Piping E - Book
Piping
Contents
I. Preface
II. Forward
III. Dedication
IV. Symbols
V. About the Author
VI.Acknowledgements
1. Introduction
2. Piping Basics
3. Piping Design
4. Flow in Piping
5.Stress analysis of Piping
6. Supports for Piping
7. Construction of Piping
8. Testing of Piping
9. Operation of Piping
10. Maintenance of Piping
A. Bibliography
B. Formulas
C. Conversion factors
D. Appendix
E. Index
   
Course Content:
 
1. Introduction
2. Symbols
3. Conversion factors
4. Formulas
5. List of Tables
6. List of Figures
7. Piping basics
8. Shape
9. Size
10. Material
11. Thickness
12. Loads
13. Load combinations
14. Allowable stress
15. Deformations
16. Vibration
17. Flow and pressure drop
18. Flow in multiple pipes
19. Economic size
20. Scheme
21. Process Flow Diagram (PFD)
22. Piping & Instruments Diagram (P & ID)
23. Layout
24. Isometrics
25. Valves, gages and instruments
26. Fittings and attachments
27. Supports and restraints
28. Anchors and guides
29. Hangers and limit stops
30. Variable Load Hangers (VLH)
31. Constant Load Hangers (CLH)
32. Bends and elbows
33. TEE and Y-piece
34. Temperature and its effects
35. Creep and fatigue
36. Corrosion and erosion
37. Insulation and refractory
38. Liner and casing
39. Surface preparation
40. Surface treatment
41. Paints and painting
42. Detailing, drafting and documentation
43. Fabrication and transportation
44. Storage, erection and commissioning
45. Economics and availability
46. Codes, standards ad regulations
47. Life, failure and maintenance
48. Run or repair or replace
49. Objective type questions
50. References
1. Introduction
   Pipes are used from time immemorial. Pipes are generally hollow cylindrical in shape. Pipes are used for conveying fluids. The fluids may be gas or liquid or gas-solid mixture or liquid-solid mixture or gas-liquid mixture or gas-liquid-solid mixture. In the early days of civilization, bamboo sticks were used as pipes. In the modern world, metals and non-metals are used widely. Use of ferrous materials for piping is popular in industries. Ferrous materials have good strength to cost ratio. The shape of the pipes popularly used is given below.
Figure: 1.1 Hollow Cylindrical Pipe
    According to the dictionary, a pipe is a tube is a pipe. In the common mans parlance the pipe is a large tube. The tube is a small pipe. In technical use the pipe refers to a device that is used for conveying fluids. The tube refers to a device which participates in heat transfer. As per The Indian Boiler Regulation, 1950, the hollow cylindrical devices with the outside diameter less than or equal to 127 mm (5 inch) are considered as pipes. However, this classification is ambiguous. A universally acceptable classification on pipe and tube does not exist. The piping can be subjected to various loads and load combinations. The primary load on piping considered in the industry is the internal pressure. The diameter of the pipe is computed considering the flow, pressure drop and pumping power required. The materials of the piping is selected based on the design temperature. The materials for critical and lethal applications are selected considering corrosion, erosion, etc. The thickness of the piping is computed considering the hoop stress due to the internal pressure. The requirements of supports and restraints are based on the loads on the piping. The flexibility of the piping is checked considering expansion loads. At present, the occasional loads such as wind, earth quake (seismic load), fire, flood, blast, Tsunami, etc. are also considered in the piping design.
2. Symbols
 
Do = Outside diameter of pipe, mm
T = Nominal thickness of pipe, mm
R = Radius of pipe bend (neutral axis), mm
S = Allowable then, MPa
Pi = Pipe inside pressure, Mpa (g)
Po = Pipe outside pressure, Mpa (g)
3. Conversion factors
 
1.0 inch = 25.4mm
1.0 feet = 12.0 inch = 304.8mm
1.0 Mpa = 1000.0 Kpa = 10.197 Kg/ cm2
1.0 Ksi = 1000.0 Psi = 70.308 Kg/cm2
1.0 Kg (f) = 9.80665 N
4. Formulas
 
(4.1) From IBR-338 (a), 1950 (tuber),
T = (WP D / 2f + WP) + C(4.2) From IBR-350, 1950 (piper),
T = (WP D / 2fe + WP) + C
Note: For symbols, see IBR, 1950 (with amendments)
5. List of Tables
 
5.1. Suggested support spam for horizontal pipes (m)
(see page: 40/84)
5.2. Allowable stnener (MPa)
(see ASME Section II, Part D)
5.3. Selection of Materials
(see page: 10/84)
5.4. Types of piping supports
(see pages: 36/84 to 39/84)
6. List of Figures
 
