Recent Posts

What is a Cold Box in Cryogenic Plants-Air Separation Unit

Written by Animesh Chakraborty in Piping Design Basics,Process

Cryogenic plants play a vital role in the production and processing of gases at extremely low temperatures, such as liquefied natural gas (LNG), liquid oxygen (LOX), and liquid nitrogen (LIN). At the heart of these facilities lies a crucial component known as the “cold box.”

What is a Cold Box?

A cold box is a specialized enclosure that houses key cryogenic equipment, such as heat exchangers, distillation columns, and other components necessary for the liquefaction and separation of gases. Its primary purpose is to maintain low temperatures while minimizing heat transfer from the external environment, ensuring optimal performance of the cryogenic processes.

Key Functions of a Cold Box

  • Thermal Insulation: The cold box is designed with advanced insulation materials to reduce heat ingress. This insulation is critical to maintaining the extremely low temperatures required for cryogenic operations.
  • Separation and Liquefaction: Inside the cold box, the gases undergo processes like distillation and heat exchange. The design facilitates the efficient separation of different components based on their boiling points.
  • Safety Containment: The cold box also provides a safe environment for operating cryogenic processes. It is equipped with safety features to handle pressure fluctuations and prevent leaks.
  • Condensation and Phase Change: The cold box allows for the condensation of gases into liquids, which is essential for transporting and storing cryogenic fluids.

What is a Cold Box in an Air Separation Unit?

The cold box in an air separation unit is a highly engineered large rectangular box enclosing the major cryogenic equipment. Some suppliers use a round silo design in which the equipment is primarily supported by the cold box foundation. The cold box wall is made up of steel panels that are welded onto the cold box frame. The space between the cold box wall and the equipment is filled with insulating material.

The cold box frame and foundation are designed to support the weight of all process equipment, as well as piping and valves containing the maximum operating level of liquid. It must also withstand high wind loadings as required by national codes and be suitable for the earthquake zone in which it is installed.

In air separation plants you can see square columns installed. Those are actually cryogenic cold boxes used to minimize heat leakage to the environment. The temperature inside the cold box is usually in the range of -196 Deg C. To prevent heat transfer vacuum is used.

Insulating Material used in Cold Box

The insulation material used in a cold box is either perlite, a fine powder, or slag wool, similar to glass wool but denser.

Typically, perlite is used for insulating the bulk of the cold box where access is unlikely to be required. Slag wool is used in areas where access may be necessary as it can be removed more easily than perlite. Slag wool is typically used in turbine, pump, and valve boxes.

Equipment housed in a Cold Box

The common equipment housed within the cold box typically includes:

The equipment associated with the cold box typically includes:

  • adsorbers
  • cryogenic pumps
  • expansion turbines.

Access to the internal equipment of a cold box is not possible during operation. Hence, all equipment functions are controlled through valves with extended stems that pass through the cold box wall. Access to the valves in a cold box for operation and maintenance is usually provided by a series of linked platforms and stairs or ladders.

Why does water cause a hazard to the Cold Box?

Water entering a cold box will freeze. It can become a hazard by preventing piping from free movement or causing excessive weight loads.

Ice may greatly extend the time required when a cold box is thawed. Therefore, it is extremely important to maintain the integrity of the seal at an opening (for example, at the valve and piping seal boots and manways). Water should be prevented from pooling on any horizontal surface.

Cold Box Purging

If the space inside the cold box contains air then oxygen could condense on liquid nitrogen pipework and create a hazard, also moisture can form ice in the perlite or slag wool, reducing the insulation and making it difficult to remove.

The insulation space inside the cold box is filled with nitrogen for this reason. This is known as the cold box purge. The cold box purge must be maintained whenever the cold box equipment is at cryogenic temperatures. It is usually maintained at other times also, except during internal work on the cold box equipment.

Different Types of Piping Involved in Cold Box

There are four types of piping involved in a cryogenic cold box:

1. Process piping

The process piping is used to carry fluids between the equipment items. Process pipes in a cold box vary in size from the very large low-pressure waste piping (up to 36 inches (0.9 m) on a large tonnage ASU) to small liquid lines such as liquid argon product (1 inch, 25 mm). Click here to know more about Cryogenic Piping.

2. Relief Valve Piping

The Relief valve piping connects pressure vessels to external pressure relief Valves. The major pressure relief pipes are for the high-pressure and low-pressure columns. These may have to handle large flows of gas with small pressure drops and can therefore be large in diameter. They must discharge to safe locations because of the potential for very high oxygen or nitrogen concentrations and low temperatures and are typically routed to the top of the cold box.

