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ASME B 31.3 is the bible of process piping engineering and every piping engineer should

frequently use this code for his knowledge enhancement. But to study a code similar to B 31.3 is time

consuming and also difficult because the contents are not at all interesting. Also every now and then

it will say to refer to some other point of the code which will irritate you. But still every piping

engineer should learn few basic points from it. The following literature will try to point out 11 basic

and useful points from the code about which every piping engineer must be aware.

1. What is the scope of ASME B 31.3? What does it covers and what does not?

Ans: Refer to the ASME B 31.3­Process Piping section from my earlier post.

Link: http://www.whatispiping.com/?p=44

Alternatively refer the below attached figure ( Figure 300.1.1 from code ASME B 31.3)

What is PipingAn attempt to explain process piping engineering basics in detail to help all the process piping

engineering professionals around the world.

HOME ABOUT US PIPING STRESS PIPING SUPPORTS PIPING DESIGN

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2. What are the disturbing parameters against which the piping system must be designed?

Ans: The piping system must stand strong (should not fail) against the following major effects:

Design Pressure and Temperature: Each component thickness must be sufficient to withstand

most severe combination of temperature and pressure.

Ambient effects like pressure reduction due to cooling, fluid expansion effect, possibility of

moisture condensation and build up of ice due to atmospheric icing, low ambient temperature

etc.

Dynamic effects like impact force due to external or internal unexpected conditions, Wind force,

Earthquake force, Vibration and discharge (Relief valve) reaction forces, cyclic effects etc.

Component self weight including insulation, rigid body weights along with the medium it

transport.

Thermal expansion and contraction effects due to resistance from free displacement or due to

thermal gradients (thermal bowing effect) etc.

Movement of pipe supports or connected equipments etc.

3. How to calculate the allowable stress for a carbon steel pipe?

Ans: The material allowable stress for any material other than bolting material, cast iron and

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malleable iron are the minimum of the following:

1. one­third of tensile strength at maximum temperature.

2. two­thirds of yield strength at maximum temperature.

3. for austenitic stainless steels and nickel alloys having similar stress–strain behavior, the lower

of two thirds of yield strength and 90% of yield strength at temperature.

4. 100% of the average stress for a creep rate of 0.01% per 1 000 h

5. 67% of the average stress for rupture at the end of 100 000 h

6. 80% of the minimum stress for rupture at the end of 100 000 h

7. for structural grade materials, the basic allowable stress shall be 0.92 times the lowest value

determined (1) through (6) above.

4. What is the allowable for Sustained, Occasional and Expansion Stress as per ASME B 31.3?

Ans: Calculated sustained stress (SL)< Sh (Basic allowable stress at maximum temperature)

Calculated occasional stress including sustained stress< 1.33 Sh

Calculated expansion stress< SA = f [ 1.25( Sc + Sh) − SL]

Here f =stress range factor, Sc =basic allowable stress at minimum metal temperature and

SL=calculated sustained stress. The sustained stress (SL) is calculated using the following code

formulas:

Here,

Ii = sustained in­plane moment index. In the absence of more applicable data, Ii is taken asthe

greater of 0.75ii or 1.00.

Io = sustained out­plane moment index. In the absence of more applicable data, Io is taken as the

greater of 0.75io or 1.00.

Mi = in­plane moment due to sustained loads, e.g.,pressure and weight

Mo = out­plane moment due to sustained loads, e.g.,pressure and weight

Z = sustained section modulus

It = sustained torsional moment index. In the absence of more applicable data, It is taken

as 1.00.

Mt = torsional moment due to sustained loads, e.g.,pressure and weight

Ap = cross­sectional area of the pipe, considering nominal pipe dimensions less allowances;

Fa = longitudinal force due to sustained loads, e.g.,pressure and weight

Ia = sustained longitudinal force index. In the absence of more applicable data, Ia is taken as 1.00.

5. What are steps for calculating the pipe thickness for a 10 inch carbon steel (A 106­Grade B) pipe

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carrying a fluid with design pressure 15 bar and design temperatre of 250 degree centigrade?

Ans: The pipe thickness (t) for internal design pressure (P) is calculated from the following

equation.

Here, D=Outside diameter of pipe, obtain the diameter from pipe manufacturer standard.

