1. Engineering Design Considerations
©2003, 2004, Plastics Pipe and Fittings Association

2. General Design Piping Practices
Follow generally accepted engineering practices when designing with thermoplastic piping. These include:
Selecting the proper material for the application
Controlling pressure surges and velocities
Identifying standards for piping components
Selecting and proper sizing of pipe, valves and fittings
Proper pipe supports, anchors, and guides
Proper underground design considerations
Selecting the most cost effective system for required service life
Following all applicable codes and standards
All successfully installed piping systems include generally accepted engineering piping practices transcending any particular piping material.
2 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

3. Plastic Piping Design Practices
Plastic piping has several unique engineering properties compared to non-plastic materials. To ensure an effective and long lasting piping installation, the design engineer needs to be aware of these properties:
Chemical Resistance
Pipe and System Pressure Ratings
Temperature Limits
Temperature/Pressure Relationship
Expansion/Contraction
Pipe Support
Underground Pipe Flexibility
Temperature-pressure relationships, expansion/contraction features, pipe supports, and temperature/pressure limits are design considerations that must be understood to insure a successfully engineered industrial thermoplastic piping system.
3 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

4. Chemical Resistance
Plastics in general have excellent chemical resistance; however, there are certain chemical environments that affect the properties of plastics in the following ways:
Chemical Attack: An environment that attacks certain active sites on the polymer chain.
Solvation: Absorption of a plastic by an organic solvent.
Plasticization: Results when a liquid hydrocarbon is mixed with a polymer but unable to dissolve it.
Environmental Stress-Cracking: A failure that occurs when tensile stresses combined with prolonged exposure to certain fluids generate localized surface cracks.
One of the major reasons thermoplastic piping is considered for industrial applications is its chemical resistance capabilities. This applies to both the fluid being conveyed and the outside environment.
4 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

5. Chemical Resistance Tables
Many manufacturers have tested hundreds of reagents to determine their affect on plastics. These lists are readily available and act as a guide for the user and design engineer. Listed is a rather broad chemical resistance table of chemical groups and piping material. A recommended fluid is based on performance and safety factors.
Almost 1000 different chemicals and solutions have been tested by plastic resin and product manufacturers in order to guide designers and users as to which plastic piping material will handle a particular solution. In addition, chemical resistance tables are available for elastomeric compounds (gaskets and O-rings) used in sealing plastic flanges, valves and pumping products.
5 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

6. General Chemical Resistance Tables
Chemical - Inorganics
CPVC PE PP
PVC
PVDF
Acids, dilute R
Acids, concentrated L
Acids, oxidizing NR
Alkalis
Acid gases
Ammonia gases
Halogen gases
Salts
Oxidizing salts
Chemical - Organics
CPVC PE PP
PVC
PVDF
Acids R
Acid anhydrides NR L
Alcohols-glycols
Esters / ketones / ethers
Hydrocarbons – aliphatic
Hydrocarbons – aromatic
Hydrocarbons – halogenated
Natural gas
Synthetic gas
Oils
Years of experience and testing have gone into published chemical resistance data; however, it is still recommended for particular critical applications that pipe designers and users self-test these fluids for material compatibility.
R = Recommended
L = Limited Use
NR = Not Recommended
6 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

7. Chemical Resistance Detailed Partial Chart
Shown is a partial chemical resistance table adapted from a manufacturer’s detail listing of hundreds of reagents. These and similar tables are compiled from years of testing and research, however, if involved with a critical application and conflicting chemical resistance information, self-testing is advised.
Sample Chemical Resistance Chart
Chemical
PVC
CPVC PP
PVDF PE
Temperature (° F) 70
140
185
150
180
250
Sulfuric acid, 50% R NR —
Sulfuric acid, 60%
Sulfuric acid, 70%
Sulfuric acid, 80%
Sulfuric acid, 90%
Sulfuric acid, 93%
Sulfuric acid, 100%
In addition to checking the piping compatibility to the fluid being handled, make certain the chemical resistance of any elastomeric material coming in contact with the piping be compatible with the plastic pipe material; this may be more critical in elastomeric inner pipe support liners which may have less published chemical resistance information than flange gaskets or O-rings.
R = Recommended
— = No information available
NR = Not Recommended
7 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

