Low-Profile Soot Washing Nozzles for
Telescopic & Concentric Exhaust Ducts
The most common reason a marine soot washing system cannot be retrofitted into an existing telescopic exhaust duct installation is not flow rate, not operating pressure, and not chemical compatibility — it is nozzle body protrusion depth. Standard spray nozzles protrude 30–80 mm from the pipe wall into the duct interior. Telescopic slip-joints on cruise ship and ferry HVAC and exhaust systems typically have 12.5–25 mm of radial clearance between the inner and outer duct sleeves. A standard nozzle body installed at this position will catch on the slip-joint, shear off under thermal expansion cycling, or block duct axial movement entirely.
Marine Low-Clearance Telescopic Exhaust Duct: Spec at a Glance
This is the structured specification block for engineers searching by exact constraint. All parameters are specific to telescopic slip-joint soot washing installations with radial clearance below 25 mm.
Low-Profile Soot Washing Nozzle Specification
Telescopic exhaust duct soot washing on cruise ships and large ferries requires low-profile right-angle flat-fan deflector nozzles that mount flush against the inner duct wall with a protrusion depth below 15 mm. The nozzle's supply connection enters through the duct wall radially, the nozzle body sits below the inner wall surface, and a deflector plate redirects the jet from the radial supply direction into a wide flat-fan spray pattern of 115°–130° that washes the duct interior surface. The entire wetted assembly protrudes less than 15 mm into the duct airspace — well within the 12.5–25 mm radial clearance available in a telescopic slip-joint.
The standard metallurgy is Duplex EN 1.4462 / UNS S31803. Soot washing condensate — water that has contacted soot deposits in a marine exhaust duct — is weakly acidic (pH 3–5) from dissolved carbon dioxide and sulfur compounds. Over multi-year service between dry-dock intervals, this condensate causes pitting corrosion in 316L SS nozzle bodies at the duct wall interface. Duplex 1.4462 provides the corrosion resistance margin needed for reliable service across a full dry-dock cycle.
Why Standard Nozzles Cannot Be Used in Telescopic Duct Slip-Joints
The telescopic exhaust duct is one of the most space-constrained spray installation environments in marine engineering. Understanding exactly why the geometry excludes standard nozzle designs is the starting point for specifying the correct solution.
Low-Profile Right-Angle Deflector Flat-Fan Nozzles: How They Solve the Geometry
The right-angle deflector flat-fan nozzle is purpose-designed for installations where the supply connection must approach radially but the spray direction must be parallel or near-parallel to the wall surface — exactly the geometry demanded by a telescopic slip-joint soot wash installation.
The Right-Angle Deflector Geometry
How a radial supply connection produces a wall-parallel spray fanThe right-angle deflector flat-fan nozzle consists of a low-profile body that connects to the duct wall through a radial threaded or flanged penetration, and a precision-machined deflector plate positioned directly in the path of the supply fluid. The incoming fluid jet from the supply connection impinges on the deflector plate surface, which redirects and fans the jet through 90° into a wide flat-fan pattern oriented parallel to the duct wall surface.
The critical dimension is the protrusion depth — the distance from the inner face of the duct wall to the furthest point of the nozzle assembly into the duct airspace. On correctly specified low-profile deflector nozzles for telescopic duct service, this protrusion depth is below 15 mm, achieved by keeping the deflector plate close to the wall face and machining the nozzle body to be as compact as possible in the protrusion direction. The supply connection hardware (threaded fitting, lock nut, compression gland) is entirely on the exterior of the duct wall and contributes nothing to the protrusion depth.
115°–130° Wide-Angle Coverage from a Near-Flush Position
Full circumferential surface contact from minimal standoffThe spray angle delivered by the right-angle deflector nozzle in soot washing service must achieve complete circumferential coverage of the duct interior surface from the nozzle's near-flush mounting position. For a duct with 600–1,200 mm internal diameter — the typical range for main engine exhaust ducts on cruise ships and large ferries — the required spray angle to achieve full-width coverage from a nozzle mounted at the duct wall (approximately 300–600 mm from the duct centreline) is 115°–130° wide-angle flat fan.
