Product information

SIKOThe Safety Design Concept

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Safety Design Concept SIKOSIKO is ABB Turbocharging’s Safety Design Concept forenhancing the reliability and safety of ABB turbochargers and for making their life cycle costs more predictable.

Over the past decade the output of diesel and gas engineshas been steadily increased, presenting the turbochargermanufacturer with the challenge of continually increasing thecompressor pressure ratio. Whereas in the past, turbochargerscould be operated with large design margins, the higher performance required today calls for design solutions which lie much closer to the physical limits of the turbochargers. The load factor for the rotating components in particular hasincreased dramatically – turbochargers are turning faster and faster.

At the same time, expectations regarding the reliability andsafe operation of the equipment have grown considerably.Plus there is also demand within the industry for reduced lifecycle costs and optimized maintenance of the engines andturbochargers. ABB Turbocharging addresses this issue withits Safety Design Concept “SIKO”.

SIKO is a calculation tool for determining the speed and temperature limits of turbocharger rotor components for givenexchange intervals. The program is available for the olderVTR. .4, VTC. .4 and RR. .1 turbocharger families as well asfor today’s TPS, TPL, TPR and A100 series. SIKO is regularlyupdated to keep it state-of-the-art and will also be implementedfor coming ABB turbocharger generations.

Turbine power 10,000 kW

Centrifugal force97 tons /blade

Revolutions9,900 rpm

Tip velocity480 m/s ~ 1,750 km/h

Fig. 1: TPL 91-B rotor – some key figures

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Why SIKO?Turbocharger rotor components are subject to extremely highloading under operating conditions (Fig. 1). The high rotatingspeed, for example, has the effect of producing very highkinetic energy inside the turbocharger. Failure of a rotor com-ponent often leads to total loss of the turbocharger, and thuscostly downtime.

SIKO was created to increase turbocharger reliability, maximizesafety and make life cycle costs more predictable by adoptingthe principle of preventive maintenance instead of “break andfix”.

Modules of the Safety Design ConceptSIKO consists of four modules (Fig. 2), designed specificallyto determine

Load profiles, i.e. turbocharger operating conditionsMaterial propertiesStress and material temperature distributionsSpeed and temperature limits using a damage accumulation method.

1

2

3

4

SIKO modules

Material properties2Load profile

t

Safety Design Concept

t, N

1

Stress analysis, temperature distribution3

Calculation of speed limit

damage

accumulation

method

4

t, N

σ

ABB Turbo Systems LtdTurbocharger

Type HT

n

nBmax

tMmax

tBmax

1

S °C

kg

made in Switzerland

Application according to

the Operation Manual

HZ

TL 4

28 7

65 P

2

nBmax

Mmax

Fig. 2: Structure of the Safety Design Concept

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SIKO modules1. Turbocharger operating conditions.

Knowledge of how the rotor components be have in operationis a key element of SIKO. The load profile for a turbocharger –load versus time and versus the number of load cycles (Fig. 3)– is not the same, for example, for a container vessel and alocomotive. Similarly, it is different for a base load power plant and a hospital emergency unit. Even within marine applica-tions, the load profiles can be completely different.

ABB designed special data loggers, similar to the “black box”in aircraft, in order to measure and collect real world turbo -charger operation data over an extended period of time, typi-cally four to six months and in some cases up to one year.This measuring device has allowed ABB to determine loadprofiles for a wide range of engine applications. Over theyears, the company has built up a huge database and accu-mulated a wealth of information and knowledge about the real world operating conditions of turbochargers used in many different engine applications.

The measurements include the turbocharger speed and thetemperatures at the compressor and turbine inlets. The two-part load profile (Fig. 3) allows an evaluation of the creep andfatigue loading of the rotor components.

Load

Time Number of cycles

Load

Fig. 3: Load profile

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ABB carried out extensive tests to determine the materialproperties, i.e. the tensile strength, yield strength, creepstrength and fatigue strength. Fig. 4 shows the effect on thecreep rupture strength of increasing temperature, and Fig. 5the fatigue strength.

The material properties are obtained by means of tests carriedout on laboratory specimens. One important aspect of thematerial properties is the statistical scatter. This is clearly seen,for example, when several specimens with the same geometryare loaded at the same stress level and at the same tempera-ture. The time until failure will vary strongly. It is usually neces-sary to repeat a test at the same stress and temperature levelseveral times in order to obtain statistically significant material properties. Such tests demand special laboratory resourcesand run for a very long time – a 100,000 hour creep test, forexample, lasts all of 11 years.

SIKO modules2. Determination of material properties.

Str

ess a

mp

litu

de

Number of cycles

Fig. 5: Fatigue strength curve

Cre

ep

ru

ptu

re s

tren

gth

Time

Increasing temperature

Fig. 4: Creep rupture strength development

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SIKO modules3. Stress and material temperature distribution.

Finite element analyses are carried out to obtain the stressand material temperature distribution in the rotor components.These analyses identify the critical locations and determinethe local stress and material temperature as a function of theturbocharger speed and the suction air and exhaust gas tem-peratures.

