Magnetic Particle Inspection (MPI) Procedure

Written by Anup Kumar Dey in Construction,Engineering Materials,Inspection and Testing,Mechanical,Piping Interface

Magnetic Particle Inspection (MPI) is one of the most widely used non-destructive inspection methods for locating surface or near-surface defects or flaws in ferromagnetic materials. MPI is basically a combination of two NDT methods: Visual inspection and magnetic flux leakage testing. Developed in the USA, magnetic particle inspection is extensively used to detect defects in the casting, forging, and welding industries.

MPI is simple, easy, fast, and very effective. This is the reason the Magnetic particle test is used in a variety of industries like automotive, oil & gas construction, chemical, and petrochemical plant construction, structural steel, aerospace, offshore structures, power generation industries, and pipeline industries. This is also known as the magnetic particle test or magnetic particle examination in NDT.

Basic Principle of Magnetic Particle Inspection

MPI uses magnetic fields and magnetic particles for detecting defects in ferromagnetic components. The basic principle of this inspection method is that the component specimen is magnetized to generate magnetic flux in the material which travels from the north pole to the south pole (magnetic flux exits at the north pole and enters at the south pole). Now if there is any discontinuity or flaws in the component, secondary magnetic poles are produced in the cracked faces. In this location, the magnetic field spreads out due to the air gap in the defect causing a magnetic flux leakage field. Such regions can be detected easily by using magnetic particles (iron powder), or a liquid suspension on the surface. Due to the magnetic effect, such particles are attracted to the flux leakage and make a cluster around the flaw making it visible. Refer to Fig. 1 showing the basic principle of magnetic particle inspection.

The magnetic particles can be dry or wet. Normally, dry particles can be used up to a temperature of 316 Deg C wet particles can be used up to a temperature of 50 Deg C.

Steps for Magnetic Particle Inspection

The magnetic particle inspection (MPI) is performed in the below-mentioned six steps.

1. Surface Preparation:

All surfaces and adjacent areas (within 1 inch) that will be examined must be free from rust, scale, sand, grease, paint, slag, oily films, or other interfering conditions. Unusually rough or non-uniform surfaces may interfere with magnetic particle cluster formation making interpretations of the magnetic particle inspection method’s indications difficult.

2. Inducing a Magnetic Field:

This is the most important step in the magnetic particle inspection procedure. In this step, place the equipment on the area to be tested and induce a magnetic field. Various types of magnetic particle inspection equipment are available. Widely used industrial equipment are Permanent magnets, Electromagnetic Yokes, Current flow probes, Magnetic Flow, Flexible coils, Threading bars, Adjacent cables, etc. The magnetization technique can be Longitudinal, Circular, or Multidirectional Magnetization. Equipment spacing in the inspection area is normally kept in between 3 inches to 8 inches. An ASME Pie Gauge or Burmag Castrol strip can be used to verify adequate magnetization of the part.

3. Applying Magnetic Particles on the Test Surface:

Both dry and wet magnetic particles can be either fluorescent or non-fluorescent (visible, color contrast) and are available in a variety of colors to contrast with the tested material. So accordingly choose the required particles for the magnetic particle inspection and apply them on the surfaces when the specimen is in magnetized condition.

4. Examine the component surface for defects

Remove the excess particles using light airflow and inspect the component for defects as per acceptable standards.

5. Repeat the test by changing the magnetic field

Two separate examinations are carried out on each area to be tested. The second examination is performed with the lines of flux perpendicular to those used for the first examination in that area.

Refer to Fig. 2 which shows the above 5 steps. An electromagnetic Yoke is used in the test to inspect the welding of two plates.

**Fig. 2: Steps for Magnetic particle inspection**

6. Demagnetization and Cleaning:

The presence of Residual magnetism in the component may interfere with the subsequent usage. Hence, the demagnetization shall always be performed on the parts once the magnetic particle inspection is over. The presence of residual magnetism can be verified using a calibrated Gaussmeter, Magnetic Field Meter, or a hall Probe Gauss meter. Residual magnetism must not exceed (+/-) 2 gausses.

After that, the parts shall be cleaned to remove all residual magnetic particle materials. If wet fluorescent MPI was performed, the part shall be scanned with the backlight to assure that the cleaning is adequate.

