysis as a uniform load placed over the exterior part of the pipe and fittings. The entire system can fail if the snow loads exceed the allowable of the piping systems. Snow loads are being applied to all pipe elements above ground, and fittings are in a vertical direction downward. The loads depend on the slope angle of each element. The snow loads are given to the elements by using the snow factor.
Though both snow and ice are made up of water there is a slight difference. Snow falls as precipitation of frozen water whereas ice is simply frozen water. In general snow in the piping system is usual for climatic regions. Whereas ice loading generally refers to ice storm deposits over pipes that are decided based on region-specific weather reports.
Snow Load Calculation Philosophy
Snow load calculation philosophy is based on the consideration that the snow accumulated on top of the piping system will take the shape of an equilateral triangle with its base equalling the pipe outside diameter.
The common equation used for calculating the snow loads is as follows:
Ws=(1/2)*Do*So
Here
Ws=design snow load to be added to other distributed loads acting on pipe, lb/ft
Do=outside diameter of the pipe (for bare pipe) or insulation (for pipe with insulation), in
So=Snow Factor that considers the probable snow loading for the region where the piping system is installed, lb/ft2
Ice Loading Calculation Philosophy
Ice loading is also applied in the system as uniform loading and calculated using the following formula as specified in the piping handbook:
Wice=1.36*t*(Do+t)
Here,
Wice=unit loading on the pipe, lb/ft
Do=outside diameter of the pipe (for bare pipe) or insulation (for pipe with insulation), in
t=ice covering thickness, in
Application of Snow Load in Caesar II
Once the uniform load for snow or ice loading is known or calculated, the same is applied in Caesar II and proper load cases are created to account for it. The steps follow are provided below:
Step 1: Snow load is usually not considered along with wind or seismic load. So, to add snow load in the piping system, simply click on uniform load and add the calculated uniform load value (Note this will vary depending on pipe size) in the input screen as shown below:
Fig. 1: Input screen of Caesar II for inputting Snow load
In the above example, the calculated snow load per unit length is 0.346 in N/mm for the 18-inch pipe size. The negative sign for the force will act downwards.
Step 2: Create load cases to account for the above input value as shown in Fig. 2 below:
Fig. 2: Load cases for Snow loading in Caesar II
Step 3: Now you can run the analysis and check the output results. Support loads considering snow loads must be transferred to the Civil team for structural consideration.
Ice loading on the piping system can be applied in a similar fashion if the ice loading is because of the ice storm. However, if the ice generation is because of the cryogenic fluid inside the pipe and moisture condensation, then the same can be considered similar to pipe insulation. Simply, the thickness of ice generation needs to be calculated and that thickness along with ice density can be added as insulation. This means you are roughly considering the pipe is insulated with ice.
Cryogenic Air Separation Process: A brief introduction
There are many applications of nitrogen, oxygen, and argon in Industry. Like, Gaseous nitrogen (GAN) is used as a raw material or inert gas, while liquid nitrogen (LIN) is used for refrigeration. Oxygen has various uses in steelmaking and other metals refining and fabrication processes, in chemicals, pharmaceuticals, petroleum processing, glass, and ceramic manufacture, and pulp and paper manufacture. It is also used for environmental protection in municipal and industrial effluent treatment plants and facilities.
As is the case with nitrogen, the noble gas argon is also used for its low reactivity, it can provide higher inertness than nitrogen as well as lower thermal conductivity and improved solubility in water and oils. Also, Argon is more common and cost-effective than the noble gases helium, neon, krypton, and xenon. Nitrogen, oxygen, and argon are almost exclusively separated and recovered from atmospheric air.
Components of Air
Air from the atmosphere is formed from a mix of several gases. The major components are oxygen, nitrogen, and argon, with other gases present in smaller quantities. Water vapor is additionally present in the feed air. The water content of air varies with local ambient conditions considerably based on relative humidity.
The following table (Table – 1) summarised the component of air:
Elements
Symbol
Composition in Volume
Main Elements
Oxygen
O2
20.90%
Nitrogen
N2
78.10%
Argon
Ar
0.93%
Rare Gases
Helium
He
5.24 ppm
Neon
Ne
18.18 ppm
Krypton
Kr
1.139 ppm
Xenon
Xe
0.086 ppm
Hydrogen
H2
0.5 ppm
Impurities
Steam
H2O
Variable
Carbon Dioxide
CO2
300 to 700 ppm
Hydrocarbons
CH4
3 to 5 ppm
Hydrocarbons
C2+
<0.5 ppm
Table 1: Component of Air
Dominant Cryogenic Air Separation Processes
Three separation methods are predominant for separating constituent gases from the air. They are
Membrane separation,
Pressure swing adsorption, and
Low-temperature rectification, or cryogenic distillation process.
Membrane separation
In this separation process, equipment pumps air into the membrane module and the targeted gases like oxygen and nitrogen are separated based on differences in diffusivity and solubility. For example, oxygen can be separated from the ambient air and collected at the upstream side, and nitrogen at the downstream side.
Pressure swing adsorption
The principle of Pressure Swing Adsorption (PSA) is the amount of adsorbate deposited on the adsorbent increases with increasing pressure. Adsorption increase with increasing pressure and desorption occurs at low pressure. The technique is applied for the adsorptive recovery of O2 and N2 from the air.