S=stress value at design temperature from code Table A­1

E=quality factor from code Table A­1A or A­1B

W=weld joint strength reduction factor from code

Y=coefficient from code Table 304.1.1

Using the above formula calculate the pressure design thickness, t.

Now add the sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion

allowances if any with t to get minimum required thickness, tm.

Next add the mill tolerance with this value to get calculated pipe thickness. For seamless pipe the

mill tolerance is 12.5% under tolerance. So calculated pipe thickness will be tm/(1­

0.125)=tm/0.875.

Now accept the available pipe thickness (based on next nearest higher pipe schedule) just higher

than the calculated value from manufacturer standard thickness tables.

6. How many types of fluid services are available for process piping?

Ans: In process piping industry following fluid services are available..

Category D Fluid Service: nonflammable, nontoxic, and not damaging to human tissues, the

design pressure does not exceed 150 psig, the design temperature is from ­20 degree F to 366

degree F.

Category M Fluid Service: a fluid service in which the potential for personnel exposure is judged

to be significant and in which a single exposure to a very small quantity of a toxic fluid, caused

by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even

when prompt restorative measures are taken.

Elavated Temperature Fluid service: a fluid service in which the piping metal temperature is

sustained equal to or greater than Tcr (Tcr=temperature 25°C (50°F) below the temperature

identifying the start of time­dependent properties).

Normal Fluid Service: a fluid service pertaining to most piping covered by this Code, i.e., not

subject to the rules for Category D, Category M, Elevated Temperature, High Pressure, or High

Purity Fluid Service.

High Pressure Fluid Service: a fluid service for which the owner specifies the use of Chapter IX

for piping design and construction. High pressure is considered herein to be pressure in excess

of that allowed by the ASME B16.5 Class 2500 rating for the specified design temperature and

material group.

High Purity Fluid Service: a fluid service that requires alternative methods of fabrication,

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inspection, examination, and testing not covered elsewhere in the Code, with the intent to

produce a controlled level of cleanness. The term thus applies to piping systems defined for other

purposes as high purity, ultra high purity, hygienic, or aseptic.

7. What do you mean by the term SIF?

Ans: The stress intensification factor or SIF is an intensifier of bending or torsional stress local to a

piping component such as tees, elbows and has a value great than or equal to 1.0. Its value depends

on component geometry. Code B 31.3 Appendix D (shown in below figure) provides formulas to

calculate the SIF values.

8. When do you feel that a piping system is not required formal stress analysis?

Ans: Formal pipe stress analysis will not be required if any of the following 3 mentioned criteria are

satisfied:

1. if the system duplicates, or replaces without significant change, a system operating with a

successful service record (operating successfully for more than 10 years without major failure).

2. if the system can readily be judged adequate by comparison with previously analyzed systems.

3. if the system is of uniform size, has no more than two points of fixation, no intermediate

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restraints, and falls within the limitations of empirical equation mentioned below:

Here,

D = outside diameter of pipe, mm (in.)

Ea = reference modulus of elasticity at 21°C (70°F),MPa (ksi)

K1 = 208 000 SA/Ea, (mm/m)2 = 30 SA/Ea, (in./ft)2

L = developed length of piping between anchors,m (ft)

SA = allowable displacement stress range

U = anchor distance, straight line between anchors,m (ft)

y = resultant of total displacement strains, mm (in.), to be absorbed by the piping system

9. How will you calculate the displacement (Expansion) stress range for a piping system?

Ans: Expansion stress range (SE) for a complex piping system is normally calculated using

softwares like Caesar II or AutoPipe. However, the same can be calculated using the following code

equations:

here

Ap = cross­sectional area of pipe

Fa = range of axial forces due to displacement strains between any two conditions being evaluated

ia = axial stress intensification factor. In the absence of more applicable data, ia p 1.0 for elbows,

pipe bends, and miter bends (single, closely spaced, and widely spaced), and ia =io (or i when

listed) in Appendix D for other components;

it = torsional stress intensification factor. In the absence of more applicable data, it=1.0;

Mt = torsional moment

Sa = axial stress range due to displacement strains= iaXFa/Ap

Sb = resultant bending stress

St = torsional stress= itXMt/2Z

Z = section modulus of pipe

ii = in­plane stress intensification factor from Appendix D

io = out­plane stress intensification factor from Appendix D

Mi = in­plane bending moment

Mo = out­plane bending moment

Sb = resultant bending stress

10. What do you mean by the term “Cold Spring”?

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Ans: Cold spring is the intentional initial deformation applied to a piping system during assembly to

produce a desired initial displacement and stress. Cold spring is beneficial in that it serves to

balance the magnitude of stress under initial and extreme displacement conditions.

