Section 12 Turbochargers

12.1 General

12.1.1 Turbochargers are to be approved, either separately or as a part of an engine.

12.1.2 The requirements escalate with the size of the turbochargers. The parameter for size is the engine power (at MCR) supplied by a group of cylinders served by the actual turbocharger, e.g. for a V-engine with one turbocharger for each bank, the size is half of the total engine power. Turbochargers are categorised in three groups depending on served power by cylinder groups with:

Category A: ≤ 1000 kW
Category B: > 1000 kW and ≤ 2500 kW
Category C: > 2500 kW

12.1.3 Plans and particulars are to be submitted as required by Pt 10, Ch 1, 1.4 Submission requirements 1.4.4.

12.1.4 Alarms and slowdowns for turbochargers are required as listed in Table 1.7.1 Engines for propulsion purposes: alarms and safeguards slow-downs and Table 1.7.3 Auxiliary engine alarms and safeguards.

12.1.5 Turbochargers are to be designed for the operating conditions defined in Pt 9, Ch 1, 4 Operating conditions. The component lifetime and the alarm level for speed are to be based on 45°C air inlet temperature.

12.1.6 Category B and C turbochargers (new turbocharger types or developments of existing types) are to be Type Approved. A Type test, see Pt 10, Ch 1, 14.2 Turbochargers, is to be carried out on a standard unit taken from the assembly line and is to be witnessed by the Surveyor.

12.1.7 The air inlet of turbochargers is to be fitted with a filter.

12.2 Works testing and inspection

12.2.1 LR Surveyors are to be provided with free access to the manufacturer’s works to inspect, at random, the quality control measures and to witness the tests required by Pt 10, Ch 1, 12.2 Works testing and inspection 12.2.3 as deemed necessary, and to have free access to all control records and subcontractor’s certificates.

12.2.2 Each individual unit is to be tested in accordance with Pt 10, Ch 1, 12.2 Works testing and inspection 12.2.4 to Pt 10, Ch 1, 12.2 Works testing and inspection 12.2.8. For category C turbochargers these tests are to be conducted under survey unless an alternative approach for product assurance has been approved by LR. For category B turbochargers the testing is to be documented by manufacturer’s certificate. For category A turbochargers, test results, documented by manufacturer’s certificate, are only required if specifically requested by LR.

12.2.3 Rotating parts of the turbocharger’s blower are to be marked for easy identification with the corresponding certificate. Component identification is to be in accordance with the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

12.2.4 Material tests (chemical composition and mechanical properties) and dimensional inspection, of the rotating parts and casing are to confirm compliance with the approved design and material specifications (Pt 10, Ch 1, 1.4 Submission requirements 1.4.4). Testing and inspection of turbocharger casings and rotor shafts are to comply with the requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022 as applicable.

12.2.5 Cooling spaces are to be hydraulically tested to 0,4 MPa gauge or 1,5 times maximum working pressure, whichever is higher.

12.2.6 Rotating parts are to be subjected to ultrasonic testing and surface crack detection (magnetic particle testing is to be carried out on ferro-magnetic materials, penetrant testing is only to be carried out on non-ferritic materials). Ultrasonic testing is not required for components manufactured from cast iron.

12.2.7 All rotors are to be dynamically balanced on final assembly.

12.2.8 All compressor wheels are to be overspeed tested for three minutes at either 20 per cent above the alarm level speed at room temperature, or 10 per cent above alarm level speed at 45°C inlet temperature when tested in the actual housing with the corresponding pressure ratio. The overspeed test may be waived for forged wheels that are individually controlled by an approved non-destructive method. This test will not be waived for wheels of the unit to be type tested.

12.3 Certification

12.3.1 Turbochargers are to be delivered with:

Category B turbochargers: A manufacturer’s certificate, which states the applicable type approval, including production assessment.
Category C turbochargers: An LR certificate or LR Quality Scheme Product Certificate as applicable, which states the applicable Type Approval and LR Quality Scheme reference, if applicable.

12.3.2 Where the manufacturer operates an alternative approach for product assurance approved by LR the periodic audits will include specific focus on:

Chemical composition of material for the rotating parts.
Mechanical properties of the material of a representative specimen for the rotating parts and the casing.
UT and crack detection of rotating parts.
Dimensional inspection of rotating parts.
Rotor dynamic balancing.
Hydraulic testing of cooling spaces in accordance with as per Pt 10, Ch 1, 12.2 Works testing and inspection 12.2.5.
Overspeed test of all compressor disks as per Pt 10, Ch 1, 12.2 Works testing and inspection 12.2.8

12.3.3 The above certification and test requirements also apply to replacement rotating parts and casing.

12.4 Matching with engine

12.4.1 Turbochargers are to have a compressor characteristic that allows the engine on which it is installed to operate without surging during all operating conditions. For abnormal, but permissible, operation conditions, such as misfiring and sudden load reduction, no continuous surging is to occur.

Note Surging and continuous surging are defined as follows: Surging means any phenomenon, which results in a high pitch vibration of an audible level or explosion-like noise from the scavenger area of the engine. Continuous surging means that surging happens repeatedly and not only once.

12.4.2 Category C turbochargers used on propulsion engines are to be tested to ensure an adequate operating margin without surge occurring during the engine works trials as specified below. These tests may be waived if successfully tested earlier on an identical configuration of engine and turbocharger (including same nozzle rings).

For trunk piston engines the following are to be performed without indication of surging:
1. With maximum continuous power and speed (i.e. 100 per cent), the speed is to be reduced with constant torque (fuel index) down to 90 per cent power.
2. With 50 per cent power at 80 per cent speed (i.e. propeller characteristic for fixed pitch), the speed is to be reduced to 72 per cent while keeping constant torque (fuel index).
For crosshead engines the surge margin is to be demonstrated by at least one of the following methods:
1. The engine working characteristic established at workshop testing of the engine is to be plotted into the compressor chart of the turbocharger (established in a test rig). There is to be at least a 10 per cent surge margin in the full load range, i.e. the working flow is to be at least 10 per cent above the theoretical (mass) flow at the surge limit (at no pressure fluctuations).
2. Sudden fuel shut-off to at least one cylinder is to not result in continuous surging and the turbocharger(s) is/are to stabilise at the new load within 20 seconds. For applications with more than one turbocharger, the fuel is to be shut-off to the cylinders immediately upstream of each turbocharger. This test is to be performed at two different engine loads:
  - The maximum power permitted with one cylinder misfiring.
  - The engine load corresponding to a charge air pressure of about 0,6 bar (but without auxiliary blowers running).
3. Sudden power reduction from 100 per cent to 50 per cent of the maximum continuous power is not to result in continuous surging and the turbocharger(s) is/are to be stabilised at the new load within 20 seconds.