Advantages of Magnetic Particle Inspection/Test

The main advantages of magnetic particle inspection/testing are

Find flaws on the surface and near surfaces
Fast examination method with an immediate result
This is an easy method as compared to other NDT methods
Portable and low-cost equipment.
Defects are visible directly on the surface.
Relatively safe method.
Hot testing can be performed using dry particles.
The shape and size of the cracks are indicated.
Less training requirements.

Disadvantages of Magnetic Particle Inspection

The major drawbacks of magnetic particle inspection/examination are

MPI is limited only to ferromagnetic materials like steel, cast irons, etc. Non-ferrous materials, cannot be inspected.
The inspection is limited to small sections only. The examination of large parts may require the use of special equipment.
Equipment must be calibrated, with no permanent record of the result.
Before inspection thick paints (>0.005″) shall be removed.
Post-cleaning and demagnetization are normally required.
Magnetic flux and indications must be aligned for proper results.
Access may be a problem for the magnetizing equipment.
Testing in two perpendicular directions is required.

Codes and Standards for Magnetic Particle Inspection

Normally ASME Section V: Nondestructive Examination governs the magnetic particle inspection/examination methods for most organizations. However, there are various other codes and standards that provide guidance rules for magnetic particle test procedures as listed below

ISO (International Organization for Standardization) Standards for MPI

The following ISO standards govern the inspection by MPI.

ISO 3059, Non-destructive testing – Penetrant testing and magnetic particle testing – Viewing conditions
ISO 9934, Part 1, Part 2, and Part 3– Non-destructive testing – Magnetic particle testing – Part 1: General principles, Part 2: Detection media, Part 3: Equipment
ISO 10893-5-Non-destructive testing of steel tubes. Magnetic particle inspection of seamless and welded ferromagnetic steel tubes for the detection of surface imperfections
ISO 17638, Non-destructive testing of welds – Magnetic particle testing
ISO 23278, Non-destructive testing of welds – Magnetic particle testing of welds – Acceptance levels

European Committee for Standardization (CEN) Standards for MPI

EN 1330-7, Non-destructive testing – Terminology – Part 7: Terms used in magnetic particle testing
EN 10246-12, Non-destructive testing of steel tubes – Part 12: Magnetic particle inspection of seamless and welded ferromagnetic steel tubes for the detection of surface imperfections
EN 1290, Surface Crack Testing
EN 1369, Founding – Magnetic particle inspection
EN 10228-1, Non-destructive testing of steel forgings – Part 1: Magnetic particle inspection
EN 10246-18, Non-destructive testing of steel tubes – Part 18: Magnetic particle inspection of the tube ends of seamless and welded ferromagnetic steel tubes for the detection of laminar imperfections

ASTM (American Society of Testing and Materials) Standards for magnetic particle inspection

ASTM E1444/E1444M Standard Practice for Magnetic Particle Testing
ASTM E 1316 Terminology for Nondestructive Examinations
ASTM A 275/A 275M Test Method for Magnetic Particle Examination of Steel Forgings
ASTM E543 Practice Standard Specification for Evaluating Agencies that Performing Nondestructive Testing
ASTM E 709 Guide for Magnetic Particle Testing Examination
ASTM A456 Specification for Magnetic Particle Inspection of Large Crankshaft Forgings
ASTM E 2297 Standard Guide for Use of UV-A and Visible Light Sources and Meters used in the Liquid Penetrant and Magnetic Particle Methods

The United States Military Standard: A-A-59230 Fluid, Magnetic Particle Inspection, Suspension
CSA (Canadian Standards Association) Standards: CSA W59 Welded steel construction

MPI Standards of Society of Automotive Engineers (SAE)

widely used MPI standards from the society of Automotive Engineers are listed below:

AMS 3040 Magnetic Particles, Nonfluorescent, Dry Method
AMS 2641 Magnetic Particle Inspection Vehicle
AMS 3045 Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle, Ready-To-Use
AMS 5355 Investment Castings
AMS 3041 Magnetic Particles, Nonfluorescent, Wet Method, Oil Vehicle, Ready-To-Use
AMS 3043 Magnetic Particles, Nonfluorescent, Wet Method, Oil Vehicle, Aerosol Packaged
AMS 3042 Magnetic Particles, Nonfluorescent, Wet Method, Dry Powder
AMS 3044 Magnetic Particles, Fluorescent, Wet Method, Dry Powder

Magnetic Particle Inspection Equipment

During magnetic particle examination, various kinds of equipment are required as listed below:

Electromagnetic Yokes
Magnetic Benches
Power Packs & Mobile Test Units
Demagnetising Units

These magnetic particle inspection equipment should be designed to be durable, fast, and reliable. Refer to Fig. 3 which shows a few of the magnetic particle test equipment.

