Vol3_Section07

Section 7 - Boilers and Thermal Oil Systems 7-1

H [m 2 ] N 86018000

S e c t i o n 7

Boilers and Thermal Oil Systems

I. Boilers

A. General

1. Scope

1.1 For the purpose of these Rules, the term"boiler" includes all closed vessels and piping systemsused for:

a) generating steam at pressure aboveatmospheric (steam generators) or

b) raising the temperature of water above theboiling point corresponding to atmosphericpressure (hot water generators).

The term "steam generator" also includes anyequipment directly connected to the aforementionedvessels or piping systems in which the steam is super-heated or cooled, the circulating line and the casingsof circulating pumps serving forced-circulationboilers.

1.2 Steam and hot water generators as defined in1.1 are subject to the Rules set out in B. to F., or, ifappropriate, in G.

Exhaust gas economizers are subject to the specialrequirements set out in H. In respect of materials,manufacture and design, the requirements specified inB., C. and D. apply as appropriate.

1.3 Hot water generators with a permissibledischarge temperature of not more than 120 C and allsystems incorporating steam or hot water generatorswhich are heated solely by steam or hot liquids are notsubject to these Rules, but come under Section 8.2. Other Rules

2.1 As regards their construction and installation,steam boiler plants are also required to comply withthe applicable statutory requirements and regulationsof the ship's country of registration.

3. Documents for approval

Drawings of all boiler parts subject to pressure, suchas drums, headers, tubes, manholes and inspectioncovers etc., are to be submitted to the Society intriplicate.

These drawings must contain all the data necessary for

strength calculations and design assessment, such asworking pressures, superheated steam temperatures,materials to be used and full details of welds includingfiller materials.

Details and drawings are also to be submittedcovering the valves and fittings and their arrangementtogether with a description of the boiler plantspecifying the arrangement of the boiler withreference to the ship's longitudinal axis, the essentialboiler data and equipment items, e.g. steamconditions, heating surfaces, allowable steam output,feed, firing system, safety valves, controllers andlimiters.

4. Definitions

4.1 Steam boiler walls are the walls of the steamand water spaces located between the boiler isolatingdevices. The bodies of these isolating devices formpart of the boiler walls.

4.2 The maximum allowable working pressure(PB, design pressure) is the approved steam pressurein bar (gauge pressure) in the saturated steam spaceprior to entry into the superheater. In continuous flowboilers, the maximum allowable working pressure isthe pressure at the superheater outlet or, in the case ofcontinuous flow boilers without a superheater, thesteam pressure at the steam generator outlet.

4.3 The heating surface is that part of the boilerwalls through which heat is supplied to the system,

a) the area in m2 measured on the side exposedto fire or exhaust gas, or

b) in the case of electrical heating, theequivalent heating surface:

Where N is the electric power in kW.

4.4 The allowable steam output is the maximumquantity of steam (in metric tons/hour or kg/hour)which can be produced continuously by the steamgenerator operating under the design steamconditions.

5 Lowest water level - highest flue -dropping time

7-2 Section 7 - Boilers and Thermal Oil System

5.1 The highest flue is the highest point on theside of the heating surface which is in contact with thewater and which is exposed to flame radiation orheated by gases which temperature exceeds 4000C atmaximum continuous power. The highest flue onwater tube boilers with an upper steam drum is the topedge of the highest gravity tubes.

5.2 The requirements relating the highest flue donot apply to

Water tube boiler risers up to 102 mm outerdiameter

Once-through forced flow boilers

Superheaters

Flues and exhaust gas heated parts in whichthe temperature of the heating gases does notexceed 4000C at maximum continuous power

5.3 The lowest water level must lie at least 150mm above the highest flue also when the ship heels 40to either side. Heated surfaces with a set highest fluemust remain wetted even when the ship is at the staticheeling angles laid down in Section 1, Table 1.1. Theheight of the water level is critical to the response ofthe water level limiters.

5.4 The heat accumulated in furnaces and otherheated boiler parts may not lead to any unduelowering of the water level due to subsequentevaporation when the firing system is swiched off.The lowest water level is to be set so that the droppingtime does not exceed 5 minutes.

5.5 The "dropping time" is the time taken by thewater level, under conditions of interrupted feed andallowable steam output, to drop from the lowestworking level to the level of the highest point of thegas or flame path, i.e.:

t VD v

t [min] dropping timeV [m3] volume of water in steam generator

between the lowest working leveland the highest point of the gas orflame path.

D [kg/min] allowable steam outputv' [m3/kg] specific volume of the water at

saturation temperature

5.6 The lowest specified water level is to beindicated permanently on the boiler shell by means ofa water level pointer. Reference plates are to beattached additionally beside or behind the water levelgauges pointing at the lowest water level.

6. Manual operation

6.1 The facility is to be provided for manualoperation. At least the water level limiters mustremain active even in manual operation.

6.2 Manual operation demands constant anddirect supervision of the system.

6.3 For detailed requirements in respect ofmanual operation of the firing system see Section 9.

7. Power of steam propulsion plants

On ships propelled by steam, the plant is to bedesigned that, should one main boiler fail, sufficientpropulsive capacity will remain to maintain adequatemanoeuvrability and to supply the auxiliarymachinery.

B. Materials

1. General requirements

With respect to their workability during manufactureand their characteristics in subsequent operation,materials used for the manufacture of steam boilersmust satisfy the technical requirements, particularlythose relating to high-temperature strength and, whereappropriate, weldability.

2. Approved materials

The requirements specified in 1. are recognized ashaving been complied with if the materials shown inTable 7.1 are used.

Materials not specified in the Society's Rules forMaterials may be used provided that proof is suppliedof their suitability and mechanical properties.

3. Material testing

3.1 The materials of boiler parts subject topressure, including exhaust gas economizer tubes,must be tested by the Society in accordance with theRules for Materials (cf. Table 7.1). Material testing bythe Society may be waived in the case of:

a) Small boiler parts made of unalloyed steels,such as stay bolts, stays of 100 mmdiameter, reinforcing plates, handhole andmanhole covers, forged flanges and branchpipes up to DN 150 or recognized standardand

b) Smoke tubes (tubes subject to externalpressure).


Table 7.1 Approved materials

Material and product form Limits of application

Material grades in accordancewith the Rules for Classification

and Construction, Volume V,Rules for Material

Steel plates and steel strip - Plates and strip of high-temperaturesteel, Section 3, H

Steel pipes - Seamless and welded pipes offerritic steels, Section 4, B and C

Forging and formed parts :

a) drum, headers and similar hollow components with out longitudinal seam

b) covers, flanges, branch pipes, end plates

-

Forging for boilers,vessels and pipeline

Section 5, E

Nuts and bolts

- Fasteners, Section 6,CHigh-temperature bolts to

DIN 17 240

300 C 40 bar M30

DIN 267Parts 3 and 4

or other equivalent standards

Steel castings

Cast steel for boilers, pressurevessels and pipelines.

300 CAlso GS 38 and GS 45 to DIN 1681

and GS 16 Mn5 and GS 20 Mn5 to DIN 17 182

Nodular cast iron 300 C 40 bar

DN 175 for valvesand fittings

Nodular cast ironSection 7, B

Lamellar (grey) cast iron :a) Boiler parts (only for unheated surfaces and not for heaters in thermal oil systems)b) Valves and fittings (except valves subject to dynamic stresses)

c) exhaust gas economiser

200 C 10 bar

200 mm diameter

200 C 10 bar DN 175

52 barsmoke gas temperature

600 Cwater outlet temperature

245 C

Grey cast ironSection 7, C

100 barsmoke gas temperature

700 Cwater outlet temperature

260 C

Grey cast iron of at least GG-25grade to Section 7, C

Valves and fittings of castcopper alloy

225 C 25 bar

Cast copper alloysSection 10, B

For the parts mentioned in a) and b), the properties of thematerials are to be attested by Type B works test

certificates in accordance with EN 10204.1B orother equivalent standards.


3.2 Special agreements may be made regarding thetesting of unalloyed steels to recognized standards.

3.3 The materials of valves and fittings must betested by the Society in accordance with the datasspecified in Table 7.2.

3.4 Parts not subject to material testing, such asexternal supports, lifting brackets, pedestals etc. must bemade of materials suitable for the intended purpose andin accordance with accepted engineering practice.

C. Principles Applicable to Manufacture

1. Manufacturing processes applied to boilermaterials

Materials are to be checked for defects during themanufacturing process. Care is to be taken to ensure thatdifferent materials cannot be confused. During the courseof manufacture care is likewise required to ensure thatmarks and inspection stamps on the materials remainintact or are transferred in the prescribed manner.

Boiler parts whose structure has been adversely affectedby hot or cold forming are to be subjected to heattreatment in accordance with the Rules for Materials,Volume V, Section 8, A.

Table 7.2 Testing of materials for valves andfittings

Type ofmaterials 1)

Servicetemperature

[C]

Testing requiredfor: PB in [bar]

DN in [mm]Steel, cast steel > 300 DN > 32

Steel, cast steel,nodular cast iron 300

PB x DN > 2500 2)or

DN > 250Copper alloys 225 PB x DN > 1500 2)1) No test is required for grey cast iron.2) Testing may be required with if DN is 32 mm.

2. Welding

The execution of welds, the approval of welding shopsand the qualification testing of welders are to be inaccordance with Rules for Welding, Volume VI,Section 3.

