What’s new in ASME B31.3-2020? ASME B31.3 2020 vs 2018

Hopefully, all of you are aware that the latest edition of the process piping bible ASME B31.3-2020, which revised the 2018 edition of the same code is issued on the 18th of June, 2021. Similar to earlier editions, this code also will become universally effective 6 months after the date of issuance means from 17th December 2021 onwards. Similar to the earlier new releases, ASME B31.3-2020 also provides many clarifications, updates, and changes. In this article, I will list down 10 such major changes that ASME B31.3-2020 will bring into effect with respect to ASME B31.3-2018.

Changes with respect to Units of Measurement

Additional clause 300.1.4– Units of Measure added stating that either SI or U.S. Customary units should be independently used as the stated values in the ASME B31.3-2020 are not exact equivalents. If It is required to convert from one system of units to another, conversion should be made by rounding the values to the number of significant digits of implied precision in the starting value but not less than four significant digits for use in calculations.

The earlier clause in the 2018 edition “300.1.4- Rounding” has been renumbered as clause 300.1.5 in ASME B31.3-2020.

Changes with respect to the Flexibility Factor and Stress Intensification Factor

Appendix D that was providing the equations for the Flexibility Factor and Stress Intensification Factors of Table 300.4 Status of Appendices in B31.3 has been deleted from ASME B31.3-2020 edition. In the absence of more directly applicable data, the flexibility factor, k, and stress intensification factor, i, shown in ASME B31J shall be used for flexibility calculations described in para. 319.4. Flexibility factors and stress intensification factors for branch connections are defined for in-plane, out-plane, and torsion moments on both the run and branch legs. Branch leg calculations shall use the appropriate branch factor (i.e., k_ib, k_ob, k_tb, i_ib, i_ob, and i_tb), and run leg calculations shall use the appropriate run factor (i.e., k_ir, k_or, k_tr, i_ir, i_or, and i_tr).

This is the most significant change for piping stress engineers. Now using B31J or FEA will be mandatory. Earlier, the same SIFs were used in the stress analysis programs for headers and branches which in some cases becomes too conservative. Now that problem will be resolved.

Experimental Stress Analysis for Unlisted Components

As per clause 304.7.2 sub-para (b) of the latest edition of ASME B31.3 2020, for experimental stress analysis of unlisted components following the equations from ASME BPVC, Section VIII, Division 2, Annex 5-F, the basic allowable stress from Table A-1 (or A-1M) of B31.3-2020 shall be used as allowable stress, S.

In a similar way, for proof testing of unlisted components following the equations from ASME B16.9, MSS SP-97, or ASME BPVC, Sec VIII, Division 1, UG-101, the basic allowable stress from Table A-1 or Table A-1M shall be used in place of the allowable stresses, S and S2, in Division 1 where applicable.

Bending Stress Calculation for Header and Branch

Equations 19 and 20 for calculating bending stresses in header and branch as was there in clause 319.4.4 sub-paragraph (c) have been deleted in ASME B31.3 2020 contrary to the ASME B31.3-2018. Similarly, equation 23-b2 has also been deleted.

Impact test requirement for Weld Metals

The impact test requirement criteria for Weld Metal of the welding procedure qualification test coupon has been changed in table 323.2.2 of ASME B31.3-2020. In code B31.3-2018, the impact test was required for design minimum temperature<-29 Deg C. However, the latest edition of B31.3 requires an impact test for design minimum temperature below -18 Deg C.

Additional Standards

The following additional standards are added in Table 326.1 of ASME B31.3-2020 with respect to the earlier revision B31.3-2018.

ASTM F1476
ASTM F1548.

Also, AWWA C504 has been removed from that table.

Standards ASTM D3309, D2310, D2447, and ASTM F1974 have been deleted from Table A326.1 Component standards for non-metallic piping systems.

Use of ASME B31P

Clause 330.1 in ASME B31.3-2020 provides permission to use preheating rules from ASME B31P as an alternative to general preheat requirements. Additionally, the process and temperature control methods specified in ASME B31P are recommended for heat treatment purposes.

Consideration of Frictional Clamping Force for Supporting Non-Metallic Piping

For supporting non-metallic piping systems, ASME B31.3-2020 prohibits to use of frictional forces from clamping pressure as an anchor mechanism unless the support/anchor is specifically recommended for this purpose by the manufacturer. Positive stops like shear collars can be used as axial restraints. There was no such prohibition in ASME B31.3-2018.

Shear and Bearing Allowable for High-Pressure Piping System

The allowable stress definition for shear and bearing in the case of high-pressure piping has been revised in ASME B31.3-2020. Now the allowable stress in shear should be 0.57 times S_yt (in place of 0.8 times as provided in B31.3-2018). The allowable stress in bearing shall be 1.0 times S_yt (in place of 1.6 times as provided in B31.3-2018).

Also, the basis for allowable stresses for other materials (other than bolting materials) for the high-pressure piping system has been modified with respect to the earlier edition. Refer to clause K302.3.2 sub-paragraph (b), (c), and (d) for details.