8. Operating Pressure Determination
PR = 2(HDS) • t Dm
Thermoplastic piping’s pressure-ratings are determined by ASTM and PPI standards and requirements. Pipe pressure ratings are calculated using the following ISO equation:
where: PR =
Pressure rating, psi (MPa) t
Minimum wall thickness, in (mm) Dm
Mean diameter, in (mm)
HDS*
Hydrostatic design stress = HDB** (hydrostatic design basis) • DF*** (design factor)
Most thermoplastic piping used for TIPS applications is made to ASTM Standards and is pressure rated for 73F. This pressure rating is based on the Plastic Pipe Institute ( PPI) listed HDB (Hydrostatic Design Basis) which is multiplied by the 0.5 Design Factor to yield the HDS (Hydrostatic Design Stress). For example, PVC 1120 materials have a 4000-psi HDB and a 2000-psi HDS. The last two digits in the PVC designation is derived by dividing the 2000-psi HDS by 100. *
Most values of HDS for 73°F are specified by ASTM and other standards. **
Hydrostatic design basis (HDB) is determined by long-term hydrostatic strength testing as defined by ASTM and PPI standards. Each thermoplastic pressure piping material has an established 73°F or 180°F for water and hot water applications, respectively.
***
Maximum HDS for water uses a pipe design factor of 0.5. For gas pipe, the DF is 0.32.
All thermoplastic piping manufacturers list product pressure ratings in their technical literature.
8 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

9. Pressure Ratings of Thermoplastic Piping
©2003, 2004, Plastics Pipe and Fittings Association

10. Schedule Pipe
Schedule pipe is IPS (Iron Pipe Size) OD pipe with wall thickness that matches the wall thickness of the same size and schedule steel pipe. Most vinyl pipe is available in Schedule 40, 80, and 120. (The higher the Schedule number, the thicker the pipe wall for each size.) Scheduled pipe pressure ratings vary with each pipe diameter. Pipe pressure ratings decrease as pipe diameter increases for all schedules.
In many TIPS applications IPS (Iron Pipe Size) dimensional pipe is available in Schedule 40 & 80 (Schedule 120 is also available but is infrequently used) and SDR (Standard Dimension Ration). In the Schedule 40 & 80 system, the pipe wall thickness matches that of steel pipe, however, this results in pressure ratings that decrease as the pipe diameter increases. The SDR system was developed so that the pressure ratings of all pipe sizes remain constant for a given material and SDR rating. The DR (Dimension Ration) is the ratio of the pipe outside diameter (OD) to the pipe wall thickness. Most metric-sized piping is SDR.
10 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

11. Standard Dimension Ratio (SDR)
SDR pipe is based on the IPS OD system. The SDR (Standard Dimension Ratio) is the pipe OD divided by the wall thickness. For a given SDR, the pressure ratings are constant for all pipe sizes for each plastic material. Non-standard DRs (dimension ratios) can be computed for any pipe OD and wall thickness.
For many non-industrial thermoplastic piping applications such as irrigation, water mains, sewage and gas, standard dimension ration (SDR) piping is used. The outside diameter could be similar to scheduled pipe: however, the wall thickness varies to maintain a constant pressure rated pipe.
11 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

12. Metric / Bar Rating
Metric or Bar Rated pipe is similar to SDR piping ratings in that all sizes of a single SDR and the same material have the same pressure rating. In the Metric system, one bar = one atmosphere = 14.7 psi. A bar rating of 16 = (14.7 x 16) = psi.
Metric sized piping usually is manufactured and mainly used in countries outside of North America. However, several unique piping systems used in the USA are dimensionally metric. Due to the differing pipe diameters, it is unlikely to mistakenly directly join a metric piping system to a Scheduled or SDR piping system. Always be aware of the product standard that is marked on the pipe.
12 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

13. Comparisons of SDR PVC Pipe Pressure Ratings @ 73°F
SDR Rating
Pressure Rating (psi)
Bar Rating (atm)
13.5
315
21.4
17.0
250
21.0
200
13.6
26.0
160
10.9
32.5
125
8.5
41.0
100
6.8
This table compares pressure ratings of PVC SDR rated piping systems.
13 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

14. Fittings
Pressure ratings of molded fittings are similar to that of pipe as shown in the listed tables. However, some molded fitting manufacturers have lowered or are considering lowering the pressure capability of their products in comparison to pipe. For pressure capabilities of molded and fabricated fittings, consult the manufacturer’s recommendations.
Some vinyl fitting manufacturers have de-rated the operating pressure of their fittings as compared to the operating pressure of the pipe. In critically sensitive pressure applications, check with the fitting manufacturer to determine the exact operating pressure capability of their molded and fabricated fittings.
14 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

15. Other
Other plastic piping systems have differing outside diameter dimensions and pressure ratings such as Copper Tube Size (CTS), Cast Iron (CI) and Sewer & Drain. Plastic piping made to most of these piping systems are used for non-industrial applications.
In some non-industrial piping products (i.e. sewer pipe and others), there are differing outside pipe diameters and pressure ratings available as compared to Scheduled pipe.
15 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

