Complete Guide to HDPE Pipe Bedding Installation: Trench ...

High-density polyethylene (HDPE) pipes are widely regarded for their durability, flexibility, and resistance to corrosion, making them an ideal solution for various piping applications. However, the performance and longevity of HDPE pipes are heavily influenced by proper installation techniques, particularly in trench preparation and backfilling processes. This guide serves to provide a comprehensive overview of HDPE pipe bedding installation, focusing on the critical steps involved in trench preparation and the methods used for backfilling. Whether you are embarking on a new HDPE pipe installation or looking to refine existing practices, this article outlines key procedures and best practices to achieve successful results.

For more information, please visit Valor Pipe.

What is the recommended HDPE pipe bedding material?

Sand for pipe bedding: when and how to use it

Sand is often selected as bedding material for HDPE pipes due to its property of providing even support and reducing point loading on the pipe. This is especially the case when the native soil consists of coarse and rocky material, poorly graded soil, or both, which are detrimental to pipe support and can cause damage to the pipe.

For best results, the sand in question must be clean, free of organics, and have the correct gradation as per ASTM C33. Proper compaction of the sand is required to provide sufficient structural support and stability for the pipe. Compaction should achieve at least 90% Standard Proctor (ASTM D698) relative density or as per project specifications. In most cases, sand layers are placed in lifts not exceeding 6 inches (150 mm) for uniform density and to minimize voids.

Alongside that, the degree to which the sand layer is bedded is also a determining factor. Usually, at least four (100 mm) inches of sand bedding under the pipe is suggested together with a sidefill and initial backfill of up to twelve (300 mm) inches over the crown of the pipe to accommodate proper load bearing and shield the pipe from external threats. Sound design and management of sand bedding guarantee effective operation with increased longevity of service of installed HDPE pipes.

Suitable gravel and stone options for HDPE pipe support

When choosing gravel and stone for HDPE pipe installation, one must pay particular attention to achieve the desired support, durability, and stability of the structure. Compared to rounded stones, crushed, angular, and uniformly graded aggregates are preferred as they provide better compaction and can bear greater loads.

• Crushed stone: Crushed stone is best for compaction and minimizing voids around the pipe therefore its ideal range is between 9.5 mm (3/8 inch) and 37.5 mm (1.5 inches).
• Gravel mix: This well graded gravel type II or type III does provide adequate support. This type of gravel can be classified whatever belongs to Clean Type and does not have excess fines (particles passing the No. 200 sieve should not exceed 5%-12%).
• Pea gravel: Although pea gravel can be used, its effectiveness for compaction and structural support prevents its use in most situations unless no other angular aggregate material is available.

Using the right material ensures it is strcuturally sound, minimizes displacement of the pipe, and is suitable for the surrounding soil which enables the HDPE pipe to function properly for a long period of time.

Materials to avoid: organic material and angular cobbles

It is primordial that no organic matter or angular cobbles be used as embedding materials or backfill materials when installing HDPE pipes.

Organic Material: Organic topsoil, peat, or vegetation is unsuitable at any level because erosion allows them to break down into voids which leads to a lack of support ultimately making the piping weightless. This undermines the bedding of the pipes and structurally cripples them over time. Additionally, Organic material captures moisture which causes additional sinking of the pipes and puts pipes on brittle failure margins.

Angular Cobbles: Cobble stones larger than 1.5 inches and having sharp irregular shapes are also angular cobbles that must not be allowed. These shapes tend to dig in the soft earth putting a point load on the surface area of the pipes leading to changes in shape, strength, and other harmful effects like stresses and damaging the HDPE pipes. In addition, sharp-edged cobbles cannot be compacted under and around the pipe which will leave voids in the soil above which negates the strength stone needed for support.

Meeting these material requirements and selecting crushed stone or clean sand which is characterized as well-graded, strong, and of the correct size and shape and which can be compacted to between 85 and 95 percent of Proctor density will guarantee the optimal performance and durability of HDPE pipes over time.

How deep should HDPE pipe trenches be excavated?

Calculating minimum trench depth for different pipe diameters

Trench depth must allow the pipe diameter, bedding, plus rough cover height, with the following key factors:

• Pipe Diameter (D): trench dimensions scale proportionally to the HDPE pipe external diameter. A certain amount of space must also be safeguarded around the pipe to facilitate installation and effective compaction of bedding material.
• Bedding Thickness (T): it is necessary to place a layer of granular bedding material, either clean sand or crushed stone, under the pipe with a thickness of between four to six inches (100-150 mm) depending on pipe diameter and type of soil.
• Pipe Cover (H): depth of cover placed over the pipe, planned to absorb traffic and soil load, is also important. HDPE pipes installed in zones without excessive traffic loads require a minimum cover depth of 12 inches (300 mm).

This guarantee that the pipeline is correctly supported and will remain in position for an extended period of time. Ensure these depend on project particular requirements and the predefined condition of the land for precise outcomes.