3. Riveting

Where, in special cases, boiler parts have to be riveted tobe observed

4. Tube expansion

Tube holes must be carefully drilled and deburred. Sharpedges are to be chamfered. Tube holes should be as closeas possible to the radial direction, particularly in the case

of small wall thicknesses.

Tube ends to be expanded are to be cleaned andchecked for size and possible defects. Wherenecessary, tube ends are to be annealed beforebeing expanded.

5. Stays, stay tubes and stay bolts

5.1 Stays, stay tubes and stay bolts are to bearranged that they are not subjected to undue bend-ing or shear forces.

Stress concentrations at changes in cross-section,in screw threads and at welds are to be minimizedby suitable component geometry.

5.2 Stays and stay bolts are to be welded byfull penetration preferably. Any vibrational stressesare to be considered for long stays.

5.3 Stays are to be drilled at both ends in sucha way that the holes extend at least 25 mm into thewater or steam space. Where the ends have beenupset, the continuous shank must be drilled to adistance of at least 25 mm.

5.4 Wherever possible, the angle made by gus-set stays and the longitudinal axis of the boilershall not exceed 30. Stress concentrations at thewelds of gusset stays are to be minimized bysuitable component geometry. Welds are to beexecuted as full-strength welds. In firetube boilers,gusset stays are to be located at least 200 mm fromthe firetube.

5.5 Where flat surfaces exposed to flames arestiffened by stay bolts, the distance betweencenters of the stay bolts shall not generally exceed200 mm.

6. Stiffeners, straps and lifting eyes

6.1 Where flat end surfaces are stiffened byprofile sections or ribs, the latter shall transmittheir load directly (i.e. without welded-on straps) tothe boiler shell.

6.2 Doubling plates may not be fitted atpressure parts subject to flame radiation.Where necessary to protect the walls of the boiler,strengthening plates are to be fitted below supportsand lifting brackets.

7. Welding of flat unrimmed ends to boilershells

Flat unrimmed ends (disc ends) on largewaterspace boilers are only permitted assocket-welded ends with a shell projection of 15 mm. The end/shell wall thickness ratio sB/sMshall not be greater than 1,8. The end is to bewelded to the shell with a full-strength weld.


8. Stand pipes and flanges

Stand pipes and flanges are to be of rugged design andproperly welded to the shell. The wall thickness ofbranch pipes must be sufficiently large safely towithstand additional external loads. The wall thickness ofwelded-in pipe connections shall be appropriate to thewall thickness of the part into which they are welded.

Welding-neck flanges must be made of forged materialwith favourable grain orientation.

9. Cleaning and inspection openings, cutouts andcovers

9.1 Steam boilers are to be provided with openingsthrough which the space inside can be cleaned andinspected. Boiler vessels with an inside diameter of morethan 1200 mm and those measuring over 800 mm indiameter and 2000 mm in length are to be provided withmeans of access. Parts inside drums must not obstructinner inspection or must be capable of being removed.

9.2 Inspection and access openings are required tohave the following minimum dimensions:

Manholes 300 x 400 mm or 400 mm diameter,where the annular height is > 150 mmthe opening measure shall be 320 x420 mm.

Headholes 220 x 320 mm or 320 mm diameter

Handholes 87 x 103 mm

Sight holes are required to have a diameter of atleast 50 mm; they should, however, beprovided only when the design of theequipment makes a handholeimpracticable.

9.3 The edges of manholes and other openings, e.g.for domes, are to be effectively strengthened if the platehas been unacceptably weakened by the cutouts. Theedges of openings closed with covers are to be reinforcedby flanging or by welding on edge-stiffeners if it is likelythat the tightening of the crossbars etc. would otherwisecause undue distortion of the edge of the opening.

9.4 Cover plates, manhole stiffeners and crossbarsmust be made of ductile material (not grey or malleablecast iron). Grey cast iron (at least GG-20) may be usedfor handhole cover crossbars of headers and sectionalheaders, provided that the crossbars arc not located in theheating gas flow. Unless metal packings are used, coverplates must be provided on the external side with a rim orspigot to prevent the packing from being forced out. Thegap between this rim or spigot and the edge of theopening is to be uniform round the periphery and may notexceed 2 mm for boilers with a working pressure of lessthan 32 bar, or 1 mm where the pressure is 32 bar orover. The height of the rim or spigot must be at least 5mm greater than the thickness of the packing.

9.5 Only continuous rings may be used as packing.

The materials used must be suitable for the givenoperating conditions.

10. Boiler drums, shell sections, headers andfiretubes, See the Rules for Welding Volume VI,B.

D. Design Calculation

1. Design principles

1.1 Range of applicability of designformulae

1.1.1 The following strength calculations repre-sent the minimum requirements for normaloperating conditions with mainly static loading.Separate allowance must be made for additionalforces and moments of significant magnitude.Proper treatment and adequate monitoring of thefeedwater are assumed to be carried out.

1.1.2 The wall thicknesses arrived at by applyingthe formulae are the minima required. Theundersize tolerances permitted by the Rules forMaterials are to be added to the calculated values.

The greater local undersize tolerances for tubesneed not be considered.

1.2 Design pressure pc1.2.1 In general, the design pressure is equal tothe maximum allowable working pressure. Addi-tional allowance is to be made for static pressuresof more than 0,5 bar.

1.2.2 In designing continuous-flow boilers, thepressure to be applied is the maximum workingpressure anticipated in each of the individual mainboiler sections at maximum continuous load and atthe response threshold of the safety equipment.

1.2.3 The design pressure applicable to thesuperheated steam lines from the boiler is themaximum working pressure which adequate safetydevices prevent from being exceeded.

!

" #


1.3 Design temperature t

Strength calculations are based on the temperature at thecenter of the wall thickness of the component in question.The design temperature is made up of the referencetemperature and a temperature allowance in accordancewith Table 7.3. The minimum value is to be taken as250 C.

Table 7.3 Design temperatures

Referencetemperature

Allowance to be added

Unheatedparts

Heated parts, heatedmainly by

contact radiation

Saturationtemperatureat m.a.w.p

0 C 25 C 50 C

Superheatedsteamtemperature

15 C 1) 35 C 50 C

1) The temperature allowance may be reduced to 7 Cprovided that special measures are taken to ensure thatthe design temperature cannot be exceeded

1.4 Allowable stress

The design of structural components is to be based on theallowable stress perm[N/mm2]. In each case, the minimumvalue produced by the following relations is applicable :

1.4.1 Rolled and forged steels

For design temperatures up to 350 C

where Rm, 20 = guaranteed minimum tensileR

m,20

2,7strength [N/mm2] at roomtemperature

where ReH,t = guaran teed yie ld poin t or$ %

minimum 0,2 % proof stress atdesign temperature t.

For design temperature over 350 C

where Rm100000,t= mean 100000 hour creepR

m,100000,t

1,5strength at designtemperature t

1.4.2 Cast materials

a) Cast steel : ; ; Rm,203,2

ReH,t

2,0R

m,100000,t

2,0

b) Nodular cast ; Rm,204,8

ReH,t

3,0

iron :

c) Grey cast Rm,2011

iron :

1.4.3 Special arrangements may be agreed forhigh-ductility austenitic steels.

1.4.4 In the case of cylinder shells with cutoutsand in contact with water, a nominal stress of 170N/mm shall not be exceeded in view of the pro-tective magnetite layer.

1.4.5 Mechanical characteristics are to be takenfrom the Rules for Materials or from the standardsspecified therein.

1.5 Allowance for corrosion and wear

The allowance for corrosion and wear is to bec = 1 mm. For plate thicknesses of 30 mm and overand for stainless materials, this allowance may bedispensed with.

1.6 Special cases

Where boiler parts cannot be designed inaccordance with the following Rules or on generalengineering principles, the dimensions in eachindividual case must be determined by tests, e.g. bystrain measurements

2. Cylindrical shells under internalpressure

2.1 Scope

The following design Rules apply to drums,shell rings and headers up to a diameter ratio Da/Diof 1,7. Diameter ratios of up to Da/Di 2 may bepermitted provided that the wall thickness is 80 mm.

2.2 Symbols

pc [bar] design pressures [mm] wall thicknessDi [mm] inside diameterDa [mm] outside diameterc [mm] allowance for corrosion and weard [mm] diameter of opening or cutout

hole diameter for expandedtubes and for expanded and seal-welded tubes (see Fig. 7.1 a and7.1 b)inside tube diameter forwelded-in pipe nipples andsockets (Fig. 7.1 c)

t,tl,tu [mm] pitch of tube holes (measured atcenter of wall thickness for cir-


Fig. 7.1

Fig. 7.2

cumferential seams)v [ - ] weakening factor

for welds :the qualitative ratio of the weldedjoints to the plate (weld quality rating)for holes drilled in the plate :the ratio of the weakened to theunweakened plate section

perm [N/mm2] allowable stress (see 1.4)sA [mm] necessary wall thickness at edge of

opening or cutout

sS [mm] wall thickness of branch pipeb [mm] supporting length of parent componentls [mm] supporting length of branch pipel [mm] width of ligament between two branch

pipes

l's [mm] internal projection of branch pipeAp [mm2] area under pressureA [mm] supporting cross-sectional area

2.3 Design calculations

2.3.1 The necessary wall thickness s is given by theexpression :

(1)s Da pc20 perm v pc

c

2.3.2 In the case of heated drums and headers with amax. allowable working pressure of more than 25 bar,special attention is to be given to thermal stresses.

