Can an RECD Be Installed Without Cutting the Existing Exhaust Pipe?

The short answer is: very often, yes. Most diesel generator exhaust lines are not one continuous welded tube. They are a chain of sections held together by flanges, clamps and flexible bellows, and an RECD can usually be bolted into one of those existing breaks. Whether your particular set allows it depends on where those breaks sit, how much straight run you have, and what condition the old hardware is in.

This guide takes a different route from a typical explainer. Instead of listing pros and cons, we will walk your exhaust line from the engine outwards, stopping at each point where an installer might open it. By the end you will know how to look at your own set and make a fair guess about whether the fitter will need a cutting wheel at all.

Why Owners Ask This Question

Nobody likes the idea of someone slicing into a working generator. The worry usually comes from one of four places:

• Downtime. Cutting and welding sound like days of work. For a hospital, data room or process plant, even one extra day without backup power is a real risk.
• Hot work on site. Grinding and welding need a hot work permit, fire watch and sometimes a shutdown of nearby activity. In a basement generator room or a fuel-heavy area, that is a serious conversation with the safety team.
• Reversibility. If the set is leased, rented, under warranty or likely to be sold, owners want to be able to put it back the way it was.
• Fear of making it worse. A badly executed cut can leave a leaking joint, a misaligned pipe or extra back pressure.

Each of these is a fair concern, and each one is answered differently depending on the exhaust layout. That is why the walk below matters more than any blanket yes or no.

First, What an RECD Needs From the Pipe

Before looking at joints, it helps to know what the device itself asks for. A retrofit emission control device sits inline in the exhaust path. Exhaust gas enters one end, passes through the treatment core (on Aceget units, a diesel oxidation catalyst and a particulate filter, as described on our RECD product page), and leaves the other end towards the stack.

To do that job, the device needs four things from the pipework around it:

1. An inlet and an outlet it can seal to. Usually a flange on each end, sized to the exhaust bore.
2. A physical slot. The body of an RECD is larger in diameter than the pipe and has a set length. That length has to fit somewhere along the route.
3. Support that does not load the engine. The device has weight. It must hang from or sit on its own supports, not on the turbocharger or manifold.
4. Access for servicing. Someone will need to reach it for periodic cleaning and inspection.

Notice what is missing from that list: nothing says “the pipe must be cut”. The requirement is a sealed break of the right length in the right place. If your line already has one, cutting may be unnecessary.

Walking the Exhaust Line: Six Stops

Picture yourself standing at the engine and following the hot pipe outward. Here are the places where a fitter might open the line, in order.

Stop 1: The Turbocharger or Exhaust Manifold Outlet

This is the first joint on the hot side. On turbocharged sets, the turbo outlet usually has a flange or a V-band clamp, followed closely by a flexible connector.

Can the RECD go here? Almost never directly. This zone is cramped, it moves with the engine on its mounts, and any weight added here is carried by the turbo housing. Exhaust installation guidance from the industry is blunt on this point: the weight of the exhaust system should never be carried by the engine manifold or turbocharger (see this generator exhaust system information sheet). Treat this stop as off limits for mounting, even though it is technically a bolted joint.

Stop 2: The Flexible Connector (Bellows)

Right after the engine outlet you will normally find a stainless bellows. It absorbs engine vibration and thermal growth so that the fixed pipework does not crack.

Can the RECD go here? Not in place of the bellows. The bellows must stay, because the RECD is a rigid body and would otherwise pass vibration straight into the rest of the line. However, the flanges on the downstream side of the bellows are often the first useful bolted break. If there is enough straight, supportable space after it, the RECD can sometimes start right there.

Stop 3: Intermediate Flanged Joints

On longer runs, especially in generator rooms where the pipe travels across a ceiling or through a wall, you will find flanged joints every few metres. These exist because pipe is transported and installed in sections.

Can the RECD go here? This is the most common no-cut location. If two flanged joints happen to sit a device-length apart on a straight horizontal or vertical run, the fitter unbolts that section, removes it, and bolts the RECD into the gap. If the spacing is not quite right, a short spool piece (a length of flanged pipe) can make up the difference, again without cutting.

Stop 4: The Silencer Inlet and Outlet

Most sets have a residential or industrial silencer somewhere in the line. The silencer is almost always flanged at both ends, because it is a separately supplied component.

Can the RECD go here? Yes, and this is one of the tidiest options. The RECD is typically placed on the outlet side of the silencer, where the fitter can use the existing silencer outlet flange as the inlet connection. Placement relative to the silencer is covered in more depth in our post on whether an RECD can replace a generator’s exhaust silencer (short version: it cannot, and the two do different jobs).

Stop 5: The Canopy Exit or Wall Penetration

On acoustic canopy sets, the exhaust leaves the enclosure through the roof or a side panel. In buildings, the pipe passes through a wall sleeve or roof slab.

Can the RECD go here? Rarely as a direct connection. The canopy exit is usually a welded stub or a slip fit with a rain cap. What this stop does offer is space. Many canopy installations place the RECD on the roof of the enclosure or on a frame beside it, connected to the exit stub with a flanged adapter. Whether that adapter can be clamped rather than welded depends on the stub design. Our comparison of open frame and enclosed canopy generators explains why these two layouts behave so differently for any add-on equipment.

