1. A Look At Rigid & Flexible Pipe Products
Pipe Comparisons
A Look At Rigid &
Flexible Pipe Products

2. Why Are We Here?
To examine the basics that differentiate concrete pipe from flexible alternatives
To use those basics to specify the right product for the job

3. There is NO Perfect Pipe
All pipes bring certain strengths and weaknesses.
Good designers must accommodate for strengths that best benefit the project, while making sure the weaknesses don’t affect the project long term

4. Corrugated Steel Pipe

5. HDPE - Plastic Pipe

6. Reinforced Concrete Pipe

7. What are the important attributes of a pipe?

8. The Important Attributes of a Piping System
Strength
Durability-LCA
Hydraulics
Installation
Cost
Low Risk/Maintenance

9. Conduit Buried Pipe Structure
The Bottom Line :
Buried pipe must perform two critical functions
Conduit
Buried Pipe
Structure

10. Concrete Pipe Strength Delivered on the Truck
Rigid pipe
The majority of the structural strength of this pipe system has been designed, built into,and tested in the pipe.
It is not built in the field.

11. Strength of Flexible Pipe has to be Built in the Trench
The majority of the structural strength of this type of pipeline system is not built in nor delivered on the truck.
Strength of all plastic pipe systems depends on the quality and placement of the backfill materials by the contractor.

12. Pipe Strength vs Stiffness
PRECAST RCP
f’c = 4000 psi psi min (ASTM)
Steel = 65,000 psi
RCP is a structure.
Many Class (strength) choices per load condition to choose
from.
Strength increases
with age.

13. HDPE - Pipe Stiffness
Is a measure of the inherent strength of the pipe as a function of applied load and the resulting deflection.
By the parallel
plate method.

14. Flexible Pipe Stiffness Comparison
Diameter HDPE CMP
18” 40 psi 465 psi
24” 34 psi 200 psi
30” 28 psi 103 psi
36” 22 psi 60 psi
42” 19 psi 38 psi
48” 17 psi 25 psi

15. Factors Effecting Pipe Stiffness
Temperature-plastic
Time
Resin Quality
Wall profile/thickness
Soils- In poorer soils, higher pipe stiffness is required.

16. Reduced Pipe Stiffness Results In
Increased deflections
Reduced hydraulic capacity
Inability to obtain proper compaction
Increased reliance on soil to carry load
Increased stress & strain
Decreased buckling resistance
Ground surface settlement
Joint leaks

17. The absence of structure often results in an ineffective conduit!

18. Adding Stiffness After the Fact
HDPE

19. Too Light A Gage - CMP

20. CMP Strength?

21. No Wall Strength to Resist Loads
HDPE

22. Wall Buckling - After 45 Days
HDPE states:" haunch compaction is
critical and should
be placed by hand"
HDPE

23. As Good as Concrete?

24. Wall Buckling - The Finale
HDPE states:
"the strength of
plastic pipe is
built into the trench"
HDPE

25. Deflection, Buckling & Cracking
HDPE says-"control of
deflections
and localized deformation
are very important in
design & construction"
30% Deflection
HDPE

26. HDPE says:
"it's more durable"

27. Recap - Structural
Concrete pipe is a structure. The strength is delivered on the truck.
Flexible pipe is not. Low Bidder must engineer the system with his installation of quality backfill.
Risk & Liability-Advantage Concrete Pipe!

28. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost
Low Risk/Maintenance

29. U.S. Army Corps of Engineers EM 1110-2-2902 Conduits, Culverts and Pipes
(1) Concrete. Most studies estimated product service
life for concrete pipe to be between 70 and 100 years. Of nine state highway departments, three listed the life as 100 years, five states stated between 70 and 100 years, and one state gave 50 years.
(2) Steel. Corrugated steel pipe usually fails due to
corrosion of the invert or the exterior of the pipe. Properly applied coatings can extend the product life to at least 50 years for most environments.
(3) Aluminum. Aluminum pipe is usually affected
more by soil-side corrosion than by corrosion of the
invert. Long-term performance is difficult to predict
because of a relatively short history of use, but the
designer should not expect a product service life of
greater than 50 years.
(4) Plastic. Many different materials fall under the
general category of plastic. Each of these materials may
have some unique applications where it is suitable or
unsuitable. Performance history of plastic pipe is limited.
A designer should not expect a product service life of
Excerpt from
Para. 1-4
Life Cycle Design

30. 1999 TDOT Service Life
RCP - is only pipe used in 100 year road designs
CMP - Only allowed in roadways with design life up to 50 years. 10/12 gage (Specify required gage in specifications)
HDPE - Limited usage in roadways with a 25 year maximum design life.

31. CMP Durability?

32. Poor Resin - NCHRP Report 429
49% of HDPE
fails to meet
own spec.

33. Flotation
A durability issue for both pipe and roadway!

34. At a Theater Near You!

36. Buoyancy
RCP PIPE
Specific gravity = 2.4 Resist buoyancy forces best of all pipe products.
HDPE PIPE
Specific gravity = .95
(less than water)
tendency to float.

37. HDPE

38. Recap - Durability Concrete pipe 100+ year life
HDPE is 25 year maximum design life
Risk and liability – What is the Project Design Life and LCA?

39. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost
Low Risk/Maintenance

40. Hydraulics - Proper Pipe Size

41. What Factors Determine Hydraulic Capacity
Pipe Diameter
Slope
Roughness (friction factor)

42. Downsizing RCP when CMP is Specified
The roughness coefficients or Manning’s “n” differences of RCP (.012) and CMP (.024)
Allow for reducing the concrete pipe diameters at least one pipe diameter smaller when outlet control governs.
CMP
RCP

43. We should do same for - smoothed line N-12 HDPE?

44. *Tullis Report-Waviness of liner
Manning’s ‘n’ Value
CONCRETE PIPE
Laboratory
Field
HDPE PIPE
Laboratory *
Field
They promote .010 !
*Tullis Report-Waviness of liner

45. Corrugation Growth! If this pipe were made of metal, it would
have a Manning’s “n” of .024

46. Manning’s “n” of 0.010???

47. Recap - Hydraulics A higher “n” value for HDPE, closer to value of CMP
Risk to Owner/Engineer = undersized pipe

48. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost
Low Risk/Maintenance

49. SIDD - Versatility with RCP
Type 1: Highest Quality installation using select granular soils with high compaction requirements for haunching and bedding.(A-1 & A-2)
Type 2: Allows silty granular soils with less compaction required for haunching and bedding.(A-3)
Type 3: Allows use of soils with less stringent compaction requirements for haunching and bedding.
Type 4: Allows use of onsite native material for haunching and bedding with no compaction required. (6” of Bedding is required if rock foundation)

50. Using Onsite Material is RCP’s Advantage!

51. Plastic Pipe National Standards
KY/TN & Nat'l
Specs Require
A-1, A-2 & A-3 Only!
AASHTO Section 30
ASTM 2321

52. But Nat'l Specs Say Otherwise!
Flexible pipe states that initial backfill need only to be 3/4 of pipe diameter (Manufacturers Recommendations)
But Nat'l Specs
Say Otherwise!

53. Proper Installation Takes Time

54. Faster than RCP

55. Truth in Advertising? “New” AASHTO Section 30 says Min.Cover is 2’
For M-294 pipe

57. What National AASHTO Specs Say: About Minimum Trench Width
RCP
OD/6 on each side
EX.- 48” RCP
48+5”+5”=58
58”/6=9.7”=10”x 2
Trench width is 58+20=78”
HDPE
1.5 x OD + 12”
EX.48” HDPE
=53”
1.5 x =91.5
or 92” Trench width
Concrete pipe - A 14” NARROWER TRENCH

58. pipe needs a 1" bell hole to support pipe
ADS Says-"42"-60"
pipe needs a 1" bell hole to support pipe

59. CMP Installation = ASTM A798
A-1, A-2 & A-3 soil to 12” or diam/8 over top of pipe, whichever is larger.
6-12” max. lifts
90% standard proctor
Trench width often “3xd”

60. Is flexible pipe easier to install because it is lightweight?
A contractor can only lay as much pipe a day as he can open up ditch.
It takes the same crew size to lay RCP.(3)
The next photo shows that light weight HDPE is actually a nuisance and slows production.....when placed correctly.