3. Vent, Drain, Purge Piping

Purge, vent, and drain piping which connects process equipment and process piping to the outside of the cold box for the supply of services, such as dry air or N2, and to allow venting of process gases or purge gases to the atmosphere.

These pipes are typically in the range of 4 to 1 inch (100 to 25 mm) in diameter. Purge and drain connections are usually found near the base of the cold box and maybe in groups connected to headers. Purge connections to process piping are made to the top of horizontal lines or to the side of vertical lines. For process pipes that can contain liquid, the thaw line must have a vertical lute of at least 1.5 ft (500 mm) to provide a vapor seal and prevent the backflow of liquid to the purge system.

Whenever possible, thawing and drain lines are run close to the cold box face to gain heat to maintain a warm gas seal to the valves. The liquid drain headers are connected to safe liquid disposal areas. The exhaust plume from vent piping may be O2 enriched or depleted. Vents must be located so that personnel cannot enter the plume until it has mixed with sufficient air to reach a concentration in the range of 19 to 25% O2.

Drains and vents may discharge liquid or very cold gas and must be positioned so that personnel is protected from contact and that discharge flows do not impact temperature-sensitive material and equipment.

4. Instrument piping

Instruments are connected from outside the cold box through the cold box face to the equipment items and the process piping by instrument piping. Instrument piping may also be known as impulse lines. The term instrument (for example, pressure, analysis, flow) tap also designates the connection from the valve at the cold box face to the internal process equipment.

Instrument piping is small-bore since flows are typically very small (to analyzers), or zero (for pressure, level, and flow instruments). The minimum size is determined by practical requirements for strength to withstand loads imposed by movement due to shrinkage or manual loads during cold box manufacture and maintenance.

Instrument connections are grouped at the cold box face into panels. This is for allowing easy access to both permanent and temporary instrument connections.

Why warm seal is provided in the cold box safety valve line?

To prevent relief valves from being permanently cold a warm gas seal is created on the piping. The piping runs vertically upwards from the box penetration by at least 750 mm (2.5 ft). Where feasible, the line within the cold box is routed close to the box face prior to the box penetration.

What material is used for piping?

Piping is usually manufactured from aluminum, although stainless steel and copper alloys are used in some services. All three materials remain ductile at cryogenic temperatures. Carbon steel is not used because it becomes brittle and may fail at temperatures below –29°C.

Why does a cold box require flexibility? How is the flexibility provided?

Equipment in a cold box shrinks when in operation. For example, the height of a 60-meter (197-ft) high distillation column may shrink by approximately 230 mm (9 in) when cooled to operating temperature. All the piping attached to the equipment must accommodate this shrinkage. Flexibility is provided by a series of turns in the piping, usually by a sequence of vertical and horizontal sections.

Supporting Cold Box Pipes

The long lengths of piping in a cold box require support at regular intervals. Various types of support are used which either provide a fixed anchor or allow controlled movement.

  • Horizontal runs of large pipes may have spring-assisted supports to allow controlled movement.
  • Vertical pipe supports may allow sliding movement.

What safeguard follows to minimize leaks inside the cold boxes

Once equipment and piping have been insulated, access for any repairs becomes extremely

expensive. To minimize piping leaks, all piping joints in the perlite region of a box are welded. Special transitions are required for any unavoidable transition joints between incompatible metals (for example, aluminum to stainless steel). Where it becomes absolutely necessary to use flanges connections, these are placed in a separate internal box which is insulated with slag wool. This allows access without having to remove the perlite from the larger cold box.

How does Cold Box Accommodate Shrinkage?

Shrinkage of vessels and piping in operation causes movement of piping and valves relative to the cold box surface. The amount of movement increases with box elevation. This movement is accommodated by a flexible rubber boot placed between the box face and the valve stem.

Valves in Cryogenic Service

Valves used in cryogenic service have the same functions and duties as in any other process service but have some additional requirements for operation at low temperatures. Special requirements related to materials of construction and installation.

The valve body is contained within the cold box, with the stem extending through the box wall. Both stem and bonnet are usually manufactured from type 304 or 316 stainless steel, which has the necessary strength coupled with low thermal conductivity. The bonnet is an integral part of the valve body, with the stem seal located at the warm end of the extension external to the cold box

The type of cryogenic valve used is determined by service needs such as range of control, and allowable leakage when closed but may also be limited by practical issues such as weight and availability.

  • Cryogenic globe valves are typically used to a diameter of 150 to 200 mm (6 to 8 inches).
  • Butterfly valves are used for larger services.