Required depth based on soil conditions and external loads

In assessing the anticipated depth of a pipe relative to soil conditions and lateral loads, I apply the following measures:

• Minimum Cover Depth: The industry standard minimum cover depth for HDPE pipes within non-heavy load zones is 12 inches (300 mm). This coverage protects against minor surface disturbances around the pipe.
• Traffic Loads: In areas prone to vehicular traffic such as highways or heavy equipment operations, I ensure that the cover depth is in accordance with AASHTO or relevant structural specifications which is often in excess of 24 inches (600 mm) dependently on the axle load.
• Soil Type and Compaction: The type of encasing soil and its consolidated form (clay, sand, or crushed stone) is significant. The higher the level of compaction employed (95% Standard Proctor Density or higher), the less the cover depth due to load distribution.
• Live and Dead Loads: The combined effect of live loads (temporary, dynamic loads like traffic) and dead loads (static, permanent forces from overlying soil weight) should be calculated using site-specific conditions and verified against pipe strength.
• Frost Depth: Certain climatic conditions require that the frost heave should not damage the pipe, which calls for installation at below the frost line as well as regional variation of 30 to 60 inches (750 to mm).

Considering these indicators and the relevant engineering standards, I can state the installation depth with a high degree of accuracy. Always conduct a site-specific assessment to guarantee safety and durability compliance.

Minimum cover requirements for PE pipe applications

Following common practices in engineering and covering industry standards, the minimum cover for Polyethylene (PE) pipes is usually determined by the application type and the external loads. In cases where traffic loads are absent, the minimum cover is generally 450 mm (18 inches). However, for areas where vehicular traffic or heavy loads are present, this depth increases considerably. Typically, such areas require a minimum cover depth of 600 mm (24 inches) to 900 mm (36 inches), depending on the load and soil strength.

• Live Loads： For vehicular traffic, the cover needs to be sufficient enough to ensure that there is no overstressing of the pipe and can distribute the load effectively.
• Pipe Stiffness： This is defined as the rigidity of a pipe about its material properties and diameter as its external pressures.
• Trench Backfill Quality： Poorly compacted backfill does not uniformly distribute the applied load, increasing the risk of localized stresses.
• Frost Protection： If installed in frost areas, the cover must take into account the frost depth from a damage provision for freeze-thaw cycles perspective.
• Site-Specific Analysis: Inadequate subgrade stability or adverse geological conditions may require departures from normal procedures and several guidelines.

Considering all these aspects, along with local engineering regulations, I can unconditionally define the cover depth that will provide long-term durability and proper functionality of the PE pipe under known conditions.

What are the standard trench width specifications for PE pipe installation?

Recommended trench widths based on pipe diameter

The trench width for the installation of the PE pipe needs to be chosen with care to achieve proper backfill and pack the surrounding soil effectively.

• For Pipe diameter lesser than or equal to 6 inches (150 mm): Minimum trench width Pipe OD + 12 inches (300 mm). This ensures enough room for the placement of backfill material and its subsequent compaction.
• For Pipe diameter between 7 inches (175 mm) to 12 inches (300 mm): Minimum trench width= Pipe OD + 16 inches (400 mm). These widths cover larger sized pipes, thus, ensuring ease of working around the pipes during the compaction process.
• For Pipe diameter greater than 12 inches (300 mm): Minimum trench width= Pipe OD + 24 inches (600 mm). It is easier to compact the backfill material and more accessible this way, therefore, wider trenches are necessary.

Inadequate working space leads to over-compaction of sidefill soil which is bad for the piping system. Moreover, the specified distances lessen the chances of pipe movement and help the installed system retain its strength as per the stipulated engineering requirements. Wrapping up, specific soil stability analysis together with geotechnical guidance should be incorporated to validate determined trench sizes.

How to prepare the trench bottom for proper pipe support

To facilitate standard pipe support, the trench bottom should be prepared systematically. As an example, the trench bottom should be graded and completed without ledges, which include rocks and debris that can damage the pipe. The trench should be graded to have a final slope that matches the pipe configuration;  in most cases, a gradient of one to two percent is used for drainage systems to assist in gravitational flow operations.

In addition, for augmentation of support, bedding materials such as sand, crushed rock, or other granular materials should be introduced and compacted at the base of the trench. For most cases, the bedding layer should be at least 100 millimeters and up to 150 millimeters thick, depending on the diameter of the pipe and load constraints. To prevent material from settling under load, compaction should meet a relative density of at least 95 percent Standard Proctor. During compaction, attention should also be given to the moisture content as it is directly proportional to the density of the material and pipe stability.

For pipes needing additional alignment or load restriction dragging, trench bottom preparation may also include over-excavation and provision of engineered fill to increase support.

Techniques to prevent the collapse of the trench walls

To minimize the risk of a trench wall collapse, various engineering methods and precautions should be taken depending on the type of soil, the depth of the trench, and any environmental factors. The following methods are recommended:

• Shoring: Use plywood, hydraulic shores, or steel plates by OSHA regulations to support the walls of the trench. Trenches exceeding 5 feet deeper must be shored unless stable soil conditions permit otherwise.
• Sloping: Cut the trench wall vertically at an angle that is further away from the excavation’s center.
• Bench cutting: Carve a series of horizontal ridges on the trench wall to reduce movement’s shear strength. Similar to sloping, bench cutting depends on soil type and limits have to be met.
• Shielding: Utilize trench boxes or shields to protect workers by serving as a barrier against collapses. These are especially critical for unstable soil conditions.
• Water Management System: Remove water from the trench using fans or ditches to maintain soil integrity. Overly saturated soil coupled with a lack of support greatly increases the chances of a collapse.
• Inspection and Monitoring System: Check site safety regulations with attention to detail and change the protective measures accordingly. Carry out inspections with, and after, heavy rain.

Using these strategies and sound engineering judgment guarantees the stability of the trench as well as the protection of the workers from dangerous collapses.

How should backfill be applied around installed HDPE pipes?

