Blowdown valves in process plants are special types of piping valves that find a variety of applications. The main purpose of a blowdown valve in a piping or pipeline system is to initiate a blowdown when the valve is activated. Blowdown valves depressurize a system or equipment for maintenance or emergency situations by sending unwanted fluids usually to flare. Blowdown valves are basically emergency on-off valves that work using the signals from emergency shutdown systems.
Applications of Blowdown Valves
Blowdown valves are widely used in:
Vessels and equipment to prevent their contribution during explosive or fire incidents.
Compressor systems to relieve trapped pressure during the shutdown.
Industrial boilers, Heat exchangers, and Cooling Towers control the dissolved and suspended solids level in the water.
In pipes to remove unwanted materials.
The use of blowdown valves reduces operational costs by removing the requirement for regular operator intervention. For boilers, this type of valve increases the heating efficiency and reduces the consumption of feed water.
Working of Blowdown Valves
Blowdown valves can maintain a continuous fluid flow under high differential pressure while still maintaining fluid-tightness. To drain some amount of liquid from any equipment, blowdown valves can be used. The required blowdown rate is decided by considering various parameters like:
Equipment Pressure
Size of the blowdown line
Length of the blowdown line, etc.
Two blow-down valves in series are usually used. One of them serves as the sealing valve, while the other works as a blow-down valve. The sealing valve is opened at the start of the process and is closed at the last. Both sealing and blowdown valves are fully opened and work rapidly to prevent erosion of the disk faces and the seat.
Care must be exercised to avoid the trapping of scale or rust particles. This can be achieved by opening the valve for flushing the particles through if some resistance is felt at the time of closing. In the case of boiler operation, the bottom blow-down valves are usually replaced during their maintenance.
For boiler operation, the blowdown percentage is calculated as,
Blowdown percentage = (Quantity of blowdown water/ Quantity of feed water) x 100
Types of Blowdown Valves
Depending on the working philosophy, there are two types of blowdown valves as listed below:
Continuous Blowdown valves and
Intermittent blowdown valves
Continuous Blowdown Valves:
This type of blowdown valve works continuously to release liquid. For boiler operation, continuous blowdown valves maintain the TDS level in the boiler drum by working continuously.
Continuous blowdown valves usually consist of an angle valve having a needle-shaped trim in a venturi diffuser to provide sufficient area for the high-velocity fluid to avoid choking.
Intermittent Blowdown Valves:
As the name suggests, this type of blowdown valve works at predetermined intervals and releases fluids. Intermittent blowdown valves provide tight shut-off even after repetitive blowdown operations.
They use a multi-step throttling plug to perform both blowdown and sealing operations; blowdown in an open position while sealing in the closed position. The throttling area and sealing area are different for intermittent blowdown valves which reduces erosion to provide prolonged leak tightness.
Depending on the Solid precipitation rates, Blowdown valves are classified into two groups:
Surface blowdown valves and
Bottom Blowdown valves
Surface Blowdown Valves:
This type of valve provides relatively slower solid impurity precipitation. One of the simplest designs of the surface blow-down valve in boiler service is to insert the pipe near the surface of the water level and permit the water to flow out through the blowdown valve. It helps the equipment to continuously operate in a steady-state condition. For boilers, the water flows out and is then sent to the flash tank to generate flashed steam for heating up the feed water.
A more efficient design can be obtained using a swivel joint. A short length of pipe is suspended on the float. This mechanism helps to collect the floating oil from the water’s surface. The oil must be removed from the water to avoid the generation of foam inside the boiler.
Surface blow-down valves are used to feed the heat exchanger and flash tanks for recovering heat. They continuously flow off a small volume of water to get rid of the dissolved impurities present. When the concentration of impurities is higher, surface blowdown valves efficiently work.
Bottom Blowdown Valve:
In a bottom blow-down valve, compounds are added for water treatment. The impurities of water form a sludge through the accumulation of solid impurities which settle at the bottom quickly. A mud drum collects it. The bottom blowdown valve is periodically opened for a short span of time to remove the settled sludge.
Opening the bottom blowdown valve for a long period of time is not suggested as it may affect the water level in the equipment. The level of water decreases very fast which may result in the equipment being shut down to avoid it from running dry. The pipe diameter is usually sufficiently large to avoid blocking flow due to sludge.
Materials Used for blowdown Valve
Blowdown valves can be made up of various materials. The most common materials used to manufacture blowdown valves are:
Anchor bolts attach and secure structural elements to concrete structures. In general, anchor bolts are used to secure skids, equipment, and structural members to concrete. One end of the anchor bolts is embedded in the concrete, while the other end is kept exposed. The exposed end is usually threaded to attach structural elements or the equipment. In this article, we will explore the different types of anchor bolts, their uses, and selection criteria.