Design Considerations

The design of a cold box is complex and requires careful consideration of various factors:

  • Materials: The materials used in constructing a cold box must withstand low temperatures and high pressures. Common materials include stainless steel, aluminum, and specialized alloys.
  • Insulation Technology: Multi-layer insulation (MLI) or vacuum insulation techniques are often employed to achieve the required thermal efficiency. These methods minimize heat transfer and keep the internal environment stable.
  • Size and Layout: The dimensions and configuration of the cold box depend on the specific applications and the volume of gases being processed. Proper layout ensures efficient flow and minimizes dead spots where heat could accumulate.
  • Safety Features: Given the risks associated with cryogenic materials, cold boxes are equipped with safety relief valves, pressure monitoring systems, and emergency shutdown mechanisms.

Applications of Cold Boxes

Cold boxes are used in various industries, including:

  • Natural Gas Processing: In LNG plants, cold boxes are essential for liquefying natural gas, allowing for easier storage and transportation.
  • Medical and Pharmaceutical Industries: Cold boxes play a role in producing liquid oxygen and nitrogen for medical applications, ensuring the safe delivery of critical gases.
  • Aerospace and Defense: Cryogenic technologies are vital in aerospace for rocket propellants, making cold boxes crucial for testing and production.
  • Industrial Gas Production: Cold boxes are also used in the production of industrial gases, such as argon, krypton, and xenon, through air separation processes.

Benefits of Using a Cold Box

  • Enhanced Efficiency: By optimizing the conditions for gas liquefaction and separation, cold boxes significantly improve the efficiency of cryogenic plants.
  • Cost-Effectiveness: Reduced heat transfer and improved thermal management lead to lower energy consumption and operational costs.
  • Improved Safety: Advanced design and safety features in cold boxes minimize the risks associated with cryogenic operations, protecting both personnel and equipment.
  • Space Optimization: Cold boxes can be designed to maximize space usage, allowing for more compact plant layouts while still maintaining operational efficiency.

The cold box is a fundamental component of cryogenic plants, enabling the efficient processing of gases at extremely low temperatures. Its sophisticated design, combined with advanced insulation and safety features, ensures optimal performance while mitigating risks.

More details about cryogenic valves are already covered in the following article: What is a Cryogenic Valve? Features and Applications of Cryogenic Valves

An Overview of Linear and Non-Linear Analysis in Piping Stress Calculations

Written by Wasim Khan in Caesar II,Piping Stress Analysis,Piping Stress Basics

In reality, the behavior of any system is not completely linear. Linear analysis can only approximate the behavior of the system to an extent. Generally, Non-linear behavior may be due to,

  1. Geometry,
  2. Material and
  3. Boundary conditions.

In Piping stress analysis,

  • Geometry non-linearity is taken care of by means of Stress Intensification factors (SIF).
  • Material nonlinearity is not considered, as the material is considered to be in the elastic limit.
  • However, in Elasto-plastic analysis (For e.g. Blast), Material non-linearity shall be considered.
  • Boundary condition non-linearity means having non-linear restraints (+Y), Supports with Gap and Friction.

However in Linear analysis (Linear Boundary condition)- Rigid restraints (two-directional) are to be used, No support gaps to be used and the effect of friction to be neglected.

The Static stress problems are solved by first assembling the equation,

[K]{X} = {F}

Where,

  • K is the global stiffness matrix of the piping system,
  • X is the unknown Nodal displacement vector,
  • F is the known Nodal load vector (For each load case).

In Non-linear analysis, this Stiffness [K] changes during the iteration sequence when solving for
displacement in a particular load case. For e.g. When there is Rest support in a piping system, and if the pipe lifts off, then [K] is adjusted to remove the stiffness of that restraint. In Non-linear analysis, each Operating load Case (for particular support) could produce a different sustained stress distribution.

Whereas in Linear analysis, the model stiffness never changes since there are no Non-linear restraints,
those equations are assembled and solved just once for each load case, and stiffness is not updated
when the Piping system is deforming. Thus linear analysis follows a straight path. In stress analysis software packages the time taken by the software for convergence is lesser in linear analysis, whereas, in Non-linear analysis, the time taken is more because the stiffness is changed continuously.

Lift-up Support

If a Support lifts up in an operating cycle, it means it is inactive and the piping loads are distributed to
other supports in the vicinity, hence increasing the sustained stresses and with temperature, expansion
stresses change. When this operating cycle is maintained for a period, Sustained stresses remain the
same as there are no further lifts up of other supports in the system. Also, the expansion stresses will be
reduced due to yielding. During a shutdown, the pipe moves back to the support and hence the sustained stresses are reduced as the pipe comes (all supports become active) to its original cold condition.