16. Temperature Ratings of Plastic Piping
Thermoplastic piping materials decrease in tensile strength as temperature increases, and increase in tensile strength as temperature decreases. This characteristic must be considered when designing TIPS. The correction factor for each temperature and material is calculated. To determine the maximum suggested design pressure at a particular temperature, multiply the base pressure by the correction factor.
For the engineer, knowing the relationship of temperature and pressure of thermoplastic piping is critical for a successful installation. The rule in thermoplastic piping is as the temperature of a fluid increases, the pressure rating of the piping decreases.
16 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

17. Comparison of Schedule 80 Pipe Pressure Ratings (psi) @ 73°F
Nominal Pipe Size (in.)
PVC / CPVC
PE (SDR 11)*
PP**
PVDF
850
160
410
580
690
330
470 1
630
310
430
1 ½
230
320 2
400
200
270 3
370
190
250 4
220 6
280
140 8
N/A 10 12
Notice, that in Schedule pipe, thermoplastic piping working pressure decreases as the pipe diameter size increases.
* PE is not Schedule 80. ** Pipe pressure ratings shown are piping manufacturer’s values. PPI, as of yet, does not publish PP HDB or HDS ratings.
17 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

18. Temperature Correction Factors for Piping
Operating Temp. (°F)
CPVC PE PP
PVC
PVDF 70
1.00 80
.90
.97
.88
.95 90
.91
.84
.75
.87
100
.82
.78
.85
.62
.80
110
.72
.74
.50
120
.65
.63
.40
.68
130
.57
.30
140
.22
.58
150
.42 * NR
.52
160
.49
170
.29
.26
.45
180
.25
200
.20
.36
210
.15
.33
220
240
Temperature correction factors for de-rating the working pressure of thermoplastic piping at varying temperatures are similar for each material and are listed by each piping manufacturer.
* Drainage only NR = Not recommended
18 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

19. Example
What is the maximum pressure rating of 3” PP Sch °F?
Maximum Pressure Rating: 0.75(190) = psi
Nominal Pipe Size (in.)
PVC / CPVC
PE (SDR 11) PP
PVDF 2
400
160
200
270 3
370
190
250 4
320
220
The pressure rating and temperature correction factors for this example are shown in red.
Operating Temp. (°F)
CPVC PE PP
PVC
PVDF
110
.77
.74
.80
.50
.75
120
.70
.63
.40
.68
130
.62
.57
.30
19 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

20. Operating Pressure of Valves, Unions, and Flanges
One of the limiting pressure ratings of TIPS and other piping systems is the 150-psi pressure rating of most valves, unions and flanges (some manufacturers list some valves and unions at higher pressure ratings). As in pipe, as the temperature goes up, the pressure rating goes down.
Generally, thermoplastic valves, unions and flanges can present a pressure limit to a thermoplastic piping system. For many of these products, 150-psi is the maximum pressure rating at ambient temperature (some products may have higher pressure ratings; check with the manufacturer).
20 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

21. Maximum Operating Pressure (psi) of Valves* / Unions* / Flanges
Operating Temp. (°F)
CPVC PP
PVC
PVDF
73-100
150
110
140
135
120
130
118 75
105 50
100 93 NR
160 90 80
133
170 70
125
180
115
190 60
106
200 97
220 67
240 52
As in pipe, valves, unions and flanges have their working pressure de-rated as temperature increases. Each manufacturer may have slightly different temperature correction factors for their products.
* Valve and union pressure ratings may vary with each manufacturer. Consult manufacturer’s published information. NR = Not recommended
21 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

22. Operating Pressure of Threaded Pipe
Direct threading of thermoplastic piping is accomplished using only proper threading equipment. However, do not thread pipe below the thickness of a Schedule 80 pipe wall. Threading vinyl pipe reduces operating pressures by 50%. With most other Schedule 80 thermoplastic piping, threading reduces operating pressure for all pipe sizes to 20-psi or less. If threaded thermoplastic piping systems must be used, increased working pressure could be obtained using transition fittings such as molded unions and adapters.
If at all possible, refrain from directly threading thermoplastic piping, since pipe threading decreases the working pressures of all thermoplastic piping.
22 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

23. Vacuum Collapse Rating and Underground Loading
Most industrial thermoplastic piping systems can handle a vacuum as low as 5 microns. With atmospheric pressure at 14.7 psi and a perfect vacuum, most plastic piping cannot be brought to collapse unless the pipe is brought to a partial out-of-round condition, or an external radial pressure is added. If a vacuum line is to be installed underground, special care must be taken to assure a minimum of deformation. Contact the pipe manufacturer for assistance if this condition is encountered.
Collapse rating and loading is mentioned but, in most industrial applications, collapsing of pipe walls is not a major consideration.
23 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