For heated drums not located in the first pass (gastemperature up to 1000 C max.), special certification inrespect of thermal stresses may be waived subject to thefollowing provision:

Wall thickness up to 30 mm and adequate cooling of thewalls by virtue of close tube arrangement. Thedescription "close tube arrangement" is applicable if theligament perpendicular to the direction of gas flow andparallel to the direction of gas flow does not exceed 50mm and 100 mm respectively.

2.3.3 Weakening factor v

The weakening factor v is shown in Table 7.4.

Table 7.4 Weakening factor v

Construction Weakening factor vSeamless shellrings and drums 1,0

Shell rings anddrums withlongitudinalweld

weld quality rating see Rulesfor Welding

Rows of holes1)

1) The value of v for rows of holes may not be madegreater than 1,0 in the calculation. For staggeredpitches, see Appendix, Fig. 7.27.Refer also to Figures 7.1a-7.1c under paragraph 2.2

2.3.4 Weakening effects due to cutouts or indi-vidual branch pipes are to be taken into account byarea compensation in accordance with theexpression:

(2)Pc10

ApA

12

perm

The area under pressure Ap and the supportingcross-sectional area A are defined in Fig. 7.2.

The values of the supporting lengths may notexceed:

for the parentcomponent b (Di sA c) ( sA c)for the branch pipe ls 1,25 (d sS c) ( sS c)


Fig. 7.3

Where a branch projects into the interior, the valueintroduced into the calculation as having a supportingfunction may not exceed l's 0,5 lsCutouts exert a mutual effect if the ligament

l 2 (Di sA c) ( sA c)The area compensation is then as shown in Fig. 7.3.

Where materials with different mechanical strengths areused for the parent component and the branch orreinforcing plate, this fact is to be taken into account inthe calculation. However, the allowable stress in thereinforcement may not be greater than that for the parentmaterial in the calculation.

Disc-shaped reinforcements should not be thicker thanthe actual parent component thickness, and this thicknessis the maximum which may be allowed for in thecalculation.

Disc-shaped reinforcements are to be fitted on theoutside.

The wall thickness of the branch pipe should not be morethan twice the required wall thickness at the edge of thecutout.

In the case of tubular reinforcements, the following wallthickness ratio is applicable :

sS c

sA c 2

2.4 Minimum allowable wall thickness

For welded and seamless shell rings the minimumallowable wall thickness is 5 mm. For non-ferrous metals,stainless steels and cylinder diameters up to 200 mm,smaller wall thicknesses may be permitted. The wallthickness of drums into which tubes are expanded is to besuch as to provide a cylindrical expansion length of atleast 16 mm.

3. Cylindrical shells and tubes with an outsidediameter of more than 200 mm subject toexternal pressure

3.1 Scope

The following Rules apply to the design of smoothand corrugated cylindrical shells and tubes with anoutside diameter of more than 200 mm which aresubjected to external pressure. Firetubes are tubesexposed to fire.

3.2 Symbols

pc [bar] design pressures [mm] wall thicknessd [mm] mean diameter of smooth tubeda [mm] outside diameter of smooth tubedi [mm] minimum inside diameter of

corrugated firetube

l [mm] length of tube or distancebetween two effective stiffeners

h [mm] height of stiffening ringb [mm] thickness of stiffening ringu [%] percentage out-of-roundness of

tube

a [mm] greatest deviation fromcylindrical shape (see Fig. 7.5)

perm [N/mm] allowable stressEt [N/mm] modulus of elasticity at design

temperature

SK [-] safety factor against elasticbuckling

v [-] transverse elongation factor (0,3for steel)

c allowance for corrosion andwear

3.3 Design calculations

3.3.1 Cylindrical shells and smooth firetubes

Calculation of resistance to plastic deformation:

(3)Pc 10 perm

2(sc)d

1 0,1 dl

1 0,03 dsc

u

15 dl

Calculation of resistance to elastic buckling:

pc 20 EtSk

sc

da

(n 21) 1 nZ

2 2

sc

da

3

3 (12 )


Fig. 7.4

(4) n 21 2 n 211 n

Z

2

where : Z d

a

2 land n 2

n > Z

n (integer) is to be chosen as to reduce pc to its minimumvalue. n represents the number of buckled folds occurringround the periphery in the event of failure. n can beestimated by applying the following approximationformula:

n 1,63 4 d

a

l

2

da

s c

3.3.2 In the case of corrugated tubes of Fox andMorrison types, the necessary wall thickness s is given bythe expression:

(5)s pc20

diperm

1 mm


Contrary to 1.4, the values for the allowable stress offiretubes used in the calculations are to be as follows:

- Plain firetubes, horizontalR

e,H,t

2,5

Plain firetubes, verticalR

e,H,t

2,0

Corrugated tubesR

e,H,t

2,8 Tubes heated by

Re,H,t

2,0exhaust gases

3.5 Design temperature

Contrary to 1.3, the design temperature to be used forfiretubes is shown in Table 7.5.

3.6 Stiffening

Apart from the firetube and firebox end-plates, the typesof structure shown in Figure 7.4 can also be regarded asproviding effective stiffening.

3.7 Safety factor SkA safety factor Sk of 3,0 is to be used in the calculation ofresistance to elastic buckling. This value is applicablewhere the out-of-roundness is 1,5 % or less. Where theout-of-roundness is more than 1,5 % and up to 2 %, the

safety factor Sk to be applied is 4,0.

3.8 Modulus of elasticity

Table 7.6 shows the modulus of elasticity for steelin relation to the design temperature.

Table 7.5 Design temperatures for shellsand tubes under externalpressure

For tubes exposed to fire(firetubes) :

but at least 250 oC

plain tubest = saturation

temperature + 4 . s + 30 oC

corrugatedtubes

t = saturationtemperature + 3 . s + 30 oC

For tubes heated by exhaust gases

t = saturation tem-perature + 2 . s+ 15 oC

Table 7.6 Values for the modulus of elasticity

Designtemperature

[oC]

Et 1)[N/mm2]

20250300400500600

206000186400181500171700161900152100

1) Intermediate values should be interpolated

3.9 Allowance for corrosion and wear

An allowance of 1 mm for corrosion and wear is tobe added to the wall thickness s. In the case ofcorrugated tubes, s is the wall thickness of thefinished tube.

3.10 Minimum allowable wall thicknessand maximum wall thickness

The wall thickness of smooth firetubes shall be atleast 7 mm, that of corrugated firetubes at least 10mm. For small boilers, non-ferrous metals andstainless steels, smaller wall thicknesses are


u 4 a

d 100

& '& '& '& '

allowable. The maximum wall thickness may not exceed20 mm. Tubes which are heated by flue gases < 1000 oCmay have a maximum wall thickness of up to 30 mm.

3.11 Maximum unstiffened length

For firetubes, the length l between two stiffeners may notexceed 6 d. The greatest unsupported length shall notexceed 6 m or, in the first pass from the front end-plate,5 m. Stiffenings of the type shown in Figure 4 are to beavoided in the name zone, i. e. up to approximately 2 dbehind the lining.

The plain portion of corrugated firetubes need not beseparately calculated provided that its stressed length,measured from the middle of the end-plate attachment tothe beginning of the first corrugation, does not exceed250 mm.

3.12 Out-of-roundness

The out-of-roundness [%]

u 2 (d

max d

min)d

max d

min 100

of new smooth tubes is to be given the value u = 1,5 % inthe design formula.

In the case of used firetubes, the out-of-roundness is tobe determined by measurements of the diametersaccording to Fig. 7.5.

3.13 Firetube spacing

The clear distance between the firetube and boiler shellat the closest point shall be at least 100 mm. The distancebetween any two firetubes shall be at least 120 mm.

4. Dished end-plates under internal andexternal pressure

4.1 Scope

4.1.1 The following Rules apply to the design ofunstayed dished end-plates under internal or external

pressure (see Fig. 7.6). The following requirementsare to be complied with:

The radius R of the dished end may not exceed theoutside end-plate diameter Da, and the knuckleradius r may not be less than 0,1 Da.

The height H may not be less than 0,18 Da.

The height of the cylindrical portion, with theexception of hemispherical end-plates, shall be3,5 s, s being taken as the thickness of theunpierced plate even if the end-plate is providedwith a manhole. The height of the cylindricalportion need not, however, exceed the followingvalues in Table 7.7.

Table 7.7 Height h of cylindrical portion

Wall thickness s[mm]

h[mm]

up to 50over 50 up to 80

over 80 up to 100over 100 up to 120

over 120

1501201007550

4.1.2 These Rules also apply to weldedend-plates. Due account is to be taken of thequality rating of the weld (cf. 4.5 ).

