api 570 part 2 - pipe design

8/12/2019 API 570 Part 2 - Pipe Design

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API 570 Piping Inspection CodePart 2: Pipe Design


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Objectives

Understand B31.3sscope and organization

Know the three needed B31.3 piping classes

Determine the allowable stress S

Determine the Quality Factor E

Calculate pipe thickness

Calculate blank (blind) thickness

Familiarize yourself with basic design issues

Other B31s:

B31.1 Pow er Piping (Boi ler)

B31.4 Pipel ine Systems for Liq uids

B31.8 Pipel ine Systems for Gases

B31.11 Slurry Pip ing Systems

B31.2 Fuel Gas PipingB31.5 Refr igerat ion Piping

B31.9 Bui ld ing Services


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B31.3 Piping Classes

Normal ServiceMajority of plant Piping

Severe Cyclic ServiceHigh Stress

Over 7000 stress cycle

Category DNot damaging humansPressure Limit 150 psig

Temp: -20 thru 366oF

DuhUtility Piping

Category MVery Toxic

Nonmetallic

High PressureExcess of Flange Class 2500

Not covered

in API 570exam

Category D

None Code

-20oF -366oF

0 psig

15 psig

150 psig

Normal or Severe

Cycle

None Code & Category D

Non-Toxic

Non-Hazardous

Non-Flammable


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B31.3 Organization

Table of Content

Chapter IScope

Definition

Chapter II-VIThree Piping Services

Normal Service

Severe Cyclic Service

Category D

Chapter VII-IXThree Piping Services

Nonmetallic

Category M

High Pressure

Appendix A-ZApp A: S& E

App C: Thermal Growth

Index

Note: Two important tools for finding open book

infoTable of Contents and the Index!


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B31.3 Organization Basic Concept

1. Piping classes in Chapter II-VI?

Only Normal Service, Severe Cyclic and Category D. The other three are in Chapter VII-IX not

covered in API exam.

2. How Chapter II-VI organized?

By sequence of project activity. DESIGN the pipethen BUILD the pipethen INSPECT the

pipethen TESTthe pipe.

3. How the 3 piping classes (Severe, Normal, Cat D) identified in Chapter II-VI?

Rule 1: If code mentions a piping class then rule applies only to that piping class.Rule 2: If code does not mention piping classes, then the rule applies to all 3 piping classes

(Severe, Normal, Cat D).

Eg: 304.1.2 Wall Thickness Calcs (class not mentioned)

341.4 Required Examinations

341.4.2 Category D

341.4.7 Normal Service

341.4.3 Severe Cyclic

4. All paragraphs in B31.3 are 3xx. The 3stands for B31.3


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The B31.3 Players

Owner Overall responsibility for compliance with the Code

DesignerDesign complies with Code

ManufacturerProvides materials & workmanship that complies with the Code

OwnersInspectorAssure that the Code requirements for inspection, examination and testing are met (TIE)

Full access to all piping work

Owner

Designer Manufacturer Inspector

B31.3 Organization


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Exercise 1

1. What are the qualification requirements for NDE personnel?

2. What are the requirements for the weld metal of tack welds?

3. The OwnersInspector must have how many years of related inspection experience?

4. A hydrotest must be held for at least ______ minutes.

5. Describe the heat treatment called Normalizing


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Answers 1

1. What are the qualification requirements for NDE personnel?

SNT-TC-1A

2. What are the requirements for the weld metal of tack welds?

328.5.1 Made by qualified welder or welding operator

3. The OwnersInspector must have how many years of related inspection experience?

10 years

4. A hydrotest must be held for at least 10minutes.

5. Describe the heat treatment called Normalizing

A process in which a ferrous metal is heated to a suitable temperature above the

transformation range and subsequently cooled in still air at room temperature.


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Retirement Thickness

The Formula

PD

2(SE+PY)t = 304.1.2

P = design pressure (psig)

D = outside diameter (inch) see B16.5 TableS = allowable stress (psi)

E = quality factor

Y = coefficient from Table 304.1.1

Y produces very minor affect on the calculated thickness. Generally it reduces the retirement

thickness by about 1%. The Coefficient Y for our calculations will be 0.4.