Code Acceptance Criteria for Magnetic Particle Inspection

As per ASME Sec VIII Div 1 and Div 2, all surfaces examined by magnetic particle inspection shall be free from

Linear indication
Rounded indication with size greater than 3/16 inches.
Four or more rounded indications in a line separated by 1/16 inch or less.
Crack-like indications, irrespective of surface condition.

As per ASME B31.3, any cracks or linear indications are unacceptable.

Magnetic Particle Inspection/Testing Questions

The following pdf link provides a few sample questions for examinations for level 1 and level 2. Go to page no 46 directly to prepare answers for magnetic particle testing questions. Click here to open the pdf and start preparing.

Creep Rupture Usage Factor for Allowable Variations in Elevated Temperature Service

Written by Alex Matveev in Caesar II,Piping Design Basics,Piping Stress Analysis,Piping Stress Basics,Start-Prof

Appendix V of ASME B31.3 code covers the application of the Linear Life Fraction Rule, which provides a method for evaluating variations at elevated temperatures above design conditions where material creep properties control the allowable stress at the temperature of the variation.

What is Creep-Rupture Usage Factor?

The calculated value of Creep-Rupture Usage Factor “u” indicates the nominal amount of creep-rupture life expended during the service life of
the piping system. If u ≤ 1.0, the usage factor is acceptable. If u > 1.0, the designer shall either increase the design conditions (selecting a piping system components of a higher allowable working pressure if necessary) or reduce the number and/or severity of excursions until the usage factor is acceptable

i – as a subscript, 1 for the prevalent operating condition

ti – total duration, h, associated with any service condition, i, at pressure, Pi, and temperature, Ti

tri – allowable rupture life, h, associated with a given service condition i and stress, Si

Ti – temperature, °C (°F), of the component for the coincident operating pressure-temperature condition i under consideration

C – Larson-Miller constant. C = 30 for 9Cr–1Mo–V; C = 20 for carbon, low, and intermediate alloy steels, except 9Cr–1Mo–V; C = 15 for austenitic stainless steel and high nickel alloys

TE – effective temperature, °C (°F) from Table A-1 or Table A-1M, find the temperature corresponding to basic allowable stress equal to the equivalent stress, Si, using linear interpolation if necessary. This temperature, TE, is the effective temperature for service conditions i.

The equivalent stress, Si, is calculated as follows

SL – the maximum stress due to sustained loads, during service conditions i

Spi – pressure-based equivalent stress, MPa (ksi)

Pmax – maximum allowable gage pressure, kPa (psig), for continuous operation of pipe or component at design temperature, considering allowances, c, and mill tolerance, but without considering weld joint strength reduction factor, W; weld joint quality factors, Ej; or casting quality factor, Ec

Sd – allowable stress, MPa (ksi), at design temperature, °C (°F)

Pi – gage pressure, kPa (psig), during service condition i

Calculation of Creep-Rupture Usage Factor

The latest version of modern professional PASS/START-PROF software includes the ability to automatically calculate the Creep-Rupture Usage Factor for the piping system.

Firstly, the material database contains the Larson-Miller constant for every material as shown in Fig. 1 below.

**Fig. 1: Larson-Miller Constant in Start-Prof**

Secondly, the operation mode editor contains the time duration for each operation mode

**Fig. 2: Time Duration in Operation mode editor**

And thirdly, the code stress table contains the column, where the “u” factor is printed. If you move the mouse over the table cell, you will see the calculation details (As shown in Fig. 3 below)

**Fig. 3: Creep-Rupture Usage Factor output in Start-Prof**

The more information about the new modern pipe stress analysis software PASS/START-PROF and analysis methods you may learn from the resources web page and from Start-Prof basics and tutorials.