Low-temperature rectification i.e. cryogenic air separation process, or cryogenic distillation process (Linde Double Column)
Here, a double column is used for the cryogenic distillation of air. In air separation plants is a combination of two columns used. It was the idea of Dr. Carl von Linde, to build together two columns, as shown in Fig -1.
Fig. 1: Linde Double Column Air Separation Process
The lower part is a “half” single column with a condenser at the top and an air feed at the bottom whereas the upper part is a single column without a condenser but with a reboiler.
The condenser in the lower column acts as the reboiler for the upper column, those two are thermodynamically attached. Air normally at a temperature that is just above the dew point is fed to the bottom of the lower column. Vapor raises the column to the condenser and forms reflux. “Rich liquid” contains approx. 35-40 % oxygen, is taken out as the bottom product and nitrogen has been taken out as the top product. The bottom product, the rich liquid is then fed to the center part of the upper column for further separation. In this upper column, there is no condenser, but reflux is taken from the pure top product of the lower column.
There is a reboiler at the bottom of the upper column, which is heated from the condensing of nitrogen in the lower column. The upper column can have pure oxygen at the bottom, as oxygen has a higher boiling point than nitrogen.
Comparison of Membrane Separation, Pressure Swing Adsorption, and Cryogenic Distillation Process (Cryogenic rectification)
The three separation techniques have different process properties, and there is a requirement for different ranges of investment and operating costs. The table below characterizes these segments by their production capacity and gas purity. Of course, the numbers given in the table therein are no sharp limits but indicate reasonable application ranges.
Gas
Capacity (mN3h-1)
Typical purities
Preferred Separation Method
Load range
N2
1-1000
<99.5% (including argon)
Membrane
30-100%
N2
5-5000
<99.99% (including argon)
Pressure Swing Adsorption
30-100%
N2
200-400000
any with residual concentrations down to ppb range
Cryogenic rectification
60-100%
O2
100-5000
<95%
Vacuum Pressure Swing Adsorption
30-100%
O2
1000-150000
any with residual concentrations down to ppb range. (O2 content mostly>95%)
Cryogenic rectification
60-100%
Ar
–
–
Cryogenic rectification
–
Table 2: Application range of membrane separation, pressure swing adsorption, and cryogenic rectification process
Conclusions:
Oxygen is not recovered with membranes.
Cryogenic air separation is applied whenever high purity, large quantities, liquid products, or argon is required.
Membrane and adsorption plants have a high load range in production and can be started and powered up to full production within a few minutes. Especially when the gas consumption fluctuates very high, the flexibility of these types of plants reduces the overcapacity, which has to be provided by design and allows to save energy of manufacturer by fast load matching. A cryogenic plant needs about 2-3 hours to start from the cold condition until the beginning of production of oxygen and nitrogen when in the cold start but from the hot start it takes almost 24 hrs. Membrane and adsorption types of plants are suitable to cover the demands of small and medium-sized gas consumers on-site. This on-site supply competes with the delivery of liquid N2, O2, and Ar by trucks in merchant sites.
Comparison of Energy Consumption in different air separation processes
The operating costs of the separation processes are mainly determined by their energy consumption. Tables -3 and -4 show the specific energy demand for the production of N2 and O2 by the three separation methods. The figures are only guidelines. However, the actual values depend on the detailed process design. Cryogenic air separation requires the smallest work, which, however, is still significantly larger than the minimal separation work needed for a completely reversible process.
O2 content in nitrogen
2%
0.5%
0.1%
1 ppm
Membrane
0.43
0.65
Pressure Swing adsorption
0.26
0.34
0.45
Cryogenic rectification
0.15-0.25
Theoretical minimal separation work
0.08
Table 3: Energy Needed for the production of one standard cubic meter of nitrogen at 8 bar (kWh)
O2 purity
90%
93%
99.5%
Pressure Swing adsorption
0.36
0.39
0.45
Cryogenic rectification
0.32
0.35
Theoretical minimal separation work
0.07
Table 4: Energy Needed for the production of one standard cubic meter of unpressurized oxygen (kWh)
An Overview of Cryogenic Air Separation Plant
A cryogenic air separation unit (ASU) is a process plant in which air is separated into its component gases by distillation at low temperatures.
The plant comprises an assembly of equipment like distillation columns, heat exchangers, adsorbers, and supporting machinery for compression, expansion, and control of gases and liquids. The component gases are sold and distributed to customers for a wide variety of industrial, medical, and other specialist applications as per requirement. Air separation plants are constructed in different forms depending on what products are produced and the production capacity and purity requirements of the client. Moreover process equipment and machinery from different manufacturers are used as per requirement. However, the basic principles of construction and operating methods for all these different plants are nearly the same.
The design of a cryogenic air separation plant depends on the scale of operations and the nature of the products required from it. While basic principles are always the same, process cycles and flow for each plant can vary significantly based on the requirement.
Air separation plants operate on a range of different process cycles to meet specific customer requirements, in a range of plant capacities extending to the production of over 2,300 tonnes per day of oxygen, with co-production of nitrogen and argon, and sometimes krypton and xenon.
Hazards of Oxygen
Oxygen is a hazardous material in nature and the misoperation of an air separation plant can lead to large energy releases with hazards to personnel and equipment and it needs to be taken care of during detailed engineering of the plant. The operation must always be by specified safe practice guided by the operating procedure mentioned in the operating manual.