What is an Anchor Bolt?
An anchor bolt is a mechanical fastener that fixes one or more objects to a concrete surface. They are heavy-duty fasteners and are widely used by civil engineers. The unique design of anchor bolts keeps the equipment and structures stable and in place.
Types of Anchor Bolts
Depending on the installation requirements, Anchor bolts used in industrial projects are categorized into the following two groups:
Cast-in-Place anchor bolts and
Post-Installed anchor bolts
Cast-in-Place Anchor Bolts
From the name itself, it is quite clear that the cast-in-place anchor bolts are cast directly into the concrete material. They are the simplest but the strongest of all anchor bolts used. This type of anchor bolt is placed in the wet concrete that becomes fully secured when the concrete cures and hardens.
Anchor bolts of cast-in-place types are again categorized into various groups. The most common types of cast-in-place anchor bolts are:
Drop-in Anchor Bolts
Bent-bar anchor bolts (J-bolts or L-Bolts)
Plate Bolts
Sleeve Anchor Bolts
Headed Anchor Bolts
Swedge Bolts
Drop-in Anchor Bolts:
Drop-in bolts are quite simple and straightforward. When the concrete slab is wet, a cork-screwed sheath is inserted into the mixture keeping it flush with the slab’s surface to insert a matching bolt when the mixture dries.
Bent-bar Anchor Bolts:
These are basically steel rods or bars bent into either L or J shapes. These types of anchor bolts have threads at one end with the other bent end bent is embedded into the concrete. J-bolt and L-bolt anchor bolts are quite common in signposts, poles, heavy equipment, tooling, and other steel structures.
Plate Bolts:
Plate bolts usually consist of a T-shaped bolt mounted upside down into wet concrete. The “T” end of these bolts is provided with a corkscrewed section for mounting a nut and a circular plate. This type of anchor bolt is also known as a Double End rod with a Plate. The plate is usually welded to the anchor bolt or a nut is embedded in the concrete.
Sleeve Anchor Bolts:
Resembling similar to standard drop-in anchors, Sleeve anchor bolts are primarily used in bricks and have a longer length.
Headed Anchor Bolts:
Headed anchor bolts have a forged hexagonal or square head on one end which is embedded in the concrete.
Swedge Bolts:
They are basically round bars with thread on one end and “swedged” on the other. The term “swedge” signifies the numerous indentions made on the bar for the purpose of getting a better grip on the concrete. This type of anchor bolt is commonly used in the construction of girders and piers.
Post-Installed Anchor Bolts
Post-installed anchor bolts are installed after the concrete has already been laid down at the site. In this type of anchor bolt, a hole is required to be bored into that concrete surface and the screw is installed.
Some common post-installed anchor bolts are as follows:
Lag Screw
Hammer Driver Pin
Toggle Wing
Double Expansion Shield
Wedge
Lag Screw:
This type of anchor bolt is quite similar to plastic wall anchors and is easy to install. The lag Screw mounting system uses a metal sheath that expands when the lag screw is inserted into it.
Hammer Driver Pin:
Resembling a specialty nail, hammer driver pins are used for mounting thin materials onto concrete. The anchor contains a skinny metal sheath for inserting into the floor prior to being filled with a hammer driver pin.
Toggle Wing:
A toggle wing is good when working with a hollow wall. This type of anchor bolt has a long corkscrewed bolt with a hinged wing mechanism. Both of them are inserted through a pre-bored hole for combination. The wings expand after passing through the hole. They are used for holding smaller weights.
Double Expansion Shield:
A double expansion shield anchor bolt uses two parallel expansion points within a regular shielded anchor point. This type of anchor bolt doubles the amount of contact between the sheath and the material which in turn reduces the pressure at each point.
Wedge Anchor Bolt:
Wedge Anchor bolts consist of a specialized bolt featuring a moving wedge device at its base. Because of this, these types of anchor bolts tighten upward towards the fastening nut and the nut is fastened downward toward the surface level.
Depending on the working philosophy anchor bolts are classified into two types. They are:
Mechanical Anchor Bolt and
Chemical Anchor Bolt
Mechanical anchor bolts
use the frictional force to fix themselves in location. Once installed, the mechanical anchor bolts expand which grips the base material tightly and act as an anchor. All the above anchor bolts explain above are mechanical anchor bolts.
Chemical Anchor Bolts
Chemical anchor bolts provide more flexibility as compared to mechanical anchor bolts. In this type, a resin is injected into the hole before inserting the stud. The chemical resin fills all irregularities of the hole and makes it waterproof and airtight. The bond produced by chemical anchor bolts is stronger than the base materials. Examples of chemical anchor bolts are:
Polyester chemical anchors
Vinylester chemical anchors
Epoxy acrylate chemical anchors
Pure epoxy standard anchors
Resin anchors
Chemical threaded anchor rods
Powder–actuated anchors
Hybrid chemical anchors
Selection of Anchor Bolts
Choosing or Selecting the Best Anchor Bolt depends on various factors. Some of the important parameters to consider while anchor bolt selection are:
Size of anchor bolt hole: As the diameter increases, the load-carrying power also increases.