Minimum Design Metal Temperature (MDMT) and Impact Test

Written by Alex Matveev in Engineering Materials,Piping Design Basics,Piping Stress Analysis,Piping Stress Basics,Start-Prof

Minimum Design Metal Temperature or MDMT is the lowest temperature that a piping system with specified material and thickness can withstand. While designing piping systems (equipment) in cold regions where the environment temperature falls drastically or piping systems carrying cryogenic temperature fluid, MDMT is a critical factor. Considering the metal’s resistance to brittle failure, MDMT is the lowest permissible metal temperature for that thickness.

The piping designer shall verify that materials are suitable for service throughout the operating temperature range (maximum and minimum possible temperatures). Table A-1 and Table A-1M of ASME B31.3 code contain the minimum design metal temperature for which the material is normally suitable without impact testing. Refer to Fig. 1 where minimum design temperatures for a few carbon steel pipe materials are highlighted.

**Fig. 1: MDMT of Carbon Steel Pipe and Tube**

The MDMT for Carbon Steel in -29°C. So what does it mean? Can we use it below that temperature?

Below -29°C, ductile Carbon steel starts converting into brittle material. So impact test requirements as per the code arise as brittle carbon steel can easily fail catastrophically. However, the code provides few rules to use such materials below its minimum design metal temperatures as provided below:

Rules for using materials below its MDMT without impact testing

The use of a material at a design minimum temperature colder than −29°C (−20°F) is established by para. 323.2.2 and other impact test requirements. For carbon steels with a letter designation in the Minimum Temperature column, the curve in Figure 323.2.2A of ASME B 31.3 (Reproduced in Fig. 2) is used. MDMT depends on the nominal thickness.

Impact testing of the base metal is not required if the design minimum temperature is warmer than or equal to the calculated value of MDMT.

However, for steels, impact testing is not required if the stress ratio “r” 323.2.2 (b) is 0.3 or less, and the design minimum temperature is warmer
than or equal to −104°C (−155°F), and temperature reduction may be used if 323.2.2 (c) rules are satisfied:

(1) The piping is not in the Elevated Temperature Fluid Service.
(2) Local stresses caused by shock loading, thermal bowing, and differential expansion between dissimilar metals (e.g., austenitic welded to ferritic) are less than 10% of the basic allowable stresses at the condition
under consideration.
(3) The piping is safeguarded from maintenance loads, e.g., using a valve wheel wrench on a small-bore valve.

Also, for carbon, low alloy, and intermediate alloy steel materials (including welds) that have not been qualified by impact testing, the minimum temperature from Table A-1, Table A-1M, or Figure 323.2.2A may be reduced to a temperature no colder than −48°C (−55°F) by the temperature reduction provided in Figure 323.2.2B if 323.2.2 (c) rules are satisfied.

**Fig. 3: Temperature Reduction calculation as per stress ratio**

What is the Stress Ratio, r?

The stress ratio “r” is calculated as the maximum value from the following:

From all operating modes and force-based loadings, we calculate the maximum rating value r

mt% – mill tolerance, C – corrosion allowance, S – allowable stress

From all operating modes’ force-based loadings (force+displacement)-based loadings we calculate the maximum value of r

How does Start-Prof take care of MDMT?

The latest version of professional PASS/START-PROF software includes the ability to check automatically if the impact test is needed or not.

Firstly, the PASS/START-PROF has a material database that includes the minimum metal temperature for all materials. For carbon steels with a letter designation in the Minimum Temperature, PASS/START-PROF calculates the minimum metal temperature automatically, according to Figure 323.2.2A.

**Fig. 4: MDMT Consideration in Start-Prof**

Secondly, the software automatically calculates “r” values for all operating modes of the piping system. And has the special option “Use MDMT Allowable Reduction” in project settings to verify if the temperature reduction is allowed or not as shown in Fig. 5

**Fig. 5: Using MDMT Allowable Reduction in Start-Prof**

Thirdly, for each pipe element in the system, the software determines if the impact test is needed or not according to the previously described rules of 323.2.2 (a), (b), (d), (e), (f), (g), (h), (i), (j) ASME B31.3-2018. The result is shown in the special MDMT table as shown in Fig. 6 below:

After analysis, if the minimum design or ambient temperature from all operating modes is lower than the calculated MDMT value, the “Impact Test” requirement note is printed. Otherwise, the result simply shows “OK” for proceeding further.

