dnvgl-ru-uwt-pt4ch7 pressure vessels … · ship pt.4 ch.7, where applicable. 2 references the...

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DNV GL AS

RULES FOR CLASSIFICATION

Underwater technologyEdition December 2015

Part 4 Machinery and systems

Chapter 7 Pressure Vessels

FOREWORD

DNV GL rules for classification contain procedural and technical requirements related to obtainingand retaining a class certificate. The rules represent all requirements adopted by the Society asbasis for classification.

© DNV GL AS December 2015

Any comments may be sent by e-mail to [email protected]

If any person suffers loss or damage which is proved to have been caused by any negligent act or omission of DNV GL, then DNV GL shallpay compensation to such person for his proved direct loss or damage. However, the compensation shall not exceed an amount equal to tentimes the fee charged for the service in question, provided that the maximum compensation shall never exceed USD 2 million.

In this provision "DNV GL" shall mean DNV GL AS, its direct and indirect owners as well as all its affiliates, subsidiaries, directors, officers,employees, agents and any other acting on behalf of DNV GL.

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Rules for classification: Underwater technology — DNVGL-RU-UWT-Pt4Ch7. Edition December 2015 Pressure vessels

DNV GL AS

CURRENT – CHANGES

This is a new document.

The rules enter into force 1 July 2016.

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CONTENTS

Current – changes...................................................................................................... 3

Section 1 General....................................................................................................... 51 Introduction............................................................................................52 References.............................................................................................. 53 Documentation, certification and testing requirements.......................... 54 Marking and signboards......................................................................... 6

Section 2 Pressure vessels and gas cylinders............................................................ 71 Pressure vessels.....................................................................................72 Gas cylinders.......................................................................................... 73 Design.....................................................................................................84 Manufacture............................................................................................9

Section 3 Acrylic hull and windows..........................................................................101 General................................................................................................. 102 Materials............................................................................................... 123 Manufacture of windows.......................................................................124 Certification of windows.......................................................................135 Window shapes and sizes.....................................................................146 Window seats and installation of windows........................................... 217 In service inspection............................................................................ 22

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SECTION 1 GENERAL

1 Introduction

1.1 Application

1.1.1 The following rules apply to all pressure vessels excluding pressure hulls, that are fitted to anunderwater system.

1.1.2 The requirements of this chapter shall be regarded as supplementary to those given for main classSHIP Pt.4 Ch.7, where applicable.

2 ReferencesThe documents to be submitted to the Society for approval and the initial tests and trials are stated in Pt.5Ch.1 to Ch.9.The necessary markings for pressure vessels are summarized in Pt.4 Ch.1 Sec.2.The pressures on which the design is to be based shall be taken from the relevant Chapters/Sections.

3 Documentation, certification and testing requirements

3.1 Documentation requirementsFor documentation requirements see RU SHIP Pt.4 Ch.7 Sec.1 [3.1].

3.2 Certification requirementsFor certification requirements see RU SHIP Pt.4 Ch.7 Sec.1 [3.2].

3.3 Initial testing requirements

3.3.1 Requirements for and guidance on inspection and monitoring associated with the production ofpressure vessels can be found in SHIP Pt.4 Ch.7 Sec.7 or the applied standard.

3.3.2 For welded pressure vessels the following tests shall be carried out in addition to the tests specified inthe applied design code or standard:

a) all butt welds in diving chambers shall be radiographed over their full lengthb) branches and reinforcement of openings, including all weld connections to the shell, shall be subjected to

100% magnetic particle testing.

3.3.3 When the applied code or standard for welded pressure vessels requires heat treatment of dished endsafter hot or cold forming, mechanical testing may be required after the final heat treatment.

3.3.4 The details between intermediate heads and cylindrical shells of chambers shall be done in accordancewith requirements given in:

a) EN 1708-1:1999 Welding - Basic weld joint details in steel Table 9:Internal diaphragms and separators,or

b) ASME Section VIII - Division I Figure UW-[13.1].