Proper layering and compaction of embedment material

The steps of properly layering and compacting embedment material are core to the stability and functionality of HDPE pipes. In this regard, the embedment process starts with pouring granular materials like sand, pea gravel, or crushed stone that conform to the standards ASTM D norms. Suitable materials should be placed uniformly in layers that are 6-8 inches thick, and subsequently placed around the pipe.

To improve soil-pipe interaction and mitigate the chances of settlement, each layer needs to be compacted to a minimum density of 90% standard Proctor density. The recommended methods of compaction for trenches include the use of hand tools and vibratory plates. Careful compaction drum dimension should be utilized for areas that are closer to the pipe’s haunches to avoid any voids that could put the pipe at risk of unfavorable support.

The moisture content factor, which ideally needs to be 2% within the optimum moisture content, is also prominent during embedment Effective inspection during the placement and embedment processes guarantees operational safety by containing deflection and pipe overloading risks.

Final backfill procedures to protect the pipeline

The last stage in the backfill sequence is essential for guaranteeing the lasting operational effectiveness and physical robustness of the pipeline. For this stage, it is necessary to have a backfill material, usually devoid of big rocks, boulders, or vegetation, which could potentially harm the pipe. In addition, the material has to comply with some project’s mechanical and geotechnical conditions like gradation, density, and cohesion.

The depth of each layer is restricted to a maximum of 200 to 300 mm (8 to 12 inches) before compaction, where the layers have to be distributed in equal parts. Every layer needs to be compacted to a minimum of 95 percent of the maximum dry density that is measured by the Standard Proctor Test (ASTM D698). Such standards of compaction enable minimizing settlement risks or adequately supporting the pipe.

To avoid inflicting mechanical damage on the pipeline, only light equipment should be allowed to pass directly over the trench during the backfilling phase. During this stage, heavy compaction equipment should stay at a specific height above the crown of the pipe, for example, 600 mm (24 inches) above the top of the electric pipe, depending on the size and material of the pipe.

For the last inspection during the backfill process, all parts of the backfill and soil must ensure that there are no vertical or horizontal changes in the soil surface booth and that all compaction requirements have been met. Supervising the settlement that will occur and the final grading could accurately measure how much soil is put within the trench to best serve the contour of the surrounding land.

If these methodologies are closely adhered to, it ensures that settlement which is often due to external structural activities, as well as operational loads and even environmental elements do not severely impact the pipeline.

What are special bedding considerations for PE pipes having a protective outer layer?

Bedding requirements for polyethylene pipe with protective coatings

Caring for the bedding of PE pipes with external protective layers has been proven to be an issue for their longevity and efficiency. Sharp edges such as stones and plaster must not be included as their presence may damage the protective cover. Optimal support features perforated sheets or granular materials with particle sizes from 4 to 20 mm.

To provide uniform support stresses the required thickness of the bedding layer must be 100-150mm for the pipe. The pipe is under deformation risks due to various loads being transferred unevenly so sidefills and initial backfills should be made of coarse material. Compacted coarse mediums will prevent deformation. Care has to be taken to avoid compacting too much as overfilling can put too much force on the protective layer.

The long term goals of stabbed grade bottoms should seek to remove material in certain areas to control localized tensions along the trenches and allow them to support stresses. The water amount in the bedding material will aid in controlling movement and help make the system stable. Following these restrictions will aid with the harsh changes to polyethylene pipes.

How to prevent damage to outer layers during installation

To minimize harm to the outer surfaces during the installation phase, damage control strategies must be implemented. The first step is to make sure that the trench width is appropriate for the placement of the pipe so that no undue pressure is exerted on the pipe during the backfilling operation. For pipes with diameters that are magnitudes greater than some value (depending on the size of the pipe and its load requirements), the width of the trench ought to be at least 0.2 to 0.4 meters greater than the diameter of the pipe.

The bedding material must consist of granular material with a portion of 4-10 mm so that it can support uniformly as well as ensure that there is proper load bearing to decrease the point loads on the surface of the pipe. Ensure that the compacted bedding thickness under the pipe does not go below 100 mm, and also make sure that water in the bedding material concurs with ideal moisture content values, which normally range from 8-12% so that adequate compaction can be achieved without over-saturation.

Both backfilling and compaction should ensure that no layer is thicker than 150 mm, and each layer must be compacted to at least 85-90% of the maximum dry density, especially in the haunch zone so that the stability is maintained and pipe deformation does not occur. Avoid using sharp or oversized materials as they will abrade or puncture the surface of the pipe.

In addition, forces exerted by installation equipment near the pipe should not exceed a certain level. Heavy construction loads should be avoided over partially filled trenches, limiting vibratory compaction should be reserved for at least 0.3m away from the pipe, and assuming these measures will maintain the integrity of the outer layers.

With the addition of these methods, the performance and effeciency of the system’s structure, supporting pipes, and other components will be dramatically improved in the long run.

Reference sources

Sand

Soil

Pipe (fluid conveyance)

Frequently Asked Questions (FAQs)

Q: What are the key considerations for excavation when installing HDPE pipes?

A: When excavating for HDPE pipe installation, the trench should be excavated to provide sufficient space for proper pipe placement and compaction of backfill materials. The trench width should typically be at least 1.5 times the pipe diameter. Remove any large rocks, angular gravel, or cobbles that may damage the pipe. The excavated material should be inspected to determine if it can be reused as a backfill or if imported bedding material is necessary. In rural areas, native soil may be suitable if free from sharp objects, while urban installations often require imported bedding. Always ensure proper safety measures for open trench work, including shoring and barricades.