Length of the anchor bolt: The deep the embedment inside the concrete, the more load-holding power. The National Concrete Masonry Association provides a rule of thumb for the anchor bolt length embedded in the concrete. As per them, the effective embedment length must be greater of (4*d or 2′′).
The base material of the object.
Environmental conditions of the structure
Maximum load or weight that the anchor can support
Type of load: The holding power of anchor bolts slowly decreases for vibrating and shocking loads.
Strength of the anchor bolt material.
Type of the concrete
The size and location of the fixtures
The desired appearance of the finished product
Anchor spacing requirement.
The table in Fig. 1 by americanfastener.com can serve as a reference for selecting mechanical anchor bolts.
Fig. 1: Anchor Bolt Selection Table
Grouping Anchor Bolts
To increase the load capacity of anchor bolts, they are grouped. However, the mechanical behavior of the group of anchor bolts depends on
The spacing between anchor bolts and
The difference in applied forces.
Anchor Bolt Failure Modes
The anchor bolts can fail by any of the following failure modes:
By tensile loads, examples include breakage of the anchor bolt steel, pull-out from the hole, etc.
By shear loads, examples are Concrete edge failure, steel failure, and pry failure.
By combined action of tensile and shear loads.
Uses of Anchor Bolts
Anchor bolts are used to attach and secure structural and non-structural elements to the concrete. They are used almost in every industry. Some of the industries where anchor bolts find wide applications are:
Chemical, Petrochemical, Oil and Gas Industry: For fixing various pieces of equipment, support foundation, and other structural members.
Power and Steel Industry.
Building Services.
Hospital industries: To install equipment on ceilings or walls.
Railways and the Aviation industry.
manufacturing plants
Pipeline industries.
Pharmaceutical and food processing plants.
Nuclear industries.
What is Hastelloy? Properties, Types, and Applications of Hastelloy Material
Hastelloy is a nickel super-alloy having very high corrosion resistance. It consists of nickel, chromium, and molybdenum as the main constituent elements. Along with corrosion resistance, Hastelloy metal has high-temperature resistance. In the chemical, petrochemical, pharmaceutical, and oil & gas industries, the application of Hastelloy material is increasing. In this article, we will discuss the properties, applications, and grades of Hastelloy.
What is Hastelloy Metal?
Hastelloy is an incredibly strong and corrosion-resistant nickel alloy used widely for highly corrosive chemicals and acids. The addition of chromium and molybdenum improves its high-temperature and corrosion resistance properties. Hastelloy metal is ductile and therefore, can be easily formed.
Hastelloy is manufactured by combining raw elements during the hot liquid state. In general, Hastelloy material possesses 1% to 25% chromium, 5% to 30% molybdenum, 0% to 30% iron, and balance nickel material. Sometimes, other elements like carbon, tungsten, vanadium, and titanium are also added.
Once the metals are combined, smelted, and mixed together, they are cast to produce the required component.
Properties of Hastelloy
Though the properties of Hastelloy vary depending on the grades, it usually has the following properties:
High-Resistance against oxidizing agents and acids
Hastelloy Alloy Types and Grades
Depending on the chemical composition of the Hastelloy material, there are various grades of Hastelloy. Common Hastelloy metal grades are:
B-type Hastelloy materials
C-type Hastelloy materials
Hastelloy G-types
Hastelloy X, and
Hastelloy N
B-Type Alloys
Hastelloy B-type superalloys have a high percentage of nickel and molybdenum. B-grade Hastelloy is known for withstanding extremely reducing environments. Some of the B-type Hastelloy materials are:
B-2 Alloy (UNS N10665): B-2 Hastelloy material contains 65% nickel and 30% molybdenum. It also has a small percentage of carbon, iron, silicon, chromium, cobalt, manganese, and sulfur. B-grade alloy provides superior corrosion resistance to hydrochloric acids but is poor for oxidizing agents.
B-3 Alloys (UNS N10675): This alloy provides excellent resistance against pitting corrosion and has superior thermal stability as compared to B-2 alloys. B-3 alloys have 65% nickel and 30% molybdenum in chemical composition with traces of chromium, cobalt, and manganese.