This is a significantly wider angle than most standard flat-fan nozzles, which are typically available in 65°–110°. The 115°–130° range is the key specification that distinguishes soot washing deflector nozzles from general flat-fan nozzles — it is what provides coverage across the full duct cross-section from a near-wall mounting position rather than from the duct centreline where a wider standoff distance would make standard angles adequate.
Calculating Soot-Removal Impact Force: Flow Rate, Pressure, and the Turbocharger Back-Pressure Limit
Marine exhaust duct soot deposits are carbonaceous — primarily composed of partially combusted heavy fuel oil residues that are both adhesive and hydrophobic. Simply wetting the duct surface with a fine mist is insufficient; the water jet must deliver enough mechanical impact force at the duct wall surface to physically shear the soot deposit from the metal substrate. At the same time, the total water volume injected into the duct during the wash cycle must not exceed the drainage capacity of the duct system — water backing up into the turbocharger or auxiliary boiler casing is a serious mechanical damage risk.
The Impact Force Requirement for Carbonaceous Soot Removal
Carbonaceous marine exhaust soot has an adhesion strength to steel surfaces of approximately 5–25 kPa, depending on soot age, fuel oil sulfur content, and whether the deposit has been repeatedly wetted and dried (which consolidates the soot layer and increases adhesion). Removing this deposit requires a shear stress at the soot-steel interface that exceeds the adhesion strength — which in a spray washing context is delivered by the dynamic pressure of the water jet at the wall surface.
The dynamic pressure of a water jet at the target surface is given by: P_dynamic = ½ × ρ × v² — where ρ is the water density (approximately 1,000 kg/m³) and v is the jet velocity at the surface (in m/s). For a flat-fan nozzle producing a jet with exit velocity of 15 m/s at the nozzle (achievable at 4–6 bar supply pressure for typical soot wash nozzle orifice sizes), the dynamic pressure at the nozzle exit is approximately 112 kPa — well above the adhesion strength range for most fresh marine exhaust soot. However, the jet decelerates as it travels across the duct cross-section; at the opposite duct wall (300–600 mm from the nozzle), the dynamic pressure has dropped by 40–70% due to air resistance and jet spreading. This is why the spray angle, supply pressure, and duct diameter must all be used together to calculate the actual impact pressure at the most distant point of the coverage zone — not the jet exit velocity alone.
The Turbocharger Back-Pressure Limit: Why Wash Cycle Timing Matters
The total water flow rate injected into the exhaust duct during a soot wash cycle must not exceed the drainage flow capacity of the duct drainage system — typically 50–150 liters per minute for a main engine exhaust duct, depending on the drain line diameter and the duct inclination. If the injected water exceeds the drainage rate, the duct floods: water level rises in the duct until it reaches the turbocharger exhaust inlet flange, where water ingestion into the turbine causes immediate and severe mechanical damage. This is why soot washing systems are always specified with a maximum total flow rate constraint derived from the drainage system capacity — and why wide-angle coverage from fewer high-flow nozzles is often preferred over fine-coverage from many low-flow nozzles in this application. More nozzles at the same supply pressure means more total water volume; the array must be sized so that total flow across all active nozzles simultaneously does not exceed the duct drain capacity with a safety factor of at least 1.5.
Multi-Stage Concentric Duct Wash Systems
Many cruise ship HVAC exhaust and funnel installations use multi-stage concentric duct designs — multiple coaxial duct sleeves of progressively smaller diameter that provide thermal insulation, structural support, and acoustic attenuation. Each concentric sleeve presents its own soot washing challenge: the innermost sleeve sees the highest soot deposit rate (it is the hottest surface in closest contact with the exhaust gas), but it also has the smallest diameter and the tightest available clearance for nozzle installation at each sleeve interface.
For a three-stage concentric exhaust duct installation, a complete soot washing system requires three separate nozzle rings — one at each sleeve interface — each sized for the internal diameter of that sleeve stage, each using deflector nozzles with protrusion depths confirmed to be within the clearance at that specific interface. The spray angle at each ring must be recalculated for the different internal diameter at that stage. Contact NozzlePro with the internal diameter at each concentric stage, the available radial clearance at each slip-joint, and the estimated soot deposit thickness for a position-by-position specification.