The majority of the changes or revisions in ASME B31.3-2020 have been made for High-Pressure and High-purity piping systems.

Few more related articles for you.

Changes in the 2018 Edition of ASME B 31.3 2018 with respect to 2016 edition
Stress Intensity Factor (SIF), Flexibility Factor: ASME B31.3 vs ASME B31J
How to use ASME B31J-2017 and FEM for SIF and k-factors for Stress Analysis
ASME B31J & B31J Essentials: Why these are useful in Piping Stress Analysis?
An Issue about USER DEFINED SIFs

Further Studies:

ASME B31.3 Process Piping – Substantive Changes In The 2020 Edition

Methods for Welding Stainless Steel

Written by Anup Kumar Dey in Mechanical

Welding stainless steel is the principal joining method employed during the fabrication of stainless steel products and components. Because of its excellent corrosion resistance, and elevated and cryogenic temperature properties, stainless steel is one of the widely used engineering materials. Stainless is extensively used in the oil and gas, chemical, petrochemical, power plant, food, and pharmaceutical industries.

Stainless Steel Welding Processes

Welding of stainless steel is generally performed by two basic methods: Fusion Welding and Resistance Welding.

Welding Stainless Steel by Fusion Welding

Fusion welding of stainless steel generates heat by an electric arc struck between the metallic electrode and the stainless steel material. Four widely used principal processes that are used for fusion welding of stainless steels are:

SMAW (Shielded Metal Arc Welding)
GTAW (Gas Tungsten Arc Welding)
GMAW (Gas Metal Arc Welding)
SAW (Submerged Arc Welding)

There are some other fusion weldings methods like electron beam, laser, and plasma arc welding. Note that, To preserve optimum corrosion resistance and mechanical properties in the joint, the weld zone must be protected from the atmosphere by a gas, vacuum, or slag.

Welding Stainless Steel with SMAW:

SMAW, being a fast and versatile process, is very popular for stainless steel welding. The manual welding method uses a solid electrode wire with an extruded baked-on coating material. One end of the electrode that is held in a spring-loaded electrode holder is bare. The operator holds the electrode at an angle at a minimum distance from the base metal to maintain the arc and moves it along the joint.

The alloy composition of the SS material decides the selection of electrodes for SMAW. Depending on the type of power supply and welding types, the coatings of electrodes are usually lime-based or titania-based materials. The coating creates a gas envelope that protects the molten metal from air contact. Refer to Fig. 1 for a basic representation of the SMAW stainless steel welding process.

Welding Stainless Steel with GTAW:

Also known as Tungsten Inert Gas Welding or TIG welding, the welding of stainless steel by GTAW uses Argon or any other inert gas to protect the welding zone from atmospheric contact. An intense electric arc generated between the non-consumable tungsten electrode and the SS workpiece creates the necessary heat for welding. In case filler metal is required, a bare welding rod is fed into the weld zone to melt with the base metal.

GTAW is widely used for welding stainless steel pipes, and joining tubes to tube sheets in shell and tube heat exchangers. There are two variations for GTAW for stainless steel welding to increase welding speed and get higher deposition rates.

In the first variation, known as hot-wire GTAW, an automated process is used and the filler wire is heated by resistance heating.
Pulsed-arc GTAW is another variation where a pulsing arc is used that controls the molten weld puddle to increase penetration.

The following figure (Fig. 1) shows a typical representation of welding stainless steel with TIG.

**Fig. 1: Stainless Steel Welding Process**-SMAW and GTAW

Welding Stainless Steel with GMAW:

Also widely popular as MIG welding, the gas metal arc welding of GMAW is a gas-shielded arc welding process using a consumable electrode that melts in a gas atmosphere. Refer to Fig. 2, which schematically shows the basic equipment like a torch, supply of shielding gas, DC power supply, and control for wire feed speed through the torch. The coiled form electrode filler metal is mechanically driven into the welding zone. Depending on the method of metal transfer, three variations of the GMAW process are found. They are:

Spray Transfer
Short-circuiting transfer, and
Pulsed-type transfer.

The spray transfer or free flight transfer is characterized by a hot arc and fluid puddle. A short-circuiting transfer that is effective for welding thin stainless steel material utilizes small diameter wire (<0.045 inches). The pulsed-arc welding is characterized by a controlled free-flight metal drop rate of 60 drops per second at a lower current density.

Welding Stainless Steel with SAW:

SAW or Submerged Arc welding is a welding method where the heat for fusing the metal is generated by an electric current between the welding wire and the stainless steel workpiece. A layer of mineral flux composition covers the arc, the workpiece weld area, and the welding wire tip. No visible arc, spark, spatter, or smoke is found in this welding method and hence the name submerged arc welding. Refer to Fig. 2, which represents the SAW method schematically.