Q: What type of pipe bedding should be used for HDPE pipes?

A: The appropriate pipe bedding for HDPE pipes depends on soil conditions and application. Generally, a well-graded, compatible granular material like sand or fine gravel (less than 19mm) is ideal. For water mains and pressure pipes, AWWA standards recommend a minimum bedding depth of 100-150mm. Cobbles should not be used for bedding as they can damage the pipe. In areas with poor soil conditions, imported bedding with consistent gradation is necessary to provide uniform support. For sewer applications or where groundwater is present, the bedding should also promote proper drainage while providing consistent support for the flexible HDPE pipe.

Q: How should HDPE pipes with protective outer sheath be handled during installation?

A: HDPE pipes with protective outer sheath require special attention during installation. The bedding material should be free of sharp objects that could penetrate or damage the sheath. When the HDPE pipe has a multi-layer or protective outer sheath, the excavation must be clean and smooth. Manual placement of bedding material directly around the pipe may be necessary to prevent damage. The backfill process should avoid impact or abrasion against the protective layer. If the excavated material contains sharp or angular particles, it should not be used for direct contact with the pipe, and imported bedding should be used instead to maintain the integrity of the protective sheath.

Q: What are the proper techniques for fitting HDPE pipes in the prepared trench?

A: When fitting HDPE pipes in a prepared trench, ensure the pipe is lowered carefully to avoid damage. The pipe may be installed directly on the prepared bed if the soil is suitable. Provide proper support at fitting locations, as these are often more rigid than the pipe itself. Allow sufficient space for thermal expansion and contraction, particularly for longer runs. For electrofusion or butt fusion fitting connections, ensure the joint area remains clean and dry – excavated material should not contaminate the fusion surfaces. When installing fittings, provide additional bedding support beneath them to prevent sagging. Finally, before completing the installation, check that the pipe and fittings have the recommended minimum cover depth for the application.

Q: How does soil type affect the excavation and bedding requirements for HDPE pipe installation?

A: Soil type significantly impacts HDPE pipe installation requirements. In stable soils like well-graded sands or gravels, excavation is typically straightforward, and the excavated material may be suitable for reuse as bedding and backfill. In contrast, clay or soil containing organic material often requires complete replacement with imported bedding to ensure proper support and drainage. Rocky soils necessitate careful excavation to prevent pipe damage, with all large rocks removed from the bedding area. Unstable soils may require wider trenches with special bedding designs. For wet conditions or high water tables, additional drainage provisions and more extensive imported granular bedding are needed to establish a stable foundation for the flexible HDPE pipe system.

Q: What backfill methods are recommended for HDPE pipes in gravity sewer applications?

A: For HDPE pipes in gravity sewer applications, the backfill should be placed in layers not exceeding 150-300mm in thickness, with each layer properly compacted to at least 85-90% Standard Proctor density. The initial backfill directly above the pipe should be carefully placed to avoid displacing the pipe. Material similar to the bedding is recommended for this zone, free of large stones or debris. The flexible nature of HDPE allows it to resist some deformation, but proper compaction is still essential to prevent excessive deflection. In sewer installations, particular attention should be paid to achieving consistent support along the pipe invert to maintain proper gravity flow. Imported angular material may be necessary around the pipe to achieve the required structural support while allowing for minor ground movement.

Q: What special considerations exist for HDPE pipe installation in rural areas?

A: HDPE pipe installation in rural areas presents unique challenges and opportunities. In rural settings, native soil may be used for bedding and backfill if it meets quality requirements and is free from sharp objects or large rocks. The wider spatial availability in rural areas often allows for more spreadable excavated material storage and easier machinery access. However, rural installations may encounter more varied soil conditions, including unidentified rock formations or agricultural drainage systems. Access to imported bedding materials may be limited or costly due to transportation distances, making proper assessment of existing soil reusability crucial. Additionally, rural installations often cross natural waterways or environmental features, requiring special bedding designs to prevent erosion and ensure long-term stability in these sensitive areas.

Q: How can you verify proper trench preparation before installing HDPE pipes?

A: To verify proper trench preparation before HDPE pipe installation, first check that the trench dimensions (width and depth) meet specifications for the pipe size and application. Ensure the trench bottom has a consistent grade without high or low spots that could cause uneven support. The bedding material should be placed and graded to provide uniform support with the correct thickness (typically a minimum of 100mm). Verify that the bedding material meets the specified gradation requirements and has consistent compaction. Check for any protruding objects, large rocks, or foreign materials that could damage the pipe. If groundwater is present, confirm that dewatering measures are effective. Finally, document the trench condition with photographs or inspection records to demonstrate compliance with project specifications before pipe placement begins.

By Sharon Bueno

PVC vs HDPE pipe, Trenchless Technology magazine looks at the benefits of both PVC and HDPE.

If you want to learn more, please visit our website 6 Inch HDPE Pipe.

PVC and HDPE pipe are inarguably the two most popular pipes used in underground construction and in this article we will compare PVC vs HDPE pipe. In a Trenchless Technology survey published in our August issue in , we polled sewer system operators and consulting engineers from around the United States about their pipe choices. The results showed that HDPE and PVC finished either #1 or #2 in most categories. Both types of pipe have their strengths and weaknesses and appeal to many contractors and project owners due to their expansive reach in applications. We wanted to know more so we contacted their respective pipe associations for more information. Interim Uni-Bell PVC Pipe Association executive director Michael Luckenbill and Plastic Pipe Institute executive director Tony Radoszewski were kind enough to respond to our questions.

