Double containment pipework provides an engineered route for moving hazardous media while limiting the consequences of an inner-line failure. This guide explains the IPS options available to UK specifiers, installers and procurement teams, using the terminology applied across DuoSafe®, DuoSafe® FLEX, Poly-Flo® and AgruSafe. It shows how material choice affects joining, why specialist fittings shape the layout and where zoning supports repair planning. The focus stays firmly on supported IPS information, helping readers compare flexible, solvent-weld and butt-fusion arrangements without losing the technical distinctions that matter when selecting, installing or maintaining pipework for demanding industrial applications across complex process settings.
What Is Double Containment?
Double containment places a carrier pipe inside a second, protective pipe. The inner pipe transports hazardous media or another liquid that must remain isolated from people and the environment. If leakage occurs, the outer pipe provides secondary containment, collecting the escaped material and directing it towards a safe bunded area. This design reduces the risk of uncontrolled release, although effective protection still depends on suitable materials, secure joints and planned leak detection. IPS Flow Systems supplies flexible and rigid options for different chemical duties, installation environments and operating requirements. Later sections explain how leaks are identified and contained sections repaired.
Double Containment Systems Available
IPS supplies flexible and rigid double containment systems, each suited to different route conditions and media. DuoSafe FLEX provides a hose-based solution for continuous point- to-point dosing lines. Rigid DuoSafe uses imperial PVC-U or PVC-C pipework joined by solvent welding, while Poly-Flo and AgruSafe use metric PP, PE or PVDF construction with butt-fusion joining. Flexible runs require fewer connections but provide less scope for complex direction changes. Rigid systems offer a wider fitting range, although installation is more involved. Chemical compatibility comes first. Pressure and temperature narrow the choice further, while pipe size and installation environment determine which configuration remains practical.
Applications of Double Containment Pipework
Double containment pipework supports the safe transport of hazardous fluids where uncontrolled leakage could threaten people, assets or the surrounding environment. It is used across nuclear operations and within the gas, petroleum and chemical industries, including demanding industrial treatment and waste applications. The piping may be installed above or below ground, depending on the project design and operating conditions.
Material options include PVC-U, PVC-C, PE, PP and PVDF, allowing chemical compatibility
and installation requirements to guide the final technical specification.
- Piping systems in the nuclear, gas, petroleum & chemical industries
- Transporting dangerous fluids
- Protecting ground water
- Above or below ground use
- Choice of materials including PVC-U, PVC-C, PE, PP and PVDF
DuoSafe® Rigid Double Containment System
DuoSafe Rigid is a solvent-weld double containment system manufactured in PVC-U and PVC-C. Its carrier pipe is suspended within the outer pipe using centralisers, with several pipe pressure-rating combinations available up to a maximum of 16 bar. Specified joints require Weld-On® 724™ cement with Weld-On® P-70™ primer, selected for use with hazardous chemicals. Use of Weld-On® 724™ is a requirement of the system warranty.
The pipe can be disassembled for measuring and cutting, while most fittings remain free floating to support installation. Terminations and zone fittings are fixed, and certain other components cannot be separated.
An installation bush helps centralise elbows and tees before solvent welding, limiting unwanted movement while the inner connection is located. It is removed once the weld has been completed correctly, leaving the assembly ready for the next connection in the required installation sequence.
DuoSafe Fittings
DuoSafe includes the tees and elbows required to build direction changes and branches throughout a rigid installation. A valve can be supplied within a dedicated box, following the DuoSafe FLEX arrangement, or incorporated through a pressure-rated tee. Fitting selection should reflect the route design and the access available for solvent welding, operation and future maintenance. Because some free-floating components cannot be disassembled, their position and installation sequence must be confirmed before cutting or joining the surrounding pipework begins on site.
DuoSafe Zone Fittings
DuoSafe zone fittings divide the outer containment into defined sections without interrupting the carrier pipe. Their socket-within-a-socket construction blocks the annular space, keeping escaped liquid within the designated zone and directing it towards an assigned detection point. A zone fitting can be positioned anywhere along the system, but the corresponding visual leak-detection fitting must sit at the lowest point. Planning both components together allows leakage to collect where it can be observed and limits the pipework affected by future repairs.