**Fig. 2: Welding of Stainless Steel-MIG & SAW**

Welding Stainless Steel by Resistance Welding

One of the most economical and popular methods of joining stainless steel is by electrical resistance welding where heat is produced by the resistance to the flow of the electric current through the parts to be welded. For the mass volume of repetitive works, resistance welding for stainless steel products is particularly suitable. The widely used resistance welding processes for stainless steel welding are:

Spot Welding
Seam Welding
Projection Welding
Butt Welding

Welding of Stainless Steel using Spot Welding:

In spot welding of stainless steel, coalescence is produced by the heat generated from electric resistance and pressure on the electrodes. The contour of the electrodes limits the shape and size of the welds. The process uses two water-cooled electrodes or wheels which are brought together with the work parts using a mechanical force by foot, air, hydraulic, or motor-operated cam. The welding cycle consists of squeeze time, weld heat time, hold time, and off time. The parameters that affect the welding process are:

Electrical resistance
Thermal conductivity
Expansion coefficient
Strength at elevated temperature, etc

A typical process of spot welding is shown in Fig. 3.

**Fig. 3: Welding of Stainless Steel-Spot Welding, Seam Welding, and Projection Welding**

Welding of stainless steel by Seam Welding:

In the seam welding of stainless steel, circular electrodes (copper-based alloy) are used. A series of overlapping spot welds are progressively made by the rotating circular electrodes (Refer to Fig. 3) which supply the current as well as the pressure to hold the work parts. To get proper weld spacing, the electrode speed and current off-time must be adjusted. Usually, three types of seam welding machines are used:

Circular
Longitudinal, and
Universal

Welding of stainless steel with Projection Welding:

Projection welding is best suited for heavy-gauge stainless steel workpieces. Localized welding is performed at predetermined points by projections, embossments, or intersections. At these projections, heat is concentrated and can be made in one or both pieces as shown in Fig. 3. Projection welding can be performed in almost all stainless steel.

Stainless Steel Welding by Butt Welding Process:

The butt welding process can be grouped into two classes; Flash Welding and upset Welding.

Flash Welding:

In the flash welding process, the work parts initiate a flashing action from the current delivered through the clamped electrodes. The basic sequence of flash welding of stainless steel is:

load machine
clamp workpiece
apply weld current
establish flash by contacting parts
flashing
apply upset force
interrupt current
unclamp workpiece
unload and
return platen.

Flash welding machines are manual, semi-automatic, or fully automatic and can perform various additional operations like pre and post-heating, clamping, shearing, flash trimming, etc. All types of stainless steel can be welded using flash welding.

**Fig. 4: Butt Welding of Stainless Steel**

The alignment of the parts to be welded is very important so that heat is generated over the entire surface.

Upset Welding:

In the upset welding process, no flash occurs. The coalescence is produced over the entire area by the heat generated from the resistance of the electric current flow through the contact area of the abutting surfaces. The applied force is maintained throughout the heating period. The joining surfaces are brought together under pressure and the current is applied until the correct upset takes place and then the current is interrupted.

The non-heat-treatable stainless steels are easily weldable by this process. Continuous tube mills use this process quite extensively.

Other forms of resistance welding are high-frequency resistance welding, percussion welding, etc.

Welding of Stainless Steel Pipes

The selection of welding method for joining stainless steel pipes is dependent on:

Pipe Size
Pipe Thickness
Possibility of pipe rotation, etc

TIG is widely used for stainless steel pipes of 4 inches and smaller sizes. Whereas for large-diameter pipes fully automatic methods are used.

Welding Courses Online

When developing in-depth knowledge about the welding processes and techniques, then the following online welding courses will surely serve the purpose:

Learn MIG Welding
Introduction to Welding Engineering
A guide to become a Welding Inspector to start a Lucrative Career

Few more welding articles for you.

Welding Galvanized Steel
Overview of Pipeline Welding
Welding Positions: Pipe Welding Positions
Welding Defects: Defects in Welding: Types of Welding Defects
Welding Inspector: CSWIP and AWS-CWI
General requirements for Field Welding
Underwater Welding & Inspection Overview
Methods for Welding Stainless Steel

References and further Studies

What is Nitriding? Benefits and Types of Nitriding Process

Written by Anup Kumar Dey in Engineering Materials,Mechanical

What is Nitriding?

Nitriding is a type of heat treatment process to create a case-hardened surface by diffusing Nitrogen. The most common applications of the nitriding process are valve parts, gears, forging dies, crankshafts, extrusion dies, camshafts, firearm components, bearings, textile machinery, aircraft components, turbine generation systems, plastic mold tools, etc. The material widely used for the nitriding treatment process are low-alloy steels, aluminum, molybdenum, and titanium. Depending on the case depth, the nitriding process can take 4 to 60 hours.

Developed early in 1900, the nitriding process is widely used in many industrial applications. During nitriding, no phase change occurs. It is one of the simplest case-hardening processes.

What are the Purposes of Nitriding?