61. Why a Mandrel Test? Fact: HDPE is installation sensitive and will over
deflect!
Fact: deflections greater than 5% can cause excessive stress in pipe walls.
Fact: excessive wall stress
leads to pipe buckling
and cracking.

62. Mandrel Test Simple - deflection of more than 5% fails
Proof of proper installation
Confirms smooth joint and may catch poor vertical alignment required in specs
The Designer and Inspector are well advised to require a mandrel test no sooner than 30 days after backfilling and again prior to the surrender of the performance bond (12 months).
Same test is required for flexible sanitary sewer pipes.

65. Failure To Follow Installation Specifications Will Result in Failure!

66. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost/Value
Low Risk/Maintenance

67. Value - Cost Effective
HDPE/CMP have lower “off-the-shelf” prices, but they are not more cost effective
HDPE/CMP requires additional:
Bedding & Backfill
Compaction Efforts
Inspection
Testing-Mandrel
Its shorter service life decreases the value more.

68. Value?
Is the projects pipe performance enhanced by using flexible products?
Is structural performance (integrity) enhanced when you make the switch to flexible pipe?
Is hydraulic efficiency improved when specifying a flexible pipe?
What are the important engineering enhancements flexible pipes contain?

69. Plastic Pipe Will Never
Out-perform concrete pipe in terms of:
Durability - long life
Hydraulics
Strength - structural integrity
Peace of mind to Owner/Specifier

70. And…………
Price is the first thing you forget
if something goes wrong!

71. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost/Value
Risk/Maintenance

72. High Maintenance

73. Slip-Lining CMP
CMP-Durable, Long lasting??

74. Flammability

75. Low Risk ? -- High Maintenance -- Value?

76. Risk & Liability Concrete Pipe Flexible Pipe (HDPE/CMP)
Engineer stays in constant control of design.
Pipe is a structure designed to withstand all live & dead loads.
Not installation sensitive. TYPE 4
Flexible Pipe (HDPE/CMP)
Pipe is just a form for the granular soil envelope which becomes the structure.
Dependent upon contractor to build the soil /pipe system.
Installation sensitive

77. The Important Attributes of a Piping System
Strength
Durability
Hydraulics
Installation
Cost/Value
Low Risk/Maintenance

78. There’s a Lot More to Quality Than Pretty Looks
Concrete pipe is plant tested by numerous specifying agencies for a host of quality requirements
Concrete pipe has national quality standards
Concrete pipe is one of the few elements of our infrastructure that has exceeded expectations
NCHRP reports that nearly half of the new HDPE pipe specimens tested in its study failed current AASHTO standards

79. Poor Resin? - NCHRP

80. We’ll Be Happy to Discuss Quality
We pass scrutiny
Risk if you don’t specify a quality product
Q Cast

81. What do you hear about flexible pipe?
You can save 20% to 40% with HDPE
The DOT accepts it
You can use a smaller pipe size
You can install it just like concrete
Deflection is not a concern
Light weight is always a benefit
HDPE is more durable

82. This Is What Is Being Said
They have equal or better hydraulics than RCP.
Lower handling costs
Standard bell & spigot gasket joints have higher performance than O-Ring RCP.
Lower maintenance costs-no steel to rust.
Concrete Pipe has a lock on the market as a sole supplier so let us in and see RCP prices plummet.

83. Resource Tools

84. Precast Concrete
On Target !