How to Manage Scope Changes After an RECD Order Is Placed

The purchase order went out on a Monday. By Thursday, the site engineer calls: the exhaust run from the DG room to the terminal point is six metres longer than the survey sketch showed, with two extra bends. A week later the housing society committee asks whether the unit can sit on the roof instead of the stilt parking. Then the facility head mentions that a second generator, bought last year, also needs a device before the winter restrictions begin. None of this is unusual. It is simply what an RECD scope change looks like in real life, and how you handle it decides whether the project lands on time or drifts into disputes.

Retrofits differ from new installations. You are fitting a device onto a generator, exhaust and building designed years earlier, often with missing drawings and altered pipe routes. Surprises are normal. What hurts is a change that nobody writes down, prices or checks against the certification of the model being supplied.

Unmanaged changes cost you in five ways. The price creeps up through informal “extra work” bills. The schedule slips because fabrication restarts. The supplied model may no longer match the engine it was certified for. Warranty terms get muddy when the installation departs from the approved drawing. And in regions with seasonal restrictions, such as the GRAP rules for DG sets in Delhi NCR, a two-week slip can mean a generator that cannot legally run when you need it most. This guide organises change management around one idea: the later a change arrives, the more it costs, so the process should match the stage.

What Counts as a Scope Change (and What Does Not)

Many disputes start because the buyer calls something a clarification and the vendor calls it a variation. The scope itself is usually fixed by the purchase order, the technical offer and the bill of quantities for the RECD retrofit. Anything outside those documents is a candidate for a change; anything inside them is not.

Category	What it means	Example	Who usually bears the cost
Scope change	The buyer asks for something different from, or additional to, the agreed scope	Moving the RECD from ground level to the terrace; adding a second DG set	Buyer, through an agreed RECD change order
Clarification	Detail the contract left open is confirmed, without adding work	Confirming flange orientation or paint shade within the quoted specification	No cost change, as long as it stays within the original intent
Defect correction	Work that does not meet the agreed specification is put right	Wrong flange size supplied, mismatched gasket, missing nameplate	Vendor
Buyer-side delay	The buyer’s site, access, approvals or information hold up the vendor	DG room not ready, shutdown not given, civil plinth incomplete	Usually buyer for idle time and remobilisation, subject to the contract
Vendor-side deviation	The vendor proposes something different from the specification	Alternative mounting arrangement to save space	Vendor proposes; buyer accepts or rejects in writing

Vendor-proposed deviations deserve a special mention, because they often arrive dressed as helpful suggestions. Treat them exactly as you would treat deviations at the offer stage, with the same discipline described in our guide on how to review deviations in an RECD technical offer.

The Cost-of-Change Curve: Five Stages

At each project stage, more decisions get locked into steel, paperwork and site work. A change that costs a phone call in week one can cost a fresh fabrication slot in week five. Use the stage to decide how formal the process needs to be.

Stage 1: Before Drawing Approval

Typical changes: corrected exhaust pipe diameter after a fresh site measurement, updated generator nameplate data, a change of preferred location, an extra inlet or outlet transition piece.

What it affects: mostly the general arrangement drawing and the bill of materials.

How to handle it: send the change in writing, ask the vendor to revise the drawing and confirm whether the price or delivery moves. If the generator details are the issue, sending clear DG nameplate photos at this point avoids a much bigger problem later.

Rule of thumb: this is the cheapest moment to change your mind. Hold back drawing approval until the site survey is genuinely complete.

Stage 2: After Drawing Approval, Before Manufacture

Typical changes: switching from horizontal to vertical mounting, adding a bypass or inspection port, changing flange standards, asking for a different support frame.

What it affects: the approved drawing, material procurement and the production slot. Raw material may already be ordered.

How to handle it: raise a formal change request. Ask for a revised drawing with a new revision number, a written statement of any price and time impact, and confirmation that the certified internals are unaffected. Orientation changes look simple but can alter drain points and access, so read up on horizontal versus vertical RECD mounting layout before asking for one.

Rule of thumb: once a drawing is signed, every change needs a revision number. No revision number, no change.

Stage 3: During Manufacture or After Factory Testing

Typical changes: different inlet connection, extra insulation or cladding, an alarm or monitoring panel added, a change of the generator to be fitted.

What it affects: fabricated parts, factory test records, the dispatch date and sometimes the inspection already witnessed.

How to handle it: ask the vendor to separate the change into what can be done as a site-fitted accessory and what genuinely needs factory rework. Many add-ons, such as monitoring hardware or extra transition pieces, can be supplied loose. If factory test records need repeating, agree who pays and whether you will witness again.

Rule of thumb: if it can be bolted on later, do not reopen the factory build.

