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Section 7b

Thermal Oil Systems

A. General

1. Scope

The following requirements apply to thermal oil sys-tems in which organic liquids (thermal oils) are heatedby oil fired burners, exhaust gases or electricity totemperatures below their initial boiling point at at-mospheric pressure.

2. Other applicable requirements

In addition, the following GL Rules and Guidelinesare to be applied analogously:

Section 7a, B., C.and D. For materials, fabricationand design of the heaters

Section 8, B., C.and D. For materials, fabricationand design of the expan-sion vessel and the tanks

Section 9, A.and B. For oil burners and oilfiring systems (additional

shutdown criteriasee B.4and C.4)

Section 10, A.,B.and D. For thermal oil tanks

Section 11, A.to D., Q.and R.

For pipes, valves andpumps

Section 12 For fire protection andfire fighting equipment

Chapter 3 ElectricalInstallations

For electrical equipmentitems

Chapter 4 Automation For automated machinery

systems

VI Additional RulesandGuidelines,Part 7 Guide-lines for the Performanceof Type Approvals

For type approved com-ponents

3. Definitions

3.1 The "maximum allowable working pressure"is the maximum pressure which may occur in theindividual parts of the equipment under service condi-tions.

3.2 The "thermal oil temperature" is the tempera-ture of the thermal oil at the centre of the flow cross-section.

3.3 The "discharge temperature" is the tempera-ture of the thermal oil immediately at the heater outlet.

3.4 The "return temperature" is the temperatureof the thermal oil immediately at the heater inlet.

3.5 The "film temperature" is the wall tempera-ture on the thermal oil side. In the case of heated sur-faces, this may differ considerably from the tempera-ture of the thermal oil.

4. Documents for approval

The following documents are to be submitted for ap-proval:

a description of the system stating the dischargeand return temperatures, the maximum allow-able film temperature, the total volume of thesystem and the physical and chemical character-istics of the thermal oil

drawings of the heaters, the expansion vesseland other pressure vessels

pipingandequipmentschedules(forinformation)

circuit diagrams of the electrical control system,respectively monitoring and safety devices withlimiting values

a functional diagram with information about thesafety devices and valves provided (for informa-tion)

If specially requested, mathematical proof of themaximum film temperature in accordance with DIN4754 is to be submitted.

5. Thermal oils

5.1 The thermal oil has to remain serviceable forat least 1 year at the specified thermal oil temperature.Its suitability for further use is to be verified at appro-priate intervals, but at least once a year.

5.2 Thermal oils may only be used within thelimits set by the manufacturer. A safety margin ofabout 50 C is to be maintained between the dischargetemperature and the maximum allowable film tem-perature specified by the manufacturer.

5.3 Precautions are to be taken to protect thethermal oil from oxidation.

5.4 Copper and copper alloys are to be avoideddue to their catalytic effect on the thermal oil.

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6. Manual operation

6.1 The facility is to be provided for manualoperation. At least the temperature limiters on the oilside and flow limiters shall remain operative even in

manual operation.

The heater heated by exhaust gas may be operatedwithout temperature and flow monitoring if the per-missible header temperature can be kept.

6.2 Manual operation demands constant anddirect supervision of the system.

For details of requirements in respect of the manualoperation of the oil firing system, see Section 9.

B. Heaters

1. Acceptable materials

Heaters of thermal oil systems are to be fabricatedfrom the same materials as boilers as per Section 7a,B.2.

2. Testing of materials

The materials of the parts of the heaters which are incontact with the thermal oil are to be tested in accor-dance withSection 7a, B.3.

For coils with a maximum allowable working pressure

up to 10 bar and an allowable operating temperatureup to 300 C Manufacturer Inspection Certificates1are sufficient.

3. Design

3.1 Heaters are to be designed thermodynami-cally and by construction that neither the surfaces northe thermal oil become excessively heated at anypoint. The flow of the thermal oil is to be ensured byforced circulation.

3.2 The surfaces which come into contact with

the thermal oil are to be designed for the maximumallowable working pressure subject to a minimumgauge pressure of 10 bar.

3.3 Heaters heated by exhaust gas are to be de-signed that damages by resonances resulting fromoscillation of the exhaust gas column cannot occur.

3.4 The exhaust gas intake is to be arranged thatthe thermal oil cannot penetrate the engine or theturbocharger in case of a leakage in the heater respec-tively the cleaning medium cannot penetrate duringheater cleaning.

1 See GL Rules II Materials and Welding, Part 1 Metallic

Materials, Chapter 1 Principles and Test Procedures, Section1, H.

