How the Right Types of Pipe Fittings Reduce Delays in Utility Projects

A crew opens a trench, lays 500 feet of conduit in a morning, and then stops. The elbows on the truck are Schedule 80 but the conduit run is Schedule 40. The transition adapter shipped is IPS when the spec calls for DIPS. The reducer needed to step down from 4" to 3" at a pedestal entry was never ordered at all. Each of these scenarios plays out on utility jobsites every week, and each one means the same thing: the crew waits while somebody drives to a supply house or places an emergency order.

Fittings account for a small fraction of a project's total material cost, but they are responsible for a disproportionate share of field delays. Understanding the types of pipe fittings used in underground utility work, and ordering the right ones before the crew mobilizes, is one of the simplest ways to keep a conduit installation on schedule.

This guide covers the major categories of utility pipe fittings, explains when each type is used, identifies the material and sizing variables that cause compatibility problems, and provides a practical approach to fitting selection that minimizes rework and downtime.

Why Fittings Cause More Delays Than Pipe

Conduit itself is relatively simple to specify. A project calls for 4" Schedule 40 PVC, or 2" SDR 11 HDPE, or 6" fiberglass. The pipe arrives on reels or in bundles, and it either fits the spec or it does not.

Fittings are where complexity multiplies. A single conduit run might require three or four different fitting types, each in a specific material, schedule, size, and connection method. Miss any one of those variables, and the fitting either does not physically connect or does not meet the project specification, both of which stop work.

The most common fitting-related delays fall into predictable categories. Material mismatches occur when a PVC fitting is ordered for an HDPE conduit run, or when a standard PVC coupling arrives for a fiberglass system that requires a different joint geometry. Size errors happen when nominal sizes between systems do not align, a 4" IPS fitting has a different outside diameter than a 4" DIPS fitting, even though both are called "4 inch." 

Schedule mismatches create problems when a Schedule 80 fitting is paired with Schedule 40 conduit or vice versa, resulting in wall thickness differences that prevent a proper joint. And incomplete orders, the most preventable cause of all, occur when the bill of materials accounts for every foot of pipe but omits the elbows, reducers, and adapters needed at direction changes, size transitions, and termination points.

Elbows and Sweeps: Direction Changes Without Damage

Elbows are the most frequently used fitting type in underground conduit work. Every direction change in a conduit run, whether around a foundation, under a road crossing, or up a riser into a pedestal, requires either a factory-made elbow or a field bend. Factory elbows produce cleaner, more consistent results and reduce the friction cable experience during pulling.

Standard elbow angles include 11-1/4°, 22-1/2°, 30°, 45°, and 90°. The smaller angles are used for gentle directional adjustments in long duct bank runs, while 45° and 90° elbows handle sharper turns at building entries, vault penetrations, and riser transitions. Sweep elbows, which have a longer, more gradual radius, are the preferred choice in underground installations because they reduce cable-pulling tension and protect conductor insulation.

Material selection for elbows must match the conduit system. PVC conduit uses PVC elbows joined with solvent cement. HDPE systems use butt-fused or electrofusion elbows. Fiberglass conduit elbows are common in corrosive environments and high-temperature applications where PVC would degrade. Steel conduit runs require 45° galvanized RMC conduit elbows with threaded NPT connections.

The NEC limits total bends between pull points to 360°, including offsets. Exceeding this limit requires adding a pull box, which changes the layout and adds cost. Selecting the right combination of elbow angles during design, rather than improvising in the field, prevents pull-point violations that trigger inspection failures.

Couplings: Joining Pipe Sections Into Continuous Runs

Couplings are straight connectors that join two sections of conduit end-to-end to create a continuous pathway. They are the highest-volume fitting on most utility projects, needed at every joint in a conduit run.

The connection method varies by conduit material. PVC conduit couplings use solvent cement for a permanent chemical bond. Many PVC conduit products ship with one bell end per length, which reduces the number of separate couplings needed, but cut pieces and repair sections still require standalone couplings. HDPE conduit couplings use either mechanical compression connections or thermal fusion. Double E-Loc couplings provide a tool-free mechanical connection for HDPE IPS conduit, which speeds installation in the field by eliminating the need for fusion equipment. Fiberglass conduit typically uses an expansion joint or O-ring compression coupling that accommodates the material's thermal movement.

Coupling compatibility is a frequent source of field problems. A coupling designed for Schedule 40 PVC will not properly seat on Schedule 80 pipe of the same nominal size because the wall thicknesses differ, changing the spigot diameter. Similarly, IPS-dimensioned couplings and DIPS-dimensioned couplings are not interchangeable even at the same nominal size, the outside diameters do not match.

