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

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

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

Corrugated Steel Pipe

HDPE - Plastic Pipe

Reinforced Concrete Pipe

What are the important attributes of a pipe?

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

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

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.

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.

Pipe Strength vs Stiffness PRECAST RCP f’c = 4000 psi - 6000 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.

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.

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

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

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

The absence of structure often results in an ineffective conduit!

Adding Stiffness After the Fact HDPE

Too Light A Gage - CMP

CMP Strength?

No Wall Strength to Resist Loads HDPE

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

As Good as Concrete?

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

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

HDPE says: "it's more durable"

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!

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

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

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.

CMP Durability?

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

Flotation A durability issue for both pipe and roadway!

At a Theater Near You!

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.

HDPE

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?

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

Hydraulics - Proper Pipe Size

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

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

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

*Tullis Report-Waviness of liner Manning’s ‘n’ Value CONCRETE PIPE Laboratory - .010 Field - .012 HDPE PIPE Laboratory - .009-015* Field - .012-.026 They promote .010 ! *Tullis Report-Waviness of liner

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

Manning’s “n” of 0.010???

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

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

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)

Using Onsite Material is RCP’s Advantage!

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

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!

Proper Installation Takes Time

Faster than RCP

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

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 48+2.5+2.5=53” 1.5 x 53 +12=91.5 or 92” Trench width Concrete pipe - A 14” NARROWER TRENCH

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

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”

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.

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.

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.

Failure To Follow Installation Specifications Will Result in Failure!

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

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.

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?

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

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

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

High Maintenance

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

Flammability

Low Risk ? -- High Maintenance -- Value?

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

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

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 04-24 reports that nearly half of the new HDPE pipe specimens tested in its study failed current AASHTO standards

Poor Resin? - NCHRP

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

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

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.

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Precast Concrete On Target !