6.1. Straight pipe
6.2. Bent pipe
6.3. Ovality in pipe
6.4. Thinning in pipe
Fig. 6.1. Straight pipe Fig. 6.2. Bent pipe
Fig. 6.3. Ovality in pipe Fig. 6.4. Thinning in pipe
%Ovality = 2(Dmax Dmin) X 100
7. Piping Basics (Dmax + Dmin)
    Piping is subjected to various and load combinations. The limiting stress depends on several parameters. The following influence the piping design:
7.1. Piping material
7.2. Piping design temperature
7.3. Environment
7.4. Corrosion
7.5. Erosion
7.6. Abrasion
7.7. Fluid conveyed
7.8. Type of soil for buried piping
7.9. Corrosion protection methods
7.10. Life of piping
    The following steps are involved in design and analysis of piping and supports:
a) Conceptual design
b) Scheme
c) Process Flow Diagram (PFD)
d) Piping and Instruments Diagram (P & ID)
e) Isometric drawing
f) Stress analysis
g) Hanger engineering
h) Design and selection of primary supports
i) Design and selection of secondary supports
j) Detailing
k) Drafting
l) Documentation
m) Document approval
n) Issue of documents for construction
8. Shape
    The shape of the pipes is usually hollow cylindrical. Hollow cylindrical shape leads to economic design. Hollow square pipes are also used in cases where space restriction is predominant. The pipes (also known as tubes) used for structural applications are usually hollow rectangular. The shape plays an important role in pressure drop, pumping power, thickness selection, joining, etc. hollow cylindrical pipes are simple o manufacture, fabricate and construct. As the hollow cylindrical pipes are economical this shape is used world-over. The internal forces induced in a hollow cylindrical shape are primarily of membrane type. Hence, the thickness required for the hollow cylindrical shape is the minimum among various shapes. Cylinder is a natural shape. The hollow cylindrical shape can be classified into thin cylinder and thick cylinder. As per the American Society of Mechanical Engineers Code for Power Boilers (Section I), the thickness of more than one half the internal radius is considered as a thick cylinder. All other hollow cylinders are considered as thin cylinder. The thickness formula as per The Indian Boiler Regulations, 1950 (with amendments), only the thin cylinder formula is used for all applications. Codes and standards world-over use different practices. The shapes of the fittings, valves, gages, instruments and supports are of different shapes. There are no uniform practices in these applications. The shapes play an important role in the economics of piping. Even-though detailed research have been done on several alternate shapes, only few shapes are used. The allowable deviations to the preferred shapes are different in different codes. The oval shape allowable for a straight pipe is usually one percent of the diameter. The oval shape permitted for the bend pipe is generally ten percent. The thinning allowed for the pipe bend thickness is usually ten percent. The codes and standards specify separate limits for different deviations. A composite stress analysis of these shapes is possible using the Finite Element Analysis (FEA). Detailed stress analysis indicates that a composite stress analysis exposes various in-accuracies in the present practice.
    The practices used in the following industries are different, due to differing applications.
1. Pipe under internal pressure
2. Pipe under external pressure
3. Pipe for lethal application
4. Pipe for Nuclear application
5. Pipe for domestic use (non-metallic pipe)
6. Pipe for aeronautical and space application
7. Pipe for defense use
9. Size