24. Pressure Losses in Plastic Piping Systems
To determine the pressure drop through a valve, the following equation is used:
As fluid flows through a piping system, it experiences head loss depending on fluid velocity, pipe wall smoothness and internal pipe surface area. Pipe and fitting manufacturers, using the Hazen-Williams formula, have calculated and have readily available the friction loss and velocity data for all their products. Valve manufacturers have calculated liquid sizing constants (Cv values) for each type and size of valve in determining the pressure drop for a given condition.
∆ P =
Q² • S.G. Cv²
Almost all thermoplastic piping products have had their pressure loss calculated and listed using the Hazen and Williams’s formula. Due to the very smooth surfaces of plastic products, friction losses in plastics are usually lower than other piping products; and because corrosion is normally not a problem, this characteristic is maintained over years of service.
where:
∆ P =
Pressure drop across the valve (psi) Q
Flow through the valve (gpm)
S.G.
Specific gravity of the liquid Cv
Flow Coefficient
24 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

25. Example
Find the pressure drop across a 1 ½ PVC ball check valve with a water flow rate of 50 gpm: Cv for valve = 56 (from manufacturer’s manual)
∆ P =
Q² • S.G. Cv²
(50)² • 1.0 (56)²
0.797 psi
Most plastic valve manufacturers list the Cv factor for each of their valves.
25 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

26. Sample Partial Listing of Flow Capacity and Friction Loss for Sch
Sample Partial Listing of Flow Capacity and Friction Loss for Sch. 80 PVC per 100 ft.
1” Pipe
GPM
Velocity (ft/sec)
Friction Head (ft)
Friction Loss (psi) 7
3.26
4.98
2.16 10
4.66
9.65
4.18 15
6.99
20.44
8.86 20
9.32
34.82
15.09 25
11.66
52.64
22.81 30
13.99
78.78
31.97 35
16.32
98.16
53.36
1 ½ ” Pipe
GPM
Velocity (ft/sec)
Friction Head (ft)
Friction Loss (psi) 7
1.31
0.54
0.23 10
1.87
1.05
0.46 15
2.81
2.23
0.97 20
3.75
3.80
1.65 25
4.69
5.74
2.49 30
5.62
8.04
3.48 35
6.56
10.70
4.64 40
7.50
13.71
5.94 45
8.44
17.05
7.39 50
9.37
20.72
8.98
Complete friction loss tables exist for most pressure-rated thermoplastic pipe, fittings and valves.
26 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

27. Example
Find the velocity and friction head loss of 1 ½ PVC Schedule gpm: Using table: Velocity = 4.69 ft/sec Head loss = 5.74 ft
1 ½ ” Pipe
GPM
Velocity (ft/sec)
Friction Head (ft)
Friction Loss (psi) 20
3.75
3.80
1.65 25
4.69
5.74
2.49 30
5.62
8.04
3.48
Knowing the pipe diameter size and flow rate, one can calculate the velocity and friction loss of a piping system.
27 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

28. C Factors for Common Piping Materials
Constant (C)
Type of Pipe
150
All Thermoplastics / New Steel
140
Copper / Glass / New Cast Iron / Brass
125
Old Steel / Concrete
110
Galvanized Steel / Clay
100
Old Cast Iron
All commonly used thermoplastic piping materials have a C factor of 150 or higher. This feature allows less friction loss in thermoplastic piping as compared to most other piping products.
28 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

29. Hydraulic Shock The following formula determines the surge pressure:
Hydraulic shock or water hammer is a momentary pressure rise resulting when the velocity of the liquid flow is abruptly changed. The longer the line and higher the liquid velocity, the greater the shock load from the surge. For the piping system to maintain its integrity, the surge pressure plus the pressure existing in the piping system must not exceed 1 ½ times the recommended working pressure of the piping system. P = v
S.G.-1
C + C 2
where: P =
Maximum surge pressure (psi) v
Fluid velocity (ft/sec) C
Surge wave constant
S.G.
Specific gravity of the liquid
By properly designing a piping system, the engineer can minimize the effect of hydraulic shock or water hammer; however, it is prudent to calculate this possible event, especially if the fluid velocity is higher than five feet per second and there are long runs of pipe and, or quick closing pumps and valves exist.
29 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

30. Example
What would the surge pressure be if a valve were suddenly closed in a 2” PVC Sch. 80 pipe carrying fluid with a S.G. of 1.2 at a rate of 30 gpm and a line pressure of °F? C = 24.2 (from Surge Wave Constant Table) v = 3.35 (from Flow Capacity & Friction Loss Table)
This example shows how to calculate the surge pressure and if this pressure is within the operating pressure of the piping system. P = v
S.G.-1
C + C 2
30 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