Disadvantage of Air Separation Plant: Release of Green House Gas
The air separation process is intrinsically clean and does not generate undesirable side products like the fossil fuel industry. However, because it is energy-intensive, for example, a plant making 2,000 tonnes per day of oxygen consumes around 30 megawatts (MW) of electricity. The major part of power consumption is consumed by the plant’s main machinery like the air feed and product compressors. It indirectly causes the release of a significant quantity of greenhouse gases and uses operating a plant most efficiently, both to minimize cost and reduce the impact on the environment.
Industrial gases are only transported over economically viable distances and since these distances are limited by transport costs and the physical properties of the gases, production facilities are located close to the markets they serve. For higher-value products (eg, argon, helium, specialty gases), it may be economically feasible to locate the plant some distance from the customer.
Location of Cryogenic Air Separation Plant
Typically, air separation sites are located close to large tonnage customers such as steelworks, chemical works, petrochemical plants, oil refineries, and smelters so that the gas may be supplied directly to the customer by pipeline.
Raw Materials for Cryogenic Air Separation Plants
The raw material for a cryogenic air separation plant is air from the atmosphere, called feed air on an air separation site. Most air separation plants produce these three gases (oxygen, nitrogen, and argon) in liquid form. Moreover, some plants produce oxygen and/or nitrogen in gas form for pipe delivery to the customer. Exceptionally some plants produce only gaseous nitrogen called Nitrogen generators.
Products of Cryogenic Air Separation Plant
Product names are LOX Liquid Oxygen, LIN Liquid Nitrogen, LAR Liquid Argon, GOX Gaseous Oxygen, and GAN Gaseous Nitrogen.
Design Consideration of Cryogenic Air Separatin Plant
When a new plant is to be constructed after capacity is finalized and the production capacity and purity determined, the most appropriate process which has the lowest energy consumption and purchase price is selected based on rigorous process cycle simulation. It can be seen that the process equipment and manufacturer can vary widely and it is optimized based on plant life selection, local regulation requirements, etc.
Other components other than nitrogen, argon, and oxygen are in the air:
Dust, Water vapor, Carbon dioxide, Hydrocarbons (eg methane, ethane, propane, and acetylene), Rare gases (helium, neon, krypton, and xenon), and Diverse air contaminants.
Requirements of Pre-Purification System
The Pre purification system is designed to remove water vapor, carbon dioxide, and other potentially unsafe impurities contained in the incoming process air. This is important for the safe operation of the plant as it ensures that the water and carbon dioxide does not enter the cryogenic portion of the plant where they could plug the main vaporizer exchange passages placed in the cryogenic distillation column. Plugged passages can lead to ‘dead-end boiling’ of liquid oxygen creating areas of localized high concentrations of impurities (e.g.; hydrocarbons) within the main vaporizer.
The Pre purification system effectively stops ozone, acetylene, and propylene. It also partially adsorbs propane and ethylene. All of these components are hazardous if found in the cryogenic portion of the plant and will eventually accumulate in the liquid oxygen main vaporizer bath and increase the process risk of explosion in some plants. Pre purification system (PPU) is also known as the Air purification system (APU) and Front End Purification system (FEP).
Basic Principle of Cryogenic Distillation Process
Table 5: Boiling points of component of Air
In the cryogenic process, the liquids are close to the boiling point and that heat is leaking in. Table -5 below gives a brief idea of the boiling point of components in the air. These boiling points are measured at atmospheric pressure. The differences in boiling points influence the separation of liquids by distillation.
Process overview of Cryogenic Air Separation Plant
Fig. 2: Process Overview of Cryogenic Air Separation Plant
The basic process for large-scale air separation has remained unchanged for decades but the orientation of equipment will change based on process requirements. In this process, the air is compressed, then purified by removing carbon dioxide and water vapor, after that dried and cleaned air is cooled to nearly its liquefaction temperature, and then separated by cryogenic distillation into oxygen, nitrogen, and argon products.
Steps of Cryogenic Air separation
Here are the steps of air gases separation by the cryogenic processes :
– COMPRESSION of air feed lines: it means « make the air enter » the separation unit by bringing it under pressure, and measuring out the flow required to assure the production aimed.
equipment: compressor
– PURIFICATION of air feed lines: to be treated in a cryogenic way, the air has to be purified mostly of water and carbon dioxide (plus some secondary impurities)
equipment: reversible exchangers (abandoned)
alumina + molecular sieve adsorbers: Pre-purification unit
– HEAT EXCHANGE: to permit a continuous functioning of the cryogenic part, the cold recovery of the products getting out is necessary to cool the air feed lines.
equipment: exchangers
– DISTILLATION of air feed lines: to separate it partially into its different components, that is to say, nitrogen, oxygen, and, should this happen, argon.
equipment: distillation columns
– COLD PRODUCTION: to balance the permanent cold losses due to the cold box conception itself and to the liquid productions (if necessary), and for the initial cooling down of the cold box (start).
The products can be provided under pressure. The following two processes are adopted for this:
– external compression: products compressors downstream the cold box.
– internal compression: pumping of the products in liquid form and vaporization in the main exchange line.
What is a Cold Box and Why is this required?