C-Type Alloys
Hastelloy of this grade contains a high percentage of nickel, chromium, and molybdenum. Chromium increases high-temperature properties and resistance against reducing environments. Hastelloy C grades are suitable for cold and hot working. Grade C Hastelloy metal is the most widely used Hastelloy material. Common C-type Hastelloy materials are:
C-4 Hastelloy (UNS N06455): Type C-4 Hastelloy contains 60% nickel, 18% chromium, 16% molybdenum, 3% iron, 2% Cobalt, and remaining silicon, carbon, sulfur, titanium, etc. It has high ductility and corrosion resistance.
C-22 Hastelloy (UNS N06022): C-22 Hastelloy consists of 58% nickel, 20% chromium, 13% molybdenum, 3.5% tungsten, 2.5% cobalt, and traces of other elements. Widely known for its weldability, the C-22 Hastelloy is the most used alloy for pharmaceutical reaction vessels and desulfurization systems.
Hastelloy C-276 (UNS N10276): This grade of Hastelloy finds application in petrochemical industries. It contains 59% nickel, 16% molybdenum, 15% chromium, 4% tungsten, and traces of other elements. It has high corrosion resistance against oxidizing agents, pitting, stress corrosion cracking, and intergranular corrosion.
C-2000 Hastelloy: It has excellent resistance against oxidizing media and is used in chemical process equipment applications.
G-Type Alloys
Suitable for welding using TIG, SAW, SMAW, and G-type Hastelloy materials contain tungsten as one of the alloying elements. The main alloys of this group are:
Hastelloy G-3 (UNS N06985): This superalloy contains nickel, chromium, tungsten, iron, molybdenum, and cobalt as the dominant components.
G-30 Hastelloy (UNS N06030): It consists of 43% nickel, 30% chromium, 15% iron, 5% cobalt, 4% tungsten, 1.5% Manganese, and traces of other elements.
X-Type Alloys
Hastelloy X alloy (UNS N06002): It has superior oxidation resistance, high-temperature strength, and SCC resistance. Chemically Hastelloy X contains 44% Nickel, 23% Chromium, 20% iron, 10% molybdenum, 1% of Manganese and Silicon, and traces of other elements. They can be cold-worked and welded. This type of Hastelloy material is used for industrial furnace and gas turbine applications.
Hastelloy N (UNS N10003)
Hastelloy N contains 71% nickel, 16% molybdenum, 7% chromium, 5% iron, 1% silicon, and traces of other elements. Due to its higher temperature oxidation resistance properties, Hastelloy N is used in industrial applications like chemical process equipment.
Other Hastelloy grades are:
Hastelloy D-205
Hastelloy G50 (UNS N06950)
Hastelloy S (UNS N06635)
Hastelloy W (UNS N10004)
Hastelloy G-2 (UNS N06975)
Applications of Hastelloy Material
The outstanding corrosion resistance of Hastelloy makes it an ideal choice for any moderate to severely corrosive environment. Hastelloy pipes, exchangers, pressure vessels, and valves are quite common in the chemical and petrochemical industries. This metal is also used in reactor vessels in the chemical and nuclear industries. Other industries that use Hastelloy are:
Geothermal
Mining
Solar Power
Biomass
Sea-Water
Petrochemical
LNG
Aerospace
Water Desalination
Paper and Pulp, etc
Hastelloy works as fully resistant to the following fluid services:
Inch Dia and Inch Meter are the terms frequently used in the piping construction industry. Both Inch-dia and inch-meter are units for measuring the quantum of piping construction jobs for fabrication, erection, and hydro test purposes. Inch-Dia is also known as Dia-Inch or abbreviated DI in some organizations. Similarly, the Inch-Meter is denoted by the acronym IM. In this article, we will explore the significance of Inch Dia and Inch Meter and their calculations with examples.
What is Inch Dia?
Piping Inch-dia and Inch-meter are used during the construction of chemical, petrochemical, fertilizer, refinery, power, and oil&gas industries. The progress of piping spool fabrication mainly welding is measured by the term Inch Dia, which is a short form of Inch-Diameter.
In piping welding, the pipe size is converted to the equivalent inch-dia and reported.
Example and Equation for Inch-Dia Calculation
Let’s understand the calculation of inch diameter with some examples,
Assume a 6″ NPS pipe of length 60 m needs to be produced. We all know that pipes are not manufactured with indefinite lengths. Single random length pipes are manufactured in the length of 5 to 7 m whereas double random length has a length in the range of 11 to 13 m. So to make a pipe of length 60 m we have to weld smaller length pipes. So even if we consider a maximum length of 13 m, there will be a minimum of 4 welding joint requirements. This pipe welding requirement is denoted by Inch dia.
As per the above example, the Total required inch dia=Diameter of pipe in inches X No of joints required =6 X 4=24 inch dia.
Similarly, if the pipe NPS is 12 inches and the required number of joints is 6 then the inch dia will be 12 X 5=60 inch dia. The joints with Pipe Spool, Elbow, Tee, Reducer, Flanges, Valves, or other piping components are denoted and calculated using Inch-Dia in a similar way.