31. Example
What would the surge pressure be if a valve were suddenly closed in a 2” PVC Sch. 80 pipe carrying fluid with a S.G. of 1.2 at a rate of 30 gpm and a line pressure of °F? C = 24.2 (from Surge Wave Constant Table) v = 3.35 (from Flow Capacity & Friction Loss Table) P =
3.35 2
31 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

32. Example
What would the surge pressure be if a valve were suddenly closed in a 2” PVC Sch. 80 pipe carrying fluid with a S.G. of 1.2 at a rate of 30 gpm and a line pressure of °F? C = 24.2 (from Surge Wave Constant Table) v = 3.35 (from Flow Capacity & Friction Loss Table) P =
3.35 ( 26.6 )
90 psi
32 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

33. Example
What would the surge pressure be if a valve were suddenly closed in a 2” PVC Sch. 80 pipe carrying fluid with a S.G. of 1.2 at a rate of 30 gpm and a line pressure of °F? C = 24.2 (from Surge Wave Constant Table) v = 3.35 (from Flow Capacity & Friction Loss Table) Total line pressure = = 250 psi Note: 2” PVC Sch. 80 pipe has a pressure rating of 400 psi at 73°F; therefore, 2” PVC Sch. 80 pipe is acceptable for this application. P =
3.35 ( 26.6 )
90 psi
33 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

34. Avoiding Hydraulic Shock
Fluid velocity < 5 ft/sec
Actuated valves with specific closing times
Start pump with partially closed valve in discharge line
Install check valve near the pump discharge to keep line full
Vent all air out of system before start-up
To avoid hydraulic shock, incorporate the same general principles as in other non-thermoplastic piping systems.
34 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

35. Thermal Expansion & Contraction
Thermoplastics compared to non-plastic piping have relatively higher coefficients of thermal expansion. For this reason, it is important to consider thermal elongation when designing thermoplastic piping systems.
Use the following formula to calculate the expansion/contraction of plastic pipe: ΔL = y
(T1-T2) • L 10
100
where: ΔL =
Expansion of pipe (in.) y
Constant factor (in./10°F/100 ft) T1
Maximum temperature (°F) T2
Minimum temperature (°F) L
Length of pipe run (ft)
Thermal expansion and contraction of thermoplastic piping is a significant factor when designing plastic piping systems. Plastics expand or contract at a greater rate than other piping materials. Engineers must calculate and design for these changes in pipe length.
35 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

36. Example
How much expansion will result in 300 ft of PVC pipe installed at 50°F and operating at 125°F? (y for PVC = 0.360) ΔL = y
(T1-T2) • L 10
100
This straight forward example simplifies calculating the expansion of plastic piping systems. ΔL =
0.36
(125-50) •
300 10
100 ΔL =
0.36 75 •
300
8.1 in. 10
100
36 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

37. Values of y for Specific Plastics
Material
y Factor
PVC
0.360
CPVC
0.456 PP
0.600
PVDF
0.948 PE
1.000
Constant factor value (y) is a function of the coefficient of elasticity of the piping material. The larger the ‘y” value, the greater the expansion/contraction.
37 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

38. Managing Expansion / Contraction in Piping System
Forces which result from thermal expansion and contraction can be reduced or eliminated by providing piping offsets, expansion loops or expansion joints. The preferred method of handling expansion/contraction is to use offsets and, or expansion loops. Expansion joints require little space but are limited in elongation lengths and can be a maintenance and repair issue. As a rule-of-thumb, if the total temperature change is greater than 30ºF (17ºC), compensation for thermal expansion should be considered.
Managing the expansion and contraction of thermoplastic piping systems is similar to other piping systems. And, like other piping systems, expansion legs or loops are the preferred methods of handling this phenomenon. Fabricated or bellow-type expansion joints can be installed but should be used as a last resort due to the possibilities of increased maintenance, lower reliability and increased cost.
38 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

39. Expansion Loops & Offsets
Expansion Loop Formula L =
3 ED (ΔL) 2S
where: L =
Loop length (in.) E
Modulus of elasticity at maximum temperature (psi) S
Working stress at maximum temperature (psi) D
Outside diameter of pipe (in.) ΔL
Change in length due to change in temperature (in.)
By using the listed equation, lengths of expansion loops and legs may be calculated.
39 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

40. Example
What would the loop length be to compensate for 4” of expansion of 3” CPVC Sch. 80 pipe with a maximum temperature of 110°F ?(outside diameter of 3” pipe = 3.50 inches; E=371,000; S = 1500) L =
3 ED (ΔL) 2S L =
3 • 371,000 • 3.5 • 4
2 • 1500
Expansion loops are easy to make and can be prefabricated at the installers facility and installed at the job site to minimize labor costs. L =
15,582,000
≈ 72 inches
3000
40 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