The cold equipment needs much insulation to get an acceptable cold loss. So columns, heat exchangers, and parts of the cold production equipment like a turbine, and valves are built in a large tower-like box, the so-called cold box. The cold box is insulated by perlite.
The unique feature of air separation is the great interdependency of the different flows because it is a cryogenic process, in which external media such as cooling water and steam cannot be used. The different products or internal flows are used for boiling and condensing in the columns, like reflux, cooling the incoming air, and for sub-cooling the liquid products based on the process cycle.
Cold nitrogen gas coming out from the cryogenic distillation column is used in the recycling for cold production for liquefaction etc.
A changed gas flow in a stable plant gives a different pressure, and a change of pressure can have a considerable effect on the other flows as their boiling points change with pressure. Also changed temperatures, for example, in a condenser due to a change in pressure will change the rate of heat exchange and therefore change the gas flow in the column which will alter the purity.
Process Description of Cryogenic Air Separation Unit
The clean, compressed air after pre purification unit enters the cold box and is cooled down almost to its liquefaction temperature, about -170 deg C by out-flowing cold product streams in the main heat exchanger. The air then enters the high–pressure column (hereinafter referred to as the “HP column”) where it is separated by distillation into overhead nitrogen streams and a bottom-rich liquid stream containing about 37% oxygen.
Fig. 3: Cryogenic Air Separation process Description
Gaseous nitrogen from the HP column flows into the main vaporizer where it contacts low–pressure liquid oxygen in the sump of the Low-Pressure column (hereinafter referred to as the “LP column”). The liquid oxygen boils (at about -179 deg C ) against condensing high-pressure nitrogen providing reflux in the HP column. The final separation occurs in the LP column, which operates at approximately 1.4 bar a.
Reflux and feed streams are provided by liquid nitrogen and rich liquid from the HP column. These liquids are subcooled against gaseous nitrogen in the liquid sub-cooler before being expanded into the LP column.
The boiling oxygen in the LP column provides the energy necessary to strip nitrogen and argon from the rich liquid stream.
Gaseous oxygen product is taken from the bottom of the LP column and pure nitrogen product from the top. An intermediate waste nitrogen stream, used for reactivation of the adsorber beds, is withdrawn near the top of the LP column. It is typically composed of less than 2% oxygen and contains virtually all the argon that exits the cold box.
Use of LOX Filter
The hydrocarbons not removed from the air by the PPU unit accumulate in the liquid oxygen bath around the main vaporizer. To reduce this hazard, an adsorbent-filled liquid oxygen filter (hereinafter referred to as “LOX filter”) may be provided. Two filters in parallel are installed, with one in the adsorption phase and the other in regeneration.
Function of Turbine in Cryogenic Air Separation
To maintain the proper operating temperatures in the process and to offset the heat leak into the cold box, a cold production unit is required. Normally for a low–pressure gas plant, an expansion turbine is provided as a cold production unit. This machine takes partially warmed nitrogen from the HP column, equal to about 10% of the airflow to the cold box, and through expansion cools it to join the outgoing products. A small flow of high-pressure nitrogen for utility purposes may be further warmed along with the other products in the main heat exchanger. In the more recently designed plants, the turbine operates on a small, clean airflow that has been boosted in pressure by its compressor brake (expander–booster).
Purpose of Liquefier
In the case of large LOX (and LIN) production, a separate liquefier may exist with a permanent liquid assist from the liquefier (for storage, when the liquefier is stopped).
What is Hot Bolting? Its Procedure, Hazards, Best Practices, and Advantages
Hot bolting is defined as the process of removing and replacing or re-tightening bolts in the flange connection assembly when a pipe or equipment is in operation and full of liquid or gas. So, from the definition itself, you can understand that hot bolting is regarded as a high-risk activity.
In normal engineering practice, working on live pipes is prohibited (except hot tapping). Any repair or replacement is done in shut-down condition after detaching the part from the live stream. Working on a live system is always hazardous and therefore, hot bolting must be performed after a thorough risk assessment and job safety analysis. Utmost caution should be exercised and any benefit that is received from hot bolting activity must be weighed against the risks associated with it.
Hot bolting is basically a part of preventive maintenance activity. A specified sequence is followed to remove and replace nuts/studs during the hot bolting operation.
Reason for using Hot Bolting
There are various reasons for performing hot bolting in piping and equipment flanges. Some of these are:
Replacing Damaged or Corroded Bolts: Sometimes during an inspection, if corroded or damaged bolts are found and there is no planning for an immediate shutdown, hot bolting is suggested to replace the damaged ones.
Upgrading Material Specification or Bolt Grades.
Minimizing the time required during plant shutdown.
Advantages of Hot Bolting
There are several benefits of hot bolting like
Avoidance of unplanned shutdown.
Increased safety by replacing the damaged bolt.
Improved joint integrity as the weak link is removed.
Shutdown time reduction.
Increased efficiency.
Reduction of the number of ‘containment breaks’.
No downtime means production is not hampered.
Considerations prior to Hot Bolting Procedure
As working on live lines are hazardous, a number of factors must be considered prior to hot bolting. Some of these factors are:
The work must follow all the guidelines as mentioned in the operator’s working procedures.