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3.3.5 Welded pressure vessels and seamless steel gas containers for internal pressure shall be hydrostatictested to an internal pressure in accordance with the design code. Each compartment in chambers shall betested separately if the design allows for separate pressurisation. In addition pressure test shall be performedwith test pressure in each compartment simultaneously.

3.3.6 Pressure vessels for external pressure shall, in addition to the internal pressure testing, be hydrostatictested to an external pressure in accordance with the design code.

3.3.7 For seamless gas cylinders production tests shall be carried out in accordance with the requirementsgiven in the applied code or standard. Further production tests, and required attendance during testing, maybe given in the specifications.

3.3.8 The gas storage and chambers shall be tested for leakage at low pressures and the maximum workingpressure.

4 Marking and signboardsFor marking and signboards see Pt.4 Ch.1.

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SECTION 2 PRESSURE VESSELS AND GAS CYLINDERS

1 Pressure vessels

1.1 Pressure vessels under internal or external pressure are typically used for:

— manned hyperbaric chambers— gas storage— compensating tanks— trimming tanks— fuel bunkers (if existing)— battery compartments— equipment containers/housings, e.g. for rescue equipment, cameras, searchlights, etc.— pressure storages for hydraulic systems.

1.2 For quantitative design parameters and functional requirements, reference is made to relevant standards andguidelines, including normative references given in Sec.1.

1.3 All manned hyperbaric chambers shall be designed, constructed and tested according to one of the followingcodes and standards:

— the Society rules for Underwater Technology Pt.4 Ch.7 Sec.3 Acrylic pressure hull and windows— EN 13445 Unfired pressure vessels.— ASME PVHO-1, referencing ASME VIII Div.1 or 2 Boiler and Pressure Vessel Code— other codes and standards may be evaluated and accepted on a case by case basis.

Manned hyperbaric chambers shall be classified in the highest category in the applied code or standard.Further requirements for manned hyperbaric chambers are listed in Pt.5

2 Gas cylinders

2.1 Gas cylinders are amongst others utilized for:

— compressed air for blowing tanks and bunkers— breathing gases.— gases for drives of submersibles, e.g. cyclic motors as well as fuel cell drives.

2.2 Gas cylinders shall be designed, constructed and tested according to one of the following standards, norms ordirectives:

— EN-1964-1 Transportable gas cylinders (part 1:1999, part 2:2001 or part 3:2000)— EN ISO 11120 Gas cylinders - Refillable seamless steel tubes for compressed gas transport, of water

capacity between 150 l and 3000 l - Design construction and testing

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— other codes and standards may be evaluated and accepted on a case by case basis.Guidance note:For permanent installations within EU, the directives apply as regulations. (ref. EU directive 1999/36/EEC.)

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3 Design

3.1 GeneralThe objectives of this sub-section are to give additional requirements that relate to the function of thesepressure vessels in an underwater system.Pressure vessels shall be designed and manufactured to internationally recognised codes and standards.Pressure vessels subjected to internal pressure may also be designed and manufactured according toSHIP Pt.4 Ch.7.Pressure vessels subjected to external pressure may also be designed and manufactured according to Pt.3Ch.3.Pressure vessels shall be designed under consideration of Pt.2 Ch.5 Sec.1 [2] and to be tested according toPt.5 Ch.1 or Pt.5 Ch.6 Sec.2 [6].Other materials not specifically covered by the rules will be considered case by case.

3.2 Verification by testingFor pressure vessels subjected to external pressure outside the pressure hull of manned submersibles, whosestrength cannot be proven sufficiently by computation, verification by testing may be accepted.A replica of the pressure vessel built under the same conditions as the actual pressure vessel shall besubjected to a pressure test at 1.1 x collapse diving pressure (CDP). No yielding shall occur.For unmanned underwater systems a test pressure of 1.0 x CDP may be applied.Type and scope of such a test shall be agreed with the Society.If it is guaranteed by suitable technical measures that at any time a defined internal pressure is existing, thetest may be performed only with the differential pressure.