So, the equation for inch dia calculation can be represented as below:
Inch Dia=Pipe Size in Inches X Total Number of Joints for that size.
Other than welding, NDT tests like radiography and DPT requirements are also measured in terms of Inch Dia. The payment for all these construction activities is calculated based on Inch-Dia.
What is an Inch Meter?
An Inch Meter is specifically used to measure the progress of Piping erection and hydro-testing. The pipe length that is erected or hydro-tested at the construction site is converted to the equivalent Inch Meter of erection or hydro testing.
Example and Formula for Inch-Meter Calculation
The equation for calculating Inch-Meter is
Inch Meter=Pipe NPS in Inches X Length of Pipe in Meters
Let’s understand the concept of the Inch-Meter Calculation with some examples,
Assume a 20-inch NPS pipe of 100 meters in length is to be erected at the site. So, the quantum of the piping erection job is 20 X 100= 2000 Inch-Meter.
Similarly, If a 12-inch pipe of 50 m length is required to be hydro-tested the quantum of piping hydro-testing job is 12 X 50=600 Inch-meter.
All piping erection jobs, insulation, etc. are converted to Inch-meters for measuring progress for payment purposes.
The estimated inch-dia and inch-meter also help to calculate the required number of professionals and associated cost and time requirements for any project.
Sample Calculation of Inch-Dia
Let’s calculate the Inch dia for the configuration shown in Fig. 1.
Fig. 1: Explanation of Inch-Dia calculation
In this diagram, the size of the larger pipe is 10 inches NPS and the total number of joints in the 10-inch pipe is 6 (1 with the flange, 4 with the elbows, and one with the reducer). So, the Inch dia for the 10-inch line is 10X6=60 inch-dia.
Now the diameter of the smaller pipe is 8 inches NPS. The total number of joints in the 8-inch pipe is 2 (1 with the flange and the other with the reducer). So, the Inch-dia for the 8-inch pipe = 8 X 2=16 inch dia.
Hence, the total calculated inch-dia=60+16=76 inch-dia
Significance of Inch-Dia and Inch-Meter Concept in Piping
In the piping industry, the inch meter and inch diameter concept is used for various purposes:
To find out the piping erection load
Proper manpower planning and estimation
Piping work progress reviewing and monitoring, and
Cost estimation and budget planning
Difference of Inch-Dia and Inch-Meter Calculation in Unit Piping and Rack Piping
In the usual unit piping, two pieces of equipment are connected using the piping work in the process and utility areas. As the piping in such areas is usually complex, more joints are required with respect to total pipe length. On the other hand, in rack piping or cross-country piping (/pipeline), the pipework connection is usually straight which requires less number of joints. So, the inch diameter requirement for complex unit piping jobs is more as compared to usual rack piping. Let’s take an example to understand this concept.
Fig. 2: Inch Dia and Inch Meter for Unit Piping vs Rack Piping
In the above figure (Fig. 2), the dia-inch for the unit piping is 6 X 8 =48 inch-dia (6 joints in 8 inch diameter pipe; J1, J2,…., J6 denotes joints) whereas the same for the rack piping is 3 X 8= 24 inch-dia (as only 3 joints) even though the inch-meter for both the piping configuration=24 X 8=192 Inch-Meter.
The Inch-Diameter in piping is basically a unit of measurement for fabrication and inspection processes like welding, Dye Penetration Inspection, Radiographic Testing, etc. for a basis of payment. On the other hand, the inch-meter in piping defines the job quantum for piping erection, piping insulation, etc., and estimates related payments to sub-contractors.
What is a Stud Bolt? Types, Selection, Materials, and Standards of Stud-Bolt
A stud bolt is an externally threaded mechanical fastener. An assembly of stud bolt connections is usually formed by two nuts and the stud. Sometimes, washers and additional nuts may be used. In high-pressure piping and pipeline flange connections, stud bolts are widely used. In this article, we will learn about the types, standards, materials, selection, and sizes of stud bolts.
What is a Stud Bolt?
A stud bolt is a mechanical fastener having external threads without a head. The external thread is either for the full length of the stud or partially threaded from each end. It uses at least two nuts, one on each side for assembly connection. Stud bolts are available in various sizes, types, and threading patterns.
Types of Stud Bolts
Depending on the threading pattern and design, various types of stud bolts are available as listed below:
Fully threaded stud bolt or continuous threaded stud bolt having uniform thread throughout its length.
Tap end stud bolts having unequal threads from each end and non-threaded center.
Double-end stud bolts having both ends threaded of equal lengths and a non-threaded center.
Flange Stud bolts: Fully threaded stud bolts with chamfered ends specifically used for flanged connections.