The operating pressures and temperatures of the system shall be checked and decided if suitable for hot bolting. Some companies follow the operating pressure to be less than 75% of the MAWP as allowed under ANSI B16.5 at the operating temperature as a guideline for hot bolting.
There should be a minimum of eight bolts in the flange joints that are considered for hot bolting operation.
Prior to work commencement, the site supervisor shall review the maintenance history of the joint. Any important relevant history must be checked.
The joint under the purview must be visually checked. If the joint show significant corrosion or necking signs, hot bolting shall not be performed.
Hot bolting shall be performed only for those flanges for which records exist.
The consequences of joint leakage during hot bolting shall be carefully studied and considered. All necessary precautions due to possible toxicity, flammability, and temperature of escaping fluids shall be kept in place during an emergency situation.
Pipework near the zone where hot bolting will be performed must be reviewed thoroughly. In case, the pipework shows any vibration around the concerned flange joint, then hot bolting should not be considered.
The design specifications of the flanged joint, bolting, and gasket specifications need to be reviewed.
Hot Bolting Procedure
Hot bolting, in general, is performed following a series of steps. These are:
Permits and necessary approvals for hot bolting need to be taken from safety professionals.
All the necessary personnel, materials, and equipment are arranged at the worksite.
Inspect each bolt for tightness. Any abnormal conditions shall be intimated to the responsible authority.
Follow the operator’s correct sequence and carry out hot bolting on one bolt at a time. The usual sequence is:
Remove–>Examine–>Clean–>Lubricate each bolt as required–>check if the nuts can be reused–>Tighten the bolt
Any damaged/questionable bolts or nuts shall be disposed of and replaced with new items as per the correct piping specification. Clean all exposed flange surfaces.
Once all bolts are replaced, inspect to ensure proper tightness.
Best Practices for Hot Bolting
Even though hot bolting is hazardous, it is one of the cheapest options. So, the hot bolting is usually performed under controlled conditions. The following practices will reduce the chances of potential problems:
The technicians must be thoroughly trained in all the processes and possible consequences.
A full examination and evaluation of the piping network where hot bolting is required to be performed.
Visual and non-visual tests by multiple people to ensure no error goes unnoticed.
Inspection, service history, and analysis are based on logical and practical possibilities.
A ready escape plan in case of a fault.
Properly developed guidelines that have already been followed in other organizations or locations without fault.
So, using the above best practices during hot bolting, a majority of the problems can easily be avoided. So, even though there are safety concerns during hot bolting, they must be minimized using safe, established procedures.
Standards for Hot Bolting
The ASME standard PCC-1 provides certain guidelines for hot bolting work.
What is a Flange Alignment Tool? Applications, Types, and Working of Flange Alignment Tools
Flange alignment tools are mechanical or hydraulic devices that are used to align or re-align flange joints during pipework construction, maintenance, commissioning, or shut-down activities. During initial bolting or after opening the bolting for maintenance and repair work, the flanges are, in general, misaligned. For proper fit-up of the flanges and smooth working, the flanges are required to be properly aligned. The flange alignment tools are very useful in such activities.
Various industries like chemical, petrochemical, pipeline, water, wastewater, refinery, oil and gas, power, food processing, etc use flange alignment tools to ensure that pipes and other fittings are perfectly aligned. Flange alignment tools are very cost-effective solutions for alignment and they make the alignment job easier.
Working of a Flange Alignment Tool
At the location of the greatest misalignment, the flange alignment tool is attached to the flange joint. The tool then pushes and pulls the flanges to bring them in the correct alignment. Depending on the sizes of the flanges, a range of flange alignment tools is available. The working steps of a typical flange alignment tool can be explained as follows:
Step 1: Determine the location of the greatest misalignment.
Step 2: Attach the Flange Alignment tool at the location of the greatest misalignment.
Step 3: Adjust and secure the tool to the pipe using the strap.
Step 4: Rotate the Screw handle until contact is made with the flange circumference.
Step 5: Continue to rotate the handle till the flanges are pushed and pulled and aligned
All the above-mentioned 5 steps can be represented graphically as shown in Fig. 1 below.
Fig. 1: Flange Alignment tool working steps
Types of Flange Alignment Tools
Depending on the working mechanism, there are two types of flange alignment tools that are used for industrial flange alignment purposes.
Mechanical Flange Alignment Tools and
Hydraulic Flange Alignment Tools
Mechanical flange alignment tools generate the pulling force by mechanical action whereas hydraulic flange alignment tools use the hydraulic action of a fluid to generate forces for alignment. The load-carrying capability of hydraulic flange alignment tools is usually more and they are more suited for very large-diameter piping and pipeline flanges. Mechanical flange alignment tools are preferred for small diameter lower pressure flange applications.
Applications of Flange Alignment Tools
The main purpose of flange alignment tools is to align both flanges for getting a smooth joint during fit-up. The main applications of flange alignment tools are:
The main characteristic features of a flange alignment tool include the following
Compact
Light-weight
Portable
Available in wide ranges
Precise operation
Suitable for both vertical and horizontal pipe flanges.