3.3 PenetrationsAll penetrations in manned hyperbaric chambers shall be designed to minimise corrosion from any fluidpassing through them.

Guidance note:In some cases this requirement may best be met by the use of a sleeve passing through the hull penetration.


3.4 Shut-off and pressure reliefPressure vessels shall be fitted with over pressure relief devices and shut-off valves.Pressure vessels without individual shut-off valves and with: p V < 50 bar m³, installed in groups with a totalp V < 100 bar m³, can have a common overpressure relief device and shut-off valve.For gas storage of breathing gases and oxygen, the pressure relief device shall be a safety valve. Safetyvalves shall be set to open at a pressure approx. 3% above the developed pressure at 55°C, based on fillingthe cylinders at 15°C to maximum filling pressure.The total relieving capacity shall be sufficient to maintain the system pressure at not more than 110% ofdesign pressure.

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Developed pressure under above-mentioned conditions may be taken as given in reference to a standardsuch as BS 5355 Specification for filling ratios and developed pressures for liquefiable and permanent gases.

3.5 DrainageDrainage devices shall be provided where water can accumulate (e.g. volume tanks and filters).

4 Manufacture

4.1 Welding of pressure vessels and general workmanship requirements are given in the relevant rules, codesand standards.

4.2 Pressure vessels shall be produced by manufacturers approved for such production and certified when:

p V ≥ 1.0

where:

p = design pressure in barV = volume in m3

Smaller pressure vessels shall be certified if they provide an essential function in the system.Guidance note:Cylinders on-line in a breathing gas systems will be considered essential.


Gas cylinders shall be cleaned and sealed according to accepted industry standards.

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SECTION 3 ACRYLIC HULL AND WINDOWS

1 General

1.1 ScopeThese rules cover requirements to acrylic windows used for the viewports of pressure hulls which are made ofcast, unlaminated polymethyl methacrylate plastic.

1.2 Limits of applicationFor acrylic windows following limits for application apply:

– designed service life 10 resp. 20 years (see guidance notes below)

– temperature range –18°C to +66°C

– rate of pressurization max. 10 bar/s

– pressure cycles at design pressure max. 10 000

– period under pressure at design pressure max. 40 000 h

– maximum allowable working pressure max. 1380 bar

The design service life for acrylic windows depends on numerous factors, in particular on the kind of loading.The maximum design service life to be assumed for spherical or cylindrical windows subjected to externaloverpressure, which are exclusively exposed to compressive stresses or minor bending stresses only, isgenerally 20 years, while for flat windows with flat seat it is 10 years. The design service life starts with thedate of manufacturing regardless of the date of use.Depending on the previous actual loads acting on the windows and testing to be agreed with the Society indetail, extension of the service life of acrylic windows may be approved.

1.3 Procedural requirements1.3.1 Certification requirementsThe required certificates for design and manufacturing are summarized in Table 1.

Table 1 Certification required for acrylic hulls and windows

Object Certificatetype Issued by Certification standard* Additional description

Material manufacturer VL Society ASME PVHO-1 For details see Pt.2 Ch.5 Sec.6

Acrylic material W Manufacturer ASME PVHO-1 For details see Pt.2 Ch.5 Sec.6

Design of acrylic hull VL Society For each form of application

Design of acrylicwindow VL Society For each type of window and

form of application

Manufacturer of acrylichulls VL Society Types of acrylic hulls to be

defined

Manufacturer of acrylicwindows VL Society Types of windows to be defined

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Object Certificatetype Issued by Certification standard* Additional description

Manufacturinginspection VL Society All manufacturing steps to be

checked

Pressure tests W Manufacturer For details see [1.3]

*Unless otherwise specified the certification standard is the rules.