    The size indicates the diameter and the thickness. The diameter is decided based on flow considerations. In the boiler industry a pipe (also known as tube) size is computed considering heat transfer. Higher the pipe diameter, higher is the initial cost. Lower the diameter, lower is the initial cost. Higher the pipe diameter, lower is the running cost. Lower the diameter, higher is the running cost. Higher the diameter, higher is the thickness required. If the internal pressure is doubled, the thickness doubles. If the diameter is doubled, the thickness required doubles.
    The size increase leads to higher cost of valves, fitting, instruments and the associated components. An appreciation of the effects of the diameter can be seen from the formula given below.
T = (WP x Do / 2fE + WP) + C
Where,
T = Thickness required as per The Indian Boiler Regulations (IBR), 1950, mm
WP = Working pressure, kg / sq cm, (g)
Do = Outside diameter of pipe, mm
f = allowable stress at working metal temperature, kg / sq cm
E = Joint efficiency = 1.0 for seamless pipes
C = Allowance (as per IBR) = 0.75 mm
    The thickness required as per the codes and standards are the minimum thickness. Hence, the nominal thickness used for procurement of different pipes should consider the applicable negative tolerance on thickness. The negative tolerances on thicknesses per various codes are different. The ASME used a 12.5% negative tolerance. The thickness of pipe selected considers thinning of pipes during bending operation. The thicknesses of the fittings are computed considering the fabrication process. The thickness at locations of shape change should take care of additional stresses. The holes made on the pipe weaken the pipes. Hence, additional thicknesses are provided where required.
10. Materials
Commonly Used Seamless Steel Pipes & Tubes Specifications in Boiler Pressure Parts & Piping and applicable Service Temperatures
Nominal
Composition		 Product ASME CSN DIN BS Temperature
Limit		 Re-
marks
Carbon Steel Tube SA192
SA210GrA1
SA210GrC
 - St35.8 BS3059
P2S 45		 800°F
(427°C)		  
Pipe SA106GrB
SA106GrC		 - St35.8
St45.8		 BS3602
HFS27		  
Mo Tube SA209T1 - 15Mo3 - 900°F
(482°C)		  
1 Cr Mo Tube - - 13CrMo44 BS3059
P2S2 620		 995°F
(535°C)		  
Pipe SA335P12 15111.1 13CrMo44 BS3604
HF620		  
1 Cr Mo Tube Sa213T11 - - - 1025°F
(552°C)		  
2 Cr Mo Tube SA213T22 - 10CrMo910 BS3059
P2S2
622/50		 1070°F
(577°C)		  
Pipe SA106GrB
SA106GrC		 - St35.8
St45.8		 BS3602
HFS27		  
Cr Mo
V		 Tube - 15123.1 14MoV63 BS3604
CD660		 1070°F
(577°C)		  
Pipe - 15123.1 14MoV63 BS3604
HF660		  
18Cr8Ni Tube SA213TP304H - - - 1300°F
(704°C)		  
18Cr10Ni
4CTi0.6		 Tube SA213TP321H - - -  
18Cr10Ni
8CCo+Tal		 Tube SA213Tp347H - - -  
18Cr10Ni
5CTi0.7		 Tube - - - B3605
822Ti		  
Legend: (1) ASME - American Society of Mechanical Engineers
(2) CSN - Czeckoslovian Standard
(3) DIN - German Standard
(4) BS - British Standard
11. Thickness
    The thickness of the pipes and the piping components are decided based on the loads and the strength of the piping components. The materials and the design temperatures play major role in selection of the thickness of the piping. The formulas for selection of the thickness of the pipes are given in various codes, standards, regulations and rules based on experience and experimentation. The formulas given by the codes, standards, regulations and rules are based on empirical relations. All the formulas use Factors of Safety. The Factors of Safety used by various methods are different.
    The formula for calculation of the thickness of flat end covers for the piping as per The Indian Boiler Regulations, 1950 IBR-342 (b) is given below.
  t = d K WP / f + 1.0, mm
Where,
 