Flange Alignment Tool Set
A mechanical flange alignment toolset usually consists of the following:
One flange alignment tool,
One hand wrench (including 22mm socket),
Strap belt, and
One portable case
Whereas a hydraulic flange alignment toolset consists of the following:
One flange alignment tool,
One hydraulic hose (2m),
One hand pump (including pressure gauge and adapter),
Rachet Belt, and
One portable case
Specification of Flange Alignment Tools
The flange alignment tools are usually specified by their maximum reaction force. The main parameters to specify a typical flange alignment tool are as follows:
Capacity or Maximum Reaction Force
Minimum Bolt Size
Minimum Bolt Hole Diameter
Case Dimensions
Weight
Working Pressure
What is a Spiral Wound Gasket? Applications, Types, Construction, and Specifications of Spiral Wound Gaskets
A Spiral Wound Gasket is the most widely used common metallic gasket used in industrial applications involving a range of pressure and temperatures. They are popular in the oil and gas, chemical, petrochemical, power, and food industries and prevents leak through flange joints. The concept of spiral wound gasket was first developed by Flexitallic in the year 1912 to serve US refinery operations involving severe temperature and pressure fluctuations.
Spiral wound gaskets are used for
High-Temperature service applications.
High-pressure applications.
Corrosive fluids.
Flammable Fluids.
Hydrogen, etc.
Construction of Spiral Wound Gaskets
A spiral wound gasket is a semi-metallic gasket. It consists of a spirally wound v-shaped metallic with a non-metallic filler material. There are three elements that constitute a spiral wound gasket. They are:
Outer ring:
Also known as a guide ring or centering ring, the outer ring of a spiral wound gasket is usually made of carbon steel material. The main purpose of this element is to center the gasket while inserting it into a bolted flange joint.
Inner ring:
The inner ring is one of the most important parts of a spiral wound gasket as it prevents windings from buckling inside the pipe. In the situations of buckling of a gasket, parts of it get sucked into the pipe and eventually flow through the piping system to get caught/wrapped on something. Inner rings prevent this phenomenon and help in avoiding the problem.
Sealing element:
This is the element of the spiral wound gasket that creates a tight seal to prevent leaks. The sealing element encompasses both windings and filler material. In general, spiral wound gaskets use a flexible graphite filler material rated for high temperatures. Graphite as filler material also helps the gasket avoid flange distortion and joint misalignment. Another common filler material is PTFE (Polytetrafluoroethylene). However, PTFE is not suitable for use in high-temperature applications. The most widely used winding materials are Stainless Steel and Monel.
Refer to Fig. 1, which clearly shows these three elements of a spiral wound gasket.
Fig. 1: Spiral wound gasket identification
Markings on Spiral Wound Gasket
Spiral wound gaskets are identified using different markings on the gasket. Each marking provides brief information about the spiral wound gasket specification important during the gasket selection process.
Some of the necessary information that the markings on the spiral wound gasket provide are:
Design Standard or Code: The code based on which the spiral wound gasket is designed and manufactured is clearly marked. In Fig. 1, you can easily find the standard ASME B16.20.
Name of the Spiral Wound Gasket Manufacturer: One can easily understand the manufacturer of the gasket by looking at the manufacturer name mentioned on the gasket.
Winding and Filler Material: Both the winding and filler materials are clearly specified on the spiral wound gasket. Specific gasket colors also provide a lot of information regarding the materials.
Diameter and Pressure class: The size of the gasket and the load the spiral wound gasket can handle, are specified by the Diameter and Pressure Class marking on the gasket. The usual pressure classes for spiral wound gaskets are 150, 300, 400, 600, 900, 1500, and 2500. With an increase in pressure class, the ability of the spiral wound gasket to withstand pressure increases.
Inner and Outer ring material
Materials for Spiral Wound Gaskets
The usual materials that are used in a spiral wound gasket are provided in table-1 below:
All spiral wound gaskets are color-coded. The colors of the outside rim, and the color of the stripe along the rim provides the material information of the gasket elements. The color of the outside rim tells the material of the gasket’s winding whereas the rim strip color tells about the gasket’s filler material.
Some typical outside rim colors that tell the material for the inner ring and metallic windings are as follows:
In the oil and gas industry, the most frequently seen outside rim colors are Yellow, Green, and Orange signifying that SS-304, SS-316, and Monel are the most widely used spiral wound gasket outside rim materials. The most common strip color in the oil and gas industry is gray which indicates graphite. Fig. 2 below provides a typical cross-section of a spiral wound gasket.
Fig. 2: Cross-Sectional view of a Spiral Wound Gasket
Spiral Wound Gasket Types
Spiral wound gaskets are manufactured in various styles. Some of the common spiral wound gasket styles are:
Style CG – This type of spiral wound gasket is composed of a sealing element and an outer metal ring. The outer ring ensures optimum sealing performance by preventing over-compression. The ring also helps in locating the gasket on the mating flange faces. Style CG gaskets are designed to use on raised and flat-faced flanged connections. They are widely used for mild to moderate service conditions.
Style CGI – This spiral wound gasket types have an inner metal ring in addition to the outer metal ring. The inner metal ring of the CGI-style gasket constrains the sealing element on both internal and external diameters. It works as an additional compression stop and prevents the inner buckling of the sealing element. At the same time, It creates a physical barrier between the sealing element and the process stream that shields the sealing element from heat and media and prevents erosion. Style CGI type of spiral wound gaskets is recommended for use on raised and flat-faced flanged connections with moderate to severe service conditions.
Refer to Fig. 3, which shows a typical example of different spiral wound gasket types.