4.2 Symbols

pc [bar] design pressures [mm] wall thickness of end-plateDa [mm] outside diameter of end-plateH [mm] height of end-plate curvatureR [mm] inside radius of dished endh [mm] height of cylindrical portiond [mm] diameter of opening measured

along a line passing through thecenters of the end-plate and theopening. In the case of openingsconcentric with the end-plate, themaximum opening diameter.

perm[N/mm2] allowable stress (cf. 1.4) [-] coefficient of stress in flange


Fig. 7.6

o [-] coefficient of stress in sphericalsection

v [-] weakening factorc [mm] allowance for corrosion and wearEt [N/mm2] modulus of elasticity at design

temperature

sA [mm] necessary wall thickness at edge ofopening

Ss [mm] wall thickness of branch pipeb [mm] supporting length of parent

component

l [mm] width of ligament between two branchpipes

ls [mm] supporting length of branch pipe

l's [mm] internal projection of branch pipeAp [mm] area subject to pressureA [mm] supporting cross-sectional areaSk [-] safety factor against elastic bucklingS'k [-] safety factor against elastic buckling

at test pressure

4.3 Design calculation for internal pressure

4.3.1 The necessary wall thickness is given by theexpression:

(6)s Da pc 40 perm v

c

The finished wall thickness of the cylindrical portion

must be at least equal to the required wall thickness ofa cylindrical shell without weakening.

4.3.2 Design coefficients and oThe design coefficients are shown in Fig. 7.7 inrelation to the ratio H / Da and parameters

and s / Da. ( ) *

For dished ends of the usual shapes, the height H canbe determined as follows :

Shallow dished end (R = Da)H 0,1935 Da + 0,55 s

Deep dished end, ellipsoidal shape (R = 0,8 Da)H 0,255 Da + 0,36 s

The values of for unpierced end-plates also apply todished ends with openings whose edges are locatedinside the spherical section and whose maximumopening diameter is d 4 s, or whose edges areadequately reinforced. The width of the ligamentbetween two adjacent, non-reinforced openings mustbe al least equal to the sum of the opening radiimeasured along the line connecting the centers of theopenings. Where the width of the ligament is less thanthat defined above, the wall thickness is to bedimensioned as though no ligament were present, orthe edges of the openings are to be adequately rein-forced.


Fig. 7.7 Values of coefficient for the design of dihed ends


Fig. 7.8

Fig. 7.9

4.3.3 Reinforcement of openings in the sphericalsection

Openings in the spherical section are deemed to beadequately reinforced if the following expressionrelating to the relevant areas is satisfied.

(7)pc10

ApA

12

perm

The area under pressure Ap and the supportingcross-sectional area A are shown in Fig. 7.8.

For calculation of reinforcements and supportinglengths the formulae and prerequsites in 2.3.4 areapplicable.

The relationship between respective areas of cutoutsexerting a mutual effect is shown in Fig. 7.9.

The edge of disk-shaped reinforcements may notextend beyond 0,8 D a .

In the case of tubular reinforcements, the followingwall thickness ratio is applicable:

sS c

sA c 2

4.4 Design calculation for external pressure

4.4.1 The same formulae are to be applied toend-plates under external pressure as to those subjectto internal pressure. However, the safety factor usedto determine the allowable stress in accordance with1.4.1 is to be increased by 20 %.

4.4.2 A check is also required to determine whetherthe spherical section of the end-plate is safe againstelastic buckling.

The following relationship is to be applied:

(8)pc 3,66 EtSk

s c

R

2

The modulus of elasticity Et for steel can be takenfrom Table 7.6.

The safety coefficient Sk against elastic buckling andthe required safety coefficient Sk' at the test pressureare shown in Table 7.8.

Table 7.8 Safety coefficient against elasticbuckling

s - cR

Sk1) Sk'1)

0,001 5,5 4,0

0,003 4,0 2,9

0,005 3,7 2,7

0,01 3,5 2,6

0,1 3,0 2,21) Intermediate values should be interpolated


Fig. 7.10

Fig. 7.11

4.5 Weakening factor

The weakening factor can be taken from Table 7.4 in2.3.3. Apart from this, with welded dished ends-except for hemispherical ends - a value of v = 1 maybe applied irrespective of the scope of the testprovided that the welded seam impinges on the areawithin the apex defined by 0,6 Da (cf. Fig. 7.10).

4.6 Minimum allowable wall thickness

The minimum allowable wall thickness for weldingneck end-plates is 5 mm. Smaller minimum wallthicknesses are allowed for non-ferrous metals andstainless steels.

5. Flat surfaces

5.1 Scope

The following Rules apply to stayed and unstayed flat,flanged end-plates and to flat surfaces which aresimply supported, bolted, or welded at their peripheryand which are subjected to internal or externalpressure.

5.2 Symbols

pc [bar] design pressures [mm] wall thicknesss1 [mm] wall thickness in a stress

relieving groove

s2 [mm] wall thickness of a cylindrical orsquare header at the connectionto a flat end-plate with a stressrelieving groove

Db [mm] inside diameter of a flat, flangedend-plate or design diameter ofan opening to be provided withmeans of closure

D1, D2 [mm] diameter of circular platesDl [mm] bolt-hole circle diameter of a

plate subject additionally to a

bending moment

de [mm] diameter of the largest circlewhich can be described on a flatplate inside at least threeanchorage points

da [mm] outside diameter of expandedtubes

a, b [mml clear supporting or designwidths of rectangular or ellipticalplates, b always designating theshorter side or axis

tl, t2 [mm] pitch of uniformly spaced staysor stay bolts

e1, e2 [mm] distances between centers ofnon-uniformly spaced stays andstay bolts

f [mm2] cross-sectional area of ligamentrK [mm] inner corner radius of a flange,

or radius of a stress relievinggroove

h [mm] inner depth of a flat,welding-neck end-plate

C [-] design coefficienty [-] ratioperm [N/mm2] allowable stress (see 1.4)c [mm] allowance for corrosion and

wear

5.3 Design calculation of unstayed surfaces

5.3.1 Flat, circular, flanged, unpierced end-plates(cf.Fig.7.11).The necessary wall thickness s is given by theexpression:

(9)s C ( Db rK ) p

c

10 perm c

5.3.2 Circular plates


Fig. 7.12a - 7.12d

Fig. 7.13

Fig. 7.14

Fig. 7.15

Fig. 7.16 Fig. 7.17

The required wall thickness s is given by theexpression :

(10)s C Db p

c

10 perm c

5.3.3 Rectangular and elliptical plates.

The required wall thickness s is given by theexpression:

(11)s C b y pc10 perm

c

5.3.4 Welding-neck end-plates.

The thickness of the plate s is determined by applyingformula 10 or 11 as appropriate.

In the case of end-plates with a stress relievinggroove, provision must be made for the effectiverelieving of the welded seams. The wall thickness s1in the stress relieving groove must therefore satisfythe following conditions, cf. Fig. 7.17:

For round end-plates : s1 0,77 s2For rectangular end-plates : s1 0,55 s2Here s2 represents the wall thickness of the cylindricalor rectangular header in [mm]. In addition, provisionmust be made to ensure that shear forces occurring inthe cross-section of the groove can be safelyabsorbed.

It is therefore necessary that for round end-plates:

(12)s1 p

c

10

Db2

rK 1,3perm

and for rectangular end-plates:

(13)s1 p

c

10

a ba b

1,3perm


Fig. 7.18 Fig. 7.19

Fig. 7.20

Fig. 7.21

Radius rK shall be at least 0,2 s and not less than5 mm. Wall thickness sl must be at least 5 mm.

Where welding-neck end-plates in accordance withFig. 7.16 or Fig. 7.17 are manufactured from plates,the area of the connection to the shell is to be testedfor lamination, e. g. ultrasonically.

5.4 Design calculation of stayed surfaces

5.4.1 For flat surfaces which are uniformly bracedby stay bolts, circular stays or stay tubes, cf. Fig. 7.18.

The required wall thickness s inside the stayed areasis given by the expression:

(14)s C pc ( t21 t

22 )

10 perm c

5.4.2 For flat plates which are nonuniformlybraced by stay bolts, circular stays and stay tubes, cf.Fig. 7.19.

The necessary wall thickness s inside the stayed areasis given by the expression:

(15)s C e1 e22

pc

10 perm c

5.4.3 For flat plates which are braced by gussetstays, supports or other means and flat plates betweenarrays of stays and tubes, cf. Fig. 7.20.

The design calculalion is to be based on the diameterde or a circle, or on the length of the shorter side b ofa rectangle which can be inscribed in the free un-stiffened area, the least favourable position from thepoint of view of stress being decisive in each case.

The required wall thickness s is given by theexpression:

(16)s C de

pc

10 perm c

or

(17)s C b y pc10 perm

c

The higher of the values determined by the formulaeis applicable.

5.4.4 Flat annular plates with central longitudinalstaying, see Fig. 7.21.

The required wall Thickness s is given by theexpression:

(18)s 0,25 ( D1 D2 rK1 rK2 ) p

c

10 perm c

5.5 Requirements for flanges

5.5.1 Application of the above formulae to flangedend-plates and to flanges as a means of staying issubject to the provision that the corner radii of theflanges should have the following minimum values inrelation to the outside diameter of the endplate (cf.Table 7.9).In addition, the flange radii rK (Figs. 7.11, 7.20 and7.21) must be equal to at least 1,3 times the wallthickness.

5.5.2 In the case of welding-neck end-plateswithout a stress relieving groove for headers, theflange radius must be rK 1/3 s, subject to aminimum of 8 mm, and the inside depth of theend-plate must be h s, s for end-plates withopenings being the thickness of an unpierced


end-plate of the same dimensions, cf. Fig. 7.16.