Double-end stud bolt with reduced shank: the non-threaded center part is of a reduced diameter than the actual diameter.
Depending on the Stud bolt material strength they are divided into three groups;
High-Strength stud bolt
Intermediate-strength stud bolt, and
Low-strength stud bolt.
Types of Stud Bolt Threads
Stud bolts use a variety of screw thread profiles depending on the application. Some of the most common thread profiles are:
ISO metric thread
ACME thread
UNC thread
UNF thread
UN thread
WHITWORTH thread
Stud Bolt Standards
The design and manufacturing of stud bolts are governed by a range of ASME standards as listed below:
ASME B16.5 & ASME B16.47 cover the diameter and length.
ASME B1.1 covers coarse and fine thread series.
ASME B18.2.1 is used for Square and Hex Bolts and Screws
ASME B18.2.2 provides details for Square and Hex Nuts
ASME B18.21.1 provides Lock Washer details
ASME B18.22.1 is used for Plain Washers
Various other international standards like DIN, ISO, BS, SAE, IS, etc also provide details of stud bolts.
Stud Bolt Materials
For high-temperature and pressure services, ASTM A193 is the most widely used flange material. Grade B7 and B7M are the most frequently used A193 material grades. For low-temperature services, ASTM A320 Gr L7, L7A, and L7B are used. Other stud bolt materials include the following:
The nut and washer material must be compatible with the selected stud-bolt material to avoid galvanic corrosion. Sometimes stud bolts are coated to increase corrosion resistance. The common coating materials are:
The material of the stud bolt mainly depends on the process design temperature and flange materials. however, there are many other parameters that must be considered. The following image from blog.projectmaterials.com provides rough guidance on the stud bolt material selection based on design temperature and flange material:
Fig. 1: Stud Bolt Material Selection
Stud Bolt Ends and Lengths
The ends of stud bolts are usually rounded, sheared, saw cut, flat, or chamfered. The length of a stud bolt is measured parallel to the axis from one end to the other. They are available in 1/4″ length increments.
Stud Bolt Size/Dimension
The size and dimension of the stud bolt are decided by the governing standard. ASME B16.5 and ASME B16.47 provide stud bolt charts that provide the bolt diameter and the number of bolts required depending on the pressure class, flange type, and pipe size.
In general, with an increase in pressure class and NPS, the bolt area increases. There are two parameters that decide the bolt area; bolt diameter and the number of bolts. So, any of the two or both parameters can increase to get an increase in bolt area. Refer to Fig. 2 below for a typical Stud-bolt chart for pressure class 150, 300, and 600 based on ASME B16.5 standard.
Fig. 2: Stud Bolt Chart and Dimensions for 150, 300, and 600 Pressure Class
What is Nitrogen Blanketing? Purpose, Procedure, and Applications of Tank Blanketing
Nitrogen blanketing is the process of supplying the N2 (or other inert gas) gas to the vapor space of a container to control its composition. It provides improved process safety and better product quality, along with a longer equipment life cycle. Nitrogen blanketing practices can be applied to a wide variety of container sizes. The process is widely used for storage tanks, and because of that, nitrogen blanketing is often termed tank blanketing, tank padding, or nitrogen padding. In this article, we will explore more about nitrogen blanketing: its procedure, purpose, application, and controls.
What is Nitrogen Blanketing?
Nitrogen blanketing is the process of supplying the storage tank with an inert gas (the most economical), such as nitrogen, to counteract the effect of oxygen (and other reactive gases) on the storage material, which is usually liquid. When purging the vessel with inert or inert gas, the vessel material does not come into contact with oxygen. This extends product life and mitigates potentially explosive conditions by reducing the risk of chemical reactions, corrosion, and fire hazards.
Applications of Nitrogen Blanketing
Nitrogen blanketing is used in all industries wherever flammable or explosive products are used or generated. Some of the industries that widely use nitrogen padding methods are:
Chemical Plants and Petrochemical Industries: In these sectors, nitrogen blanketing is crucial for preventing unwanted chemical reactions and ensuring the stability of sensitive products. It helps maintain the purity of chemicals and pharmaceuticals by preventing contamination.
Oil and Gas Industry: Nitrogen blanketing is employed to safeguard storage tanks and pipelines containing volatile substances. It prevents the formation of explosive mixtures and minimizes the risk of corrosion.
Food Processing: To extend shelf life and preserve the quality of food and beverages, nitrogen blanketing is used in packaging and storage. It helps prevent oxidation, which can lead to spoilage and degradation.
Electronics Manufacturing: Nitrogen blanketing is used in the manufacturing of electronic components to prevent oxidation and contamination of sensitive materials.
Pharmaceutical industries
Petroleum Refining plants
Aerospace industries
Ships and Transformers
Chemical and Petrochemical Transportation Industry,
Chemical tankers
Personal Care, Cosmetics, and Semiconductor.