t = Minimum required thickness, mm
d = Internal diameter of the pipe, mm
WP = Working pressure, kg / sq cm (g)
f = Permissible stress, kg / sq cm
Exercise 11.1
 
Working pressure = WP = 120.0 kg / sq cm (g)
Material   = SA516 Gr70
Working metal temperature   = 350 Degree C
Permissible stress = f = 1309 kg / sq cm
Pipe outside diameter = Do = 219.1 mm
Schedule of pipe   = Sch 80
Pipe nominal thickness = tn = 12.7 mm
Negative tolerance on thickness = tol = 12.5%
Pipe minimum thickness = tm = [12.7 x (100 12.5)] / 100 = 11.1
Pipe inside diameter = d = 219.1 2 x 11.1 = 196.9 mm
Thickness required = t = 196.9 √(0.28 x 120.0 / 1309)
+ 1.0 = 32.6 mm
use 36 mm thick plate.
Tube Thickness Calculation as per IBR-338, 1950 (with amendments)
Prepared: 3d-labs
Date: 23-Feb-05		 Checked: PSK
Date: 23-Feb-05		 Approved: 3d-labs
Date: 23-Feb-05
Refrence Drawing No. Drg Rev No. 00
Document No. XXX/XXX/XXXX/1001 Rev No. 00
Serial Number Description,
Symbol
&
Formula		 Calculation for
Item-01		 Unit Item-01 Item-02 Re-
marks
1 Tube location     Water Wall Radiant
Super-Heater		  
2 Tube location   mm 63.5 44.5  
Diameter = D
3 Tube working   Kg/ sq cm (g) 75 75  
Pressure = WP
4 Tube inside fluid   Degree C 310 480  
Temperature = t1
5 IBR Temperature   Degree C 28 50  
Margin = t2
6 Tube working
metal temperature
= t3 = t1 = t2		 338 Degree C 338 530  
7 Tube material     SA210Gr SA213  
A1 T22
8 Tube metal
allowable		   Kg/ sq cm 1201 617  
Stress = f
9 Code Factor C   mm 0 0  
10 Tube thickness
required = T
= (WP x D) /
(2f + WP) + C		 (75x63.5)/ (2 x
1202 + 75) + 0.0		 mm 1.92 2.55  
11 Tube thickness   mm 4 4.5  
Provided = T1
12 Negative tolerance   % 0 0  
on thickness = Tol
13 Tube bend thinning
allowance = Thin		   % 12.5 12.5  
14 Minimum
thickness of tube
required as per
IBR = Tm		   Mm 3.35 3.25  
15 Required tube
thickness (Final) =
T2		   mm 3.35 3.25  
16 IS Design Safe? Is {15}<{11}   Yes Yes  
17. Flow and Pressure Drop
    The piping can carry a single phase fluid or two phase fluid or three phase fluid. The following fluids are conveyed by the piping: (1) Liquid, (2) Gas, (3) Liquid-solid slurry, (4) Gas-solid mixture, (5) Liquid-gas mixture, (6) Gas-liquid-solid mixture. In a maze of piping, flow distribution plays a major role. The following formulas are commonly used to calculate the pressure drop and the pumping power required for a hollow cylindrical horizontal pipe carrying a liquid (single phase).
∆P = f W2 L / 2 g d HP = ∆P ρ W A / 75 x 109
Where,
∆P =Pressure drop in terms of head, mm of fluid column
d = Average inside diameter of pipe = 102.26 mm (for NPS4 STD pipe ф114.3 x 6.02 mm)
ρ = Density of fluid = 1.0 gm / cu cm (for water at ambient temperature)
A = Flow area = π d2 / 4 = π x 102.262 / 4 = 8,213 sq mm
f coefficient of friction in pipe, from Moody Diagram = 0.02
W = Velocity of fluid (for water at ambient temperature ρ = 1.0 gm / cu cm)
  = (Flow in cu mm per sec / Flow area in sq mm), mm / sec, for flow = 100 tonne / hr,
W = 100 x 109 / (1.0 x 3600 x 8,213) = 3,380 mm / sec
L = Total length of pipe = 100 mm = 100,000 mm
g = Acceleration due to gravity = 9806.65 mm/ sq sec
HP = Pumping power in metric Horse Power
∆P = 0.02 x 3,3802 x 100,000 / (2 x 9806.65 x 102.26) = 11,392 mm water column
HP = 11,392 x 1.0x 3,380x 8,213 / (75 x 109) = 4.22 HP
Considering a motor efficiency of 80%, motor rating = 4.22 / 0.8 = 5.28HP
Use a 6 HP motor.
 
L0 = L1 + L2 + LEXIT + LELBOW
= 873.2 + 7953.2 + 40 x 219.1 + 12 x 219.1
= 20219.6 = 20.2 m
∆P1 = f W2 L / 2 g d = (0.02 x 22.3 x 20.2) / (2 x 9.81 x 0.1937)
= 53 x = 53 x (42.2) = 2.2 kg / m
1000
= 2.2 = 0.00022 kg / cm
10000
21. Flow in Multiple Pipes
    Analysis of flow in multiple pipes is complex. To get results of reasonable accuracy complicated computations, using modern digital computers are used. These computer programs are available commercially. The computer programs are based on well-established concepts and procedures. The computers are used to analyze flow in piping of complicated shapes and layout. Computers can handle piping of any size and length. The computer uses numerical methods. These methods are approximate. But, they are accurate-enough for Engineering applications. The following simple layouts can be analyzed using the computers.
19. Economic Size
    The piping design activity includes selection of diameter, selection of material and selection of thickness. The diameter is selected based on past experience. The diameter is selected from the available sizes. Economic considerations lead to optimum design. The following gives recommendations for selection of diameter of the piping, based on velocity of the fluid:
Table: 19.1 Recommended Velocity of Fluids Inside Piping
1. Water service: 2 to 5 m /sec
2. Saturated steam service: 10 to 20 m / sec
3. Super-heated steam service: 30 to 50 m / sec
4. Gas service: 20 to 60 m / sec
    Even-though a wide range is given for the velocity of fluids inside the pipes, the economic diameter is decided based on several considerations.
    The material for piping is selected based on availability and economy. Even-though two materials can be used for a given application, economics decide the relevant material. In selecting ferrous material, oxidation potential plays a major role.
    The piping thickness selection is based on several issues. The following play a major role in piping thickness selection:
 
a) Fluid conveyed
b) Diameter of pipe
c) Total length of pipe
d) Transportable dimensions
e) Type of joints
f) Place of joining (shop or field)