41. Thermal Stress
To calculate the induced stress of restrained pipe, use the formula: St = ECΔT
If provisions are not made for expansion/contraction, the resulting forces will be transmitted to the pipe, fittings and joints. Expansion creates compressive forces and contraction creates tensile forces.
where: St =
Stress (psi) E
Modulus of elasticity (psi x 105) C
Coefficient of thermal expansion (in./in./°F x 105) ΔT
Temperature change between the installation temperature and max/min temperature, whichever produces the greatest differential (°F)
Thermal stress can easily be calculated in restrained thermoplastic piping applications. In many case, plastic piping may be able to absorb the thermal stress of the pipe, therefore, not requiring any expansion products or design changes.
41 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

42. Example
What is the induced stress developed in 2” Schedule 80 PVC pipe with the pipe restricted at both ends? Assume the temperature extremes are from 70°F to 100°F. St = ECΔT = (3.60 x 105) x (3.0 x 105) x (100-70) St = 324 psi Note: Steel pipe stress is approximately 15 – 20 times higher than most plastic piping.
The example shown will not allow the 2-inch Schedule 80 pipe to internally handle the pipe stress (see operating pressures in previous tables in this section where 2-inch Schedule 80 pipe has an operating pressure of 400-psi x .62 correction or 248-psi). Therefore, expansion provisions have to be included in this design.
42 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

43. Longitudinal Force
To determine the magnitude of the longitudinal force, multiply the stress by the cross-sectional area of the plastic pipe. The formula is: F = St • A
where: F =
Force (lbs.) St
Stress (psi) A
Cross-sectional area (in2)
The longitudinal forces in thermoplastic piping are normally much less than metal piping systems due to lower thermal stresses in plastics. This in effect means that metal pipe could generate enough longitudinal force in a restrained system without proper design for expansion to break brick walls while plastic pipe under similar conditions would tend to have the piping bend abnormally or fail without affecting the restraining barriers.
43 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

44. Example
With the stress as shown in the previous example, calculate the amount of force developed in the 2” Schedule 80 PVC pipe? (cross-sectional area of 2” pipe = in2) F = St • A = 324 psi • in2 F = 504 lbs.
As you can see in this example, there is not a very large force developed in this piping system.
44 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

45. Above-ground Design
©2003, 2004, Plastics Pipe and Fittings Association

46. Support Spacing
The tensile and compressive strengths of plastic pipe are less than those of metal piping. Consequently, plastics require additional pipe support. In addition, as temperature increases, tensile strength decreases requiring additional support. At very elevated temperatures, continuous support may be required.
Support spacing is another significant factor to consider when designing thermoplastic piping systems. For most applications, thermoplastic piping systems require more piping supports than other piping systems. If using rubber inserts in piping support or clips, make certain the elastomer is compatible to the piping material.
46 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

47. Support Spacing of TIPS Schedule 80 Pipe (ft)*
Nominal Pipe Diameter (in.)
CPVC PP
PVC
PVDF
60°F
100°F
140°F
5 ½ 5
4 ½ 4 3 2
2 ½ 6 1
6 ½
4 ¾
1 ½ 7
3 ½
7 ½
5 ¼ 9 8
5 ¾ 10
7 ¼ 11
8 ½
9 ½
* Listings show spacing (ft) between supports. Pipe is normally in 20-ft lengths. Use continuous support for spacing under three feet.
The number of pipe supports for thermoplastic piping increase with an increase in temperature and decrease with an increase in pipe diameter size.
47 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

48. Pipe Support Spacing with Specific Gravities Greater Than 1.0*
Specific Gravity
Correction Factor
1.0
1.00
1.1
0.98
1.2
0.96
1.4
0.93
1.6
0.90
2.0
0.85
2.5
0.80
Pipe support spacing is affected by the specific gravity of the fluid being handled… the heavier the fluid the more supports are required.
* Above data are for un-insulated lines. For insulated lines, reduce spans to 70% of values shown.
48 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

49. Pipe Hangers
Use hangers that have a large bearing area to spread out the load over the largest practical area. The basic rules for hanging plastic pipe are:
Avoid point contact or concentrated bearing loads.
Avoid abrasive contact.
Use protective shields to spread the loads over large areas.
Do not have the pipe support heavy valves or specialty fittings.
Do not use hangers that “squeeze” the pipe.
Although more pipe hangers are used with thermoplastic piping systems, the hangers are usually lighter in weight than other piping systems. If higher temperatures require excessive supports, the use of continuous metal v-channel or half-round metal piping may be used to minimize the number of supports.
49 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