Table 7.9 Minimum corner radius of flanges

Outside diameter of endplate[mm]

Corner radius offlanges[mm]

over 500over1400over 1600over 1900

up to 500up to 1400up to 1600up to 1900

3035404550

5.6 Ratio y

The ratio y takes account of the increase in stress, ascompared with round plates, as a function of the ratioof the sides b/a of unstayed, rectangular and ellipticalplates and of the rectangles inscribed in the free,unstayed areas of stayed, flat surfaces, cf. Table 7.10.

Table 7.10 Values of ratio y

Shape Ratio b/a 1)1,0 0,75 0,5 0,25 0,1

Rectangle 1,10 1,26 1,40 1,52 1,56

Ellipse 1,00 1,15 1,30 --- ---1) Intermediate values are to be interpolated linearly.

5.7 Coefficient C

Coefficient C takes account of the type of support, theedge connection and the type of stiffening. The valueof C to be used in the calculation is shown in Tables7.11 and 7.12.

Where different values of C are applicable to parts ofa plate due to different kinds of stiffening accordingto Table 7.12 coefficient C is to be determined by thearithmetical value :

C = (C1 + C2 ......Cn) / n

5.8 Minimum ligament with expanded tubes

The minimum ligament width depends on theexpansion technique used. The cross-section f of theligament between two tube holes for expanded tubesshould be for :

steel f [mm2] = 15 + 3,4 dacopper f [mm2] = 25 + 9,5 da

Table 7.11 Values of coefficient C for unstayedsurfaces

Type of end-plate or cover C1)Flat, forged and-plates or end-plates withmachined recesses for headers and flat,flanged end-plates 0,35Encased plates tightly supported and boltedat their circference

Inserted, flat plates welded on both sided

Welding-neck end plates with stress re-lieving groove

0.40

Loosely supported plates, such as man-holecovers; in the case of closing appliances, inaddition to the working pres-sure, allowanceis also to be made for the additional forcewhich can be excerted when the bolts aretightened (the permitted loading of the bolt orbolts) distributed over the cover area).

0,45

Inserted, flat plates welded on one side

Plates which are bolted at their circum-ference and are thereby subjected to anadditional bending moment according to theratio :

Dl/Db = 1,0

= 1,1

= 1,2

= 1,3

Intermediate values are to be interpolatedlinearly

0,45

0,50

0,55

0,60

Table 7.12 Values of coefficient C for stayedsurfaces

Type of stiffening and/or end-plate C

Boiler shell, header or cumbustion chamberwall, stay plate or tube area

0,35

Stay bolts in arrays with maximum stay boltcentre distance of 200 mm

0,40

Round stays and tubes outside tube arraysirrespective of whether they are welded-in,bolted or expanded

0,45

5.9 Minimum and maximum wall thickness

5.9.1 With expanded tubes, the minimum platethickness is 12 mm. Concerning safeguards againstthe dislodging of expanded tubes, see 6.3.2.

5.9.2 The wall thickness of flat end-plates shouldnot exceed 30 mm in the heated portion.

5.10 Reinforcement of openings


Fig. 7.22 - 7.24

Where the edges of the openings are not reinforced,special allowance is to be made when calculatingthickness for cutouts, branches etc. in flat surfaceswhich lead to undue weakening of the plate.

6. Stays, stay tubes and stay bolts

6.1 Scope

The following Rules apply to longitudinal stays, gus-set stays, stay tubes, stay bolts and stiffening girdersof steel or copper and are subject to the requirementsset out in C.5.

6.2 Symbols

pc [bar] design pressureF [N] load on a stay, stay tube or stay

bolt

A1 [mm2] c a l c u l a t e d r e q u i r e dcross-section area of stays, staybolts and stay tubes

A2 [mm2] supported area of expandedtubes

Ap [mm2] plate area supported by onestay, stay bolt or stay tube

da [mml outside diameter of stay, staybolt or stay tube

di [mm] inside diameter of stay tubelo [mm] length of expanded section of

tube

a1 [mm] weld height in direction of loadperm [N/mm2] allowable stress

6.3 Design calculation

The supporting action of other boiler parts may betaken into consideration when calculating the size ofstays, stay tubes and stay bolts. Where the boundaryareas of flanged end-plates are concerned, calculationof the plate area Ap is to be based on the flat surfaceextending to the beginning of the end-plate flange.

In the case of flat end-plates, up to half the load maybe assumed to be supported by the directly adjacentboiler wall.

6.3.1 For stays, stay bolts or stay tubes, thenecessary cross-sectional area is given by:

(19)A1 Fperm

6.3.2 Where expanded tubes are used, a sufficientsafety margin must additionally be applied to preventthe tubes from being pulled out of the tube plate. Sucha safety margin is deemed to be achieved if thepermissible load on the supporting area does notexceed the values specified in Table 7.13.

For the purpose of thecalculation, the suppor-ting area is given bythe expression : A2 = (da - di) losubject to a maximumof : A2 = 0,1 da lo

Table 7.13 Loading of expanded tube

Type ofexpandedconnection

Permissible load onsupporting area

[N/mm2]

Plain F / A2 150

With groove F / A2 300

With flange F / A2 400

For calculating the supporting area, the length of theexpanded section of tube (lo) may not be taken asexceeding 40 mm.

6.3.3 Where longitudinal stays, stay tubes or staybolts are welded in, the cross-section of the fillet weldsubject to shear shall be at least 1,25 times therequired bolt or stay tube cross-section:

da a1 1,25 A1 (20)


The allowable stress is to be determined in accordancewith 1.4.1. In departure from this, however, a value of

is to be expected in the area of the weld in theR

e,H,t

1,8case of stays, stay tubes and stay bolts made of rolledand forged steels.

7. Boiler and superheated tubes

7.1 Scope

The design calculation applies to tubes under internalpressure and, up to an outside tube diameter of 200


mm, also to tubes subject to external pressure.7.2 Symbols

pc [bar] design pressures [mm] wall thickness da [mm] outside diameter of tubeperm [N/mm2] allowable stressv [-] weld quality rating of

longitudinally welded tubes

7.3 Calculation of wall thickness

The necessary wall thickness s is given by theexpression :

(21)s da pc20 perm v pc


The design temperature applied is to be as specified inTable 7.3.

In the case of once through forced flow boilers, thecalculation of the tube wall thicknesses is to be basedon the maximum temperature expected in theindividual main sections of the boiler under operatingconditions plus the necessary added temperatureallowances.


The allowable stress is to be determined in accordancewith 1.4.1.

For tubes subject to external pressure, a value of is to be applied.

ReH,t

2,07.6 Quality rating of weld, vFor longitudinally welded tubes, the value of v to beapplied shall correspond to the approval test.

7.7 Wall thickness allowances

In the case of tubes subject to relatively severemechanical or chemical attack an appropriate wallthickness allowance shall be agreed which shall beadded to the wall thickness calculated by applyingformula (21). The permissible minus tolerance on thewall thickness (see 1.1.2) need only be taken intoconsideration for tubes whose outside diameterexceeds 76,1 mm.

7.8 Maximum wall thickness of boiler tubes

The wall thickness of intensely heated boiler tubes(e.g. where the temperature of the heating gas exceeds800 C) shall not be greater than 6,3 mm. Thisrequirement may be dispensed with in special cases,

e. g. for superheater support tubes.

8. Plain rectangular tubes and sectionalheaders

8.1 Symbols

pc [bar] design pressures [mm] wall thickness2 m [mm] clear width of the rectangular

tube parallel to the wall inquestion

2 n [mm] c l e a r w i d t h o f t h erectangular-tube perpendicularto the wall in question

Z [mm] coefficient according toformula (23)

a [mm] distance of relevant line ofholes from center line of side

t [mm] pitch of holesd [mm] hole diameterv [-] weakening factor for rows of

holes under tensile stress

v' [-] weakening factor for rows ofholes under bending stress

r [mm] inner radius at cornersperm [N/mm] allowable stress (see 1.4)8.2 Design calculation

8.2.1 The wall thickness is to be calculated for thecenter of the side and for the ligaments between theholes. The maximum calculated wall thickness shallgovern the wall thickness of the entire rectangulartube.

The following method of calculation is based on theassumption that the tube connection stubs have beenproperly mounted, so that the wall is adequatelystiffened.

8.2.2 The required wall thickness is given by theexpression :

If there are several different rows of holes, thenecessary wall thickness is to be determined for eachrow.

(22)s p

c n

20 perm v

4,5 Z pc

10 perm v,

8.2.3 Z is calculated by applying the formula:

(23)Z 13

m 3 n 3

m n

12

(m 2 a 2 )


Fig. 7.25

Fig. 7.26

Where Z has a negative value, the sign is to be disre-garded when incorporating the term into formula (22).8.3 Weakening factor v

8.3.1 If there is only one row of holes, or if thereare several parallel rows not staggered in relation toeach other, the weakening factors v and v' are to bedetermined as follows :

v t d

t

for wholes where d < 0,6 mv v t d

t

for wholes where d > 0,6 mv t 0,6 m

t

8.3.2 In determining the values of v and v' forelliptical holes, d is to be taken as the clear width ofthe holes in the longitudinal direction of therectangular tube. However, for the purpose ofdeciding which formula is to be used for determiningv', the value of d in the expressions d > 0,6 m andd < 0,6 m is to be the clear width of the holeperpendicular to the longitudinal axis.