The main purposes of nitriding treatment are:

To get high hardness on the surface. Hardness achieved in nitriding is usually higher than carburizing method.
To increase the wear resistance.
To improve fatigue life and other fatigue-related properties.
To improve the corrosion resistance of the material.
To obtain a high-temperature property of the surface (Resistance to tempering or softening up to the nitriding temperature).
To get anti-galling properties.

Also, the nitriding process helps in reducing notch sensitivity. It is a diffusion-related surface treatment process that causes very small volumetric changes. Nitriding treatment can significantly improve properties like fatigue strength, resistance to wear, corrosion resistance, friction, and hardness.

What is the Principle of Nitriding?

Nitriding is a thermochemical treatment process to enrich the surface with nitrogen for the purpose of increasing the surface’s hardness. The process is based on the low solubility of nitrogen in the ferritic crystal structure to promote the precipitation of iron nitrides or alloy nitrides. The connecting nitriding is connected to a diffusion zone where precipitated nitrides are evenly diffused in the steel matrix. The usual nitriding temperature range is 350°C to 590°C. With a decrease in temperature, the nitriding time to reach a given depth increases. The depth of nitriding hardness may reach 500 μm with maximum hardness levels of > 1000 HV.

The nitriding layer formation occurs in the following steps:

adsorption of nitrogen atoms on the surface of the component,
absorption of nitrogen atoms by the component surface, and
diffusion of the nitrogen atoms along the grain boundaries and within the grains.

What are the Types of Nitriding?

There are three types of nitriding processes that are commonly used in industries. They are:

Gas Nitriding,
Plasma Nitriding, and
Salt-bath Nitriding.

What is Gas Nitriding?

In the gas nitriding process, the metal is heated to a suitable temperature (500⁰C to 575⁰C for Steel) and held in contact with a nitrogenous gas, usually ammonia. This is why the process is sometimes known as ammonia nitriding. When ammonia comes into contact with the heated steel, it breaks down into hydrogen and nitrogen. This nitrogen then diffuses onto the metal surface and creates a nitride layer. Depending on the temperature the solubility of nitrogen into iron varies as can be seen from the attached iron-nitrogen equilibrium diagram in Fig. 1.

**Fig. 1: Iron Nitrogen Equilibrium diagram**

The effectiveness of the gas nitriding process depends on various factors like

Gas Flow
Temperature
Time
Gas activity control
Process control
Process chamber maintenance, etc

What are the Advantages and Disadvantages of Gas Nitriding?

The main advantages of gas nitriding over other types of nitriding treatment are:

Possibility of larger batch sizes (limited by the furnace size and gas flow)
An all-around nitriding effect is achieved.
Relatively low equipment cost as compared with plasma nitriding.

The disadvantages of gas nitriding are:

Ammonia as a nitriding medium can be harmful if inhaled in large quantities. Also, it has the risk of explosion when heating in the presence of oxygen; so must be controlled carefully.
Reaction kinetics are heavily influenced by surface conditions. Poor contaminated surface delivers poor results.

What is Plasma Nitriding?

Also popular as ion nitriding or glow-discharge nitriding, plasma nitriding uses a plasma discharge of reaction gases to heat the metal surface and supply nitrogen for the nitriding process. The main advantage of plasma nitriding is that the process is not dependent on the decomposition of ammonia gas to release nascent nitrogen. Invented by Dr. Bernhardt Berghaus of Germany, Plasma nitriding has a shorter cycle time. Fig. 2 below shows a typical schematic diagram of the plasma nitriding furnace layout.

**Fig. 2: Schematic of Plasma Nitriding Furnace layout**

In plasma nitriding, intense high-voltage electric fields in a vacuum are used to generate ionized nitrogen gas molecules. This highly active gas with ionized molecules, known as plasma accelerates to impinge on the work surface. This ion bombardment cleans the surface, heats the workpiece, and provides active nitrogen ions. Plasma nitriding helps in close control of the nitriding microstructure and its efficiency is not dependent on the temperature.

Metallurgically versatile, the ion nitriding process provides excellent retention of surface finish and ensures repetitive metallurgical properties. Ion nitriding can be conducted at temperatures lower than those conventionally employed. The plasma nitriding process does not cause any pollution and insignificant gas consumption which are important economic and public policy factors.

What are the Advantages and Disadvantages of the Ion Nitriding Process?

The main advantages of plasma nitriding are:

Close control of Nitrided microstructure.
The working lifespan of the component also increases.
No polishing or machining is required post-nitriding process.
Causes very little or no distortion.
Energy-efficient and the fastest process.

The disadvantages of the plasma nitriding process are:

Limited only on the compound zone thickness.
Poor temperature control.

What is Salt Bath Nitriding?

Salt bath nitriding used molten salt as the source of nitrogen. The nitriding process uses the nitrogen liberated from the decomposition of cyanide to cyanate. The process also releases carbon and thus the process is also known as a nitrocarburizing treatment. The metal is normally submerged in a bath of preheated molten cyanide salt. The high concentration of nitrogen in the liquid chemically combines with iron to produce a hard and ductile iron nitride (Fe3N) thin outer layer.