DuoSafe Leak Detection
DuoSafe leak detection is available in two visual formats. The first uses a standard tee with its branch reduced to one inch, supplied with one foot of clear pipe and a lockable valve for installation during assembly. The second uses a clamp saddle with equivalent fittings, clear pipe and valve, allowing it to be added after the pipework is installed. Either version can be adapted for mechanical or electrical detection, although IPS does not supply the chosen detection device itself.
DuoSafe Closure Fitting
The DuoSafe closure fitting is a specially machined component for joining pipework installed from opposing directions between two fixed points. In this situation, the carrier and containment joints cannot be completed together because movement is needed to form the inner connections first. Once those joints are secure, the closure fitting enables both outer joints to be completed around them. It is intended only for this installation condition, with the required planning and joining sequence explained in the IPS Installation Guide.
DuoSafe® FLEX Double Containment
DuoSafe FLEX is intended for long, continuous small-diameter dosing and chemical distribution lines, particularly in water treatment where several dosing points draw from one storage unit. Aquachem and Hydrachem carrier hoses are manufactured with the outer containment in a single extrusion process, providing resistance across varied conveyance duties.
Developed with Copely Developments, a UK thermoplastic hose and tube manufacturer with more than 50 years in the industry. Coils reach standard lengths of 300 metres, although shorter lengths or longer manufactured lengths may be supplied for an application. Connections between coils and termination points use rigid PVC-U fittings. Carrier sizes extend from DN 6mm to DN 38mm, and to 50mm in Aquachem, with a maximum working pressure of 10 bar. Continuous construction reduces intermediate joints while retaining secondary containment.
Poly-Flo® Twin-Wall Double Containment
Poly-Flo is a rigid twin-wall system in which the carrier and containment pipe are co-extruded as one product. Fittings use the same construction and include extended inner ends, which are machined back to virgin material and matched for wall size before joining. Installation uses standard butt fusion with dedicated welding parameters, placing particular importance on the inner weld. Available sizes are 32mm x 50mm, 63mm x 90mm and 110mm x 160mm, with the manufacturer also offering a larger 160mm x 225mm size at a reduced pressure rating for non-pressurised drainage duties. The range includes tees, 45-degree elbows and 90-degree bends fabricated in three sections, alongside dedicated reducers unavailable within the solvent-weld range. AGRU also now supplies a single-piece moulded 90-degree bend. Segmented and fabricated fittings carry derating factors of 0.5 or 0.8. Specialist components extend the range beyond direction changes. Fixed points control movement and establish zones, while other specialist fittings provide leak detection, instrumentation access, termination and flanged connections.
Fixed Point and Restrained Fixed Point
Poly-Flo fixed-point fittings create inline zone boundaries by isolating the containment around the carrier connection. This directs escaped liquid towards the selected leak- detection fitting. The restrained version includes a recess around its circumference, allowing a clip to anchor that position within the piping. Expansion is then directed away from the fixed point in both directions rather than moving the anchored section. A separate
restrained fitting is available where movement must be controlled but containment needs to continue through the connection.
Outer Wall and Termination Fittings
The Poly-Flo outer-wall fitting connects to a tee branch and closes the inner branch while leaving the outer passage open. This open containment branch can then be extended by butt fusion to provide a leak-detection point. The termination fitting serves a different purpose. It joins both walls, ends the containment and leaves the carrier as a butt-fusion spigot for connection to ordinary single-wall pipework. Selection therefore depends on whether the design requires monitoring access or a transition beyond secondary containment.
Leak Detection Fittings
Poly-Flo offers three leak-detection fittings, each using a 1¼-inch BSP outlet. One inline version receives leakage from one side and can also function as a zone fitting. Another inline option accepts a leak path from both directions. The third combines detection with termination, connecting to double containment before reducing to a single butt-fusion spigot. The correct version depends on the expected annular flow, the intended zone boundary and whether containment must continue beyond the monitoring point.
Instrumentation Fitting
The Poly-Flo instrumentation fitting provides an inline connection between adjoining pipe sections while giving direct access to the carrier line. It can accommodate a gauge or another instrument required to monitor operating conditions within the transported media. This connection is separate from leak detection, which monitors the surrounding containment space instead. Instrument requirements should be established before fabrication, ensuring the connection type remains compatible and accessible after installation without requiring alteration to the completed twin-wall piping system during later service.