8.3.3 In calculating the weakening factor forstaggered rows of holes, t is to be substituted in theformula by t for the oblique ligaments (Fig. 7.25).8.3.4 For oblique ligaments, the value of Z to beused in formula (22) is that determined by applyingformula (23), with a = 0, and multiplying by cos .

8.4 Stress at corners

In order to avoid undue stresses at corners, thefollowing conditions are to be satisfied :

r 1/2 s, subject to a minimum of:3 mm for rectangular tubes with a clear width of up to50 mm.

8 mm for rectangular tubes with a clear width of80 mm or over.

Intermediate values are to be interpolated linearly.The radius shall be governed by the arithmetical meanvalue of the nominal wall thicknesses on both sides ofthe corner. The wall thickness at corners may not beless than the wall thickness determined by applyingformula (22).

8.5 Minimum wall thickness and ligamentwidth

8.5.1 The minimum wall thickness for expandedtubes shall be 14 mm.

8.5.2 The width of a ligament between twoopenings or tube holes may not be less than 1/4 of thedistance between the tube centers.

9. Straps and girders

9.1 Scope

The following Rules apply to steel girders welded tothe combustion chamber crown.

9.2 General

The supporting girders are to be properly welded tothe combustion chamber crown at all points. They areto be arranged in such a way that the welds can becompetently executed and the circulation of water isnot obstructed.

9.3 Symbols

pc [bar] design pressureF [N] load carried by one girdere [mm] distance between center lines of

girders

l [mm] free length between girdersupports

b [mm] thickness of girderh [mm] height of girderW [mm3] section modulus of one girderM [Nmm] bending moment acting on

girder at given load

z [-] coefficient for section modulusperm [N/mm2] allowable stress (see 1.4)9.4 Design calculation

9.4.1 The simply supported combustion chambergirder shown in Fig. 7.26 is to be treated as a simplysupported beam of length l. The support afforded bythe plate material crown may also be taken intoconsideration.


9.4.2 The required section modulus of a combus-tion chamber crown is given by:

(24)W M

max

1,3 perm z

b h 2

6

The coefficient z for the section modulus takesaccount of the increase in the section modulus due tothe combustion chamber crown plate forming part ofthe girder. It may in general be taken as z = 5/3.

For the height h, a value not exceeding 8 b is to beinserted in the formula.

9.4.3 The maximum bending moment is given bythe expression :

(25)Mmax F l

8

where

(26)F p

c

10 l e

10. Bolts

10.1 Scope

The following Rules relate to bolts which, as forcetransmitting connecting elements, are subjected totensile stresses due to the internal pressure. Normaloperating conditions are assumed.

10.2 General

Necked-down bolts should be used for elastic boltedconnections, particularly where the bolts are highlystressed, or are exposed to service temperatures ofover 300 C, or have to withstand internal pressuresof 80 bar or over. All bolts > M 30 (30 mm diametermetric thread) must be necked-down bolts.Necked-down bolts are bolts to DIN 2510 with ashank diameter dS = 0,9 dk (dk being the root dia-meter). In the calculation special allowance is to bemade for shank diameters < 0,9 dk.

Bolts with a shank diameter of less than 10 mm arenot allowed.

Bolts may not be located in the path of heating gases.

At least 4 bolts must be used to form a connection.

To achieve small sealing forces, the jointing materialshould be made as narrow as possible and preferenceshould be given to the tongue and groove system.

Where standard pipe flanges are used, the strengthrequirements for the bolts are considered to besatisfied if the bolts used comply with DIN 2500 andconform to the specifications contained therein inrespect of the materials used, the maximum allowable

working pressure and the service temperature.

10.3 Symbols

pc [bar] design pressurep' [bar] test pressureFS [N] total load on bolted connection

in service

F'S [N] total load on bolted connectionat test pressure

FSo [N] total load on bolted connectionin assembled condition with nopressure exerted

FB [N] load imposed on boltedconnection by the workingpressure

FD [N] force to close joint underservice conditions

FDo [N] force to close joint inassembled condition

FZ [N] additional force due to stressesin connected piping

Db [mm] mean jointing or bolt pitchcircle diameter

di [mm] inside diameter of connectedpipe

ds [mm] shank diameter of anecked-down bolt

dk [mm] root diameter of threadn [-] number of bolts forming

connection

perm [N/mm2] allowable stress [-] surface finish coefficientc [mm] additional allowancek1 [mm] jointing factor for service

condition

ko [mm] jointing factor for assembledcondition

KD [N/mm2] jointing material deformationfactor

10.4 Design calculation

10.4.1 Bolted joints are to be designed for thefollowing load conditions:

a) Service conditions(design pressure pc and design temperaturet),

b) Load at test pressure


(lest pressure p', t = 20 C) andc) Assembled condition at zero pressure

(p = 0 bar, t = 20 C).10.4.2 The necessary root diameter of a bolt in abolted joint comprising n bolts is given by :

(27)dk 4 F

s

perm n c

10.4.3 The total load on a bolted joint is to becalculated as follows :

a) For service conditionsFS = FB + FD + FZ (28)

(29)FB D 2b

4

pc

10

(30)FD Db k1 p

c

10 1,2

(Where the arrangement of the bolts deviateswidely from the circular, due allowance is tobe made for the special stresses occurring)The additional force Fz due to connectedpiping must be calculated from the stressespresent in these pipes. Fz is 0 in the case ofbolted joints with no connected pipes. Whereconnecting pipes are installed in a normalmanner and the service temperatures are< 400 C, Fz may be determined, as anapproximation, by applying the expression :

FZ d 2i

4

pc

10

b) For the test pressure:

(31)Fs

pp

c

FB FD1,2

FZ

For calculating the root diameter of thethread, Fs is to be substituted by F's informula (27).

c) For the zero-pressure, assembled condition:FSO = FDO + FZ (32)FDO = Db ko KD (33)For calculating the root diameter of thethread, Fs is to be substituted by FSo informula (27).In the zero-pressure, assembled condition,the force FDO is to be exerted on the bolts

during assembly to effect an intimate unionwith the jointing material and to close thegap at the flange bearing surfaces.

If the force exerted on assembly FDO > FS,this value may be replaced by the followingwhere malleable jointing materials with orwithout metal elements are used :

(34)FDO 0,2 FDO 0.8 FS FDO

Factors ko, k and KD depend on the type and design ofthe joint and the material used. The relevant values areshown in the Tables 7.16 and 7.17.

10.4.4 The bolt design is to be based on the greatestroot diameter of the thread determined in accordancewith the three load conditions specified in paragraphs10.4.1 a) to 10.4.1 c).


The design temperatures of the bolts depend on thetype of joint and the insulation. In the absence ofspecial proof as to temperature, the following designtemperatures are to be applied:

Loose flange steam temperature - 30 C+ loose flange

Fixed flange steam temperature - 25 C+ loose flange

Fixed flange steam temperature -15 C+ fixed flange

The temperature reductions allow for the drop intemperature at insulated, bolted connections. Fornon-insulated bolted joints, a further temperature re-duction is not permitted because of the higher thermalstresses imposed on the entire bolted joint.


The values of the allowable stress perm are shown inTable 7.14.

Table 7.14 Allowable stress perm

Condition for necked-down bolts

for full-shank bolts

Servicecondition

Re,H,t

1,5R

e,H,t

1,6


Test pressureand zero-pressureassembledcondition

Re,H,20

1,1

Re,H,20

1,2

10.7 Surface finish coefficient

10.7.1 Full-shank bolts are required to have asurface finish of at least grade mg to DIN 267.Necked-down bolts must be machined all over.

10.7.2 In the case of unmachined, plane-parallelbearing surfaces, = 0,75. Where the bearing sur-faces of the mating parts are machined, a value of =1,0 may be used. Bearing surfaces which are notplane-parallel (e. g. on angle sections) are notpermitted.

10.8 Additional allowance c

The additional allowance c mm shall be as shown inTable 7.15.

Table 7.15 Additional allowances c

Condition c [mm]For service conditions :

up to M 24M 27 up to M 45M 48 and over

35 - 0,1 . dk

1

for test pressure 0

for assembled conditions 0

E. Equipment and Installation

1. General

1.1 The following requirements apply to steamboilers which are not constantly and directlymonitored during operation. Note is also to be takenof the official regulations of the flag country of thevessel, where appropriate.

1.2 In the case of steam boilers which are monitoredconstantly and directly during operation, some easingof the following requirements may be permit ted,while maintaining the operational safety of the vessel.

1.3 In the case of steam boilers which have amaximum water volume of 150 litres, a maximumallowable working pressure of 10 bar and where theproduct of water volume and maximum allowablewater pressure is less than 500, an easing of thefollowing requirements may be permitted.

1.4 With regard to the electrical installation andequipment also the Rules for Electrical Installations,Volume IV and Rules for Automation,Volume VII areto be observed.

2. Safety valves

2.1 Any steam boiler which has its own steam spaceis to be equipped with at least two reliable, spring-loaded safety valves. At least one safety valve is to beset to respond if the maximum allowable workingpressure is exceeded.

In combination, the safety valves must be capable ofdischarging the maximum quantity of steam which canbe produced by the steam boiler during continuousoperation without the maximum allowable workingpressure being exceeded by more than 10 %.