What are the Advantages and Disadvantages of Salt-bath Nitriding?

The advantages of salt nitriding are:

Quick processing time and higher diffusion in the same period.
A simple operation involving the heating of the salt and workpieces to a temperature of 550 to 5700C and submerging for the specified duration.

The disadvantages of the salt bath nitriding process are:

Used cyanide salts are highly toxic.
Only one process is possible with a particular salt type.

What are the Prerequisites for Nitriding?

To get the best results in nitriding the following prerequisites should be followed:

The steel should be hardened, quenched, and tempered to get a uniform structure.
The surface must be cleaned to remove oils, grits, etc using vapor degreasing or abrasive cleaning.

Advantages of the Nitriding Process

The nitriding process provides various advantages like:

Quick processing time.
Low-temperature process.
Clean pollution-free operation.
Economic and energy-efficient operation.
Lower friction coefficient.
Improved fatigue properties.
Uniform surface.
High surface hardness.
Distortion is very less.
Improved corrosion resistance.
Quenching is not required for getting high hardness.

Disadvantages of the Nitriding Process

The drawbacks of the nitriding process are

High initial cost.
Closer process control is required.
Skilled personnel requirement.

Nitriding vs Carburizing: What is the difference between nitriding and carburizing?

The main differences between Nitriding and Carburizing are:

Nitriding	Carburizing
In nitriding, the nitrogen is diffused to increase the surface hardness	On the other hand, Carbon is diffused in Carburizing process.
The temperature range for nitriding treatment is lower.	Carburizing is done at very high-temperature ranges.
Energy-efficient and quick process.	Higher energy requirement.

Nitriding vs Carburizing

What are Agitators? Selection and Types of Agitators

Written by Anup Kumar Dey in Mechanical,Process

What are Agitators?

An agitator is a mechanical device that helps in shaking or stirring a liquid or mixture of liquids. Agitators are widely used for multiple operations in the chemical, pharmaceutical, food, grease, metal extraction, paint, adhesive, water, and cosmetic industries.

What are agitators used for?

The main functions of using an agitator in any plant are:

To get proper mixing of liquids.
To promote chemical reactions inside the equipment.
To increase heat transfer during heating or cooling
To keep homogeneous liquid bulk during storage.
To disperse immiscible liquids.
To keep the product in a mixed state till used.
To blend miscible liquids.
To dissolve some solids into liquid.

The agitators are defined as a machine where an impeller with a rotating shaft imparts energy by mechanical means to mix various process media.

What are the Types of Agitators?

Various types of agitators are available for industrial purposes. The common type of agitators are:

Paddle Agitators
Anchor type agitators
Propeller type agitators
Blade type agitators
Turbine type agitators
Helical Agitators

1. Paddle Agitators: Containing paddle-shaped blades, these agitators are the most basic types of agitators. Their capability is limited and used mainly for laminar flow fluids requiring little shearing. They are adjustable and contain an equal number of forwarding and reversing paddles to move ingredients from one end of the vessel to the other.

A modified version of paddle agitators is Sawtooth Paddle Agitators. The forward puddles of such agitators contain notches or saw teeth.

2. Anchor Agitators: For mixing highly viscous and non-Newtonian fluids, anchor agitators are widely used. Their name indicates the impeller shape that resembles an anchor. They are normally mounted in tanks and vessels with conical or rounded bottoms.

3. Propeller Agitators: For low-viscosity products, Propeller agitators are highly suitable. Functions like homogenization, suspension, and dispersion are easily achieved using propeller-type agitators operating at medium to high speeds. These axial flow agitators are ideal for solid-in-liquid suspensions as they prevent the deposition of solid particles.

4. Blade Type Agitators: These are suitable for low and medium-viscosity fluids. Blade-type agitators are axial type.

5. Turbine Agitators: For emulsification and dispersion of fluids at very high speed, Turbine agitators are used widely. Turbine Agitators are characterized by highly effective mixing capability across a broad viscosity range. Turbine agitators have an axial input and radial output. They combine rotation and centrifugal motion during work.

6. Helical Agitators: As the blades are arranged in a structure of a helix, they are known as helical agitators. Appearing like a threaded screw, helical agitators are axial flow agitators that provide vigorous motion within the vessel or tank. This type of agitator is widely used in polymer industries.

The following table provides the main applications, advantages, and disadvantages of various types of agitators.

Type of Agitator	Applications	Advantages	Disadvantages
Paddle Agitator	Mixing of Solids, Slurry Mixing, Used during the Crystals forming phase during Supersaturated Cooling	Heavy-duty, Slow Operation, 2 to 4 blades.	High power consumption, Inefficient mixing.
Turbine Agitator	Liquids and gas reactions are widely used for reaction and extraction operations.	High radial flow, good for dispersion operation.	Not preferred for highly viscous solvents
Anchor Agitators	Widely used in the pharma industry.	High heat transfer rate.	High power and high-efficiency gearbox requirement.
Propeller Agitators	Can handle corrosive materials with a glass lining.	Increase homogeneity. Can be used for drying and pressing.	High-speed requirement.
Helical Blade	The Paint Industry.	Can efficiently handle visco-elastic liquids.	Low possibility for radial Mixing.