Fig. 3: Spiral Wound Gasket Types
Style R – Style R gaskets consist of a sealing element, and metallic plies are used at the start and termination of the winding process. This improves the stability and sealing performance of this type of spiral wound gasket. Style R gaskets are used on tongue and grooves, male and female, and flat-to-groove flanged connections.
Style RIR – It is comprised of a sealing element and an inner metal ring. The inner ring provides the function of a compression stop as well as creates a physical barrier between the sealing element and the media stream. The inner ring is specially designed such that it reduces turbulent flow. This will minimize flange erosion and prevent debris build-up in the annular space between the pipe bore and the internal diameter of the gasket. They are suitable for use on male and female (spigot and recess) flanged connections.
There are various other types of spiral wound gasket types that are used specifically for special applications.
Spiral Wound Gasket Specification
Spiral wound gaskets are specified using various parameters like:
Nominal Pipe Size
Pressure Rating Class of the Connecting Flange
Gasket Design and Manufacturing Standard
Gasket Style required
Outer Ring, Inner Ring, and Winding Materials
Flange Standard
Fluid Service where it will be used (Optional)
Design and operating temperatures (Optional)
Spiral Wound Gasket Thickness
The thickness of spiral wound gaskets usually ranges between 3.2 mm and 4.5 mm. However, for very large diameters, more thickness ranging from 5.5 mm to 7 mm is recommended. The full range of spiral wound gasket thicknesses available in the market is 1.6 mm to 7.2 mm.
Spiral Wound Gasket Pressure Rating
As mentioned earlier, spiral wound gaskets are available in seven pressure-rating classes. They are 150, 300, 400, 600, 900, 1500, and 2500 classes. Spiral wound gasket dimensions are referred to from the design standards. For example, ASME B16.20 has spiral wound gasket size charts in tabular formats that provide all required dimensions with respect to pressure class and pipe size.
What is A Vibration Analyzer? Applications and Working of Vibration Analyzers
A Vibration Analyzer is a tool to measure, store, diagnose, and analyze the vibration produced by systems or machinery. They work using FFT-based tools that display the magnitude of the vibration and how it varies over the frequency. The main of vibration analyzers is to identify and predict faults and fix them by finding the origin of that vibration.
Vibration analyzers can be used to inspect manufacturing plants, product development labs, building sites, and other places. For the preventative maintenance of manufacturing equipment, a vibration analyzer analyses vibration. The machine’s axis of rotation is also evaluated using a vibration analyzer. If the rotor is out of balance, it can be replaced during the machine’s scheduled downtime.
Vibration analyzer measurements usually detect vibration acceleration, velocity, and displacement characteristics. Vibration is accurately captured in this manner. Vibration measurements may be taken effectively and simply in the field using portable vibration analyzers, which provide precision and mobility. Many vibration analyzers have a memory for saving vibration data for later examination.
For the on-the-job professional, the vibration analyzer is an indispensable instrument. Regardless of the technological issue, each vibration analyzer can complete the tough duty. A sound pressure level meter can also evaluate acoustic vibration (to analyze vibration frequency). It’s possible to detect critical frequencies that can cause harm or create distracting noise levels.
Working Principle of Vibration Analyzers
The working principle of the vibration analyzer is almost identical to the voltmeter; the only variation is measured. The method begins with the sensor or magnetic base device placed on the object whose vibration will be detected. The sensor will instantly give a voltage signal in response to the object’s vibration, which will be relayed over the cable into the vibration analyzer’s transmitter. Take it easy, though, because the numbers indicated on the vibration meter are vibration values in the form of acceleration and velocity, not voltage (speed per unit time). So, given how this vibration meter works, hand-arm and body vibration have two effects.
The operator must choose an appropriate accelerometer based on the mechanical type. Low-frequency accelerometers monitor low acceleration levels and are therefore extremely sensitive. Simultaneously, high-frequency accelerometers record high acceleration levels and are compact with limited sensitivity.
The piezoelectric accelerometer is typically used to measure vibrations with a frequency greater than one hertz (Hz). It features a high-frequency feature to measure vibrations in the higher frequency range. They are mostly utilized in industrial operations for automated installation vibration monitoring and diagnostic tests.
Uses of Vibration Analyzer
The application of a vibration analyzer is multi-fold. Some of the common uses of vibration analyzers are listed below:
A vibration analyzer can measure the vibration of structures such as buildings, motorways and bridges, railway tracks, airport quarries, and other major industrial facilities.
The vibration occurs in this building due to natural events such as wind, weather, and earthquakes, or interior components such as the elevator, ventilation, and HVAC systems. As a result, vibration testing aids in identifying building regions that are more susceptible to vibration.
A vibration analyzer is also used to determine how much the human body vibrates.
The instrument’s metrics include vibration acceleration, velocity, and displacement.
Features of a Vibration Analyzer
The following are the important elements to consider when purchasing a vibration analyzer:
1. Make sure the number of input channels is accurate:
Vibration analyzers come in various configurations, with the most common being two to four input channels. Recording two channels simultaneously is generally sufficient for balancing, phase analysis, Bode graph, and ODS functions. On the other hand, using triaxial accelerometers and balancing two planes necessitates the usage of four channels.