2.2 Any steam boiler which has a shut-off but whichdoes not have its own steam space is to have at leastone reliable, spring-loaded safety valve fitted at itsoutlet. At least one safety valve is to be set to respondif the maximum allowable working pressure isexceeded. The safety valve or safety valves are to bedesigned so that the maximum quantity of steamwhich can be produced by the steam boiler duringcontinuous operation can be discharged without themaximum allowable working pressure being exceededby more than 10 %.

2.3 External steam drums are to be fitted with atleast two reliable, spring-loaded safety valves. At leastone safety valve is to be set to respond if theallowable working pressure is exceeded. Incombination, the safety valves must be capable ofdischarging the maximum quantity of steam which canbe produced in continuous operation by all connectedsteam generators without the maximum allowableworking pressure of the steam drum being exceededby more than 10 %.

2.4 The closing pressure of the safety valves shallbe no more than 10 % below the response pressure.

2.5 The minimum flow diameter of the safety valvesmust be 15 mm.

2.6 Servo-controlled safety valves are permittedwherever they are reliably operated without anyexternal energy source.

2.7 The safety valves are to be fitted to the saturatedsteam part or, in the case of steam boilers which donot have their own steam space, to the steam-wateroutlet of the boiler.

2.8 In the case of steam boilers which are fitted withsuperheaters with no shut-off capability, at least twosafety valves must be located at the discharge from thesuperheater. Superheaters with shut-off capability areto be fitted with at least one safety valve.

Safety valves which are located at the discharge fromthe superheater must be designed for at least 25 % ofthe required blow-off capacity. When designing safetyvalves, allowance is to be made for the increase in the


volume of steam caused by superheating.

2.9 Steam may not be supplied to the safety valvesthrough pipes in which water may collect.

2.10 Safety valves must be easily accessible andcapable of being released safely during operation.

2.11 Safety valves are to be designed so that nobinding or jamming of moving parts is possible evenwhen heated to different temperatures. Seals whichmay prevent the operation of the safety valve due tofrictional forces are not permitted.

2.12 Safety valves are to be set in such a way as toprevent unauthorized alteration.

2.13 Pipes or valve housings must have a drain facilitywhich has no shut-off capability fitted at the lowestpoint on the blow-off side.

2.14 Combined blow-off lines from several safetyvalves may not unduly impair the blow-off capability.

The discharging mediums are to be drained awaysafely.

3. Water level indicators

3.1 Steam boilers which have their own steamchamber are to be fitted with two devices giving adirect reading of the water level.

3.2 Steam boilers which have their own steam spaceheated by exhaust gases whose temperature does notexceed 400 C, are to be fitted with at least one devicegiving a direct reading of the water level.

3.3 External steam drums of boilers which do nothave their own steam space are to be fitted with twodevices giving a direct reading of the water level.

3.4 Cylindrical glass water level gauges are notpermitted.

3.5 The water level indicators are to be fitted so thata reading of the water level is possible when the shipis heeling and during the motion of the ship when it isat sea. The limit for the lower visual range must be atleast 30 mm above the highest flue, but at least 30 mmbelow the lowest water level. The lowest water levelmay not be above the centre of the visual range.

The water level indicators must be well illuminatedand visible from the boiler control station.

3.6 The connection pipes between steam generatorand water level indicators must have a inner diameterof at least 20 mm. They must be run in such a way thatthere are no sharp bends in order to avoid water andsteam traps, and must be protected from the effects ofthe heated gases and against cooling.

Where water level indicators are linked by means ofcommon connection lines or where the connectionpipes on the water side are longer than 750 mm, the

connection pipes on the water side must have an innerdiameter of at least 40 mm.

3.7 Water level indicators are to be connected to thewater and steam chamber of the boiler by means ofeasily accessible, simple to control and quick-actingshut-off devices.

3.8 The devices used for blowing through the waterlevel indicators must be designed so that they are safeto operate and so that blow-through can be monitored.The discharging mediums are to be drained awaysafely.

3.9 Remote water level indicators and displayequipment of a suitable type to give an indirectreading may be approved as additional displaydevices.

3.10 In place of water level indicators, once-throughforced flow boilers must be fitted with two mutuallyindependent devices which trip an alarm as soon aswater flow shortage is detected. An automatic deviceto shut down the heating system may be provided inplace of the second warning device.

3.11 The cocks and valves of the water levelindicators which cannot be directly reached by handfrom floor plates or a control platform must be have acontrol facility using pull rods or chain pulls.

4. Pressure gauges

4.1 Each steam boiler is to be fitted with twopressure gauges which are linked to the steam space.The allowable maximum working pressure is to bemarked on the dial by means of a permanent andeasily visible red mark. The display range of thepressure gauge must include the test pressure. Onepressure gauge must be located on the boiler andanother at the machinery control station or at someother appropriate site.

Where several steam boilers are incorporated on oneship, the steam chambers of which are linked together,one pressure gauge is sufficient at the machinerycontrol station or at some other suitable location, inaddition to the pressure gauges on each boiler.

4.2 The pipe to the pressure gauge must have awater trap and must be of a blow-off type. Aconnection for a test gauge must be installed close tothe pressure gauge. In the case of pressure gaugeswhich are set off at a lower position the testconnection must be provided close to the pressuregauge and also close to the connection piece of thepressure gauge pipe.

4.3 Pressure gauges are to be protected againstradiant heat and must be well illuminated.

5. Temperature gauges

5.1 A temperature gauge is to be fitted to the fluegas outlets of fired steam boilers.


5.2 Temperature gauges are to be fitted to theexhaust gas inlet and outlet of steam boilers heated byexhaust gas.

5.3 Temperature gauges must be fitted at theoutlets from superheaters or superheater sections, atthe inlet and outlet of attemporators, and also at theoutlet of once-through forced flow boilers, where thisis necessary to assess the behaviour of the materialsused.

6. Regulating devices (Controllers)6.1 With the exception of boilers which areheated by exhaust gas, steam boilers are to beoperated with rapid-control, automatic firing systems.In main boilers, the control facility must be capable ofsafely controlling all rates of speed and manoeuvresso that the steam pressure and the temperature of thesuper-heated steam stay within safe limits and thesupply of feed water is guaranteed. Auxiliary boilersare subject to the same requirements within the scopeof potential load changes.

6.2 Steam pressure must be automatically regu-lated by controlling the supply of heat. The steampressure of boilers heated by exhaust gas may also beregulated by condensing the excess steam.

6.3 In the case of boilers which have a specifiedminimum water level, the water level must be regu-lated automatically by controlling the supply of feedwater.

6.4 In the case of forced-circulation boilerswhose heating surface consists of a steam coil andonce-through forced flow boilers, the supply of feedwater may be regulated as a function of fuel supply.

6.5 In the case of steam boilers which are fittedwith superheaters, the temperature of the superheatedsteam must be automatically regulated unless thecalculated temperature is higher than the maximumattainable temperature of the superheater walls.

7. Monitoring devices (Alarms)7.1 A warning device is to be fitted which istripped when the specified maximum water level isexceeded.

7.2 In exhaust-gas heated boilers, a warningdevice is to be fitted which is tripped when themaximum allowable working pressure is exceeded.

7.3 In exhaust-gas heated boilers with a specifiedminimum water level, a warning device is to be fittedwhich is tripped when the water falls below this level.

7.4 Exhaust gas boilers with finned tubes are tohave a temperature monitor fitted in the exhaust gaspipe which trips an alarm in the event of fire. Cf.Rules for Automation, Volume VII.

7.5 Where there is a possibility of oil or greasegetting into the steam or condensate system, a suitableautomatic and continuously operating unit is to beinstalled which trips an alarm and cuts off the feedwater supply if the concentration at which boileroperation is put at risk is exceeded.

7.6 Where there is a possibility of acid, lye orseawater getting into the steam or condensate system,a suitable automatic and continuously operating unitis to be installed which trips an alarm and cuts off thefeed water supply if the concentration at which boileroperation is put at risk is exceeded.

7.7 It must be possible to carry out function test-ing of the monitoring devices, even during operation,if an equivalent degree of safety is not attained byself-monitoring of the equipment.

7.8 The monitoring devices must trip visual andaudible fault warnings in the boiler room or in themachinery control room or any other suitable site. CfRules for Automation, Volume VII.

8. Safety devices (Limiters)8.1 The suitability of safety devices for marineuse is to be proven by type testing.

8.2 Fired boilers are to be equipped with a reli-able pressure limiter which cuts out and interlocks thefiring system when the maximum allowable workingpressure is exceeded.

8.3 In steam boilers on whose heating surfaces ahighest flue is specified, two reliable, mutuallyindependent water level limiters must respond to cutout and interlock the firing system when the waterfalls below the specified minimum water level. Thewater level limiter must also be independent of thewater level control devices.

8.4 The receptacles for water level limiterslocated outside the boiler must be connected to theboiler by means of lines which have a minimum innerdiameter of 20 mm. Shut-off devices in these linesmust have a nominal diameter of at least 20 mm andmust indicate their open or closed position. Wherewater level limiters are connected by means ofcommon connection lines, the connection pipes on thewater side must have an inner diameter of at least40 mm.

Operation of the firing system may only be possiblewhen the shut-off devices are open or else, afterclosure, the shut-off devices must reopenautomatically and in a reliable manner.

Water level limiter receptacles which are locatedoutside the boiler are to be designed in such a waythat a compulsory and periodic blow-through of thereceptacles and lines can be carried out.