To avoid impact testing, the stress ratio “r” value should be reduced as low as possible for the critical piping system elements. To do this, you need to create the piping stress analysis model in PASS/START-PROF and reduce the sustained and operation stresses by adding more support or flexibility to the piping system.

More information about the new modern pipe stress analysis software PASS/START-PROF you may learn from the resources web page.

Few more useful resources for you.

Stress Analysis basics using Start-Prof
What will you do if Carbon Steel pipe is installed in place of LTCS
Stress Analysis using Caesar II
Piping Materials Basics

Modeling Piping Connection to Storage Tank

Written by Alex Matveev in Piping Stress Analysis,Piping Stress Basics,Start-Prof

The tank nozzle can be modeled using the special “Tank Nozzle” object in START-PROF software.

Tank connection modeling has a special significant features in comparison with pressure vessel modeling.

Tank Nozzle Movement due to Tank Temperature Expansion

Due to the large tank diameter, the temperature expansion can cause significant nozzle movement along its axis. This movement can be calculated by the following formula:

Storage Tank nozzle movement due to temperature change

Tank nozzle displacement due to tank temperature expansion is modeled automatically using the “Tank Nozzle” object.

Tank Nozzle Movement due to Tank Settlement

Tank diameter is very large, due to this tanks usually have no foundation that can distribute its weight over the big soil area. Due to this, the tank settlement happens. Settlement value depends on soil type, tank weight, and dimensions, and should be calculated based on the geo-technological investigation report. The greatest settlement value is at the center of the tank, the lowest value is at the edges.

Since the piping connected to the nozzle is connected to the tank shell, we need to consider it during stress analysis. The settlement value should be specified in the “Tank Nozzle” object properties.
To reduce the effect of tank settlement on piping the first support shall be kept sufficiently away from the tank nozzle

Tank Nozzle Movement due to Tank Bulging Effect

Storage Tanks are used for liquid storage and hence, are filled with liquid. The height of the liquid level is varying therefore the pressure on the tank shell is varying. The greatest pressure is near the bottom. The tank shell tries to expand near the bottom, but the bottom holds it. Due to this the nozzle moves radially outward and rotates in a vertical plane. This effect is significant for tanks with a diameter greater than 36 m.

According to API 650 code Appendix P radial growth of shell due to hydrostatic pressure:

Rotation of shell due to hydrostatic pressure:

G is the design specific-gravity of the liquid;
H is the maximum allowable tank filling height, in mm (in.);
L is the vertical distance from the nozzle centerline to the tank bottom, in mm (in.);
R is the nominal tank radius, in mm (in.);
t is the shell thickness at the opening connection, in mm (in.);
β is the characteristic parameter, 1.285/(R*t)^0.5 (1/mm) (1/in.);
E is the modulus of elasticity, in MPa (lbf/in.2);
DT is the normal design temperature minus installation temperature, in °C (°F);
a is the thermal expansion coefficient of the shell material, in mm/[mm-°C] (in./[in.-°F])
To reduce the nozzle rotation effect, it is recommended to turn the pipe 90° very close to the tank nozzle.

To consider this effect you need to specify the filling height and product density in the “Tank Nozzle” object.

Storage Tank Nozzle Flexibility

Tank nozzle flexibility can be calculated using the API 650 code or Nozzle-FEM software.

Storage Tank Nozzle Allowable Loads

Allowable loads are calculated using two methods.

The first method is according to API 650. The allowable values envelopes for moments ML, MC, and axial force FR are shown in the pictures below

The second method is according to STO SA 93-002-2009 code (Russian Standard). The allowable values envelopes for moments ML, MC, and axial force FR are shown in the pictures below

The method can be used if D and DN values are inside the following envelope

Also, Nozzle-FEM software may be used.

Few more related articles to clear your doubts.