Table 1: Comparison of different types of agitators

Components of an Agitator

An agitator is usually composed of three main components. they are:

A shaft with an impeller and impeller blades
A mechanical seal and
A motor with a gearbox option for speed control.

The shaft of the agitator is connected to the motor and gearbox and the impeller rotates to perform mixing. The number of impellers depends on the height of the liquid inside the vessel or tank. Each impeller usually has 2 to 6 blades. Magnetic-driven agitators are also available where a hermetic seal is used in place of a mechanical seal. Fig. 2 below shows typical components of an agitator (Reference: Wikipedia)

The impellers used in agitators can be of various types like:

Standard or Wide blade Hydrofoils
Straight blade or Pitched blade turbines.
Retreat curved impellers.
Gas dispersion impellers.
Rushton turbine impellers
Sawtooth disk impellers, etc

Selection Criteria of Industrial Agitators

The selection of agitators for a particular application depends on various factors like:

The phase to be mixed (single-phase or multiphase).
The viscosity of the bulk.
Exact function required (blending, dissolving, dispersion, heat exchange, chemical reaction, crystallization, emulsification, suspension, etc).
The mixing cycle (batch size, the time required for agitation, material addition sequence, etc)
Properties of the materials to be mixed.
Initial ingredient and final product viscosities.
Solubility of solids and concentration used.
Desired process outcomes.
Corrosive or flammable properties.

Number of Agitators

There could be more than one agitator connected to the shaft. The number of agitators and the Gap between the two agitators can be found in the following equation:

Number of Agitators=(Maximum liquid height X Specific gravity)/Diameter of the Vessel.
The gap between two Agitators=Liquid Height/(Number of Impellers-0.5).

Data required for the design of an Agitator

The following data are required for the industrial design of an agitator:

Purpose/Function of agitation.
Mixing cycle.
Foaming tendency
Individual physical characters and their quantities of the materials to be mixed.
Tank/Vessel/Reactor dimensions preferably with a sketch.
Duty hours.
Electrical duties
Material of Construction

Applications of Industrial Agitators

Industrial agitators are used in various applications like

Mixing in tank
Viscous products and non-newtonian liquids
Clean and lightly contaminated liquids,
Fibrous and Non-fibrous slurries
Liquids with high gas or solid content

What is Concurrent Engineering?

Written by Anup Kumar Dey in Mechanical,Project Management

Concurrent Engineering is a long-term business strategy that provides long-term benefits to any business or manufacturing process. In this methodology, several teams within an organization work concurrently to develop products and services. Product design, quality, unit cost, and manufacturing time are the most important parameters that impact the profitability of an organization. Concurrent engineering helps in improving these factors and provides companies with a highly competitive edge. In this article, we will learn about the definition and principles of concurrent engineering, Its benefits, elements, challenges, and product development process using concurrent engineering.

Definition of Concurrent Engineering

Concurrent engineering is a systematic method of designing and developing products where different activities run simultaneously. This is also known as simultaneous engineering. By performing different tasks simultaneously, concurrent engineering decreases production time leading to reduced costs. The philosophy of concurrent engineering is derived from Japan.

What are the benefits of concurrent engineering? | Advantages of Concurrent Engineering

The main benefits that the application of the concurrent engineering principle provides are:

Reduced Production time: As all the required activities are performed simultaneously, the idling time for each activity reduces. So the actual time required for any product reduces and the product can easily enter the market in less time and at a reduced cost. Concurrent Engineering works on the principle of parallel project life cycles that speed up product development.

Highly Innovative Solutions: As many of the development facets and employee skills overlap, great innovative solutions are achieved by valuable inputs from all departments. Brainstorming the problems among all disciplines avoids big mistakes during the design phase itself which in turn saves time and money.

Enhanced Productivity and Competitive Advantage: As the potential problems are corrected by various departments easily and the production time is reduced, all these provide enhanced productivity and a highly competitive edge over the competitors.

Elements of Concurrent Engineering

There are four basic elements in the concurrent engineering principle. They are

Cross-functional teams: Cross-functions teams are formed by people from different work areas related to that particular process or product development.
Concurrent product realization: Performing several tasks simultaneously is the basis of concurrent engineering.
Incremental information sharing: Information must be shared immediately it is available to succeed in concurrent engineering. Even the information can be shared in the form of advance information if the actual information approval process takes time.
Integrated project management: It ensures the responsibility of the project to the key professionals.