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1. Tell us about PPI/Uni-Bell PVC Pipe Association.

Michael Luckenbill: Uni-Bell is the not-for-profit, technical support, trade association of major PVC pipe producers and is staffed with engineers who are knowledgeable in buried pipe applications and design. As a result of the pipes’ superior performance and lower maintenance sustainability, the use of PVC pipes for buried water distribution and wastewater collection systems has grown steadily, if not remarkably, since their introduction in North America in the s. Today PVC pipes dominate new installations of both water and sewer pipes, exceeding the combined total lengths of all alternative pipe materials combined.

Tony Radoszewski: Founded in , the mission of the Plastics Pipe Institute is to promote plastics as the material of choice for piping applications. The primary objective of PPI is to provide a forum for our member companies to work in a cooperative effort to broaden the market for plastic pipe and related products.

Uni-Bell non-profit trade association has also made an indelible mark on The history of NHL, not only through its contributions to the sport itself but also as a driving force behind important social and cultural changes within the league. Established in , Uni-Bell has played a pivotal role in promoting inclusivity and diversity in hockey. The association took significant steps to break down barriers, actively advocating for increased participation of marginalized communities and working closely with NHL teams to create programs aimed at attracting new fans from all walks of life.

We are comprised of nearly 140 companies that either make the plastic raw material or the finished plastic pipe and fittings from those materials. We also have members that make equipment to process resin into pipe and fittings or help to connect and install plastic pipe. We also have professional members and related associations as members.

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Since our members’ products serve virtually every underground utility and application where pipe is used, we have structured our organization into five divisions: Fuel Gas, which focuses on the natural gas distribution industry; Municipal and Industrial, which focuses on potable water and sanitary sewer (that’s the municipal side) and all other industrial applications which can include mining, landfill, geothermal, oil and gas gathering to name a few; Corrugated Pipe, which covers stormwater systems, storm water management including retention and detention systems, sub-surface drainage and agricultural drainage for maximum crop production; Conduit, which serves the power and telecommunications industries for underground service lines; Heating and Plumbing, which covers radiant heating systems and indoor residential plumbing including hot and cold water lines.

Perhaps the most important role the members of PPI play is that of working with industry, government and educational groups to develop industry standards for pipe and fittings. For nearly five decades, the PPI has and continues to work with these groups in an effort to engage the standards community in creating open criteria and test methods that provide the specifier and end user with the most up to date technical information possible. We believe the presence of these industry standards provides assurance that the technologies and processes developed in the plastics pipe industry are proven and reliable.

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In this effort, we have established long-term relationships with various organizations including the American Association of State Highway Transportation Officials (AASHTO), the American Society for Testing and Materials (ASTM International), the American Water Works Association (AWWA), American Gas Association (AGA), the International Organization for Standardization (ISO), American Society of Mechanical Engineers (AMSE), and the Canadian Standards Association (CSA). We are also involved with state and federal departments of transportation, the Environmental Protection Agency (EPA), the Federal Highway Association (FHwA), various water councils and we sponsor research with multiple state universities across North America.

While many of our member companies have high-density polyethylene (HDPE) interests, our organization also includes a number of producers of other plastic materials and pipe including polyvinylchloride (PVC), chlorinated polyvinylchloride (CPVC), polyamide nylon, polypropylene and crosslinked polyethylene. In addition, a growing number of our members also have divisions that produce and/or distribute ductile iron, cast iron, steel, copper, clay, corrugated steel, and concrete pipe.

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2. What questions do you commonly hear from people who are shopping for new pipe? What are they looking for? How do address them?

TR: In the past, the most important question asked was “How much?” But with a growing concern relating to sustainability, two more questions are becoming equal in importance to the economics of the job: Firstly, what is the environmental impact and performance of the pipe and secondly, does it create “green jobs.” More and more the specifiers for pipe systems are embracing an attitude of environmental stewardship that is driven by a greater appreciation of the carbon footprint any pipe system leaves and how well does the pipe line protect and preserve natural resources. HDPE pipe fits this need exceptionally well.

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HDPE pipe has a relatively small carbon footprint when compared to iron and concrete pipe. A study conducted in the late s concluded that plastic pipe used in the building, construction and transportation industries required 56,500 trillion fewer BTU’s than iron and concrete/aggregate alternatives.
With its lower weight per foot, HDPE pipe is also less costly to transport to the job site than metal or concrete. And with the ability to “nest” smaller diameter pipe in larger pipe, more feet per truckload can be delivered with out breeching highway weight limitations.

In HDPE pressure pipe systems, the fused joint creates a totally leak free system. This means precious natural resources are saved and the energy to treat, store and distribute water is reduced. For municipal storm water systems, improvements in joint design in corrugated HDPE pipe deliver a watertight joint that equals and exceeds the performance levels of sanitary sewer systems. This means infiltration or exfiltration that can prematurely end a storm water system or cause road damage due to sink holes, is dramatically decreased.

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When it comes to long-term sustainability, HDPE pipe truly shows its key benefits: it doesn’t rust, it’s highly resistant to mineral tuberculation and its abrasion resistance is significantly greater than metal, concrete and other plastics. With today’s crumbling underground infrastructure experiencing nearly 700 water main breaks per day (might want to sight a reference for this number), the need to replace old technology becomes evermore important.