Stress Analysis using Start-Prof
An article on Tank Bulging effect or bulging effect of tank shells
Tank Settlement for Piping Stress Analysis
Various Types of Atmospheric Storage Tanks
A Brief Presentation on Storage Tanks
Considerations for Storage Tanks Nozzles Orientation
Equipment and Piping Layout for Storage Tanks
Case Study of Tank Farm Design and Dike Wall Height Calculation
Difference between API 650 and API 620 Tanks: API 650 vs API 620
Camouflaging of Oil Storage Tanks
Storage Tank Failure: Examples, Causes, and Prevention
Storage Tank Erection: Conventional vs Jacking Method

Two-Phase Separator Design Basics

Written by Nisarg Sonawane in Mechanical,Piping Interface,Process

A Separator is a type of pressure vessel that is used to separate the gas and liquid from a two-phase mixture. The two-phase separator separates the liquid and gas phases from the mixture.

Pressure vessels are widely used in the process plant industry. Pressure vessels serve various functions such as

short-term hold-up, i.e. day tanks, surge vessels,
pressurized storage storages, i.e. bullets, Horton spheres,
2-phase (V/L) / 3-phase (V/L/L) separators,
Special purpose vessels such as reactors, columns, and jacketed vessels.

The most common shape of pressure vessels is a cylindrical shell with dished ends. Other types of end closures such as conical, and hemispherical are also used when appropriate. For large pressurized storage, a spherical shape may be chosen. The Standard Engineering codes used for the design of 2-phase separators are GPSA guidelines, and API 12J.

Orientation of Separators

Pressure vessels/Separators can be installed in vertical or horizontal orientation.

Vertical Pressure Vessels

Vertical orientation is preferred to horizontal orientation owing to the following advantages:

Lower plot space required: In most cases length (or height) of pressure vessels is more than the diameter. Therefore, the layout space required is lower when a vessel is placed vertically.
Pumps are commonly used for the transfer of liquids from pressure vessels. The vertical vessel provides a higher NPSH available for the pump, as the operating level is at a higher elevation. This is advantageous for the design of the pumps.
The vertical installation provides better utilization of vessel volume as the working volume between the high and low operating levels. This is illustrated in Fig. 1 below:

**Fig. 1: Vertical vs Horizontal Pressure Vessel**

Horizontal Pressure Vessels

A vessel may be oriented horizontally when higher mechanical strength is needed to support the weight. This is especially important in the case of high-pressure vessels and very long vessels (high L/D ratio). Horizontal vessels can be provided with two or more saddles.

Two-Phase (V/L) Separator Design

Depending on fluid phases the separators can be classified into two groups.

Two-Phase Separator and
Three-Phase separator

Two-phase separators handle two-phase fluids. One is the gaseous phase and the other is the liquid phase. While a three-phase separator can separate out three phases; normally a gas, oil, and water (two liquid phases and one gas phase). In the following paragraphs, we will briefly explore the design basics of two-phase separators.

Selection of Separator: Horizontal or Vertical

As a rule, a vertical drum should be chosen when the ratio of vapor to liquid volume is large (750 or more). The vertical drum is often preferred since the separation efficiency does not vary with the liquid level in the drum. Also, the plot space required is lower for the vertical drum.

The figure given below (Fig. 2) is used as guidance for the selection of the orientation of separators.

**Fig. 2: Separator Selection Guide Chart**

Choice of Separator Internals

Separator Internals are provided to increase the efficiency of the separator and reduce entrainment. The Internals available commercially is Demister Pads, Vane packs, Multi cyclones, or swirl decks. The size of droplets present in the two-phase flow entering the drum decides the type of internals to be used. Droplet size depends on the flow regime of the inlet pipe. The diameter of the inlet pipe should be selected to avoid dispersed, annular, or mist flow. The approximate size of droplets present in the vapor phase is given by:

Symbol	Description	Units
d	Drop diameter	m
D	pipeline internal diameter	m
g	acceleration due to gravity	m/s²
k	Souder’s Brown proportionality constant	k/s
ρ	density	kg/m³
σ	surface tension	N/m
v	velocity	m/s
W	mass flowrate	kg/s
P	pressure	bar
ν	kinematic viscosity	m2/s
μ	dynamic viscosity	Ns/m2

Subscripts
v	gas/vapor phase
l	liquid phase

Determining Separator Diameter

The design methods are based on Souder’s-Brown equation

Maximum Allowable velocity inside a separator

The maximum allowable velocity of the vapor phase is given by the value of vmax calculated by the Souder’s-Brown equation. The diameter of a vertical separator is calculated based on the value of v_max.