Flanges
Poly-Flo uses three flange styles, all requiring a backing ring sized to match the outer pipe. The termination stub flange ends containment and provides a flanged connection based on that outer diameter. The remaining two styles allow containment to continue through the joint and are designed to work together. One face contains two O-rings, while the corresponding flat face seals against them. This arrangement preserves containment through a removable flanged connection rather than terminating it before the equipment or pipework.
AgruSafe Double Containment
AgruSafe carrier sizes are available from as small as DN 25mm, with a standard range extending to DN 250mm carrier and larger sizes commonly manufactured up to DN 600mm. Its outer wall is proportionally wider than Poly-Flo, giving the inner fittings sufficient installation space. The manufacturer supplies assembled fittings welded around support discs and ready for preparation. Pipe lengths also contain welded support discs at both ends, with clip-on spider supports positioned along each length. Site cutting requires replacement discs and, where extra internal support is needed, an additional spider clip. After machine planing, the discs are welded around the carrier and against the outer bore using hot gas and welding wire. This reinstates both cut lengths for subsequent butt-fusion joining on site.
Zoning in Double Containment Pipework
Zoning divides a double containment installation into monitored sections. A zone fitting prevents liquid from moving beyond its boundary, while the leak-detection point identifies where escaped liquid has collected. Although these components increase initial cost, they can reduce replacement after a failure. A 100-metre run divided into four 25-metre zones requires three zone fittings and four detection fittings. If leakage occurs within one section, repairs may be limited to approximately 25 metres and the necessary adjoining fittings, rather than replacing the complete 100-metre piping system. This approach can also limit damage and disruption during reinstatement.
Leak Detection in Double Containment Pipework
Leak detection is critical because secondary containment can hold escaped media without making the failure immediately visible. Without a detection point, operators may not know that the inner line has leaked or where the affected section begins. IPS normally supplies visual detection arrangements, positioned so liquid can collect and be inspected. Clients can modify those fittings to accept mechanical or electrical detection where an automated indication is required. Detection requirements should be established during design, alongside zoning, access and inspection responsibilities, ensuring any leakage produces a clear warning that can be acted upon by operators.
How to Choose a Double Containment Pipework System
Choosing between DuoSafe, DuoSafe FLEX, Poly-Flo and AgruSafe begins with duty rather than product preference. The transported media determines material suitability. Temperature and pressure narrow the available ranges, while diameter and route configuration influence construction. Joining access, zoning and leak-detection requirements then shape the final technical specification for the project.
Chemical and Media Compatibility
Confirm the precise chemical, its concentration and operating conditions before selecting any carrier material. Compatibility must extend beyond the pipe itself to every wetted fitting and joining material. DuoSafe provides PVC-U and PVC-C carrier choices, with containment available in grey or clear PVC-U, PVC-C, ABS or polyethylene. Poly-Flo is manufactured from black polypropylene or PE100-RC, while AgruSafe offers several possible material combinations. Aquachem and Hydrachem are available for DuoSafe FLEX dosing duties. IPS guidance can inform each alternative, but no global assumption replaces a direct check against the media in the intended application.
Operating Temperature and Pressure
Temperature and pressure must be assessed together because permissible pressure can change as operating temperature increases. IPS states that DuoSafe PVC-U is suitable for temperatures up to 60°C, while DuoSafe PVC-C can be used up to 100°C. DuoSafe FLEX has a maximum working pressure of 10 bar, and Poly-Flo is rated for working pressures up to 6 bar at 20°C, with its polypropylene version suitable to 100°C and PE100-RC to 60°C. AgruSafe is available in pressure ratings up to PN 16. Confirm the ratings for both carrier and containment components before products are ordered or installation begins.
Pipe Size and System Configuration
Pipe diameter quickly narrows the available range. DuoSafe FLEX covers carrier sizes from DN 6mm to DN 38mm, extending to 50mm in Aquachem, while Poly-Flo is supplied in three defined carrier-and-outer combinations. AgruSafe carrier sizes run from DN 25mm to a standard DN 250mm, with larger sizes commonly manufactured up to DN 600mm. Size alone is not enough. Bends and branches affect fitting selection, while terminations, fixed points and instrumentation connections influence fabrication. Map the complete route before confirming quantities or formally releasing the completed design for manufacture.