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Info

Thickness Terms

The terms have not been standardized throughout different codes. As a result, the

terms used can be very confusing.

1. Retirement Thickness (this term is not used in code). The minimum thickness

allowed. If the component is below this thickness, the component should be

repaired or replaced.

In B31.3 this is called pressuredesign thickness In API 570 this is called requiredthickness

Many call it minimumthicknessor t-min

2. Retirement thickness plus Corrosion Allowance. When ordering new pipe, you

always need to add the appropriate corrosion allowance.

In B31.3 this is called minimumrequired thickness


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Strength & Stress

Stress Measures Strength Materials fail when overstressed

Stress = Load/Area

Units: psi (lbs per sq in)

Ultimate Tensile StrengthStress at which failure occurs

Determined by Tension Test

Also called SMTSSpecified Minimum Tensile Strength

Strengththe ability to withstand an applied load
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Strength Characteristics

Elastic Properties Metals stretch when loaded

Metals return to original shape when load is removed

Stretch is proportional to load. Higher load = more stretch

Plastic PropertiesHigh Stress, metal stretches

If above Yield Stress, it does not return to original shape when load is removed.

Permanentdeformation


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Info

Definitions

Yield Strength: the stress level where the material behaves plastically. No longer in

the elastic range.

Elastic: the deformation of a metal under a load which causes no permanent

deformation. Elastic behavior is considered to be linear (the greater the pull the

greater the growth/stretch).

Plastic: stressed beyond the elastic limit and results in permanent deformation.

Strength of a plate can very significantly depending on the orientation. The strength is best in

the direction of the roll. Transverse to the rolling direction the strength can be reduced by 30%.

In the through-thickness direction it can even be less!


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Allowable Stress S refer to B31.3 App A-1

Allowable Stress What the designer is allowedto use in thickness calculation.

Based on Code Safety FactorB31.1 = 3 to 1.

S = SMTS/Safety Factor

Stress vs TemperatureAs the temperature increases, the strength decreases

Also Sdecreases

Failure StressStress = Load/Area

eg 60,000 psi

Allowable StressS = SMTS/Safety Factor

eg 60,000/3 = 20,000 psi


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Exercise 2

1. What is the allowable stress for a A106 Gr B pipe that has a design temperature of 700oF?

2. What is the allowable stress for a A671 Gr CC70 that has a max operating temperature of400oF?

3. What is SMTS of A106 Gr C pipe?

4. In the stress tables what do single bars represent?

5. In the stress tables what do double bars represent?


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Answers 2

1. What is the allowable stress for a A106 Gr B pipe that has a design temperature of 700oF?

16500 psi

2. What is the allowable stress for a A671 Gr CC70 that has a max operating temperature of

400oF?

21700 psi

3. What is SMTS of A106 Gr C pipe?

70000 psi

4. In the stress tables what do single bars represent?

Affected by reference note

5. In the stress tables what do double bars represent?

Prohibited by reference note


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Stress on Welds

Circ Weld

Long Weld

Pressure in a cylinder

always creates both circ

and long stress

Circumferential (Hoop) Stress will affects Long Weld

Longitudinal Stress will affects Circ Weld

Stress on Cylinder affected by Pressure

Thickness Diameter

Circ stress on cylinder are

generally twice as high as the

longitudinal stress. So long welds

are usually more critical than circ

weld!


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Quality Factor E

What is E Additional safetyfactor

For long weld or castings

Determine EIf given a pipe descriptionTable 302.3.4

If given Material specTable A-1A & 1B

FactorsSeamless Pipe

E = 1.0, no long welds

Rolled & Welded Pipe

Type of weld

Amount of NDE (RT)

Cast Pipe

Material

Casting Method

Note: In ASME Section VIII, Eis called JointEfficiency. Same concept, just different term.