Stop 6: The Stack and Rain Cap

The final vertical section rises to the discharge height set by your consent conditions.

Can the RECD go here? Sometimes, for tall stacks with a flanged section at a reachable height. A vertical mount saves floor space, but it needs a strong structural support and safe access for maintenance at height. If the only break is ten metres up, a no-cut install may technically work but will make every future service visit harder.

Quick Reference: Joint Types and What They Mean for Cutting

What you find at the joint	What it usually means	Cutting likely?
Bolted flange pair with gasket	Designed to come apart	No, if spacing and access allow
V-band or wedge clamp	Quick-release joint, common near engines	No, but usually too close to the engine to mount the device
Slip joint with band clamp	Pipe sections pushed together	Usually no, a flanged adapter can be clamped on
Continuous weld	Pipe was welded in one piece on site	Probably yes, unless another break exists nearby
Flange welded to a badly corroded pipe	Old joint, may not survive opening	Possibly, the fitter may cut back to sound metal
Silencer flange	Factory flange on a bought-in component	No, often the best no-cut point

What “No Cutting” Does Not Mean

It is easy to hear “no cutting” and assume “no work on the pipe”. That is not quite right. Even a bolt-in installation usually involves:

• Removing a spool section. The piece of pipe that used to sit where the RECD goes has to come out. That section is kept, and it can go back in if the device is ever removed.
• New gaskets. Old exhaust gaskets are crushed and heat-hardened. Reusing them is asking for a leak.
• New or longer fasteners. Exhaust bolts are often seized. They may need to be cut off with a nut splitter or a small grinder. Cutting a bolt is not the same as cutting the pipe, but it does need a controlled approach.
• Support brackets. The RECD needs its own hangers or a floor stand. These are often bolted to existing steelwork, though some sites need a new support welded to a structural member (not to the exhaust).
• Insulation work. Lagging or thermal wrap around the section must be removed and replaced, sometimes extended to cover the new device connections.

So a more precise way to phrase the question is: “Can the exhaust pipe itself stay intact?” The answer to that is yes in a large share of installations. The answer to “Will nobody touch anything?” is no.

Five Situations Where a Small Cut Is the Better Choice

It is tempting to push for a no-cut install at all costs. That is not always the right call. Here are the cases where a clean, planned cut usually gives a better result.

1. The only flanged break is in a bad place

If the one available joint sits right next to the turbo, directly above a walkway, or in a spot with no room to support the device, bolting in there is worse than making a new break somewhere sensible.

2. Forcing the fit would add bends

Some installers avoid cutting by adding extra elbows to route the gas to wherever the device will fit. Each elbow adds resistance. Back pressure is the number one engineering limit on any exhaust add-on, and our guide on how exhaust back pressure affects a DG set explains what happens when that budget is overspent: higher exhaust temperature, fuel penalty and, over time, engine stress. One straight cut is often kinder to the engine than three extra bends.

3. The existing pipe is rusted through at the joint

Old flanges on thin, scaled pipe can crumble when unbolted. If the fitter discovers this, cutting back to sound metal and welding a new flange is the durable fix. Clamping onto rotten pipe would only move the leak.

4. The route is one long weld

Some site-built exhaust lines, especially older ones, were welded end to end. There is simply no bolted joint in the usable zone. A single cut and two flanges solve the problem permanently.

5. You want the device where it can be serviced

A device fitted in an awkward no-cut position may need scaffolding every time it is inspected. Across ten or fifteen years of service life, a better location can save far more than the one-time cost of a cut. Service access is a recurring theme in our RECD maintenance guide.

Downtime: Cut vs No-Cut, Realistically

Owners often ask how many hours each approach costs. Exact times depend on the set size and site, but the pattern looks like this.

Task	Bolt-in install	Install with one cut
Isolate and cool the set	Same	Same
Remove insulation and old spool	Short	Short
Cut and prepare pipe ends	Not needed	Adds time, plus hot work permit
Weld new flanges	Not needed	Adds time, plus cooling and inspection
Lift and position the device	Same	Same
Bolt up, fit supports, re-lag	Same	Same
Leak check and test run	Same	Same

For many sets, the difference between the two columns is measured in hours, not days, once the site is prepared. The larger delays usually come from elsewhere: waiting for the hot work permit, arranging a crane or lifting frame, or discovering an unexpected fault. Our post on what to expect from an RECD installation timeline lays out the full sequence, from survey to handover.

Can You Tell From a Photo?

Often, yes. An experienced surveyor can spot flanges, clamps and silencer connections from a clear set of photos and give a first view on whether a bolt-in install is likely. The trick is to photograph the full route, not just the engine.

When preparing an enquiry, take these extra shots in addition to the standard nameplate photos listed in our guide to DG nameplate photos for an RECD enquiry:

• One wide photo of the whole exhaust route, even if it takes a panorama.
• A close shot of every joint you can see, with a tape measure held across the pipe for scale.
• The silencer, both ends, including its support.
• The distance between the joints you think are usable. A rough tape measurement is fine.
• The canopy exit or wall penetration, from inside and outside if possible.
• Any rust, soot streaks or blackened areas near joints. These often mark old leaks.