Stage 4: After Delivery, Before Installation

Typical changes: the location moves because a neighbour objected, the civil team cannot cast the plinth where planned, the exhaust route has to avoid a newly installed duct.

What it affects: site fabrication, supports, lifting arrangements and the installation team’s schedule. The device itself is usually unchanged, but everything around it changes.

How to handle it: complete the RECD delivery inspection checklist first, so that any transit damage is recorded separately from the change. Then ask for a revised installation drawing and a fresh estimate of extra pipework, supports and labour. If the device was delivered early for a building still under construction, see the notes on ordering an RECD before your new facility is ready, including storage and preservation.

Rule of thumb: keep delivery acceptance and change requests on separate pieces of paper.

Stage 5: During Installation and Commissioning

Typical changes: an extra bend to clear a beam, retaining the old silencer after all, adding a sampling port, extending the stack to meet a height requirement.

What it affects: backpressure, commissioning readings, acceptance testing, and the documents that go into your compliance file.

How to handle it: name one person on site who can approve small changes up to a pre-agreed value, and require everything else to go back through the full workflow. Any change in the exhaust path should trigger a backpressure check before the generator runs on load. Confirm that the agreed acceptance criteria for the RECD trial installation still apply, or revise them in writing.

Rule of thumb: on-site decisions are fast but expensive. Pre-authorise a small limit and escalate everything above it.

The Most Common RECD Scope Changes and Their Ripple Effects

A change rarely touches only one thing. Moving a device a few metres can alter pipe length, supports, backpressure and even slab approval. The table traces the most common ones.

Change	Technical impact	Commercial impact	Compliance or certification impact
Longer exhaust run	Higher backpressure, more bends, possible change in device position along the run	Extra pipe, insulation, supports and labour	Backpressure must stay within engine maker’s limit; position may affect inlet temperature
Relocation indoor to rooftop	New lifting plan, structural check, longer vertical run, weather exposure	Crane or hoist, structural consultant, extra steel	Society or building approvals; installation must still match approved drawing
Change of DG set or engine	Exhaust flow and temperature may differ even at the same kVA	Possible change of model or size	Must confirm the engine’s gross kW falls within the certified power range of the model
Adding a second set	Separate device per exhaust outlet; new survey needed	New line item, often at agreed unit rate	Each set needs its own documentation and certificate reference
Silencer removal or retention	Changes overall backpressure and noise profile	Credit for removal work or extra for retention supports	Noise norms for DG sets still apply; check before removing anything
Insulation or cladding added	Heat retention, surface temperature, service access	Material and labour	Usually none, provided inspection ports stay accessible
Alarm panel or remote monitoring added	Sensors, cabling, power supply, panel location	Hardware, wiring and configuration	Helps evidence of operation; no change to certification
Change of mounting orientation	Drain points, support design, clearances	Redesign and possibly refabrication	Must remain within the arrangement permitted by the manufacturer
Change of fuel to dual fuel	Exhaust temperature and soot profile may shift	Review of model suitability	Confirm with manufacturer that the device remains suitable after conversion

A few of these deserve more reading before you raise the change. If the run has grown, our article on where to position an RECD along a long exhaust run explains why the answer is not always “as close to the engine as possible”. For a move to the terrace, the planning steps in rooftop RECD installation, structural support and lifting access will help you scope the extra work properly.

An engine swap is the change people underestimate most. Two generators with the same kVA badge can have quite different engines, which is why same-kVA DG sets may need different RECDs. Silencer questions come up often too, and the short answer to whether an RECD can replace a generator’s exhaust silencer depends on the device and the site’s noise obligations. If the generator is being converted to gas blending, read about fitting an RECD after a diesel to dual fuel conversion before you sign anything.

A Six-Step Change Request Workflow

A change request DG retrofit process does not need to be heavy, only consistent. These six steps suit a single society generator or a multi-site programme.

1. Raise a written request. Whoever wants the change, buyer or vendor, puts it in writing with a reference number. Email is fine if it follows a standard format.
2. Vendor impact assessment. The vendor responds within an agreed period, for example three to five working days, stating whether the change is feasible and what it touches.
3. Technical review. Check the change against the engine data, the certified model range and the installation layout. Any change to pipe length, bends or terminal height should include a backpressure recalculation, because exhaust backpressure affects the DG set directly.
4. Price and time. The vendor quotes the cost and schedule impact, using the agreed pricing method. A change that saves money should show a credit, not just a silence.
5. Approval by an authorised signatory. Only the person named in the contract approves. A site supervisor nodding at a welder is not approval.
6. PO amendment and drawing revision. Issue a purchase order amendment for the RECD and a revised drawing with a new revision letter. Update the project schedule and the milestone plan at the same time.