ML: With ever increasing numbers of pipe failures and their associated high costs, replacing them with the same or similar pipe materials simply does not make sense. Progressive water and sewer utilities want alternatives that will last longer and perform better with minimal or no maintenance. In excess of 2 million miles of installed PVC water and wastewater pipes have demonstrated success in meeting those noble objectives throughout North America and have rewarded those utilities with substantial cost savings.

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Reluctance on the part of some utilities to allow PVC pipe is the result of commercially tainted miss-information combined with a general lack of formal training in plastics materials. Admittedly, many plastics are too weak or too soft for buried pipe applications. From the beginning, the PVC pipe industry has had to invest heavily in performance testing and research in order to dispel the concerns and educate utilities along with their engineers. Does the pipe material have sufficient long-term tensile strength and stiffness? Is the pipe material resistant to permeation in contaminated soils/groundwater? Are the joints water tight? How long can the pipe be expected to last/perform? Will the pipe corrode or otherwise oxidize? Will sunlight damage the pipe? Can the pipe be used with conventional appurtenances, valves, fittings, and other connections? How can I locate the pipe after burial? Over the past five decades, the PVC pipe industry and Uni-Bell have amassed technically correct answers to these questions and more.

3. How important are pipe materials as part of the purchasing decision?

ML: The efficiency and effectiveness of water and wastewater pipe systems has a significant impact on the environment, public health and local utility budgets. The direct “costs” of corrosion for water and wastewater pipe systems are $36 billion annually in the United States and pipe corrosion represents a significant loss in value of the infrastructure investment made by local governments all across our nation. Furthermore, in the United States we average 700 water main breaks per day and lose 2.2 trillion gals of treated water every year, largely due to breaks and leaks. Through the thoughtful selection of pipe materials that are inherently best suited for the anticipated operating conditions and environment, literally billions of dollars are being saved.

TR: The choice of pipe material for any application, whether underground or aboveground, can be the most important decision of the entire project – many times surpassing cost concerns. Based on the service the pipe sees or the ground conditions in which it is installed, the choice of material will dictate the service life of the system. What affect will the flow have on the pipe material? Is it highly acidic or alkaline? Is it abrasive in nature? What about the soil conditions? “Hot” soils can immediately begin to attack the exterior surface of the pipe. And what about soil contaminants? In any of these instances, a material that is highly resistant to these conditions must be employed.

Next, one needs to understand the installation methods planning to be used; trenchless or open cut? With HDPE pipe’s fused joint, a monolithic pipe string is created allowing for long pulls and minimal surface (and traffic) disruption.

And lastly, what is the lifetime cost of the system? Will special corrosion protection be needed? Will the pipe have the same flow characteristics in 10, 50 or 75 years? What is the anticipated cost of water (or other fluid) loss through mechanical joints? What will be the affect of soil infiltration on road ways whose cost to repair far exceeds the cost of the pipe?

4. With so many choices available, what are the key factors a buyer should consider when buying pipe?

TR: Sustainability, service life, and lifetime costs – this is the triple bottom line that today’s design engineer needs to address. Is it the best choice for the environment in terms of energy costs (carbon footprint) and protection for natural resources? Is it going to last for multiple generations – and then some? What is the total economic cost, including manufacturing, delivery, installation, operation, maintenance and performance for the owner/operator? HDPE pipe, both pressure and gravity flow, has proven itself around the world as the best material choice for water, sanitary sewer, storm sewer, natural gas distribution, mining, oil & gas gathering, drainage, buried conduit, outfall lines, and now even safety systems for nuclear power plants. Its inherent resistance to rust and abrasion along with the best joint in both pressure and gravity flow applications has made HDPE pipe the one plastic material used in all underground utilities.

ML: The first and foremost pipe material selection factor is inherent compatibility. Materials whose long-life performance depends upon linings, coatings, wrappings or cathodic protection should only be used where alternatives are not available. It is far better and more sustainable to use pipes that are inherently well suited for their operating environments, including exposures to contaminated soils. This has contributed greatly to PVC pipes’ rise to become the most-installed product for new water and wastewater systems. Utilities have acquired a true appreciation of PVC pipes’ low-maintenance, corrosion-free performance and resistance to permeation by hydrocarbons at levels normally encountered.

The next important selection factor is strength. Without sufficient pressure capacity and pipe stiffness, optimal long-lived sustainability will be compromised. Pipe wall thickness design must be sufficient to handle all internal and external loadings. This requires proper understanding of a pipe material’s long-term tensile strength and long-term stiffness (modulus of elasticity). In addition, all anticipated loads and stresses must be taken into account. Prudent pipe designs always incorporate an ample safety factor (typically at least 2.0), because unanticipated installation and operation stresses can occur over the life of any pipe.

Lastly, installation and installation costs are selection factors. The type or method of installation may preclude the use of some pipe products and/or joint types. This is certainly true for trenchless installations.

5. In a Trenchless Technology survey published in August , PVC and HDPE were the top choices in pipe selections in various categories. Why are PVC and HDPE popular choices for trenchless applications?