2. Frequency Range:
The frequency range of a vibration analyzer is defined by two factors: the analyzer’s highest sample rate and the accelerometer’s maximum frequency range. A system’s Sample Rate is the number of measurements it can make in one second. As a result, the device’s maximum frequency will be half of its sampling rate.
3. Lines of resolution:
The number of resolution lines determines how many points will be used to integrate the spectrum. Although the actual name is “Points,” the term “Lines” is still used, most likely since it was coined for audio FFTs that were plotted with bars (or lines). The resolution of a spectrum is sometimes mistakenly equated with the lines of resolution; however, this is not valid. Because the LR does not distinguish between a large or small frequency range, a lower frequency range with the same number of lines will show better resolution than a higher range with the same number of lines.
4. Check for additional functions:
The features of analyzers are most likely the part that varies the most from one analyzer to the next.
i) FFT: The heart of an analyzer is the spectrum, which is required by practically all analysis functions. Rectangular, Hamming, and flattops are FFT measurement tools and Windows functions.
ii) Parameters of measurement: Acceleration, Velocity, Displacement, and the Envelope of Acceleration (Demodulation or equivalent, useful for early bearing fault detection)
iii) Vibration Data Collector: A decent vibration analyzer should also be able to capture vibration data. At the very least, it should have a method for storing and organizing machine recordings to keep track of their history and trends. This is an important issue to consider because you will be dealing with this part of the system daily. It’s critical to have an intuitive and simple database interface to avoid wasting time later.
iv) Waveform of Time: This chart is created by vibration analyzers as the sensor receives the signal. Although it is rarely used, some auxiliary functions, such as Circular Time Wave Form, can be beneficial in detecting patterns in gearboxes or bearings.
v) Bearing database: Bearing vibration analysis identifies fault frequencies related to bearing geometry; hence this function is critical. As a result, you’ll have access to a comprehensive bearings database, as well as manufacturer information for fault estimates.
vi) Sensor used: The vibration’s acceleration is proportional to the output voltage. Because they incorporate small amplifiers and filters to remove noise, most sensors require power. Accelerometers are often used in vibration analyzers because of their wide frequency and amplitude ranges of animal noise. In exchange, they translate acceleration into other vibration-related metrics like velocity and displacement.
vii) Probes that measure displacement: The output signal is proportional to the vibration displacement. They are typically non-contact sensors, making them excellent for sensing shaft vibrations and eccentricity. It is advantageous if the vibration analyzer you select allows you to attach various types of sensors. There are some machines for which an accelerometer is not the best tool. Oil bearings are an example because oil dampens vibrations, making inaccurate accelerometer measurements.
5. Requirement for other features like
Cloud connectivity requirements,
Technical support needs,
Portability characteristics,
Power requirements, etc.
Handheld Vibration Analyzer
A handheld vibration analyzer is a mobile phone-sized gadget with a larger screen and spectrum display and is well-prepared for route-taking. They are lightweight and convenient to use. Due to the slow CPUs in these vibration analyzers, the number of lines of resolution, memory, and functionalities is limited, necessitating the use of PC-based software to supplement capabilities.
Features Of Hand-held Vibration Analyzer
A hand-held vibration analyzer readily measures the vibration levels of bearings, gears, and spindles for maintenance purposes.
Hand-held vibration analyzer simple enough to use that only a few people need to know how to utilize it.
An industrial accelerometer, cable assembly, mounting magnet, and headphones for audio monitoring are commonly included.
A hand-held vibration analyzer is a battery-powered engine that’s small and portable.
A hand-held vibration analyzer is mostly used to check the severity of fans, motors, and pumps and test the dc bias voltage of accelerometers for troubleshooting installed sensors and connections.
Portable Vibration Analyzer
Electrical signal monitoring is a feature of a portable vibration analyzer, that assists in the diagnosis of the condition of rotating machinery. Fig. 1 below shows an example of a typical portable vibration analyzer.
Fig. 1: Portable Vibration Analyzer
Features of Portable vibration Analyzer:
The overall vibration data are given in displacement, velocity, and acceleration
A portable vibration analyzer is usually light in weight and simple to operate.
A portable vibration analyzer usually has an automatic power-off feature and displays real RMS data.
A portable vibration analyzer incorporates a back-light display that makes measuring even in dimly lit or enclosed spaces.
Portable vibration analysis can detect vibrations in machinery produced by out-of-balance, misalignment, gear breakage, bearing failures, and other factors.
Conclusion:
A vibration analyzer is a critical power and energy meter in an electrical power testing system. You may quickly test and quantify vibration values with the help of this instrument, and the findings will be accurate. So, go ahead and start looking for the best vibration analyzer for your service potential starting right now.
Online Vibration Basics Course
Hope, the subject of vibration analyzers is clear to you now. To get a detailed understanding of vibration and related theories you can opt for any of the following online courses with lifetime access:
Best Vibration Analyzer. (2019, January 24). ERBESSD INSTRUMENTS. https://www.erbessd-instruments.com/articles/best-vibration-analyzer/.
The Basics Of Vibration Analysis. (2021, October 27). Limble. https://limblecmms.com/blog/vibration-analysis/.
Vibration Meter: Types, Features & Applications. (2020, August 3). Blog on procurement of all industrial, office supplies | Shake Deal. https://www.shakedeal.com/blog/what-is-a-vibration-meter/.