If payment is linked to milestones, a change can move a milestone date or add a new one. Agree that explicitly, using the structure in our guide to RECD payment milestones and project deliverables, rather than leaving it to be argued at invoice time.

Change Request Form Fields

A one-page form is enough:

• Change request number and date
• Project name, site address and PO reference
• Raised by (name, organisation, role)
• Description of the change and reason for it
• Current project stage (drawing, manufacture, delivered, installation)
• Drawings, photos or measurements attached
• Technical impact, including backpressure and certified range check
• Cost impact (addition or credit) and pricing basis
• Schedule impact in working days
• Effect on warranty, acceptance criteria or documents
• Approved or rejected, signatory name, signature and date
• Resulting PO amendment number and drawing revision

Pricing Variations Fairly

Most friction over a variation order on an RECD job comes from price, not engineering. Agree the pricing method before any change arrives; a good order often uses all three methods below.

Method	How it works	Best for	Watch out for
Unit rate schedule	Rates agreed upfront for items such as per metre of exhaust pipe, per bend, per support, per metre of insulation	Exhaust modification extra work, longer runs, extra supports	Rates must define what is included (fittings, lagging, painting)
Lump sum	A fixed price for a defined change, quoted after the vendor’s assessment	Relocation, added monitoring panel, extra device for a second set	Clear scope description, otherwise the lump sum gets reopened
Time and material with cap	Labour hours and materials at agreed rates, with a ceiling that cannot be exceeded without approval	Unclear site conditions, such as hidden pipework or corroded flanges	Daily timesheets signed by the buyer’s site representative

If your BOQ already lists rates for extra pipe, bends and supports, a longer run becomes arithmetic, not negotiation. How much variation risk you carry also depends on the contract model. Under a supply-only order, site extras often land with your own installer; under a turnkey order, they flow back to the RECD vendor. The trade-offs are covered in supply-only versus turnkey RECD orders, and the split of duties is clearer if you have agreed customer and installer responsibilities at the outset.

What Never to Change Informally

Some items are so closely tied to compliance and liability that they must never move without a signed amendment, however small the change looks on site.

• The RECD model. Swapping a model “because it is in stock” can break the link between your generator and the test certificate. Any model change must be checked against the engine’s gross kW and the certified range.
• The certification reference. The certificate number, testing agency and model designation that appear on your documents must match the hardware on site.
• The warranty start date. Whether warranty runs from dispatch, installation or commissioning should not be reinterpreted because the project slipped. If a change delays commissioning, record the effect on the warranty in the amendment.
• Acceptance criteria. Test conditions, load points and measurement methods agreed for handover should only change in writing, signed by both sides.
• Interfaces with the generator. Changes that affect the engine’s exhaust connection can raise questions with the generator maker. The considerations are set out in our article on whether installing an RECD affects the generator’s OEM warranty.

Worked Example: Change Log for a 500 kVA Factory Retrofit

Here is how a change log might look for a single 500 kVA generator at an engineering factory. The order was placed on a turnkey basis with a unit rate schedule for extra pipework. The figures below are illustrative and describe the kind of entries you should expect, not actual prices.

CR No.	Stage	Change	Technical check	Commercial outcome	Status
CR-01	Before drawing approval	Site re-survey shows exhaust pipe diameter one size larger than enquiry data	Inlet transition revised; model unchanged	No cost change; drawing Rev B issued	Approved
CR-02	After drawing approval	Exhaust run extended by about 6 m with two additional 90 degree bends	Backpressure recalculated; still within engine limit	Charged at agreed unit rates for pipe, bends and supports; 3 working days added	Approved, PO amendment 1
CR-03	During manufacture	Factory asks for a remote alarm for high backpressure	Sensor port added at factory; panel supplied loose	Lump sum for sensor, panel and wiring	Approved, PO amendment 2
CR-04	During installation	Request to retain existing silencer instead of removing it	Combined backpressure checked; additional support needed	Credit for removal labour offset against extra support steel	Approved, net change recorded in amendment 3

Every entry records the stage, which explains why CR-01 was free and CR-02 was not. Every entry carries a technical check, not only a price, and CR-04 nets a credit against a charge in writing. This log joins the handover file and explains the final delivery date if anyone compares it with the original RECD installation timeline.