50. Typical Pipe Hangers Riser Clamp Wrought Clevis Roller Hanger
Pipe Roll & Plate
Adjustable Solid Ring
Double-belt Pipe Clamp
Single Pipe Roll
Hangers for plastic piping are similar to that of other piping systems but usually lighter in weight.
50 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

51. Pipe & Valve Supports Shoe Support Trapeze Support
Hanger with Protective Sleeve
Valve Support from Below
Supporting Plastic Pipe Vertically
Continuous Support with Structural Angle
Overhead Support for Valve
Plastic pipe and valve supports are similar to other piping systems. Remember to always support valves in the piping system.
51 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

52. Anchors & Guides
Anchors direct movement of pipe within a defined reference frame. At the anchoring point, there is no axial or transverse movement. Guides allow axial movement of pipe but prevent transverse movement. Use guides and anchors whenever expansion joints are utilized and on long runs and directional changes in pipe.
The proper installation of pipe anchors and guides are critical for above-ground piping systems in which significant expansion and contraction can occur. Not only is the proper anchor and guide products important, but equally important, is the exact placement of each anchor and guide.
52 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

53. Anchoring Pipe with Metal Chain Anchor Pipe with Metal Anchor
Pipe with Metal Sleeve and Anchor
Plastic piping anchors are similar to those in other piping systems. The anchors are used to prevent or minimize lateral pipe movement.
Pipe with Concrete Anchor
53 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

54. Anchoring & Guide Design Diagrams
Shown are typical anchor and guides for any piping system (including plastics).
54 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

55. Insulation of Plastic Piping
To calculate heat loss or gain through plastic piping, the following equation is used:
With thermoplastic piping having a thermal conductance of 1/300 of steel and 1/2700 of copper, minimum or no insulation may be required. Q =
K t A • ΔT x
where: Q =
Heat gain or loss (Btu) K
Thermal conductivity of the pipe (Btu-in./ft2-hr-°F) ΔT
Temperature difference of inside and outside pipe walls (°F) A
Surface area (ft2) x
Wall thickness (in.) t
Time (hrs.)
Plastic piping requires reduced or no insulation as compared to metal piping. In most cases, the heat loss in steel piping versus thermoplastic piping is 268 times greater or more than that of plastic piping as shown in the example to follow.
55 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

56. Example
What is the heat loss over 1 hour of a 1-foot long section of 2” PVC Sch. 80 pipe with a temperature difference of 80°F? K =
1.2 Btu-in./ft2-hr-°F (for PVC) D
2.375 in. for 2” pipe A
πDL = (3.141)(2.375 in.)(1ft/12in.)(1 ft) = ft2 x
0.218 in.
From these examples, the only major difference between PVC and steel pipe is the thermal conductivity of the piping material. Q =
K t A • ΔT
1.2 • 1 • • 80
= Btu x
0.218
56 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

57. Example
What is the heat loss over 1 hour of a 1-foot long section of 2” Carbon Steel Sch. 80 pipe with a temperature difference of 80°F? K =
321.4 Btu-in./ft2-hr-°F (for steel) D
2.375 in. for 2” pipe A
πDL = (3.141)(2.375 in.)(1ft/12in.)(1 ft) = ft2 x
0.218 in.
From this example, one can see the tremendous energy savings offered in using thermoplastic piping systems. Q =
K t A • ΔT
321.4 • 1 • • 80
= Btu x
0.218
57 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

58. Other Above-ground Design Considerations
©2003, 2004, Plastics Pipe and Fittings Association

59. Cold Environments
Most plastic piping systems handle temperatures below 0°F if the system liquid does not freeze. However, the pipe flexibility and the impact resistance decrease. This may cause the pipe to become brittle. Protect the pipe from impact if this condition can occur. To prevent liquid freezing or crystallization in piping, electric heat tracing may be used and applied directly on the pipe within the insulation. The heat tracing must not exceed the temperature-pressure system design.
When handling thermoplastic piping in cold weather, be careful not to sharply impact the piping. Even though the tensile strength of the piping increases when the temperature is lowered, the shear strength decreases causing possible brittleness in the piping.
59 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

60. Hot Environments
When pressure-piping applications exceed 285°F, the use of thermoplastic piping is limited. Make sure, in temperatures above 100°F, that expansion/ contraction, reduced working pressures and support spacing are considered.
Most thermoplastic piping systems have a narrower range of temperature capability than other piping materials.
60 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