In the case of a horizontal vessel, the full cross-section area for the flow of vapor is calculated based on the value of v_max.This is in turn used to calculate vessel diameter.

Typical Values of Proportionality Constant, k

Different values of the proportionality constant k are applied for the internals and orientation of the separator.

	k value, m/s
Vertical knock-out drums
Empty knock-out drum	0.08
Empty Compressor suction drums	0.04
Flare knock-out drum	0.07
Horizontal knock-out drums
Empty, for bulk separation	0.1
Empty Compressor suction drums	0.05

Vertical demister mat KO drum	0.105
Horizontal demister mat KO drum	0.15

Table showing values of proportionality constant, k for knock-out drums

Deciding the Height of the Separator

Determining Height of Separator — **Fig. 3: Determining Height of the Separator**

The height of the separator or drum is calculated considering the following requirements:

Between the high liquid level and the inlet pipe allow the larger of 0.3 vessel dia or 300 mm.
From the top of the inlet nozzle to the tan line allow the larger of 0.9 vessel dia or 900 mm.

Fig. 4 shows a typical separator used in the oil and gas industry.

**Fig. 4: Typical Horizontal Separator used in an oil and gas industry**

What is a P&ID Drawing | P&ID Symbols | How to Read P & ID Drawings

Written by Anup Kumar Dey in Pipeline,Piping Design Basics,Piping Interface,Process

The full form of P&ID is Process and Instrumentation Diagram. This is an engineering document developed by process engineers that shows the piping and other related items for process flow. A P&ID provides a detailed graphical representation of the actual process system that includes the piping, equipment, valves, instrumentation, and other process components in the system. All components are represented using various P&ID symbols.

The graphical representation in a P&ID drawing establishes the functional relationship of piping, instrumentation, and mechanical equipment. P&IDs are one of the most important documents for any project and are crucial in all stages of process system development and operation. This is the most extensively used engineering document and is used by all engineering disciplines like Process, piping, mechanical, civil, HVAC, electrical, and instrumentation.

What is P&ID used for?

A P&ID (Also known as PEFS, Process Engineering Flow Scheme) is a fundamental engineering document that serves various purposes as mentioned below.

P&IDs Provide key piping and instrumentation items along with their proper arrangement.
It serves as a basic document for operation, control, and shutdown schemes.
The piping and Instrumentation diagram provides a basis for maintenance and modification works.
It gives the regulatory and plant safety requirement.
A P&ID drawing serves as a guide for start-up and operational data.
P&IDs are used to develop guidelines and standards for facility operation
It is the basic training document to explain the process details to operation guys, field engineers, and maintenance professionals. The P&ID drawings help them to track the interconnection between the piping and instrumentation and equipment.
A P&ID provides the design and construction sequence for the plants for systematic planning of activities.
They serve as a basis for studying different mechanical and chemical steps to find the root cause if something goes wrong.
It also provides basic information for initial project cost estimation.
An important document for HAZOP, Model review, Process Safety Management, etc is the process and instrumentation diagram.
Finally, the P&ID drawing provides a common language for discussing plant operations.

Limitations of P&ID

P&IDs being graphical schematic process representations have some limitations like

They are not on a scale, similar to real models.
They are not standardized documents so vary from company to company.

What should a P&ID include?

There is no exact code or standard that dictates what exactly should be included in the P&ID drawing document. That is the reason P&IDs from different organizations vary slightly. Broadly, all P&IDs normally include the following:

All Mechanical equipment with equipment numbers (Tags) and names.
All valves with proper identification.
Instrumentation details with designations.
piping with line numbers, sizes, material specs, and other details.
Fluid Flow directions.
Miscellaneous items like drains, vents, special fittings, reducers, sampling lines, expansion joints, flexible hose connections, increases, and swaggers.
Piping and equipment interfaces with scope demarcation, and class changes.
Permanent start-up and flush lines.
References for Interconnections.
Interlocks, Control inputs, and outputs.
Annunciation inputs
A physical sequence of the piping items and equipment.
Equipment rating or capacity; sometimes short design and dimensional details.
Interfaces with vendors and contractors with scope.
Computer control system input.
Seismic category
Quality level
Details like equipment operating, standby, normally no flow, etc are included in some P&IDs.
Notes related to two-phase flow, special pipe length requirements, etc.
Piping slope requirements, Piping Insulation requirements.