3.5 Heaters heated by exhaust gas are to be pro-vided with manholes serving as inspection openings atthe exhaust gas intake and outlet.

3.6 Oil fired heaters are to be provided with in-

spection openings for examination of the combustionchamber.

3.7 Sensors for the temperature measuring andmonitoring devices are to be introduced into the sys-tem through welded-in immersion pipes.

3.8 Heaters are to be fitted with means enablingthem to be completely drained.

3.9 For electrically heated heaters the require-mentsaretobeappliedanalogouslytooilfiredheaters.

4. Equipment

The suitability of safety and monitoring devices (e.g.valves, limiters/alarms for temperature, flow and leak-age monitoring) for marine use is to be proven by typetesting.

4.1 General

4.1.1 The equipment on the heaters has to be suit-able for use at thermal oil heaters and on ships. Theproof of the suitability of the limiters (e.g. tempera-ture, flow, pressure) is to be demonstrated by a type

approval test according to the requirements of GLRules listed in A.2.

4.1.2 The alarms and the activation of the limitershave to create optical and acoustic fault signals in theinstallation space of the heater resp. in the enginecontrol room and another suitable location.

4.2 Safety valves

Each heater is to be equipped with at least one safetyvalve having a blow-off capacity at least equal to theincrease in volume of the thermal oil at the maximumheating power. During blow-off the pressure shall not

increase above 10 % over the maximum allowableworking pressure.

4.3 Temperature, pressure and flowindicating devices

4.3.1 Pressure indicating devices are to be fitted atthedischargeandreturnlineofbothoilfiredheatersandheatersheatedbyexhaustgas.Themaximumallowableworking pressure PB is to be shown on the scale by ared mark which is permanently fixed and well visible.The indicating range has to include the test pressure.

4.3.2 Temperature indicating devices are also to befitted in the flue gas or exhaust gas stream at the heat-er's outlet.

4.3.3 The flow of the thermal oil is to be indicated.

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3. Design

3.1 All vessels, including those open to the at-mosphere, are to be designed for a pressure of at least2 bar, unless provision has to be made for a higher

working pressure. Excepted from this requirement aretanks designed and dimensioned according to Chap-ter 1 Hull Structures, Section 12.

3.2 An expansion vessel is to be placed at a highlevel in the system. The space provided for expansionmust be such that the increase in the volume of thethermal oil at the maximum thermal oil temperaturecan be safely accommodated. The following are to beregarded as minimum requirements: 1,5 times theincrease in volume for volumes up to 1000 litres, and1,3 times the increase for volumes over 1000 litres.The volume is the total quantity of thermal oil con-tained in the equipment up to the lowest liquid level inthe expansion vessel.

3.3 At the lowest point of the system a drainagetank is to be located, the capacity of which is suffi-cient to hold the volume of the largest isolatable sys-tem section.

3.4 A separate storage tank is to be provided tocompensate any losses. The stock of thermal oil is tobe at least 40 % of the capacity of the system. De-pending on the system design or the ship's geographi-cal area of service, a smaller stock may be acceptable.

3.5 In exceptional cases, approval may be givenfor the drainage tank and the storage tank to be com-bined. Combined storage/drainage tanks are to bedimensioned that in addition to the stock of thermaloil, there is room for the content of the largest isolata-ble system section.

4. Equipment of the expansion vessel

4.1 General

4.1.1 The equipment on the expansion vessel (e.g.level indicator) has to be suitable for use at thermal oil

heaters and on ships. The proof of the suitability of thelimiters (e.g. filling level) is to be demonstrated by atype approval test according to the requirements of GLRules listed in A.2.

4.1.2 The alarms and the activation of the limitershave to create optical and acoustic fault signals in theinstallation space of the heater resp. in the enginecontrol room and another suitable location.

4.2 Level indication device

4.2.1 The expansion vessel is to be equipped with aliquid level gauge with a mark indicating the lowestallowable liquid level.

4.2.2 Level gauges made of glass or plastic are notallowed.

4.3 Low level limiter and alarm

4.3.1 A limit switch is to be fitted which shutsdown and interlocks the firing system and switches offthe circulating pumps if the liquid level falls below the

allowable minimum.

4.3.2 Additionally an alarm for low liquid level isto be installed, e.g. by means of an adjustable levelswitch on the liquid level gauge which gives an earlywarning of a falling liquid level in the expansion ves-sel (e.g. in the event of a leakage).