Gas blanketing is used to protect a diverse range of products, including but not limited to adhesives, catalysts, chemicals, fragrances, fuels, industrial coatings, inks, deionized water, fats and oils, flavors, foods, juices, pharmaceuticals, photographic chemicals, solvents, volatile combustibles, sealants, soaps, and water for injection.
Purpose of Nitrogen Blanketing
The blanket helps to maintain constant inert conditions for the product in the container. The goal is to prevent explosion, discoloration, polymerization, and other unwanted quality changes. Here, the flow and pressure of the inert gas stream and/or the oxygen level in the exhaust gas will control the operation. The main benefits that a nitrogen blanketing system provides are:
Increased safety by reducing the explosion possibility by reducing the amount of oxygen in the vapor space of a chemical storage tank.
The reduced potential of fire and explosion.
Increased equipment life by reducing the corrosion possibility due to oxygen and moisture reactions.
Reduced chances of product degradation by creating the blanket.
Reduced possibility of product property alteration.
Decreased product evaporation
Enhanced overall efficiency of industrial processes by eliminating contamination.
Nitrogen blanketing can be applied to a variety of container sizes from a multi-million-gallon tank to a large or smaller container. Although blanketing is a factory practice, there is scope for improvement. Bad choices may add costs, increase nitrogen wastage, or increase plant emissions.
Nitrogen Tank Blanketing Procedure
Before diving into the nitrogen blanketing procedure, let’s recapitulate some of the basics. We all know that a fire happens when all three elements; an ignition source, fuel, and oxygen are present. Removing any of these three elements will remove the possibility of fire. The space above the tank contains a mixture of air and steam from flammable materials that are being stored, eg solvents.
Mixtures of solvent vapors and air will only ignite and burn if the vapor mixture is within the flammability of the solvent and an ignition source is present. This can lead to tragic consequences such as serious injury to people.
Static charges can develop within the system or within the solvent itself, creating a source of ignition although storage tank facilities may be electrically grounded to reduce the probability of ignition.
A storage tank can be made inert in any of the following three ways:
Limiting the Oxygen Concentration (LOC) of the vapor space
Reducing the fuel concentration below the Lower Explosion Limit (LEL), or
Increasing the fuel concentration above the Upper Explosion Limit (UEL).
The manufacturer’s Material Safety Data Sheet (MSDS) provides the values of LEL and UEL for a chemical. LOC values are often found in chemical industry handbooks and guides such as the National Fire Protection Association (NFPA) Guide. Flammability limits of mixtures of gases, combustibles, and inert substances for high temperature and pressure can be determined by computational methods.
Refer to Fig. 1, which provides a sample example of a flammability envelope for Hydrogen in Air. The combustion will not take place beyond the LOC.
Fig. 1: Flammability Diagram of Hydrogen in Air
When considering a new or improved blanketing design, the first factor to take into account is the type of tank. This will determine if blanketing is required or not. The following rules apply to the storage tanks for the nitrogen blanketing philosophy.
When a fixed roof tank stores any flammable material, nitrogen blanketing must be applied.
Floating roof tanks do not need tank padding.
Internal floating roof tanks or covered floating roof tanks occasionally need nitrogen blanketing as there is the possibility of vapor build-up.
Fig. 2 explains the above concept of storage tanks requiring nitrogen blanketing.
Fig. 2: Nitrogen blanketing requirement for Storage tanks
In addition to the storage tanks and similar vessels, a number of sealed tanks like Non-pressurized spaces may also require blanketings, such as a pneumatic conveyor, powder and dust hoppers, or controlled atmospheric tanks.
The nitrogen blanketing procedure maintains a concentration of nitrogen within the padded tank/vessel. It also prevents the reintroduction of oxygen and other gaseous contaminants within that region. The nitrogen blanketing procedure usually employs the following methods:
Automatic pressurized vessel purging
Continuous pressurized nitrogen blanketing using manual controls
Oxygen concentration measurement and variation
Dual oxygen concentration and pressure monitoring
Maintaining a steady pressure of gaseous nitrogen and eliminating oxygen.
Nitrogen Control by Continuous Purge
The continuous purge system uses a continuous flow of nitrogen, which is simple to do but can lead to high nitrogen consumption. Nitrogen can also remove vapor in the headspace and put more uploads factory emissions management system. In addition, air may enter empty space if the tank is empty too quickly and the liquid level drops too quickly. Despite these problems, this type of system continues to be used because It’s very simple and quick to make. Replace this method with pressure or concentration control can lead to savings.