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Exercise 3

1. What is Efor A333 ERW pipe?

2. What is the quality factor for A53 Type S?

3. What is E for a pipe with a long weld that is double-butt-welded using Electric Fusion

process?

4. Determine the retirement thickness of seamless 14 NPS pipe. Design pressure is 500 psig and

allowable stress is 15,000 psi at design temperature. Y = 0.4

5. Determine the minimum allowed thickness for an 8 NPS pipe. The pipe is A53 Gr B Type E

(ERW). Design pressure is 400 psig and design temperature is 700oF.


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Answers 3

1. What is Efor A333 ERW pipe? 0.85

2. What is the quality factor for A53 Type S? 1.00

3. What is E for a pipe with a long weld that is double-butt-welded using Electric Fusion

process? 0.85

4. Determine the retirement thickness of seamless 14 NPS pipe. Design pressure is 500 psig and

allowable stress is 15,000 psi at design temperature. Y = 0.4 t = 0.230

5. Determine the minimum allowed thickness for an 8 NPS pipe. The pipe is A53 Gr B Type E

(ERW). Design pressure is 400 psig and design temperature is 700oF. t = 0.122


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PipeOrdered Thickness

Rolled and Welded Calculate tmin Add Corrosion Allowance tw/CA = tmin + CA

Select nominal thickness tnomtw/CA

Seamless PipeCalculate tmin

Add Corrosion Allowance tw/CA = tmin + CA

Adjust for mill tolerance tadjtw/CA/0.875

Select nominal thickness tnomtadj


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Exercise 4

1. An 8 NPS A-106 Gr B pipe has a calculated tminof 0.182. The specified corrosion allowance is

0.125. What pipe schedule should be ordered?

2. A 4 NPS piping system has a design pressure of 800 psig at 600oF. Pipe material is A-106 Gr C.

Specified corrosion allowance is 0.125. What pipe schedule should be ordered?

3. A rolled and welded 12 NPS pipe has a renewal thickness of 0.218 and a corrosion

allowance of 0.100. What pipe schedule should be ordered?


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Answers 4

1. An 8 NPS A-106 Gr B pipe has a calculated tminof 0.182. The specified corrosion allowance is

0.125. What pipe schedule should be ordered? 8Sch 60

2. A 4 NPS piping system has a design pressure of 800 psig at 600oF. Pipe material is A-106 Gr C.

Specified corrosion allowance is 0.125. What pipe schedule should be ordered? 4Sch 80

3. A rolled and welded 12 NPS pipe has a renewal thickness of 0.218 and a corrosion

allowance of 0.100. What pipe schedule should be ordered? 12Sch 30


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PipeStructural Minimum

The calculated tminis based only on pressure loadings

Other loadings must be considered during design Dead Loads: weight of pipe & insulation Live Loads: weight of process, personnel, ice/snow

Specified structural minimums are not listed in the codes.Usually provided by Owner

Usually a list or chartIncreases with line size

Real Steps to Order PipeCalculate tminCompare to structural tminand pick larger value

Add corrosion allowance

Adjust for mill tolerance

Pick appropriate pipe schedule

Note: Other names for Structural Minimum is Arbitrary Minimum Thickness or Mechanical

Minimum Thickness


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Blanks (Blind) - Thickness

Pressure-rated blinds are thickFlat is the worse shape for pressure containment

FormulaRetirement Thickness

dg = inside diameter of gasket

E = 1.0 if no weld

If need to order plate:Add Corrosion AllowanceSelect tnom

tnomtmin + CA

SE

Pdt g

16

3


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Exercise 5

1. Determine the retirement thickness of a blank installed in a 6 NPS line. Design pressure is 300

psig with a design temperature of 900oF. The blank is made from stainless steel material A240

Gr 316L. The gasket ID is 6.620.

2. Determine the nominal plate thickness to order for a blind. The design pressure is 325 psig at

400oF. The material is A516 Gr 70 (Carbon Steel). The gasket ID is 8.625. The specified

corrosion allowance is 0.200.