61. Outdoor Environments
Most TIPS are formulated for protection against the harmful ultraviolet rays from the sun. However, long periods of exposure to direct sunlight can oxidize the surface of the piping, causing discoloration and reduced impact resistance. To prevent these phenomena, opaque tape or paint can be applied. Be sure to use acrylic or water-based paints. Do not use oil-based paints as they may cause harm to some plastic piping.
If using thermoplastic piping outdoors for an extended period of time, coat the piping with a manufacturer’s recommended paint or other covering.
61 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

62. Compressed Air
Except for specially designed and designated plastic piping systems, most manufacturers do not recommend their product for handling of or testing with any compressed gases.
The rule of thumb is not to use any thermoplastic piping in transporting of or in testing with compressed air or gases. The exception to this rule is the use of polyethylene gas piping and other specially formulated plastic piping compounds specifically designed to handle compressed air or gases.
62 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

63. Below-ground Considerations
©2003, 2004, Plastics Pipe and Fittings Association

64. Below-ground Design
Pipe deflection or compression depends on any one or a combination of three factors:
Pipe stiffness
Soil stiffness (soil density along the sides of the pipe)
Load on the pipe (earth/static/live)
Plastic pipe in most instances is considered a flexible pipe rather than a rigid piping material. Flexible pipe is pipe that is able to bend without breaking and uses the pipe wall and buried medium to sustain external loads. When installed properly, plastic develops support from the surrounding soil.
The below-ground design of most plastic piping is for a flexible piping system. The design considerations for buried plastic piping vary by material and in some cases by manufacturer. If in doubt, always follow the piping manufacturer's installation and design instructions.
64 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

65. Pipe Stiffness
Pipe stiffness is the force in psi divided by the vertical deflection in inches. An arbitrary data point of 5% deflection is used as a comparison of pipe stiffness values in flexible piping. Each pressure piping material has a different pipe stiffness value that is based on the material’s flexural modulus. For any given SDR, the pipe stiffness remains constant for all sizes.
Pipe stiffness values are listed for each manufacturer’s piping products.
65 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

66. Soil Stiffness
Soil stiffness is the soil’s ability to resist compaction. There is a formula (Spangler’s) to determine the “E” values or deflection of buried flexible pipe in terms of soil stiffness independent of pipe size. The “E” value is also referred to as the modulus of soil reactions. The soil backfill type and amount of compaction directly affect these values.
Plastic piping manufactures publish burying instructions pertaining to soil stiffness and pipe loading.
66 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

67. Pipe Loading
Earth loads may be calculated using Marston’s load formula. Static loads are calculated using Boussinesq’s Equation. Live or dynamic loads are also calculated using Boussinesq’s Equation, by multiplying the superimposed load (W) by 1 ½. There are many existing tables available from pipe manufacturers for various piping materials listing soil conditions, soil compaction, pipe stiffness values, maximum height of cover recommendations and other useful data to design underground plastic piping systems.
See manufacturer’s tables for pipe loading information.
67 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

68. Trench Design & Terminology
Trenches should be of adequate width to allow the proper bedding and backfilling of plastic pipe, while being as narrow as practical. A trench width of two or three times the piping diameter is a good rule of thumb in determining the trench width. Following is a table listing minimum trench widths for various pipe sizes and a cross-section showing pipe trench terminology.
Trenches for thermoplastic piping should be as narrow as possible to assist in the integrity of the pipe and compacted soil.
68 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

69. Trench Design & Terminology
Nom. Pipe Sizes (Diameter in.)
Number of Pipe Diameters
Trench Width (in.) 4
4.3 18 6
2.9 8 24 10
2.5 26 12
2.4 30 15
2.0
1.8 32 21
1.6 34
1.5 36 27 40
1.4 42 33 46 50 56 48
1.3 62
Each manufacturer has published tables for trench design. Use the above table as a guide only. Also listed is typical nomenclature used in installing buried piping. With plastic piping, it is an excellent idea to map the piping for future repair or design changes or place a metal strip over the piping before covering the trench fully so that a metal detector could easily locate the buried plastic piping.
69 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

70. Minimum Cover of Buried Pipe
The following guidelines may be used when burying plastic pipe:
Locate pipe below the frost line
A minimum cover of 18 in. or one pipe diameter (whichever is greater) when there is no overland traffic
A minimum cover of 36 in. or one pipe diameter (whichever is greater) when truck traffic may be expected
A minimum cover of 60 in. when heavy truck or locomotive traffic is possible
Depending on the above ground traffic and geographic location of the piping system, the pipe burial depth is a critical design consideration with thermoplastic and other non-plastic piping systems.
70 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association

71. Environmentally sound Easy and safe to install Reliable Long-lasting
TIPS are...
Environmentally sound
Easy and safe to install
Reliable
Long-lasting
Cost-effective
71 - Engineering Design Considerations ©2003, 2004, Plastics Pipe and Fittings Association