Details excluded in a P&ID

The in-depth details are not included in the P&IDs. Various supporting documents are prepared for the detailed design and description of those items. Normally the following details are not included in a P&ID:

Process Flow Diagram
Pipe Route and length
Elbow, tees, and similar standard fitting details.
Pipe Support and Structural Details
Pressure temperature and flow data.
Manual switches and indicating lights
Extensive explanatory notes
Control relays
Instrument root valves
Primary instrument valves and tubing
Equipment rating or capacities
Equipment locations

Supporting Documents of P&ID

As the Piping and Instrumentation Diagram is not a detailed document, various supporting documents are prepared to complete the overall details of the P&ID. Few of those documents are:

PFD or Process Flow Diagram from which P&ID is generated.
PMS or Piping Material Specification which provides material details of piping and related items.
Equipment and Instrument Item datasheets specifying the required details about Equipment or instrument items.

P&ID Symbols

Process engineers use various P&ID symbols while constructing P&ID drawings. All those P&ID symbols are normally described at the start of the P&ID set. For the same design consultant, those symbols are normally constant. One should familiarize himself by studying those P&ID symbols to accurately read the P&ID drawings.

Instrumentation symbols in a P&ID are standardized as per ANSI/ISA’s S5.1 standard. This standard ensures a consistent, system-independent means of communicating instrumentation, control, and automation intent by providing standardized Instrumentation Symbols and Identification so everyone understands.

Four graphical elements are defined in ISA S5.1 for instrumentation. Those are discrete instruments, shared control/display, computer function, and programmable logic controller. The standard also groups them into three location categories as the primary location, auxiliary location, and field-mounted location category. Click here to check all the P&ID symbols that ANSI/ISA’s S5.1 standard provides.

BS 5070 and ISO 10628 also provide a few guidelines and best practices for P&ID symbols. The following images (Fig.1 to Fig. 7) provide an example of the P&ID symbols that are normally used in a typical P&ID.

Instrument Symbols in P&ID

**Fig. 1: P&ID Symbols- Instrument Identification Letters**

**Fig. 2: P&ID Symbols-General instrument or function symbols**

P&ID Equipment Symbols

**Fig. 3: P&ID Symbols- Miscellaneous Equipment**

Valve Symbols in the Piping and Instrumentation Diagram

P&ID Symbols for Pumps and Actuators

**Fig. 5: P&ID Symbols-Pumps and Actuators**

P&ID Symbols for Miscellaneous Instruments and Functions

**Fig. 6: P&ID Symbols-Instrument or Function Symbols**

P&ID Symbols for Various Control Loops

**Fig. 7: P&ID Symbols-Various Control Loop Symbols**

Please note that few organizations use the words like P&ID Legends, P&ID Lead sheets, or P&ID Legend drawings in place of P&ID Symbols.

How to Read P&ID Drawings?

Reading or tracing a P&ID drawing to understand the process or design requirements are quite easy if the P&ID symbols are properly understood. So, it is always preferable to go through the P&ID symbols repeatedly, those are provided in the initial 4-5 pages of the P&ID sets. Once that is ready open the P&ID and start reading it.

Here, we will learn how to read P&ID with a simple example.
Refer to Fig. 8 which shows a part of a P&ID. We will read part of the suction and discharge line of pump P-1519.

As can be seen clearly the suction line is coming from a different P&ID drawing and entering into the bucket strainer S-1575.
The line number, pipe size, material spec, etc of the line are provided clearly.
The line number changed from the strainer outlet, one PSV connection is attached before the pump suction reducer.
After the reducer, the material specification is changed and then the line is connected to the pump suction flange.
In a similar way, the pump discharge flange is connected to the discharge line, Line number, size, PMS, etc. are mentioned.
So in a similar way, we can easily read the P&IDs as per our requirements and extract data to use for our purpose.
Related notes are provided wherever required. We have to refer to those notes for knowing any specific requirements.

Difference between P&ID and PFD

Click here to learn about the major differences between a P&ID and a PFD.

Online Course on Piping & Instrumentation Diagrams P&IDs

If you feel the above information on P&ID is not sufficient and wish to know more details regarding piping & Instrumentation diagrams then click here to attend this 8-hour-long details P&ID online course.

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