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Answers 5

1. Determine the retirement thickness of a blank installed in a 6 NPS line. Design pressure is 300

psig with a design temperature of 900oF. The blank is made from stainless steel material A240

Gr 316L. The gasket ID is 6.620. tmin = 0.4571

2. Determine the nominal plate thickness to order for a blind. The design pressure is 325 psig at

400oF. The material is A516 Gr 70 (Carbon Steel). The gasket ID is 8.625. The specified

corrosion allowance is 0.200.

tmin = 0.4571

tw/CA

= 0.4571 + 0.2 = 0.6571

tnom 0.6571

Order round up to 1/16. Therefore need to order 0.688.


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Fluid Service - Limits

Pipe Materials (305)Cat DAll listed materials

Normal ServiceAll listed materials except those limited to Cat D.Severe Cyclicshort list

Miter Ends (306.3)

Flanges (308.2)Slip-on limits

Severe CyclicWeld Neck

Bolting (309.2)Low strengthOnly for Class 150 & 300 flanges

Socket Welds (311.2.4)Avoid in crevice corrosion or erosion services

Severe cyclic 2 NPS

Threaded Joints (314)Avoid in crevice corrosion or erosion services

Avoid in cyclic loadings

Severe cyclicnot allowed except non-load items like thermowelds


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Info

DefinitionsListed Materials: Materials listed in the Appendix A stress chart

Miter: Elbow fabricated from pipe using pie shaped sections. Often used on largediameter pipe.

Straight Thread: Non-tapered threads. Used in threaded pipe unions.
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Pipe Flexibility

A piping system will grow or shrink when the temperature changes

100

FxLG

G = Growth in inches

F = factor from B31.3 Table C-1

L = length of pipe in feet

Notice F @ 70oF. The chart

is based on the pipe being

installed at 70oF.


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Exercise 6

1. Determine the total growth of 800carbon steel line. The line operates at 400oF.

2. Determine growth of a 400SS line that operates at 700oF.

3. A 12diameter carbon steel tube is welded to a 12SS tube. The tube operates at 800oF.

a. How much does the diameter of the CS tube grow?

b. How much does the diameter of the SS tube grow?

c. Describe the condition of this dissimilar weld

Watch out:

Negative tempsthis is how much cold pipe shrinks.

Dontuse Table C-3


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Answers 6

1. Determine the total growth of 800carbon steel line. The line operates at 400oF. G = 21.6

2. Determine growth of a 400SS line that operates at 700oF. G = 30

3. A 12diameter carbon steel tube is welded to a 12SS tube. The tube operates at 800oF.

a. How much does the diameter of the CS tube grow? G = 0.067

b. How much does the diameter of the SS tube grow? G = 0.088

c. Describe the condition of this dissimilar weld Highly stressthermal fatigue


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Pipe Flexibility

Ways to increase flexibilityMake changes in direction

Expansion loopsSuitable anchors and guides

Expansion joints

Watch out for branch connections

Stresses relax over time

ComponentsAnchors and Guides

Hangars

Sliding Supports (shoes)

Spring Supports (Constant and Variable)

Counterweightsimportant to check cables and pulleys especially on large lines.

Definitions

Anchors : Prevents movement in all 3 directions (x,y,z)

Guides : Prevents movement in 1 or 2 directions. Allows movement in only 1 or 2 directions.


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Pressure Protection

Most piping is protected by relief devices that are designed to protect

other equipment (eg vessels)

Full area stop valves (block valves) can be used on inlet and outlet of

relief device

Fabrication of DevicesPer ASME Sect. VIII Div. 1

Set PressurePer ASME Sect. VIII Div. 1

Thermal relief valves can be set at 120% of Design Pressure

Thermal relief valves are typically needed on long runs of pipe that can be blocked

in (typically found in a tank farm). Heat from the sun warms the lines. As the product

temperature increases, the pressure builds in blocked-in lines. A small thermal

relief valve usually with NPS connections is installed to protect the pipe. Normallythe thermal relief outlet just bypasses one of the closed valves.

api 570 part 2 - pipe design

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