Tees: Branching Conduit Runs

Tee fittings create a branch connection from a main conduit run, forming a T-shaped junction with three openings. In utility conduit work, tees are used where a lateral service line breaks off from a main duct run, where a secondary conduit feeds a transformer pad or pedestal, or where a future stub-out is needed for planned system expansion.

Equal tees have the same diameter at all three openings. Reducing tees have a smaller branch opening than the main run, which is common when a 4" main feeds a 2" service lateral. The 523 Series reducing transition tee handles this application in HDPE systems, providing an HDPE-to-threaded transition at the branch opening for connection to metallic risers or equipment.

Tees are among the fittings most likely to be omitted from initial material orders because branch connections are sometimes added during construction as field conditions dictate. Building a small buffer of common tee sizes into the project inventory prevents delays when unplanned laterals are needed.

Reducers and Adapters: Bridging Size and Material Differences

Reducers connect two conduit sections of different diameters, creating a smooth transition that maintains the protective envelope around cables as the system steps down (or up) in size. A typical use case is transitioning from a 4" main duct to a 2" service entry at a meter base or equipment enclosure.

Concentric reducers keep the centerline of both pipes aligned, which simplifies cable pulling and maintains consistent conduit grades in underground installations. Eccentric reducers offset the centerline, which is useful when the bottom of the conduit must remain at a consistent elevation, common in gravity-flow drainage applications.

Adapters serve a related but distinct function: they connect conduit of the same nominal size but different materials or connection types. A fiberglass-to-PVC adapter, for example, allows a fiberglass conduit system to transition to a PVC riser without cutting threads or modifying the pipe ends. Bell adapters connect conduit sections with different end configurations, bell end to plain end, for instance, which is common when joining new conduit to existing duct.

Adapter selection requires careful attention to the exact dimensions and connection methods on both sides of the joint. This is where IPS versus DIPS sizing differences create the most confusion. A 6" IPS conduit has an OD of 6.625", while a 6" DIPS conduit has an OD of approximately 6.90". An adapter specified for IPS will not fit DIPS pipe at the same nominal size. Confirming the sizing system before ordering transition fittings eliminates one of the most common causes of fitting returns and reorders.

Expansion Joints: Preventing Thermal Damage

Underground conduit systems experience thermal expansion and contraction as ground temperatures change seasonally. PVC conduit has a particularly high coefficient of thermal expansion, roughly 3.4 × 10⁻⁵ in/in/°F, which means a 100-foot PVC conduit run can expand or contract by more than 2 inches over a 60°F temperature swing.

Without expansion joints, this movement creates stress at fixed points like building entries, vault penetrations, and rigid connections. Over time, that stress can crack fittings, separate joints, or buckle the conduit itself.

Fiberglass expansion joints use O-ring seals that allow the pipe to telescope within the joint body while maintaining a watertight seal. These are installed at regular intervals in long conduit runs and at every point where the conduit passes through a rigid structure. The NEC requires expansion fittings where conduits cross structural joints, and many local codes specify maximum spacing intervals.

Missing expansion fittings is a code violation that triggers inspection failures. Inspectors specifically check for expansion joints at building penetrations and duct bank-to-structure transitions, and a failed inspection means the crew returns to install the missing fittings before any other work can proceed.

Caps, Plugs, and End Seals: Protecting the System

Caps and plugs seal the open ends of conduit runs to prevent moisture, soil, insects, and debris from entering the duct system. This matters during construction when conduit stubs may sit exposed for days or weeks before cables are pulled, and it matters permanently at termination points where the conduit ends at equipment or is stubbed out for future use.

Fiberglass end caps with gaskets provide watertight seals for systems that require moisture exclusion. Thermoplastic press-fit plugs offer a quicker solution for temporary protection during construction. For conduit penetrations into handholes, vaults, or buildings, segmented mechanical seals create a permanent, watertight barrier around the cables passing through the conduit opening.

End sealing is easy to overlook during the heat of installation, but an unsealed conduit stub that takes on water or sediment during a rain event can create blockages that require jetting or rodding to clear before cable installation, a delay that is entirely preventable with a $2 cap.

Fitting Selection by Conduit Material

Each conduit material uses a specific set of compatible fittings with different connection methods, dimensional standards, and performance characteristics. Ordering fittings that match the conduit material and connection system prevents the most common compatibility-related delays.

A Practical Approach to Fitting Takeoffs

The fitting-related delays described throughout this article share a common root cause: incomplete or inaccurate material takeoffs. A disciplined approach to fitting specification during the estimating and procurement phases prevents most of these problems.