If considerable yielding occurs in hot conditions, the pipe may return to the support point before the temperature reaches the ambient temperature. A continued cooling down to ambient temperature will cause very high thermal stresses and loads due to stoppage by the support which prevents the pipe from moving further down.

Generally, it’s good to avoid lift-up supports in a piping system as its inactive during operation. In linear analysis, we model Rigid supports. In some cases, lift-up supports may be required due to layout constraints.

In offshore projects, it is recommended to use support with Hold down in case of lift-up due to occasional load cases, if it’s not possible to avoid lift-up support. Hold-down supports with higher upward loads may cause overstress of the pipe. Providing Hold down still means the pipe is not seated on the structure in the operating case!

If the piping system has lift-up supports, it is mandatory to check all the stresses by removing the lift-up
support (Hot Sustain check). While calculating the Full displacement stress range, if liberal stress is activated, then we have to remove the lift-up support and calculate the full displacement stress range.

From ASME B31.3 302.3.5(d),

Allowable Displacement Stress Range, SA = f (1.25Sc+0.25Sh).

If we are activating Liberal Stress, it means we are using the difference between Sh and SL in the above
equation.

(Generally, SL will be lesser than Sh). Then, SA = f [1.25(Sc + Sh) – SL].

In the case of lift-up supports, this has to be taken care of. Removing the inactive supports during hot conditions may increase the sustained stress SL. Hence, the Liberal stress allowable would be lesser.

Here,

  • Sc = basic allowable stress at minimum metal temperature expected during the displacement cycle under analysis= 138 MPa (20 ksi) maximum.
  • Sh = basic allowable stress at maximum metal temperature expected during the displacement cycle under analysis= 138 MPa (20 ksi) maximum
  • SL = stress due to sustained loads; in systems where supports may be active in some conditions and inactive in others, the maximum value of sustained stress, considering all support conditions, shall be used.

From CAESAR II 2016 edition onwards, the Hot sustain stress is been incorporated in load cases for
each temperature case. It calculates the Full Displacement stress range stress with liberal allowable
activated by removing the lift-up support.

The below table gives the details about Load cases considered in Linear and Non-Linear calculations.
Here, operating conditions are considered in Non-linear calculations.

Table showing Linear and non-linear load cases in Caesar II
Fig. 1: Table showing Linear and non-linear load cases in Caesar II

If some of the boundary conditions are non-linear (For e.g. If some lift-up supports) all load cases should
be evaluated considering an operating case.

Sustained case- (W+P1+T1)-T1 = W+P1
Occasional case- (W+P1+T1+WIN1)-(W+P1+T1) = WIN1 etc.,

If all the boundary conditions are linear in a piping system, the Sustained case is not impacted with respect to operating conditions.

Let us consider an example of a Pump Discharge system as shown in Fig. 2 below

A typical Pump Discharge System
Fig. 2: A typical Pump Discharge System

The above piping system is solved using Linear analysis with some lift-up supports at Nodes 10700, 11300, 11900, and 12500 let’s compare the results of the Sustained case (with and without considering operating conditions) with the same system by changing lift-up (Non-linear) into Rigid Z (Linear).

Load cases and Output Results
Fig. 3: Load cases and Output Results

It can be inferred that with the lift-up supports, load changes are observed in the Sustained case with and without the operating case.

Support with Gaps

A restraint with a gap is also a form of nonlinearity. Hence operating effect is to be considered. Practically at the site condition, it’s not possible to maintain a zero mm gap in supports (The construction gap is a maximum of 2 mm.

Hence it may be without a gap or it may have a 2 mm gap. So, shall we use this advantage to solve the stresses and Nozzle loads in our Piping system? which may reduce additional flexibility (Elbows, more
compensation leg etc.,)

Pipe supports are used to take loads (Sustained, occasional, etc.) so that overloads induced by Piping
is not transferred to the equipment nozzle and to safeguard the Nozzle. So solving the equipment nozzle
using support with gaps near the nozzle may not guarantee that this support will take the load in all
operating scenarios.

For example,

Consider a line that has a design temperature of 120°C and an operating temperature of 50°C. In this case, the line will be mostly operating at 50°C and it may or may not fluctuate between 50°C to 120°C when the plant shutdowns, it will be at ambient condition. Hence, the support considered with the gap may not take loads at a certain operating condition which may result in overloading of the nozzle. Hence, it’s not good engineering practice to consider support with gaps near the nozzle to solve them.

It is good practice that the nozzle loads shall be checked without a gap and with a 2 mm gap up to a certain point. (i.e. maybe up to two rest, guide, stop varies on the situation). But whether support with gaps can be considered (as per the Stress engineer’s view) to solve high expansion stresses? if it’s not possible to change the routing, to give adequate flexibility, and reduce the additional piping components (Cost factor!) with a good engineering approach.

