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,

Geometry,
Material and
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, S_A = f (1.25S_c+0.25S_h).

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

(Generally, S_L will be lesser than S_h). Then, SA = f [1.25(S_c + S_h) – S_L].

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 S_L. 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
S_L = 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.

**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

**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).

**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.

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:

Hastelloy	Monel
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.

**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

Written by Anup Kumar Dey in Mechanical,Piping Design Basics

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:

ASTM A354 Gr BC, BD
ASTM A540 Gr B21 to B24
ASTM A193 Gr B5, B6, B8, B16, B8M, B8A, B8T, L7, B17B.
ASTM A453 Gr 660A/B/C/D
ASTM A913 Inconel 718
ASTM A320 Gr L7M, L43, B8, B8A, B8T, B8MA, B8C
ASTM A182 Gr S31803, S32205.

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:

Electro zinc plating
Electro cadmium plating
PTFE Coating
Hot-dip galvanizing
Phosphate coating
Electroless nickel plating
Silver coating
Zinc/Nickel by electrodeposition
Zinc-nickel coating
Aluminum coating
Dacromet
Geomet
XYLAN and
Xylar

Selection of Stud Bolt Materials

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.

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