Principles of Concurrent Engineering

The concurrent engineering principle utilizes the right human resource at the right time to accelerate product development while keeping the rework to a minimum. The working principle of concurrent engineering is based on the following factors:

Teamwork: This is the basic requirement for concurrent engineering philosophy. Collaboration, cooperation, and interpersonal relationship are integral parts of concurrent engineering.

Multidisciplinary team: Multidisciplinary team for product/service/process development including experts from each discipline is important for the success of concurrent engineering principles.

Effective Communication: To get the most benefit from the concurrent engineering strategy, effective communication is a prerequisite. Fast Information exchange between members, suppliers, customers, and manufacturers is important. It must be ensured that all members are aware of what other members are doing.

Management Support: Proper management support helps in the implementation of the concurrent engineering principles.

Involvement of Customers and Suppliers: The success of product development in concurrent engineering depends on the proper integration between the customer, suppliers, and manufacturer. This reduces the design error and reworks significantly.

Concurrent Engineering vs Sequential Design

The concurrent engineering principle has mostly altered the conventional sequential design strategy to a great extent. The linear fashion of sequential design philosophy is now related to the integrated development method of concurrent engineering. The main fault with the sequential design method is that if something goes wrong the process must be altered heavily which impacts the economy of the product development. Whereas the concurrent engineering methodology smoothly resolves the problem and encourages positive changes that allow an evolutionary design approach. The difference between the two approaches can easily be recognized from the Wikipedia image attached in Fig. 1 below.

**Fig. 1: Sequential design vs Concurrent Engineering Approach**

The image in Fig. 2 below is self-explanatory to understand how the concurrent engineering design process can effectively save time with respect to the conventional sequential engineering approach:

Time Saving in Concurrent Engineering Philosophy. — **Fig. 2: Time Saving in Concurrent Engineering Philosophy**

Product development process using Concurrent Engineering

To create a timely product with the highest quality and lowest cost, concurrent engineering methodologies provide a very important concept. The basic concurrent engineering product/service development process consists of the following four main phases:

Market Investigation
Product Design Specification
Conceptual Design
- Concept Generation
- Concept Evaluation
- Concept Development
Detail Design

The typical concurrent engineering processes using concurrent engineering is clearly explained by A. Hambali, S.M. Sapuan, N. Ismail, Y. Nukman, and M.S. Abdul Karim in their paper “The Important Role of Concurrent Engineering in
Product Development Process” as shown in Fig. 3 below

**Fig. 3: Concurrent Engineering in Product development**

Challenges of Concurrent Engineering

The main challenges that arise in the concurrent engineering philosophy are:

dependency on efficient communication between team members.
implementation of early design reviews.
software compatibility.
efficient exchange of computer models/design information.
organizing and managing project teams effectively.
training people on how to perform concurrent design effectively.

Examples of Concurrent Engineering

Even though originated in Japan, various companies around the world have adopted the philosophies of Concurrent Engineering. A few such organizations that glorify the examples of concurrent engineering are:

NASA
ASI
Schlumberger
STV Incorporated
Boeing
Harley Davidson
CNES
ASML, etc

References and Further Studies

An Issue about USER DEFINED SIFs

Written by Milad Haji Mohammad Karim in Caesar II,Piping Stress Analysis,Piping Stress Basics

User-defined SIF is the stress intensification factor that the user input into the stress analysis program. The SIF values are usually calculated using FEA programs and then manually entered in the input screens of the stress analysis programs. To increase the accuracy of the output results of a stress analysis problem using the beam method, It is always suggested to extract the amount of SIFs from a Finite Element Analysis (FEA) and then implement them in stress programs like CAESAR II, AutoPIPE, Start-PROF, or Rohr II.

With the deletion of Appendix D from the 2020 edition of ASME B31.3, the use of ASME B31J and other FEA programs will be increased while stress analysis of piping systems. Hence, User-defined SIF values will be very important for stress analysis aspects.

For a branch connection (Tee), The user has to put the amount of extracted SIFs in all 3 elements that form the connection, i.e. two elements for the header and one for the branch, considering the fact that the amount of SIFs for the branch and header are different. For example, for the connection shown in the below figure (Fig. 1), the amount of the header SIFs is entered at nodes 20.1 and 20.2 while the branch SIF is defined at node 20.4.

**Fig. 1: Adding User-defined SIF in Tee joints**

In order to do this, the “SIFs & Tees” box in elements 20.4-45 should be checked, and then the In-Plane and Out-Plane SIFs and also torsion and axial SIFs (if it is necessary) are defined at node 20.4. The same method should be implemented for header elements (at nodes 20.1 and 20.2). The key point in this method is that referring to Fig. 2 below, the type of connection must be blanked.

SIF types selection while specifying user defined SIF — **Fig. 2: SIF types selection while specifying user-defined SIF**

Indeed, in the old method of defining of SIFs, when the type of connection (such as UFT, RFT, and …), is determined in one node, the program will consider that node as an intersection and apart from the calculation of the amount of SIFs, the “Effective section modulus” named “Z_e” in B31 codes, is used for the calculation of the amount of the stresses in the branch section.