Flexible vs Rigid Double Containment
Flexible double containment suits long, continuous small-bore dosing routes and can reduce the number of intermediate connections. It is most practical for point-to-point applications, including routes feeding several dosing locations from one storage unit. Rigid pipework requires more installation but provides greater freedom where the design needs branches or repeated direction changes. It also supports specialist zoning, instrumentation and flange arrangements. Route geometry should lead the decision. Fitting requirements and installation access refine it, while future maintenance remains equally important.
Solvent-Weld vs Butt-Fusion Systems
Rigid DuoSafe uses solvent-welded PVC-U or PVC-C, with Weld-On® 724™ cement and Weld-On® P-70™ primer specified for its double-contained joints. Poly-Flo and AgruSafe use butt fusion, but their joining procedures differ. Poly-Flo requires dedicated welding parameters for its co-extruded twin walls, while AgruSafe uses simultaneous welding where carrier and containment share a material, and cascade welding where they differ, which requires a specially adapted machine with a split welding plate so the carrier is welded first. Installation teams need the correct equipment and system-specific training. Jointing should follow the relevant IPS instructions because carrier joint integrity remains central to safe operation and reliable long-term containment performance.
Leak Detection and Zoning Requirements
Plan zoning and leak detection together because one controls where escaped liquid travels and the other shows that a failure has occurred. Every zone needs an accessible detection point located where liquid can collect, normally at its lowest point. Shorter zones require more fittings initially but may limit the length replaced after leakage. The client should decide whether visual inspection is sufficient or whether mechanical or electrical detection will be added. Record both requirements on installation drawings before ordering begins.
Need Help Specifying Double Containment Pipework?
Engineers, contractors and procurement teams can consult IPS before committing to a double containment specification. The technical team can compare media requirements with available materials, sizes and joining methods, then review zoning and detection needs against the proposed route. Early guidance reduces specification risk and supports a practical installation plan.
Primary CTA: Speak to the IPS Technical Team
FAQs
How does double containment pipework work?
An inner carrier transports the media, while an outer pipe surrounds it. If the carrier leaks,
the outer passage captures the escaped liquid and directs it towards a bunded area or
detection point. The arrangement reduces uncontrolled release when compatible materials,
secure joints and suitable monitoring provisions are correctly installed.
What materials are used for double containment pipework?
IPS thermoplastic options include PVC-U and PVC-C carriers for DuoSafe, with containment
also available in ABS or polyethylene. Poly-Flo uses black polypropylene or black PE100-RC,
while AgruSafe can be manufactured in polypropylene, PVDF, polyethylene and ECTFE.
DuoSafe FLEX uses Aquachem or Hydrachem carrier hose, with dedicated rigid PVC-U
fittings securely connecting individual lengths and termination points within the
installation.
Why is leak detection important in double containment pipework?
Leak detection identifies when media has escaped from the carrier into the surrounding
containment. Without it, a failure may remain hidden. IPS supplies visual arrangements,
although clients can adapt the connections for mechanical or electrical detection. Correct
positioning ensures leakage from the assigned zone reaches the monitoring point for
observation.
What are zoning fittings in double containment pipework?
Zoning fittings block the outer passage at selected points, dividing a long pipe run into
independently monitored sections. Each zone directs escaped liquid towards its own
detection fitting. If the carrier fails, this layout helps identify the affected section and may
prevent unnecessary replacement of the complete double containment piping.
What is the difference between rigid and flexible double containment pipework?
Flexible systems use continuous small-diameter coils and suit direct dosing routes with
fewer intermediate joints. Rigid systems require more installation but provide a wider
selection of direction changes and specialist fittings. The choice depends on route geometry,
carrier size, chemical compatibility, operating conditions, access for joining and the
maintenance strategy.
What is twin-wall double containment pipework?
Twin-wall double containment combines the carrier and outer wall within one product.
Poly-Flo uses this co-extruded construction with twin-wall fittings. Both walls are joined
through butt fusion using welding parameters. The compact arrangement reduces the outer
diameter needed to accommodate the carrier and its fittings compared with other rigid
systems.
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