Types of Pipe Flanges for Piping and Pipeline Systems

Written by Anup Kumar Dey in Mechanical,Piping Design Basics,Piping Interface

A pipe flange is a circular disc-shaped piping component that attaches to a pipe for blocking or connecting other components like valves, nozzles, special items, etc. After welding, piping flanges are the most popular pipe joining methods. Wherever, any dismantling of components is required for maintenance, inspection, replacement, or operational purposes piping flanged joints are preferred.

Pipe flanges use bolts and gaskets in between to ensure leakage-free piping joints. Piping flanges are selected based on pressure-temperature rating and pipe class following ASME B16.5 or ASME B16.47 standard. However, custom-made pipe flanges can be manufactured but are not preferred in industries. Piping flanges are the best alternative to welding or threading and are manufactured by forging.

Types of Flanges

Various types of pipe flanges are used in industries. They can be classified based on

Pipe Attachment /Connection
Flange Facing
Pressure-Temperature rating
Codes

Pipe Flange Types Based on Pipe Attachment or Connection

Depending on the type of pipe connection the piping flanges can be classified as below:

Weld Neck Flanges

Weld neck pipe flanges are suitable for high-temperature and pressure applications. The neck of the pipe flanges is welded to the neck of the pipe.

The main features of weld neck flanges are:

Weld neck flanges (Fig. 1) have a long tapered hub between the flange ring & weld joint; Hence, these flanges are referred to as high hub flanges. This hub provides a more gradual transition from the flange ring thickness to the pipe wall thickness and the ID matches with the pipe ID. This smooth transition of weld neck flanges reduces high-stress concentrations and consequently increases the strength of the flange.
As Pipe ID and Flange ID match, there are no flow restrictions. At the same time erosion and turbulence are eliminated.
Weld neck flange is considered the best-designed butt welded flange available in the piping industry. The welding area, being sufficiently away from the face avoids undue distortion.
This type of flange is attached to the pipe by having a butt weld which can be radiographed if required.
Weld neck flanges are suitable for extreme service conditions to handle repeated bending from line expansion, contraction, or other external forces.
This type of flange is recommended for the handling of costly, inflammable, or explosive fluids where failure or leakage of a flange joint might bring disastrous consequences.
The pipe Schedule number and I.D. or O.D. must be provided while ordering weld neck pipe flanges.
The welding neck flange needs accurate alignment of bolt holes before welding.
However, Weld Neck flanges (Fig. 2) are expensive as compared to other flange types.
Weld neck flanges require more space and are bulky. Highly skilled manpower is required for the fabrication of welding neck flanges.
Weld Neck Flange is available in all sizes & it can be Flat Face, Raised Face, or Ring Type Joint type.
Butt-weld fittings like elbows, tees, or reducers can be directly welded to the weld neck flange without requiring any pipe spool in between.

**Fig. 2: Details of Welding Neck Flanges**

Slip-On Flanges

Slip-on pipe flanges are shorter in length than the weld neck flange so can be used where there is a space constraint. The inside diameter of slip-on flanges is slightly larger than the pipe OD and so it can slide over the pipe. They are secured to the pipe using two fillet welds from inside and outside. The Slip-on type of flange is widely used in lower temperatures and pressure applications because of its low initial cost. However, their life span is around one-third that of the weld neck flange.

The main features of slip-on flanges are:

The strength of the slip-on flange (Fig. 3) is around two-thirds that of a corresponding welding neck flange.
The slip-on flange is not recommended for corrosive and/or critical services.
The use of slip-on flange is usually limited to class 300 (refer to para on pressure-temperature rating) and design temperature not exceeding 500° F.
Proper alignment of bolt holes must be ensured before the welding of this type of flange.
The joint in a slip-on flange can not be subjected to radiography due to the absence of a full penetration weld.
slip-on flanges are not suitable for cyclic loading services.
Less skilled manpower is required during installation due to the use of fillet welds. The fillet weld size on the inside of the flange is equal to the pipe wall thickness, or 6mm; whichever is lower.

Lap Joint Flange

A lap joint flange is basically a two-component flange assembly. It has a stub end and a backing lap-joint ring flange. A pipe is butt-welded to the Stub End and the Lap Joint is free to rotate around the stub end. The face of the stub end acts as a raised face of the flange and can be of different materials to save cost. Only the stub end comes in contact with the fluid.