Protecting Compliance During an RECD Scope Change

The commercial side of a change is visible to everyone. The compliance side is easier to miss. In India, the Central Pollution Control Board issued a circular dated 01.02.2022 setting out the System and Procedure for emission compliance testing of RECDs for DG engines up to 800 kW gross. Devices are tested by recognised agencies such as ARAI and ICAT, and the resulting certificate covers a specific model over a defined engine power range. In the National Capital Region, directions from the Commission for Air Quality Management refer to RECDs with at least 70% PM capture efficiency for in-use DG sets up to 800 kW. State Pollution Control Boards may apply these requirements differently, so check the rules that apply to your site.

Three checks protect you whenever scope moves:

1. Model still covers the engine. If the generator, engine or rating changes, confirm the engine’s gross kW sits within the certified range of the model being supplied. See how to verify a CPCB-tested RECD for your DG set and how to read an RECD test certificate.
2. Installation still matches the manufacturer’s conditions. Orientation, position along the exhaust, and backpressure limits are part of correct installation. A change that breaks them can undermine both performance and warranty.
3. Documents updated for the SPCB file. Update the installation certificate, final drawing, serial number record and photographs. If your consent or NOC application quotes equipment details, the final documents should agree with it. The process for getting a pollution NOC for a DG set is smoother when nothing in the file contradicts anything else.

Sample Clause Language for Change Orders

The wording below is a starting point for discussion with your legal or procurement team. It is not legal advice, and contract terms in India are shaped by the Indian Contract Act and related law, which you can read on India Code. Adapt it to your own order.

“Either party may propose a change to the scope of supply or services by written change request. Within five working days of receipt, the Supplier shall submit an impact assessment stating the technical effect, including any effect on exhaust backpressure and on the certified power range of the RECD model, together with the price and schedule effect calculated in accordance with the rates in Annexure X. No change shall be implemented, and no payment shall become due for any change, until it has been approved in writing by the Purchaser’s authorised signatory and recorded in an amendment to this Purchase Order. Any change that alters the RECD model, its certification reference, the warranty commencement date or the acceptance criteria shall require a formal amendment signed by both parties. Work carried out without such approval shall be at the Supplier’s own cost, except where required to prevent imminent danger to persons or property, in which case the Supplier shall notify the Purchaser within 24 hours.”

The emergency exception allows urgent work without inviting routine extras done first and billed later, the root of most scope creep in RECD installation.

Checklist: Managing Changes on Your RECD Project

1. Complete the site survey, including measured exhaust route, before approving drawings.
2. Include a unit rate schedule for likely extras in the original order.
3. Name the authorised signatory for changes on both sides.
4. Agree a site approval limit for small changes and an escalation route above it.
5. Use a numbered change request form for every variation, however small.
6. Require a backpressure check for any change to the exhaust path.
7. Re-check the certified power range whenever the generator or engine changes.
8. Issue a PO amendment and a revised drawing for each approved change.
9. Record the effect on warranty, milestones and acceptance criteria.
10. Keep a running change log and include it in the handover file.
11. Update compliance documents so the SPCB file matches what is installed.

Frequently Asked Questions

Can I add a second generator to an existing RECD order?

Usually yes, but treat it as a new line item rather than a small change. The second set needs its own survey, engine data check and model selection, because a different engine may need a different device even at the same rating. If your order included a unit price for additional devices of the same model, the commercial side is simple.

Who pays when the exhaust run turns out longer than the survey showed?

It depends on who did the survey and what the contract says. If the buyer provided the measurements, the extra work is normally a buyer-side change priced at agreed rates. If the vendor surveyed the site and missed it, the vendor carries more of the risk.

What if we plan to increase the generator’s load later?

Load growth is a common reason for late changes. If you already expect it, raise it before drawing approval and consult our guide to specifying an RECD for a future generator load increase. Sites where demand rises and falls through the project, such as building sites, face similar questions, covered in RECDs for construction projects with changing power demand.

Does an RECD project variation affect the warranty?

It can, if the change takes the installation outside the manufacturer’s conditions, or if it delays commissioning and nobody records how the warranty start date is affected. Documented, approved changes should not weaken it; informal site modifications are the real risk.

How quickly should a vendor respond to a change request?

A response time of three to five working days for an impact assessment is reasonable for most changes. Write the period into the order.

Conclusion: Plan for Change Before It Arrives

An RECD scope change is not a sign that something went wrong. In retrofit work it is close to certain. What separates a smooth project from a painful one is preparation: a thorough survey, unit rates agreed upfront, a named signatory, a simple form and a habit of checking every change against backpressure, certified range and documentation. Handle changes early where you can, formally where you must, and keep the change log as carefully as you keep the test certificate.

If you are planning a retrofit and want to reduce the chance of late changes, start by looking at our range of CPCB-certified retrofit emission control devices to understand the options for your generator rating. When you are ready to discuss site details, survey requirements or a change on an existing order, get in touch with our team and we will help you work through it.