4.3.3 An alarm is also to be provided for themaximum liquid level.

4.4 Quick drainage valve and emergency

shut-off valve

4.4.1 For rapid drainage in case of danger, a quickdrainage valve is to be fitted directly to the vessel withremote control from outside the space in which theequipment is installed.

4.4.2 Automatic means are to be provided to ensurea sufficient air supply to the expansion vessel whenthe quick drainage valve is operated.

4.4.3 Where the expansion vessel is installed out-side the engine room, the quick drainage valve may be

replaced by an emergency shut-off device (quick clos-ing valve).

4.4.4 The opening of the quick drainage valve orthe operation of the emergency shut-off device shallcause the automatic shutdown of the firing system andthe circulating pumps.

4.4.5 The dimensions of the drainage and ventingpipes are to be applied according to Table 7b.1.

Table 7b.1 Nominal diameter of drainage and

venting pipes as well as of expansionand overflow pipes depending on theperformance of the heater

Performance

of heater

[kW]

Expansion and

overflow pipes

Nominal

diameter DN

Drainage and

venting pipes

Nominal

diameter DN

600 25 32

900 32 40

1200 40 50

2400 50 65

6000 65 80

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4.5 Connection lines

4.5.1 A safety expansion line has to connect thesystem to the expansion vessel. This shall be installedwith a continuous positive gradient and is to be di-

mensioned that a pressure rise of more than 10 %above the maximum allowable working pressure in thesystem is avoided.

4.5.2 The expansion vessel is to be provided withan overflow line leading to the drainage tank.

4.5.3 The quick drainage line may be routed jointlywith the overflow line to the drainage tank.

4.5.4 All parts of the system in which thermal oilcan expand due to the absorption of heat from outsideis to be safeguarded against excessive pressure. Anythermal oil emitted is to be safely drained off.

4.5.5 The dimensions of the expansion and over-flow pipes are to be applied according to Table 7b.1.

4.6 Pre-pressurised system

4.6.1 Pre-pressurised systems are to be equippedwith an expansion vessel which contents are blanketedwith an inert gas. The inert gas supply to the expan-sion vessel has to be guaranteed.

4.6.2 The pressure in the expansion vessel is to beindicated and safeguarded against overpressure.

5. Equipment of the drainage and storagetank

For the equipment of the drainage and storage tank seeSection 11, Q.4.

D. Equipment Items

1. Approved materials

1.1 Materials for pipes, valves and pumps seeSection 11, B.

1.2 Grey cast iron is unacceptable for equipmentitemsinthehotthermaloilcircuitandforsafetyvalves.

2. Testing of materials

Pipe, valve and pump materials are tested in accor-dance withSection 11, B.3.

3. Equipment

3.1 Pipes, valves and pumps are governed, inaddition to the following specifications, by the provi-sions of Section 11, Q.

3.2 The outlets of the circulating pumps are to beequipped with pressure gauges.

3.3 It shall be possible to shut down the circulat-ing pumps by an emergency switch which can also be

operated from a position outside the room in whichthey are installed.

3.4 Devices for safe sampling are to be providedat a suitable location in the thermal oil circuit.

3.5 Means of venting are to be provided at thehighest points of isolatable sections of the thermal oilsystem and drainage devices at the lowest points.

Ventinganddrainageviaopenfunnelsaretobeavoid-ed.

3.6 For fitting and draining pumps see Section11, Q.1.2.

3.7 Electric equipment items are governed byChapter 3 Electrical Installations.

E. Marking

1. Heaters

The following information shall be stated on a durablemanufacturer's nameplate permanently attached to theheater:

manufacturer's name and address

serial number

year of manufacture

maximum allowable heating power

maximum allowable working pressure

maximum allowable discharge temperature

minimum flow rate

liquid capacity

2. Vessels

2.1 Vessels are to be fitted with nameplates bear-ing the following information:

manufacturer's name and address

serial number

year of manufacture

maximum allowable working pressure

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maximum allowable working temperature

capacity

2.2 For vessels with an open connection to the

atmosphere,themaximumallowableworkingpressureistobeshownonthenameplateas"0"or"Atm.",eventhoughagaugepressureof2baristakenasthedesignbasisinaccordancewithC.

F. Fire Protection

The fire precautions are governed by the provisions ofSection 12.

G. Testing

1. Heaters

The thermal oil heaters are to be subjected to a con-

structional check and a hydrostatic pressure test, at 1,5times the maximum allowable working pressure, at themanufacturer's works in the presence of the GL Sur-veyor.

2. Thermal oil system

After completion of installation on board, the systemincluding the associated monitoring equipment is to besubjected to pressure, tightness and functional tests inthe presence of the GL Surveyor.

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