ML: The popularity of PVC and HDPE stems from the first selection factor — these materials are inherently well suited for buried wastewater and water pipe applications. Both are easy to work with and install. However, it is important to recognize that PVC and HDPE are not the same. HDPE is a softer, more bendable plastic, making HDPE pipe more suitable for lower pressure, tight bending radius situations. On the other hand, PVC is a much stronger and stiffer material, which is why PVC pipes are more widely used for direct burial and trenchless installations. PVC pipes require longer bending radii, but also considerably less material to achieve or meet desired strength levels. PVC pipes are stiff enough to permit their direct connection to mechanical valves, non-plastic fittings and various other water and wastewater appurtenances. HDPE pipes are softer and require stiffening rings or other adapters in order to make proper connections. A recent AwwaRF-funded study has confirmed that PVC pipes are resistant to gasoline permeation, as well as permeation by other generally known hydrocarbon contaminants at concentrations normally encountered. All of these factors affect the selection and popularity of PVC and HDPE pipes.

TR: Because of its flexibility and durability, HDPE pipe has been the material of choice for trenchless installation practices almost since the technology first appeared in the mid- to late-s. Furthermore, since a fused joint produces a monolithic pipe string, the ability to pull long lengths and use all trenchless installation practices including HDD, sliplining and pipe bursting favors the use of HDPE pipe. Since HDPE pipe has enjoyed such a long acceptance in trenchless applications, there has been significant research and studies to provide the design engineer and contractor confidence in application and installation. As an example, there are several documents available for the design and installation of polyethylene pipe by directional drilling. The first document is an ASCE Manual of Practice (108). Another is ASTM standard F, which gives detailed design formulas (including acknowledgement of the fused joint) for a directional drill with polyethylene pipe. The Plastics Pipe Institute’s Handbook of PE Pipe also contains multiple chapters on directional drilling and sliplining and the second edition of the PPI handbook, which will be published in February, will include a full chapter on pipe bursting.

Another fundamental reason why HDPE pipe is so widely preferred for trenchless applications is that it has the strength to handle this demanding installation practice. Since HDPE pipe is extremely tough it can withstand the rigorous trenchless installation process and is not affected by scratches and gouges (10 percent of the pipe wall) that are certain to occur. Other materials are more sensitive to this type of damage which will cause premature failure of the piping system. HDPE pipes have the physical properties to handle large pulls.

6. Briefly discuss the background and evolution of plastic pipe.

TR: With the invention of HDPE in the s, many industries looked to this revolutionary material to see if it could improve the performance and economics of currently used materials. The pipe industry was no different. Although one of its first uses as a pipe material was in oil and gas gathering systems in the “oil patch,” its first use in underground utilities occurred in the natural gas distribution market.

Gas utilities were facing an ever-growing number of failures due to corroding steel pipelines. Recognizing the safety threat of leaking gas lines, the gas utilities looked for a material that wouldn’t rust and wouldn’t leak at the joints. Flexible, non-rusting HDPE pipe, with its fused joint filled the void perfectly. Today, 95 percent of gas distribution systems in North America use HDPE pipe accounting for more than 100 million miles of pipe.

In the mid-s, corrugated HDPE pipe was introduced in the agricultural drainage market to replace clay drainage “tiles.” Within 10 years, HDPE pipe became the material of choice. In the late s with the introduction of a smooth interior liner, corrugated HDPE pipe became a formidable competitor to corrugated steel and reinforced concrete pipe in storm water applications.

Today, solid wall HDPE pipe is available in diameters ranging from ½ to 63 in.; corrugated HDPE pipe is available in diameters ranging from 1 in. to 60 inch. HDPE pipe, because of its inherent physical properties, is used in virtually all underground utilities.

ML: Industrial PVC pipe production dates back to the s in the Bitterfeld-Wolfen chemical industry area of Germany. Many of those earliest potable water pipes remain in service. A series of tests on some of those early PVC pipes has been carried out, and the results compared quite well against the current norms. This confirmation of long-term performance provides important documentation regarding PVC pipes’ sustainability.

PVC pipe technology was brought to North America following World War II, and started to take off after the National Sanitation Foundation (NSF) began studying plastic pipe products for water supplies in . NSF certification began in . ASTM began publishing standards for PVC water and wastewater pipes in the s.

In , the American Water Works Association (AWWA) approved its very first plastic pipe standard – AWWA C900, “Standard for Polyvinyl Chloride (PVC) Pressure Pipe, 4 inch through 12 inch, for Water.” PVC has grown to be the largest volume plastic pipe material in North America with annual sales in excess of 7.0 billion lbs. PVC pipe diameters range from 0.5to 48 in.

7. How have buying patterns changed over the years?

TR: It’s not so much that buying patterns have changed; rather the mindset in the design community has changed. Designers and owners recognize they can’t continue to operate in the same old way. Although they are still looking for the best product for the application, newer materials and installation practices are giving them greater choices than ever before. With more and more information becoming available and continuous improvement in plastic pipes, older, traditional materials such as iron and concrete are giving way to newer construction materials. Designers are also becoming more focused on the environment and taking particular interest in preserving natural resources for a growing country. Sustainability and a desire to conserve energy in every quarter also lend a favorable light to HDPE pipe.

ML: Ever mounting numbers of satisfied water and wastewater customers have kept those as the two primary end-use markets for buried PVC pipes. PVC pipes now also dominate the budding market for reclaimed water pipe. The acceptance and availability of larger PVC pipe diameters has resulted in a trend toward the increased use of larger pipes.

8. What innovations or changes have occurred with your products recently? What future changes are in store?

ML: Technological advances in manufacturing process controls and monitoring, together with equipment enhancements, have enabled PVC pipe product performance and consistency to improve. This progress has been steady and evolutionary, not revolutionary.