- Confirm nozzle protrusion depth throughout the full axial travel range — measure clearance at the cold (minimum) and hot (maximum expansion) positions of the slip-joint; specify the nozzle protrusion depth against the cold minimum clearance, which is the tightest condition
- Calculate total system flow rate before finalising nozzle count — divide the duct drainage system capacity by 1.5 (safety factor) to get the maximum allowable total nozzle flow rate; divide by the number of nozzle positions to get the maximum per-nozzle flow rate; select the orifice size that delivers this flow at the design supply pressure
- Specify Duplex 1.4462 throughout — 316L SS nozzle bodies at the slip-joint installation position are exposed to soot wash condensate at pH 3–5 and residual duct heat up to 150°C during and immediately after wash cycles; Duplex 1.4462 provides reliable long-term service across this combined chemical and thermal environment
- Include a wash cycle interlock with the main engine and turbocharger status — soot washing should be performed only when the exhaust system is in a defined thermal state; washing during operation at very high exhaust temperatures can cause thermal shock to soot deposits, converting a controlled chemical wash into an uncontrolled thermal fracture event that generates large soot slugs rather than dissolved removal
- Inspect deflector plates at each planned maintenance interval — the deflector plate is subject to combined erosion from the supply water jet and corrosion from soot condensate; measure the deflector plate surface condition and the resulting spray angle at each inspection; replace when the spray angle has deviated more than ±5° from the specified value
Soot Washing Nozzle Selection by Duct Type and Clearance
Contact NozzlePro with the duct internal diameter at the installation position, the available radial clearance at the slip-joint, the duct drain capacity, and the estimated soot deposit characteristics. Spray angle and orifice size must be calculated for your specific geometry.
| Application | Nozzle Type | Spray Angle | Protrusion | Critical Requirement | Material |
|---|---|---|---|---|---|
| Telescopic slip-joint — standard cruise ship (12.5–25 mm clearance) | Right-angle flat-fan deflector | 115°–130° | <15 mm | Protrusion confirmed within clearance at cold (minimum) slip-joint position; 3–6 positions per ring; verify coverage calculation at duct ID | Duplex 1.4462 |
| Concentric duct outer sleeve (25–50 mm clearance) | Right-angle flat-fan deflector or low-profile flat-fan | 110°–130° | <25 mm | More clearance available — low-profile flat-fan may be acceptable if body depth is confirmed; still specify Duplex 1.4462 for soot condensate service | Duplex 1.4462 |
| Straight exhaust duct — no slip-joint (open installation) | Standard flat-fan or full-cone | 65°–120° | Standard | No protrusion constraint — standard nozzle geometry acceptable; still specify Duplex 1.4462 for soot condensate corrosion resistance | Duplex 1.4462 |
| Funnel uptake soot wash — multi-stage concentric (tight inner sleeve) | Right-angle flat-fan deflector, per-stage sizing | 115°–130° per stage | <15 mm per stage | Separate nozzle ring and spray angle calculation required at each concentric stage; recalculate for each stage internal diameter; supply NozzlePro with per-stage dimensions | Duplex 1.4462 |
| Turbocharger pre-wash nozzle — compressor side | Solid-stream or narrow flat-fan, high impact | 10°–30° | Per OEM spec | Follow turbocharger OEM water washing procedure; high-impact jet to dislodge compressor fouling; flow rate per OEM specification only; Duplex or 316L SS per OEM guidance | Per turbocharger OEM |
Materials for Marine Duct Soot Washing
All NozzlePro soot washing nozzles manufactured under ISO 9001. Classification society submission using NozzlePro hardware is the customer's responsibility.
The Duct Clearance Is the Constraint. Specify the Nozzle Around It.
Provide NozzlePro with your duct internal diameter, radial clearance at the slip-joint, axial travel range, drain system capacity, and operating temperatures. We size the deflector nozzle protrusion depth, spray angle, and orifice to your specific geometry — not to a catalog default.