When cold spring is properly applied there is less likelihood of overstrain during initial operation;

hence, it is recommended especially for piping materials of limited ductility. There is also less

deviation from as installed dimensions during initial operation, so that hangers will not be

displaced as far from their original settings.

However now a days most of the EPC organizations does not prefer the use of Cold Spring while

analysis any system.

11. How to decide whether Reinforcement is required for a piping branch connection or not?

Ans: When a branch connection is made in any parent pipe the pipe connection is weakened by the

opening that is made in it. So it is required that the wall thickness after the opening must be

sufficiently in excess of the required thickness to sustain the pressure. This requirement is checked

by calculating the required reinforcement area (A1) and available reinforcement area (A2+A3+A4)

and if available area is more than the required area then no reinforcement is required. Otherwise

additional reinforcement need to be added. The equations for calculating the required and available

area are listed below for your information from the code. Please refer the code for notations used:

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More In ANSI B 31.3

BASICS OF PIPE STRESS ANALYSIS: APRESENTATION-Part 2 of 2

Continue from Part 1 of this topic..... Basic Allowable Stress: Minimum of (As per ASME B 31.3)

1/3rd of Ultimate Tensile Strength (UTS) of Material…read more →

Piping Engineer required for Saudi Arabia for AlSuroor United Group.

Piping Engineer required for Saudi Arabia for Al Suroor United Group. Job

Responsibilities: The probable candidate should Perform stress analysis of

piping systems using CAESAR…read more →

Substantive Changes to 2014 Edition of ASME B 31.3

Many of you are aware that the 2014 edition of ASME B 31.3 is scheduled to publish on 21st

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February 2015. Similar to every new…read more →

This article has 15 comments

arun

Wednesday 11 December 2013, 4:05 pm

Please clarify my following doubts

1) the equation provided for the sustain is bit different what i learned (PD/4t+M/Z+F/A) ..but in your equation u havent consiederd longitunal stress butconsidered torsioanl stress.please clarify me?

2) in the equation for expansion stress tosional stress is to be corrected

please correct me if iam wrong

Regards

arun

Reply

Anup

Wednesday 11 December 2013, 6:57 pm

Regarding your confusion:

I suggest you to read the latest version of the ASME B 31.3 code. Caesarused to calculate the stress following your equation as no code equationwas available in earlier versions of the code. But now B 31.3 providesequations for calculating sustained stress.

The torsional term is also included in expansion stress calculation in latest

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version of the code.

Thanks for reading my blog. Request you to subscribe with your email toget instant updation about any of my posts.

Reply

arun

Wednesday 11 December 2013, 9:10 pm

Thanks for your quick reply ….and clarify my doubts iam satisfied with your reply ..1) still iam confused that why did they ddint use Longitudinalstress Pd/4t in new equation?2) In previous version was also considered torsional stress inexpansion stress as Sqrt of Sb2 +4St2…………..in your equation 4st2 havechanged to 2st2 .,..this also new changes in new version?

thankx in advancearun

Reply

Abba

Wednesday 11 December 2013, 8:59 pm

I find this site very informative. I have just attended an Intergraph C2 training for bothstatics and dynamic.

thank you for sharing

Reply

rahul sapra

Tuesday 18 March 2014, 3:20 pm

4/3/2015 11 most important questions & answers from ASME B 31.3 for a Piping stress engineer | What is Piping

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Saturday 7 June 2014, 11:57 am

My Engineer advice me cut the dummy support 150mm which is suppose to be sit inthe platform frame after cutting the grating as per design and welded in a pad for a firewater 250mm line .due to elevation difference of 25~ 40 mm they want don.t want tocut the grating rather than cut the horizontal dummy leg and weld it 25~40 mm belowwithout shifting the pad or not weld addition pad. I can’t agree .Please suggestwhether pad can be eccentric i.e on the top maximum 70 mm and on bottom 5mmfrom the OD of dummy leg.

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