Stress distribution in the rotor components of a turbochargervaries greatly according to the geometry of the part. Finite element analyses have therefore been carried out for everydesign of the compressor wheel and turbine. SIKO also takesaccount of the thermal stress caused by temperature distribu-tion in the component and, in the case of compressor wheelswith a center bore, even the prestresses induced by spinningduring manufacture.

Disk

Backwall

Hub

Damping wire

Blade at dampingwire hole section

Blade

Fir tree rootof blade

Turbine disk atfir tree profile

Center of hub

Fig. 6: Typical critical locations in a TPL compressor wheel Fig. 7: Typical critical locations in a TPL turbine

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Figs. 6 and 7 show typical critical locations in a compressorwheel and in a turbine. Figs. 8 and 9 show a finite element net of a compressor wheel and its stress distribution underoperating conditions.

The material temperature strongly influences the materialproperties, and thus the speed limit and exchange interval forthe rotor components. In addition, the temperature distribu-tion induces thermal stress in the components, as alreadymentioned. SIKO therefore takes full account of the influenceof temperature. Extensive measurements carried out onturbo chargers provided the basis for the calculation and calibration of the temperature distributions. The suction airtemperature and exhaust gas temperature at the turbine inlet,for example, directly influence the temperature level in thecompressor wheel and turbine.

Fig. 8: Finite element model of a compressor wheel Fig. 9: Stress distribution under operating conditions

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SIKO modules4. Calculation of speed and temperature limits using thedamage accumulation method.

The turbocharger speed and the inlet temperatures are the parameters directly responsible for the loading of rotorcomponents.

When the material properties, the stress distributions and thematerial temperature distributions are all known, it is possibleto determine the speed and temperature limits for the requiredexchange intervals.

Calculations are performed for every critical location in thecompressor wheel and turbine. SIKO makes use of the lineardamage accumulation method according to Palmgren-Miner(Fig. 10). An accumulated damage value of 1.0 represents thetime at which the ex change becomes due. The speed limit forthe complete component is determined by the lowest speedlimit at one of the critical locations.

The following parameters strongly influence the speed limitand exchange intervals of the rotor components:– Turbocharger speed profile (speed level and speed cycles)– Suction air temperature– Exhaust gas temperature at turbine inlet

Based on the application and ambient conditions, ABB recommends speed and exhaust gas temperature limits aswell as ex change intervals for the rotor components, allowingsafe and reliable operation from the beginning. This infor-mation is given on the rating plate of every delivered turbo-charger. In some applications, e.g. where a higher speed limit is required or when the load profile features many moreload cycles, certain restrictions may be introduced. Thesecould require, for example, shorter exchange intervals or theuse of special materials, such as titanium for the compressorwheel, as a further means of ensuring reliable turbochargerservice and avoiding cost intensive downtime of the equip-ment.

Fig. 10: Linear damage accumulation according to Palmgren-Miner

Time

T = constant

Str

ess

ti

tTi

nk

nfk

Number of cycles

T = constant

Str

ess

To prevent a fatigue fracture the followinglaw has to be observed:

∑�nk� ≤ 1nfk

For combined creep and fatigue loading the following law has to be observed:

�∑�ti� + ∑�nk�� ≤ 1tTi nfk

To prevent a creep fracture the following lawhas to be observed:

∑�ti� ≤ 1tTi

1.

2.

3.

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The results of the SIKO evaluation, i. e. the turbochargerspeed and temperature limits as well as the recommendedexchange intervals, are given on the rating plate (Fig. 11) of every delivered turbocharger. Operating the turbochargerbeyond the specified exchange interval increases the risk offailure. Timely replacement of the rotor components accordingto the rating plate is a major factor in trouble free turbo-charger operation and can prevent costly downtime.

Information on the rating plate

ABB Turbo Systems LtdTurbocharger

Type HT

n

nBmax

tMmax

tBmax

1

S °C

kg

made in Switzerland

Application according to

the Operation Manual

HZ

TL 4

28 7

65 P

2

nBmax

Mmax

Turbocharger operational limits at engine overload (110 %)

in test rig operation only

Turbocharger operational limits in service

Recommended exchange interval for the compressor wheel

Recommended exchange interval for the turbine

� �

� �

� �

� �

� ���

Fig. 11: Turbocharger rating plate

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SIKO benefits for the customer

ABB turbochargers are designed to perform efficiently andreliably in all operating environments. SIKO was developed to ensure that this performance is maintained over every turbocharger’s operating life. Systematically applied by theglobal ABB Turbocharging Service network and product support organization, SIKO provides customers with a highlyuseful tool for optimizing maintenance and minimizingunplanned downtime of equipment. SIKO is an excellent toolfor the proactive planning of overhauls, thereby helping to prevent avoidable serious breakdown which could affect theprofitability and reputation of a customer’s company.

ABB Turbo Systems LtdBruggerstrasse 71 aCH-5401 Baden/SwitzerlandPhone: +41 58 585 7777Fax: +41 58 585 5144E-mail: turbocharging@ch.abb.com

www.abb.com/turbocharging

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