Nitrogen Control by Pressure Control
Fig. 3: Pressure Controlled Nitrogen Blanketing
Pressure control systems are used for closed tanks, that can hold pressure. A valve detects pressure in the headspace of the tank and supplies nitrogen accordingly. Headspace pressure control can be set quite low; less than an inch in the water column is enough. When the tank is discharged, the liquid level is dropped, pressure is reduced, and nitrogen is added. When the tank fills, the pressure increases, and nitrogen escapes through the vent valve.
Nitrogen Blanketing Calculation
Simple Calculations for nitrogen requirement are shown where basically, the nitrogen requirements of blanketed tanks have two parts:
Nitrogen as required by the flow, or material flow through the tank(NW); and
Nitrogen is required by heat breathing or the increase and decrease of the liquid level due to external temperature (NTB). Of these two sections, usually, the NTB is significantly larger.
The equations mentioned in Fig. 4 are used to calculate the N2 requirement for the Nitrogen blanketing process.
Fig. 4: Calculation of Nitrogen Requirement for Nitrogen Blanketing
Here,
NT= Total volume of nitrogen required per month (ft3)
NW = Required Nitrogen by the material flow through the tank (working throughput)
NTB = Required Nitrogen by the rise and fall of the liquid level owing to the external temperature conditions (thermal breathing)
VT= total gallons discharged from the tank per month
VHS = Average empty headspace (gal)
Thigh = Maximum temperature in the tank (°F)
Tlow = Minimum temperature in the tank (°F)
F = Estimated number of temperature swings per month
555 = A constant (˚R) pertaining to the vapor space expansion factor
7.48 = Gallons to the cubic feet conversion factor
Components of a Nitrogen Blanketing System
A nitrogen blanketing system is designed to create and maintain an inert atmosphere within a container, tank, or pipeline to prevent contamination, oxidation, and other issues. The primary components of a nitrogen blanketing system include:
1. Nitrogen Supply
Nitrogen Generator: Produces nitrogen on-site from ambient air, usually through processes like pressure swing adsorption (PSA) or membrane separation. It ensures a continuous supply of nitrogen.
Nitrogen Cylinder or Tank: Stores nitrogen gas if it is supplied in bulk or as a compressed gas.
2. Flow Control Components
Flow Meter: Measures the rate at which nitrogen is being introduced into the system. This ensures that the right amount of nitrogen is supplied to maintain the desired blanket.
Regulator: Controls the pressure of the nitrogen gas before it enters the container or system. It ensures that the pressure is maintained at a level slightly above atmospheric pressure to prevent ingress of air.
3. Pressure Control Components
Pressure Relief Valve: Protects the system from overpressure conditions by releasing excess nitrogen if the pressure exceeds a preset limit.
Pressure Transmitter/Sensor: Continuously monitors the pressure within the container or system. It provides real-time data for maintaining the correct nitrogen blanket.
4. Blanketing and Purging Components
Blanketing Valve: Controls the flow of nitrogen into the container to maintain the desired pressure and blanket level.
Purging System: Used for initial nitrogen purging to remove any existing air or contaminants before the blanketing process begins.
5. Monitoring and Control Systems
Control Panel: A centralized unit that integrates various sensors, meters, and control valves. It allows operators to set and adjust parameters such as pressure and flow rate.
Alarm System: Provides alerts for abnormal conditions such as pressure deviations or equipment malfunctions, ensuring timely intervention to maintain system integrity.
6. Safety Devices
Check Valve: Prevents backflow of nitrogen or other substances into the nitrogen supply lines, ensuring system safety and reliability.
Ventilation System: Ensures that any excess nitrogen or displaced gases are safely vented to avoid hazardous conditions or buildup.
7. Additional Components
Filters: Remove particulates and contaminants from the nitrogen supply to prevent damage to sensitive equipment and ensure the purity of the inert atmosphere.
Temperature Control: Some systems include temperature regulation components if the process is sensitive to temperature variations.
Importance of Nitrogen Blanketing Valve
A nitrogen blanketing valve is a specialized valve used in nitrogen blanketing systems to control the flow of nitrogen gas into a container, maintaining an inert atmosphere. Its primary function is to regulate the pressure inside the container, ensuring it remains slightly above atmospheric pressure to prevent the ingress of air, moisture, and contaminants. This helps protect sensitive products from oxidation, contamination, and potential hazards, while also safeguarding equipment and ensuring safe and efficient operations.
In conclusion, nitrogen blanketing is a vital technique in modern industry, providing safety, quality, and efficiency benefits across a range of applications. Whether in chemical processing, food production, electronics manufacturing, or oil and gas, nitrogen blanketing plays a crucial role in ensuring optimal conditions and safeguarding valuable assets.
Reference and Further Studies
To learn more about the subject refer to the following article: https://www.chemicalprocessing.com/assets/wp_downloads/pdf/nitrogen-blanketing-keeps-employees-and-equipment-safe.pdf