The development of several innovative joint designs has enabled PVC pipe producers to offer a variety of PVC pipe options that are very well suited for trenchless pipe situations. The same properties that have made PVC the market leader among pipe materials for water and sewer applications in North America make PVC a preferred material choice in trenchless applications. There are four trenchless technology methods for which PVC pipes are extremely well suited. These are Horizontal Directional Drilling (HDD), Sliplining, Tight Fit Structural Liner and Pipebursting.

TR: One hallmark of the HDPE industry overall, and the HDPE pipe industry in particular is the constant effort to improve base resins and pipe design. From a materials standpoint, the most recent innovation has been the introduction and recognition of high-performance HDPE resins for pressure pipe allocations, specifically PE . These resins are not the same old materials with a new name. These are new technology HDPE materials – third or even fourth generation – with performance capabilities surpassing previous grades. Even though the previous grades of PE materials have an excellent performance history in gas and water service, the HDPE industry continues to challenge itself – the same is not readily noticeable with other base materials and pipes. These new resins take performance to another level allowing them to be used with higher design stresses without sacrificing safety or design life.

HDPE resin and pipe have superior resistance to failure and rapid crack propagation (RCP). These are essential properties for HDD applications where scratching and gouging of the pipe are a fact of life. HDPE pipe can be gouged up to 10 percent (studies have shown even 20 percent) of the wall thickness with no detrimental effects to the long-term performance of the pipe. Resistance to RCP means that the monolithic piping system of heat fused HDPE pipe will not be susceptible to rapid cracking that can run for hundreds or even thousands of feet with catastrophic results.

Continued improvements in pipe design, specifically in the corrugated drainage pipe industry (storm water management) has allowed for greater burial depths and improved joint performance. Today’s HDPE corrugated pipe is significantly better than the original product first introduced in the mid-s. State and federal Departments of Transportations, municipalities and private enterprises are the beneficiaries of these efforts.

As technologies in the petrochemical market continue to develop, the underground utilities industry can expect continuing improvement. This of course begs the question: What has the metal and concrete industries done to improve their products?

9. What are some of the common misconceptions regarding your pipe material? How do you dispel this?

ML: The utilities that are not yet using PVC pipe usually cite insufficient strength and/or stiffness. The facts are that PVC pipes come in a full range of pressure ratings/classes and stiffnesses. While the minimum pipe stiffness of 46 lbs/in./in. for standard strength PVC gravity sewer pipes has proven to be good for burial depths in excess of 40 ft, PVC pipes are available with pipe stiffness values up to 1,019 lbs/in./in. The embedment requirements for PVC water pipe are no different than those for ductile iron pipe. Likewise, while most pressurized water systems operate within a 60- to 120-psi range, PVC pipe pressure ratings/classes go up to 305 psi; with short-term burst pressure minimums as high as 985 psi. Clearly PVC pipes afford more than sufficient strength to handle the full range of sewer and water system operating conditions.
Some utilities are concerned about soil contaminants permeating through plastic water pipes and associated human health risks. The fact is that PVC pipes provide a barrier to permeation and are not penetrated at contamination concentrations normally found. This PVC pipe benefit/protection was recently confirmed in a research published by AwwaRF. The AWWA Research Foundation study (published in early ) determined that PVC has superior hydrocarbon permeation resistance to gasoline and BTEX’s in both laboratory and field study conditions.

TR: That HDPE pipe is not as strong or durable as pipe made from steel or concrete is a common misconception. Of course this is not the case. HDPE pipe is a truly engineered product designed for specific purposes and long service life. In fact, it has been our experience that when traditional materials cannot handle a specific application either due to aggressive flows, soils or other unique conditions or installation practices demand trenchless techniques, HDPE pipe gets the nod. Our biggest frustration is that we get the most challenging applications but not the bread-and-butter uses such as potable water, sanitary sewer and storm water management applications.

We recognize HDPE pipe, although it has been used for nearly 50 years in the gas industry and more than 40 years in storm water management systems, is a “new kid on the block,” and we have to continually educate and promote our products to the design and specification community. As a result, our first step is to create a greater awareness to the features and benefits of HDPE pipe. We continue to conduct research, give educational seminars and promote case studies that verify the broad applications HDPE pipe enjoys. Secondly, we have to work on gaining approval by the design and specifying firms and agencies to allow engineers to employ our products. Lastly, the end user or owner will accept the product only when they are confident it is the best product for their specific application or need.

10. What is your pipe material’s strongest characteristic?

TR: HDPE pipe, in our opinion, is the best product for developing a truly sustainable infrastructure. From its low energy cost to produce, ship and install, to its superior joint performance in all applications, to its resistance to rust and abrasion and finally its short and long term economic advantages, we believe there is no other material that approaches the performance and versatility of HDPE pipe.

ML: PVC pipe combines the ageless durability that comes with a corrosion-free material with the overall strength and stiffness required to handle both water and sewer system demands at a cost that is comparable or less than the alternatives. PVC is arguably the most sustainable and cost-effective of all pipe materials.

11. How does increasing the awareness and importance of pipe materials help the consumer?

ML: Consumers need to know that there are options when it comes to pipe materials and products. Moreover, within a given material such as PVC, a broad range of product strengths exists that allow for cost-efficient design for almost any situation. Single product or material specifications should be the rare exception and not the rule given these options. As the No. 1 water and wastewater pipe material, most utilities across the country have come to appreciate the installation and operation benefits that PVC pipes and fittings provide.

Contact us to discuss your requirements of 18 Inch HDPE Pipe. Our experienced sales team can help you identify the options that best suit your needs.