Lapped joint Flange and Blind flange — **Fig. 4: Lap Joint Flange and Blind Flange**

The main features of a lap joint flange are:

Lap joint flanges are used as a combination with a lap joint stub.
Lap joint flanges (Fig. 4) are a good alternative to costly flanges required for process design conditions. An ordinary steel flange behind the lap on alloy and stainless steel pipe without sacrificing internal corrosion protection can be used.
In plastic piping systems, Lap joint flange is used.
These flanges are comparable to slip-on flanges with respect to pressure-withstanding capability.
The major disadvantage of lap joint flanges is that it has only about 10% of the fatigue life of welding neck flanges. That is why these flanges are not used where severe bending stresses exist.
This type of joint avoids the necessity of accurate alignment of bolt holes since the flange is free to revolve on the pipe. So these flanges can be readily aligned with bolt holes of the mating flange.
These types of flanges are also useful in cases where frequent dismantling for cleaning or inspection is required or when it is necessary to rotate the pipe by swiveling the flange.

Blind Flange

A blind flange is a solid flange and without the central hole used to seal or block off a section of pipe or a nozzle on equipment that is not used. Blind flanges are designed robustly as they have to withstand remarkable pressure stress. However, they don’t have to absorb thermal stresses as they are free to expand as attached at the end of the piping connection.

The weight of blind flanges (Fig. 4) is normally more than other flange types. They are frequently used during pressure testing of piping systems. Blind flanges can be of Flat or Raised Face type.

Socket Weld Flange

Socket weld flanges use only one fillet weld on the outer side of the flange. As per ASME B31.1, in a socket weld flange connection, the pipe is inserted in the socket at first until it reaches the flange bottom and then it is lifted by 1.6 mm and finally fillet welded. This 1.6 mm gap is kept to allow proper pipe positioning inside the flange socket after the weld solidification.

Socket Weld Flanges are suitable for small-size pipes (up to 2″) and are not recommended for severe services. They can be used for high-pressure piping that does not transfer highly corrosive fluids as fluid accumulation inside the gap will easily corrode the pipe.

From a strength point of view, socket weld flanges (Fig. 5) are comparable to slip-on flanges.

Threaded or Screwed Flange

Threaded flanges are joined to pipes by screwing the pipe and are used on piping systems that prohibit direct welding on the pipe. Usually, threaded flanges are used for Galvanized Piping. Industrial Threaded flanges are made in sizes up to 4 inches with various pressure ratings. Their use is mostly limited to small pipe sizes carrying low-pressure temperature fluids.

Threaded flanges (Fig. 5) are frequently used in areas containing explosives. Cutting thread on very thin pipes is difficult, threaded flanges are used on relatively thicker pipes. The main features of screwed flanges are:

The attachment process or joining method is quick.
The threads are prone to leakage under cyclic loading, hence not recommended for cyclic services.

Pipe Flange Types Based on Flange Facing

Based on Flange Facings, the flanges are classified as

Raised Face Flanges
Flat Face Flanges
Ring Type Joint Flanges
Tongue and Groove
Male and Female

Flange Types based on Flange faces — **Fig. 6: Flange Types based on Flange Faces**

Types of Pipe Flanges Based on Pressure-Temperature Rating

Based on pressure-temperature rating flanges are of the following types:

150#
300#
400#
600#
900#
1500#
2500#

With an increase in pressure rating the flange dimensions, strength, and load-carrying capacity increase. Click here to know more about the pressure-temperature rating and flange rating.

Flange Types based on Governing Design Code

Based on governing design code piping flanges can be grouped into the following classes

ASME/ANSI Flanges (ASME B 16.1, ASME B 16.5, ASME B 16.42, ASME B 16.47)
BS Flanges (BS 10, BS 1560)
API Flanges (API 6A, API 17D)
DIN flanges
Custom made flanges, etc

Additionally, based on the pipe flange material of construction they can be classified as

Metallic Flanges
- Carbon Steel Flanges
- Alloy Steel Flanges
- SS/DSS Flanges
- Cast Iron Flanges
- Ductile Iron Flanges
Non-Metallic Flanges (FRP/GRP/GRE Flanges)

Few more hand-picked flange related articles for you

Methods for Checking Flange Leakage
Flange Insulating Gasket Kits for Industrial Application
Guidelines for Selection of Various Types of Flanges
Flange Bolt tightening Procedure/Bolt Tightening Steps

Difference Between ASME Sec VIII Div. 1 and Div. 2

Written by Anup Kumar Dey in Mechanical,Piping Interface

Both ASME Sec VIII Div 1 and Div 2 are used for pressure vessel design. Both divisions contain mandatory requirements, specific prohibitions, and non-mandatory guidance for pressure vessel materials, design, fabrication, examination, inspection, testing, certification, and pressure relief. So in a broad sense, both may seem to be similar but there are few distinct differences between both Divisions. In this article, we will explore the major differences between ASME Sec VIII Div 1 and Div 2.