**Fig. 3: Effective Section Modulus formula**

But, In the new method, since the value of branch SIFs is extracted and defined directly, therefore, the section modulus of the branch pipe must be used instead of the effective section modulus. This issue has been mentioned in the edition 2016 of the B31.3 code:

In Caesar II, When the type of an intersection is left blank, the real section modulus of pipe elements will be used in stress calculation.

However, leaving the type section blanked causes a problem that must be considered by the user and then a proper solution must be implemented as has been described in the following.

What is the problem? What is the solution?

In Caesar II, as soon as the “SIFs & Tees” box is checked for a particular node and then the type of connection is determined, that node will be considered as an intersection and both the in and out planes will be specified automatically. The procedure of how Caesar II determines these planes has been described in the “User Guide” of the program.

But if the type of connection is not determined, the related node won’t be considered as an intersection and then the in and out planes won’t be determined.

Indeed, using the new method for SIFs determination and when the type is not specified, the program will assume that the user is defining the SIFs for 3 straight elements separately. The In-plane and Out-Plane directions are meaningless for a straight element. However, the program will consider these directions even for a straight element based on the procedure that has been mentioned in detail again in the “User Guide” and then each SIF is assigned to the relevant plane(direction).

The main concept of the Caesar II program for the determination of the in and out planes of a straight element is that there are local coordinate directions and axes for each element named a, b, and c and the program always considers the moment around the b axis as the In-plane moment. The local coordinates in Caesar II are defined in this order:

But, sometimes, based on the orientation of an intersection in the global coordinate system, the In-Plane and Out-Plane directions of the 3 straight elements that form that intersection will be different from the real In-Plane and Out-Plane directions of the mentioned connection. In this case, in order to force the program to calculate the stresses correctly, the extracted SIFs from FEA software are needed to be entered in reverse order.

Some examples

Please consider the below example (Fig. 6) for instance:

**Fig. 6: Typical example for SIF definition**

Referring to the above figure it is obvious that for this intersection, the moment around Z-axis is the In-plane bending moment while for the straight element from node 20.4 to node 45, the moment around X-axis will be the In-plane moment. Now, assume that the In-Plane and Out-Plane SIFs related to the branch side of this connection have been extracted from an FEA program as 3 and 11 respectively and the user wants to import them in Caesar II and at node 20.4. Based on what was mentioned above, these amounts need to be imported in reverse order as has been shown in the below figure (Fig. 7).

Inputting user defined SIFs in Caesar II — **Fig. 7: Inputting user-defined SIFs in Caesar II**

Considering the straight elements of the header, it is obvious that the M_Z is the In-Plane moment for both the straight elements and also the connection itself. Therefore, there is no need to import the extracted SIFs of the header in reverse order.

Now, please consider another example referring to the below figure.

This is a welding Tee and the amount of In-Plane and Out-Plane SIFs are 2.55 and 3.067 respectively. The outer diameter and the thickness of the header and branch are shown in the following figure.

In the first try, the “SIFs box” of the connection has been checked at node 4060 and on the element 4040-4060.

Referring to the below figure (Fig. 9), the amount of bending stress at the branch section is 71.25 Mpa

**Fig. 9: Bending Stress at Branch Connection (first try)**

On the next try, the SIFs of the branch element are imported equal to what was obtained on the first try and also the type of the intersection is left blanked. We may expect to obtain the same results!

Entering user-defined SIF in branch connection — **Fig. 10: Entering user-defined SIFs in branch connection**

But, The below figure reveals that the bending stress has changed to 78.41 Mpa.

Fig. 11: **Bending Stress at Branch Connection (second try)**

In the last try, the obtained values of the In-Plane and Out-Plane SIFs are imported again, but, this time in reverse order, and the type is left blanked again.

Referring to the below figure, the amount of bending stress at node 4060 is again 71.25 Mpa similar to what was obtained on the first try.

Fig. 13: **Bending Stress at Branch Connection (third try)**

Indeed, for this intersection, the In-Plane direction of the branch straight element is different from the real In-Plane direction of the connection and therefore the SIFs must be imported in reverse order in order to calculate the bending stress correctly.

Finally, it should be noted that the approach of the B31.3 code is that in the absence of more applicable data, the axial SIF is supposed to be equal to Out-plane SIF (only for branches). Therefore, if the extracted Out and In-Plane SIFs are needed to be imported in reverse order, you will also have to import the amount of axial SIF manually and equal to the real Out-plane SIF of the connection in order to force the program to calculate the total code stress correctly. You may also get the axial SIF from a better source such as an FEA.

Few more related articles for you.

Stress Intensity Factor (SIF), Flexibility Factor: ASME B31.3 vs ASME B31J
Piping Elbow or Bend SIF (Stress Intensification Factor)
How to use ASME B31J-2017 and FEM for SIF and k-factors for Stress Analysis
Importance & Impact of Stress Intensification Factor (SIF) in Piping

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