Start by walking the conduit route on the drawings and counting every direction change, size transition, material transition, termination point, and structural penetration. Each of these locations requires at least one fitting, and many require two or more, an elbow plus a coupling, a reducer plus an adapter, an expansion joint plus a cap.

Build the fitting list in parallel with the pipe list, not after it. When fittings are treated as an afterthought, ordered after the pipe is already on the truck, omissions are almost guaranteed. Group fittings by conduit material and sizing system (IPS, DIPS, Schedule 40, Schedule 80) to prevent cross-ordering between incompatible systems.

Add a buffer. Experienced utility contractors add 10–15% overage on common fittings like couplings and elbows. A handful of extra couplings on the trailer costs very little but can save a full day of downtime when a field condition requires an additional joint or an installed coupling cracks during assembly.

Finally, confirm stock availability before the crew mobilizes. Specialty fittings, large-diameter reducers, fiberglass transition adapters, DIPS-specific tees, may have lead times of several days to several weeks. Identifying these items early and placing orders with adequate lead time keeps the project on schedule.

About Utility Pipe Supply

Utility Pipe Supply is a certified Woman-Owned Business Enterprise (WBE) headquartered in Illinois, specializing in conduit, pipe fittings, enclosures, and installation tools for electrical, telecommunications, and infrastructure contractors. With nationwide shipping and in-stock inventory across PVC, HDPE, fiberglass, and steel conduit systems, we help crews get the right fittings on site before the trench is open.

Frequently Asked Questions

What are the most common types of pipe fittings used in utility conduit systems? 

The primary fitting types are elbows (for direction changes), couplings (for joining conduit sections), tees (for branch connections), reducers (for size transitions), adapters (for material or connection-type transitions), expansion joints (for thermal movement), and caps and plugs (for sealing open ends). Each type is available in multiple materials and connection methods to match the conduit system being installed.

How do I know which fitting material to use? 

Match the fitting material to the conduit material. PVC conduit uses PVC fittings joined with solvent cement. HDPE conduit uses HDPE fittings joined by fusion or mechanical compression. Fiberglass conduit uses fiberglass fittings with epoxy or O-ring compression joints. Steel conduit uses threaded or compression steel fittings. Mixing materials without a proper transition adapter creates weak joints that are prone to leaks and separation.

What is the difference between IPS and DIPS fittings? 

IPS (Iron Pipe Size) and DIPS (Ductile Iron Pipe Size) refer to different dimensional standards. At the same nominal size, IPS and DIPS fittings have different outside diameters. A 4" IPS fitting has an OD of 4.500", while a 4" DIPS fitting has a larger OD to match ductile iron pipe dimensions. The two are not interchangeable, and ordering the wrong system is one of the most common causes of fitting returns on utility projects.

Why do I need expansion joints in a conduit system? 

PVC and HDPE conduit expand and contract with temperature changes. Without expansion joints, this thermal movement creates stress that can crack fittings, separate joints, or buckle conduit. The NEC requires expansion fittings where conduit crosses structural joints, and most local codes specify additional placement requirements. Missing expansion joints is a common cause of failed inspections.

How many fittings should I order as an overage? 

Most experienced utility contractors carry 10–15% overage on standard fittings like couplings and elbows. Specialty fittings such as large-diameter reducers, transition adapters, and DIPS-specific tees should be ordered to exact counts but with enough lead time to accommodate potential field changes. The cost of carrying a few extra fittings on the job trailer is minimal compared to the cost of a crew waiting for an emergency order.

Can I use Schedule 40 fittings on Schedule 80 conduit? 

No. Schedule 40 and Schedule 80 conduit have different wall thicknesses, which changes the spigot diameter at the end of the pipe. A Schedule 40 coupling will not properly seat on a Schedule 80 pipe, and the resulting joint will be structurally weak and likely fail inspection. Always verify that the fitting schedule matches the conduit schedule.

What fitting types require the longest lead times? 

Standard PVC couplings and elbows in common sizes (2"–4") are typically stocked by most distributors. Fittings that may require longer lead times include large-diameter fiberglass fittings (5"–6"), DIPS-specific fittings, specialty transition adapters between different conduit materials, and custom-angle sweeps. Identify these items during the estimating phase and order with adequate lead time to prevent schedule impacts.

Keep Your Next Project on Schedule

Utility Pipe Supply stocks a full range of conduit fittings across PVC, HDPE, fiberglass, and steel systems, from standard couplings and elbows to specialty reducers and transition adapters. Call us at (815) 337-8845 or request a quote for availability, lead times, and technical support on fitting selection.