1.3.2 Documentation requirements for acrylic hulls and windowsThe required documentation is summarised in Table 2.

Table 2 Documentation requirements for acrylic hulls and windows

Object Documentation type Additional description Info

Z050 Design philosophy AP

Z051 Design basis Including type of mission and loads, etc. FI

M030 Material specification,non metallic materials Certificate acc. to Table 1 AP

H080 Strength analyses Acc. to the Society Rules or recognisedstandard AP

C030 Detailed drawing Certificate for each form and applicationacc. to Table 1

Z030 Arrangement plan Especially the seating situation shall beincluded AP

Z090 Equipment list Fixation and sealing material, etc. AP

Z000 Manufacturerassessment

Certificates for hull or windowmanufacturers acc. to Table 1 AP

Z162 Installation manualSpecial care shall be observed for realisticgeometrical tolerances of the window andthe seating!

AP

Z170 Installation manual Including fixing and tight connection toother structures of submersible AP

Acrylic hulls and windows

Z254 Commissioningprocedure

Including certificates for manufacturinginspection and pressure tests acc. to Table1

AP

AP = For approval; FI = For information

1.4 TestingAcrylic windows shall be presented to the Society for an inspection of manufacture. In addition, each windowshall be subjected, in the presence of a surveyor, to a pressure test in accordance with Pt.5 Ch.6 Sec.2[6.3.3]. At the pressure test the direction of pressure shall be observed. If the windows are subjected topressure from both sides, this is to be considered for the testing.

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1.5 Marking

1.5.1 Each window shall have an identification marked on it for traceability.During the manufacturing process each window shall be marked for identification and a manufacture processrider shall be assigned to it for recording of all pertinent data.

1.5.2 After manufacturing each window shall be permanently marked with at least the following details:

— design pressure PR = NDP [bar]— design temperature [°C]— the Society’s approval stamp— manufacturer's name or identifying mark— serial number and year of manufacture— applied standard— direction of pressure, if it is not clear.

1.5.3 Wherever possible, the marking shall be in the non-load-bearing portion of the window edge. If anindelible marker is used, it shall be proven that the marker does not harm the acrylic material.Stamping or marking that can cause crack propagation is not permitted. The use of punches is not allowed.

2 MaterialsThe requirements for materials for acrylic windows are stated in Pt.2 Ch.5.

3 Manufacture of windows

3.1 The manufacture of acrylic windows covered by these rules may only take place in specialized workshopswhich have been approved by the Society for that purpose. Such approval can be granted only to thosecompanies which employ properly trained specialists and which have available the necessary technicalfacilities enabling them to undertake the expert forming, machining, heat treatment and quality control ofacrylic windows.Application for approval is to be made to the Society before the manufacture of windows commences.

3.2 Each window shall be annealed after all forming and polishing operations are completed. The annealing process shall be in accordance with the approved acrylic plastic manufacturer's specification or the annealing schedule in ASME PVHO-1-2012,Section 2, 4.5.After tempering no further mechanical polishing may be carried out on the window.Flat disk windows for diving chambers where only the surrounding area is professionally machined need notto undergo a heat treatment after manufacturing.

3.3 Window surfaces shall be polished in such a way as to meet the optical clarity requirement stated in Table 3.

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3.4 For each window or series of windows the window manufacturer shall issue a component certificate specifyingall the stages of manufacture such as cutting, sticking, polishing, forming and tempering. In addition thescope of tests, the test results, the marking of the windows and the date of manufacture shall be indicated.