Soot marks deserve special attention. A joint that has been leaking for years may be the one you were hoping to reuse. The surveyor will want to know that before quoting.

Questions to Ask the Installer Before Work Starts

A good installer will already cover these, but it does no harm to ask directly.

1. Which joint do you plan to use, and why that one? You want a reason based on back pressure, support and access, not just convenience.
2. Will the pipe itself be cut? If yes, where and how long will the new section be?
3. What happens to the spool piece you remove? Ask them to leave it on site, labelled. It is your route back if the device is ever moved. That matters if you might later transfer the RECD to another diesel generator.
4. Is a flexible connector staying upstream of the device? It should be.
5. How will the device be supported? Hangers, a stand, a frame on the canopy? Where will the load go?
6. Will you measure back pressure before and after? A before-and-after reading at the same load is the clearest evidence that the installation did not strain the engine.
7. Does the work affect the OEM warranty? A bolt-in installation at an existing joint is usually a lighter touch, but the right answer depends on your OEM. We cover this in detail in will installing an RECD affect a generator’s OEM warranty.

Common Mistakes on No-Cut Installations

Bolt-in jobs look simple, which is exactly why a few errors keep repeating. Several of these also appear in our wider list of common RECD installation mistakes to avoid.

• Reusing old gaskets. The single most common source of post-install leaks.
• Hanging the device from the pipe. The exhaust pipe is not a structural member. It needs independent support.
• Removing the bellows to “make it fit”. This transfers engine vibration into the device and the building.
• Ignoring thermal growth. A long run heats up and grows. If the RECD is rigidly fixed at both ends with no allowance for expansion, joints will work loose.
• Mismatched flange standards. A flange drilled to one standard will not line up with another. Adapter flanges exist, but they must be planned, not improvised on the day.
• No condensate drain. Horizontal runs should slope away from the engine with a drain at the low point, as the exhaust guidance linked above recommends. Adding a device can change where the low point is.

A Simple Self-Check Before You Call

Walk up to your set (with it switched off and cool) and answer these five questions:

1. Can I see at least one bolted flange pair between the bellows and the stack?
2. Is there a straight section of pipe near that flange, roughly as long as a small cupboard is tall?
3. Is there a beam, wall or floor nearby that could carry a support?
4. Is the flange clean metal, or is it covered in rust flakes and soot streaks?
5. Could a person safely stand next to that spot with tools?

If you answered yes to questions 1, 2, 3 and 5, and the flange looks sound, there is a fair chance your installation can be done without cutting the pipe. If not, a small cut may still be needed, and that is not a failure. It is a design choice made for a better long-term result.

Where the Decision Really Gets Made

The final call on cut versus no-cut comes after a site survey, not before. The surveyor checks the actual bore, the flange standard, the measured back pressure, the available straight run and the support structure. Only then does the device get specified with the right end connections. This order of work is shown step by step in our RECD installation process guide.

For owners, the practical takeaway is simple. Ask for a no-cut installation if your layout allows it, because it is faster and easy to reverse. Accept a planned cut if the surveyor can explain why it gives better back pressure, support or service access. The worst result is not a cut pipe. It is an RECD squeezed into the wrong place just to avoid one.

Frequently Asked Questions

Is a bolt-in RECD less effective than a welded one?

No. The treatment happens inside the device. As long as the joints are sealed and gas cannot bypass the core, the connection method does not change how well it works.

Can a clamp-on connection handle exhaust temperatures?

Properly rated exhaust clamps and flanges are designed for this service. The key is using hardware rated for the actual temperature and gas pressure, with fresh gaskets.

If no cutting is done, can the RECD be removed later?

Yes, and this is one of the biggest benefits. Keep the spool piece that was taken out. Refitting it returns the line to its original form.

Will a no-cut install mean less paperwork?

The compliance paperwork for the RECD itself stays the same. What may reduce is the site safety paperwork, since a bolt-in job may not need a full hot work permit. Check with your safety officer.

Do canopy sets always need a cut?

Not always. Many canopy installs use the silencer outlet flange or a flanged adapter on the exit stub. It depends on how the canopy manufacturer built the exhaust exit.

What does Aceget need to assess my set?

Clear photos of the exhaust route and nameplates, plus the kVA rating and site location. Send us your details and our team will tell you whether your line looks like a bolt-in candidate before a survey visit is booked.

Final Word

An RECD does not demand a cut pipe. It demands a sealed, supported, serviceable break in the exhaust line with enough straight run and a sensible back pressure budget. Many generators already have that break in the form of a silencer flange or an intermediate joint. Where they do not, a single well-planned cut is a small price for a device that will sit correctly for the next decade.

If you would like a second opinion on your own layout, share your exhaust photos with the Aceget team through our contact page. For general servicing expectations after installation, OEM guidance such as Kirloskar’s RECD page (which cites maintenance once every six months or 500 hours) gives a useful benchmark, and it is one more reason to choose a location that is easy to reach.