8.5 In the case of forced-circulation boilers with


a specified lowest water level, two reliable, mutuallyindependent safety devices must be fitted in additionto the requisite water level limiters, which will cut outand interlock the heating system in the event of anyunacceptable reduction in water circulation.

8.6 In the case of forced-circulation boilerswhose heating surface consists of a single coil andonce-through forced flow boilers, two reliable,mutually independent safety devices must be fitted inplace of the water level limiters in order to provide asure means of preventing any excessive heating of theheating surfaces by cutting out and interlocking thefiring system.

8.7 In steam boilers with superheaters, atemperature limiter is to be fitted which cuts out andinterlocks the heating system if the allowablesuperheated steam temperature is exceeded. In thecase of boiler parts which carry superheated steamand which have been designed to long-term resistancevalues, one temperature recording device is adequate.

8.8 The safety devices must trip visual andaudible alarms in the boiler room or in the machinerycontrol room or any other appropriate site. Cf. Rulesfor Automation, Volume VII.

8.9 The electrical devices associated with thelimiters are to be designed in accordance with theclosed-circuit principle so that, even in the event of apower failure, the limiters will cut out and interlockthe systems unless an equivalent degree of safety isachieved by other means.

8.10 To reduce the effects due to swell, waterlevel limiters can be fitted with a delay functionprovided that this does not cause a dangerous drop inthe water level.

8.11 The electrical interlocking of the firingsystem following tripping by the safety devices mayonly be cancelled out at the firing system controlpanel itself.

8.12 If an equivalent degree of safety cannot beachieved by the self-monitoring of the equipment, thesafety devices must be subjected to operational testingeven during operation. In this case, the operationaltesting of water level limiters must be carried outwithout the surface of the water dropping below thelowest water level.

8.13 For details of additional requirementsrelating to once-through forced flow boilers, see 3.10.

9. Feed and circulation devices

9.1 For details of boiler feed and circulation de-vices, see Section 11, F. The following requirementsare also to be noted:

9.2 The feed devices are to be fitted to the steamboiler in such a way that it cannot be drained lower

than 50 mm above the highest flue when the non-re-turn valve is not tight.

9.3 The feed water is to be introduced into theboiler in such a way as to prevent damage occurring tothe boiler walls and to heated surfaces.

10. Shut-off devices

10.1 Each steam boiler must be capable of being shutoff from all connected pipes. The shut-off devices areto be installed as close as possible to the boiler wallsand must operate without risk.

10.2 Where several boilers which have differentmaximum allowable working pressures give off theirsteam into common lines, it is necessary to ensure thatthe maximum working pressure allowable for eachboiler cannot be exceeded in any of the boilers.

10.3 Where there are several boilers which areconnected by common pipes and the shut-off devicesfor the steam, feed and drain lines are welded to theboiler, for safety reasons while the boilers arerunning, two tandem shut-off devices which are to beprotected against unauthorised operation are each tobe fitted with an interposed release device.

11. Scum removal, sludge removal, drain andsampling devices

11.1 Boilers and external steam drums are to be fittedwith devices to allow them to be drained and thesludge removed. Where necessary, boilers are to befitted with a scum removal device.

11.2 Drain devices and their connections must beprotected from the effects of the heating gases andcapable of being operated without risk. Self-closingsludge removal valves must be lockable when closedor alternatively an additional shut-off device is to befitted in the pipe.

11.3 Where the scum removal, sludge removal ordrain lines from several boilers are combined, a non-return valve is to be fitted in the individual boilerlines.

11.4 The scum removal, sludge removal or drainlines, plus valves and fittings, are to be designed toallow for the maximum allowable working pressure ofthe boiler.

11.5 With the exception of once-through forced flowboilers, devices for taking samples from the watercontained in the boiler are to be fitted to steam boilers.

11.6 Scum removal, sludge removal, drain andsampling devices must be capable of safe operation.The mediums being discharged are to be drained awaysafely.

12. Name plate

12.1 A name plate is to be permanently affixed toeach steam boiler, displaying the following


information:

Manufacturer,

Build number and year of construction,

Maximum allowable working pressure in bar,

Steam production in kg/h or t/h,

Permitted temperature of super-heated steam inC provided that the boiler is fitted with asuper-heater with no shut-off capability.

12.2 The name plate must be permanently attached tothe largest part of the boiler or to the boiler frame sothat it is visible.

13. Valves and fittings

13.1 Materials

Valves and fittings for boilers must be made of ductilematerials as specified in Table 7.1 and all theircomponents must be able to withstand the loadsimposed in operation, in particular thermal loads andpossible stresses due to vibration. Grey cast iron maybe used within the limits specified in Table 7.1, butmay not be employed for valves and fittings which aresubjected to dynamic loads, e.g. safety valves andblow-off valves.

Testing of materials for valves and fittings is to becarried out as specified in Table 7.2.

13.2 Design

Care is to be taken to ensure that the bodies of shut-off gate valves cannot be subjected to unduly highpressure due to heating of the enclosed water. Valveswith screw-on bonnets must be safeguarded to preventunintentional loosening of the bonnet.

13.3 Pressure and tightness tests

13.3.1 All valves and fittings are to be subjected toa hydrostatic pressure test at 1,5 times the nominalpressure before they are fitted. Valves and fittings forwhich no nominal pressure has been specified are tobe tested at twice the working pressure. In this case,the safety factor in respect of the 20 C yield strengthvalue may not fall below 1,1.

13.3.2 The sealing efficiency of the closed valve isto be tested at the nominal pressure or at 1,1 times theworking pressure, as applicable. Valves and fittingsmade of castings and subject to operatingtemperatures over 300 C are required to undergo oneof the following tightness tests:

a) Tightness test with air (test pressure approxi-mately 0,1 x working pressure; maximum 2 bar);

b) Tightness test with saturated or superheatedsteam (test pressure may not exceed themaximum allowable working pressure);

c) A separate tightness test may be dispensed withif the pressure test is performed with petroleumor other liquid displaying similar properties.

14. Installation of boilers

14.1 Mounting

Boilers must be installed in the ship with care andmust be secured to ensure that they cannot bedisplaced by any of the circumstances arising whenthe ship is at sea. Means are to be provided toaccommodate the thermal expansion of the boiler inservice. Boilers and their seatings must be easilyaccessible from all sides or must be easily renderedso.

14.2 Fire precautions

See Section 12.

F. Testing of Boilers

1. Constructional test

After completion, boilers are to undergo aconstructional test.

The constructional test includes verification that theboiler agrees with the approved drawing and is ofsatisfactory construction. For this purpose, all parts ofthe boiler must be accessible to allow adequateinspection. If necessary, the constructional test is to beperformed at separate stages of manufacture. Thefollowing documents are to be presented: material testcertificates covering the materials used, reports on thenon-destructive testing of welds and, whereapplicable, the results of tests of workmanship andproof of the heat treatment applied.

2. Hydrostatic pressure tests

2.1 A hydrostatic pressure test is to be carried out onthe boiler before the insulation is fitted. Where onlysome of the component parts are sufficientlyaccessible to allow proper visual inspection, thehydrostatic pressure test may be performed in stages.Boiler surfaces must withstand the test pressurewithout leaking or suffering permanent deformation.

2.2 The test pressure is generally required to be 1,5times the maximum allowable working pressure,subject to a minimum of PB + 1 bar.2.3 In the case of continuous-flow boilers, the testpressure must be at least 1,1 times the water inletpressure when operating at the maximum allowableworking pressure and maximum steam output. In theevent of danger that parts of the boiler might besubjected to stresses exceeding 0,9 of the yieldstrength, the hydrostatic test may be performed inseparate sections. The maximum allowable workingpressure is then deemed to be the pressure for which


the particular part of the boiler has been designed.

2.4 For boiler parts subject to internal and externalpressures which invariably occur simultaneously inservice, the test pressure depends on the differentialpressure. In these circumstances, however, the testpressure should at least be equal to 1,5 times thedesign pressure specified in D.1.2.4.

G. Hot Water Generators

1. Design

Hot water generators with a permissible dischargetemperature of > 120 C, which are heated by solid,liquid or gaseous fuels or by exhaust gases or electri-cally are to be treated in a manner analogous to thatapplied to boilers. The materials and strengthcalculations for hot water generators which are heatedby steam or hot liquids are subject to the requirementsin Section 8 (Pressure Vessels).2. Equipment

The safety equipment of hot water generators issubject to the requirements contained in DIN 4752with due regard for the special conditions attaching toshipboard operation.

3. Testing

Each hot water generator is to be subjected to amanufacturing test and to a hydrostatic pressure test at1,5 times the maximum allowable working pressuresubject to a minimum of 4 bar.

H. Exhaust Gas Economizers

1. Definition

Exhaust gas economizers are preheaters connected tothe exhaust gas side of boiler heating surfaces whichare used, without steam being produced in them inservice, to preheat the feedwater and which can beisolated from the water side of the boiler.

The surfaces of the preheater comprise the waterspace walls located between the shut-off devices plusthe casings of the latter. Water may be taken from theeconomizer only if the boiler feed system is speciallydesigned for this purpose.

2. Materials

See under B.

3. Design calculation

The formulae given under D are to be applied in thecalculation. The design pressure is to be at least thamaximum allowable working pressure of the

economizer.

The design temperature is the maximum feedwatertemperature plus 25 C for plain tube economizersand plus 35 C for finned tube economizers.