If we are using supports with gaps to have flexibility, then it is better to check loads, stresses and
displacements for both design and operating cases even if operating is far less than design.

Support Friction

As friction always opposes the motion, the effect of friction on a piping system can be advantageous in some scenarios, and may be non-conservative to ignore it in some scenarios. Please refer to the paper, “Treatment of Support friction in Pipe Stress Analysis” by LC Peng for a detailed explanation of Friction in the Piping system, which gives a detailed explanation of the behavior of support friction.

What is a Blowdown Valve (BDV)? Its Working, Types, and Applications

Written by Anup Kumar Dey in Engineering Materials,Mechanical,Piping Design Basics

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:

  • Carbon Steel
  • Brass
  • Copper
  • Bronze
  • Cast iron
  • Aluminum
  • Stainless steel
  • Monel
  • Nickel
  • Zirconium, etc.

Advantages of Blowdown Valve

The use of blowdown valves in operation provides various advantages like:

  • Increased productivity.
  • Savings of labor power.
  • Increased safety and efficiency.
  • Maintaining solid impurities under limited rates.
  • Reduced corrosion due to removal of impurities.
  • Prevention of scaling of internal equipment surfaces as well as the boiler tubes.
  • Prevention of steam contamination.

The blowdown valves provide the following benefits:

  • Easy maintenance due to simple design.
  • Variety of applications including steam boiler services.
  • Lower Maintenance time.
  • Manual or Automatic Operation.
  • No requirement for special tools.

Disadvantages of Blowdown Valve

However, there are some disadvantages of blowdown vales like

  • Energy loss as the hot water is going out of the water drum.
  • Huge pressure loss is valve open position.
  • Fuel consumption of the boiler increases as the blowdown of the boiler increases
  • Additional work hours are required for manual blowdown valve operation.

Types of Anchor Bolts: Their Selection and Uses

Written by Anup Kumar Dey in Civil,Construction,Piping Interface

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.

Anchor Bolt Selection Table
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

Written by Anup Kumar Dey in Engineering Materials

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:

  • Excellent corrosion resistance
  • Density: 8.89 g/cm3
  • Melting Range: 1323-13710C
  • Tensile Strength: 690 to 783 MPa
  • Good weldability
  • 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:

  • Acids like Acetic Acid, Hydrochloric acid, Sulphuric acid, phosphoric acid, nitric acid, boric acid, carbolic acid, citric acid, uric acid, malic acid, salicylic acid, gallic acid, etc.
  • Chlorides like Aluminum Chloride, Ammonium Chloride, Amyl Chloride, Barium Chloride, Calcium Chloride, Ethyl Chloride, Zinc Chloride, Potassium Chloride, Titanium Tetrachloride, Sodium Chloride, Magnesium Chloride, Ferric Chloride, etc
  • Nitrates like Ammonium Nitrate, Copper Nitrate, Cupric Nitrate, Nickel Nitrate, Sodium Nitrate, Mercurous Nitrate, Magnesium Nitrate, Potassium Nitrate, Ferric Nitrate, etc
  • Hydroxides like Ammonium Hydroxide, Calcium Hydroxide, Magnesium Hydroxide, Sodium Hydroxide, Potassium Hydroxide, Ferric Hydroxide, etc
  • Sulfates like Aluminum Sulfate, Ammonium Sulfate, Copper Sulfate, Zinc Sulfate, Nickel Sulfate, Sodium Sulfate, Magnesium Sulfate, Sodium Bisulfate, Potassium Sulfate, etc
  • and many more

Hastelloy vs Monel

The main differences between Hastelloy and Monel materials are tabulated in the table-1 below:

HastelloyMonel
Hastelloy is widely used in acidic environments.Monel is widely used for marine applications.
Hastelloy is relatively cheaper due to the low amount of nickel (Usually less than 60% nickel)Monel is relatively costlier as it has more nickel (60 to 70% nickel)
Hastelloy has a higher melting point (around 2550 Deg F)Monel has a melting point of 2460 Deg F.
The tensile strength of Hastelloy is lower (in the range of 690 to 783 Mpa)Monel has a higher tensile strength (550 to 1100 Mpa)
Table 1: Monel vs Hastelloy

What are Inch-Dia and Inch-Meter in Piping? Their Significance, Calculation, and Examples

Written by Anup Kumar Dey in Construction,Maintenance

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.

Explanation of Inch-Dia calculation
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.

Inch Dia and Inch Meter for Unit Piping vs Rack Piping
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.