Typical Pressure Vessel — **Typical Column (Pressure Vessel) during the erection stage**

ASME Sec VIII Division 1 vs ASME Sec VIII Division 2

ASME Section VIII, Division 1 is a straightforward design-by-rule method used by engineers to design pressure vessels based on rules. It’s conservative and usually leads to a sturdier design.

ASME Section VIII, Division 2 requires more detailed calculations and allows vessels to handle higher stresses, making it suitable for vessels with specific purposes and fixed locations.

The key difference between Division 1 and Division 2 is in how they handle stress. Division 1 uses normal stress theory, while Division 2 uses maximum distortion energy theory (Von Mises). The major differences between the two divisions of ASME BPVC Sec VIII Div 1 and Div 2 are tabulated below:

Parameters	ASME Sec VIII-Division 1	ASME Sec VIII-Division 2
Design Approach	ASME Sec VIII Division 1 is focused on a design-by-rule approach	ASME Sec VIII Division 2 on the other hand, is based on a design-by-analysis approach
Design Factor	The design Factor used is 3.5 on tensile and other yields and temperature considerations.	Design Factor of 3 (3.0 for Division 2, Class 1 and 2.4 for Division 2, Class 2) on tensile and other yield and temperature considerations.
Pressure Limit	Pressure typically up to 3000 psig. ASME Sec VIII Div 1 is more suitable for low-pressure applications.	Pressure is usually 600 psig and larger (less than 10000 psi). ASME Sec VIII Div. 2 caters to high-pressure applications.
Design Rules	Membrane – Maximum stress Generally Elastic analysis. Very detailed design rules with Quality (joint efficiency) Factors. Little stress analysis required; pure membrane without consideration of discontinuities controlling stress concentration to a safety factor of 3.5 or higher	Maximum Shear stress theory is the basis for Shell of Revolution. Generally Elastic analysis Membrane + Bending. Fairly detailed design rules. In addition to the design rules, discontinuities, fatigue, and other stress analysis considerations may be required unless exempted and guidance provided for in Appendix 4, 5 and 6.
Design Calculations	Simple Calculations.	requires more detailed calculations than Division 1
Failure Theory of Design	ASEM Sec VIII Division 1 is based on the normal stress theory	ASME Sec VIII Division 2 is based on maximum distortion energy (Von Mises criteria)
Experimental Stress Analysis	Experimental methods of stress analysis are not required in normal cases.	Experimental stress analysis is introduced and may be required
Material and Impact Testing	Few restrictions on materials; Impact required unless exempted; UG-20, UCS 66/67 provides extensive exemptions.	More restrictions on materials; impact required in general with similar rules as Division 1.
NDE Requirements	In ASME Sec VIII Div. 1, the NDE requirements may be exempted through increased design factors.	Div. 2 has more stringent NDE requirements; extensive use of Radiographic tests, Ultrasonic Tests, Magnetic Particle Tests, and Penetration Tests.
Welding and fabrication	Different types with butt welds and others.	Extensive use/requirement of butt welds and full penetration welds including non-pressure attachment welds.
Fatigue Evaluation	Not mandatory.	AD 160 for fatigue evaluation
Manufacturer	Manufacturers are to declare compliance with the data report.	Manufacturer’s Design Report certifying design specification and code compliance in addition to a data report.
Professional Engineer Certification	Normally not required.	Professional Engineers’ Certification of User’s Design Specifications as well as Manufacturer’s Design Report Professional Engineers shall be experienced in pressure vessel design.
Code Stamp and Marking	U Stamp with Addition markings including W, B, P, RES; L, DF, UB, HT, and RT.	U2 Stamp with Additional marking including HT.
Hydrostatic Test Pressure	1.3 times design pressure.	1.25 times design pressure.
Allowable Stress Value at a specified design temperature	Lower, hence higher design margin.	Higher, hence lower design margin.
Shell thickness at the same design pressure	Thicker	Thinner.
Material Cost	Higher.	Lower.
Minimum Pressure Design Thickness Calculation Equation	t=PD/2S – 1.2P	t=D/2{Exp(P/S)-1}
Hydrotest Stress Calculation	In ASME Sec VIII Division 1, hydro test stresses are not specifically limited, and partial penetration nozzle welds are permitted.	In the ASME Sec VIII Division 2, hydro test stress calculations are mandatory as they are limited, and full penetration nozzle welds are required
No of Vessels produced Annually	Larger	Lower
Reference Standards	ASME B 1.13M AND ASME B 1.21M related to Screw threads are not listed	Both standards are given as references.

Difference Between ASME Sec VIII Div. 1 and Div. 2

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

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