Table 3 Mechanical and optical properties of acrylic plastics

Properties Specified values Test method ASTM

Ultimate tensile strength ≥ 62 N/mm2

Elongation at break (in relationto necking zone) ≥ 2 %

DIN 53 455 1)

specimen type 3

test velocity II

standard climate 23/50

Modulus of elasticity measuredby tensile test ≥ 2760 N/mm2 DIN 53 457

D 638 1)

Compressive yield strength ≥ 103 N/mm2

DIN 53 454 1)

standard climate 23/50

size of test specimen:

25 × 12.5 × 12.5 mm

Modulus of elasticity meas-uredby compression test ≥ 2760 N/mm2 DIN 53457 1)

D 695 1)

Compressive deformation ≤ 1 %Constant compressive stress 1) of27.5 N/mm2 for 24 h at 50 °C

test cube: 12.5 mm edge lengthD 621 1)

Ulltraviolet transmittance ≤ 5 %UV-spectrophotometerwave length range: 290 – 370 nm

thickness of specimen: 12.5 mmE 308

Visual clarity Legibility

A 25 x 25 mm standard type set comprising 7lines of 16 letters each shall be clearly legiblethrough the acrylic plastic pane at a distanceof 500 mm.

D 702

Residual monomers methylmethacrylate aethyl acrylate ≤ 1.6% Gas chromatograph

1) The mechanical properties shall be verified on at least 2 specimens.

4 Certification of windowsEach acrylic plastic window used in underwater systems shall have a certificate issued by the Society. Basisfor the certification are the test results and the annealing conditions as given in e.g. the applicable forms ofASME PVHO-1-2012.

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5 Window shapes and sizes

5.1 The standard shapes and sizes shown in Table 4, Table 5 and Table 6 shall be selected for the acrylicwindows. For design pressure PR in general the nominal diving pressure (NDP) shall be used, see also Pt.3Ch.2 Sec.4.

Table 4 Standard dimensions for flat disk windows

Range of application

Minimum wall thickness: s ≥12.5 mm

Slenderness ratio: s/Do ≥0.125

Edge radius: 1 mm ≥R1 ≥2 mm

Window seating: 1.25≥Do/Df≥1.5 mm

Max. allowable working pressure: p ≤ 170 bar

Minimum wall thickness / inside diameter of seat s/Di

atDesign pressurePR

[bar]10°C 24°C 38°C 52°C 66°C

5 0.134 0.146 0.154 0.164 0.188

10 0.154 0.173 0.188 0.201 0.226

15 0.173 0.195 0.210 0.223 0.253

20 0.188 0.210 0.226 0.240 0.281

25 0.201 0.223 0.240 0.257 0.305

30 0.210 0.233 0.253 0.274 0.324

35 0.219 0.243 0.267 0.292 0.344

40 0.226 0.253 0.281 0.305 0.363

45 0.233 0.264 0.295 0.317 0.383

50 0.240 0.274 0.305 0.329 0.402

60 0.253 0.295 0.324 0.354 0.441

70 0.267 0.310 0.344 0.378 0.480

80 0.281 0.324 0.363 0.402 0.520

90 0.295 0.339 0.383 0.427 0.559

100 0.305 0.354 0.402 0.451 0.598

110 0.315 0.368 0.422 0.476 0.637

120 0.324 0.383 0.441 0.500 0.676

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Range of application

Minimum wall thickness: s ≥12.5 mm

Slenderness ratio: s/Do ≥0.125

Edge radius: 1 mm ≥R1 ≥2 mm

Window seating: 1.25≥Do/Df≥1.5 mm

Max. allowable working pressure: p ≤ 170 bar

Minimum wall thickness / inside diameter of seat s/Di

atDesign pressurePR

[bar]10°C 24°C 38°C 52°C 66°C

130 0.334 0.398 0.461 0.524 0.715

140 0.344 0.412 0.480 0.549 0.754

150 0.354 0.427 0.500 0.573 0.793

160 0.363 0.441 0.520 0.598 0.832

170 0.373 0.456 0.539 0.622 0.871

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Table 5 Standard dimensions for spherical shell windows with conical seat (opening angle60°/90°)

Range of application:

Opening angle:α≥60°

Minimum wall thickness:s≥12.5 mm

Minimum values for s/Ri:

Window seating:

Di/Df≥ 1.02

Max. allowable working pressure:

p ≤ 170 bar

Minimum wall thickness /inside diameter of seat s/Di

for 60° ≤ α < 90° atMinimum wall thickness /

inside diameter of seat s/Di

for 90° ≤ α < 120° at

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

5 0.090 0.090 0.090 0.090 0.090 5 0.042 0.042 0.042 0.042 0.049

10 0.090 0.090 90 0.090 0.112 10 0.042 0.043 0.049 0.054 0.070

15 0.090 0.090 0.097 0.108 0.140 15 0.043 0.052 0.060 0.067 0.089

20 0.090 0.097 0.112 0.126 0.166 20 0.049 0.060 0.070 0.080 0.107

25 0.090 0.108 0.126 0.143 0.191 25 0.054 0.067 0.080 0.091 0.124

30 0.097 0.119 0.140 0.160 0.215 30 0.060 0.075 0.089 0.102 0.142

35 0.104 0.129 0.153 0.176 0.238 35 0.065 0.082 0.098 0.113 0.160

40 0.112 0.140 0.166 0.191 0.259 40 0.070 0.089 0.107 0.124 0.177

45 0.119 0.150 0.179 0.206 0.279 45 0.075 0.095 0.116 0.135 0.194

50 0.126 0.160 0.191 0.221 0.298 50 0.080 0.102 0.124 0.146 0.210

60 0.140 0.179 0.215 0.248 0.332 60 0.089 0.116 0.142 0.168 0.242

70 0.153 0.197 0.238 0.274 0.363 70 0.098 0.128 0.160 0.190 0.272

80 0.166 0.215 0.259 0.298 0.391 80 0.107 0.142 0.177 0.210 0.300

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Opening angle:α≥60°

Minimum wall thickness:s≥12.5 mm


Window seating:

Di/Df≥ 1.02


p ≤ 170 bar


for 60° ≤ α < 90° at


for 90° ≤ α < 120° at

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

90 0.179 0.232 0.279 0.320 0.416 90 0.116 0.155 0.194 0.230 0.327

100 0.191 0.248 0.298 0.340 0.439 100 0.124 0.168 0.210 0.250 0.351

110 0.203 0.264 0.315 0.359 0.460 110 0.133 0.181 0.226 0.269 0.373

120 0.215 0.279 0.332 0.377 0.480 120 0.142 0.194 0.242 0.287 0.393

130 0.227 0.293 0.348 0.394 130 0.151 0.206 0.257 0.304 0.411

140 0.238 0.307 0.363 0.410 140 0.160 0.218 0.272 0.320

150 0.248 0.320 0.377 0.425 150 0.168 0.230 0.287 0.336

160 0.259 0.332 0.391 0.439 160 0.177 0.242 0.300 0.351

170 0.269 0.344 0.404 0.452 170 0.185 0.254 0.314 0.365

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Table 6 Standard dimensions for spherical shell windows with conical seat (opening angle120°/180°)


Opening angle:180 ≥α ≥120°

Minimum wall thickness:s ≥ 12.5 mm


Window seating:

Di/Df≥ 1.02


p ≤ 170 bar

Minimum wall thickness /Inside diameter of seat s/Di


Inside diameter of seat s/Di

for α = 180° at

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

5 0.021 0.023 0.025 0.028 0.034 5 0.018 0.018 0.019 0.021 0.026

10 0.025 0.030 0.034 0.038 0.050 10 0.019 0.023 0.026 0.030 0.041

15 0.030 0.036 0.042 0.048 0.067 15 0.023 0.028 0.034 0.039 0.056

20 0.034 0.042 0.050 0.059 0.083 20 0.026 0.034 0.041 0.049 0.071

25 0.038 0.048 0.059 0.069 0.100 25 0.030 0.039 0.049 0.058 0.086

30 0.042 0.054 0.067 0.079 0.117 30 0.034 0.045 0.056 0.068 0.101

35 0.046 0.061 0.075 0.090 0.131 35 0.038 0.051 0.064 0.077 0.115

40 0.050 0.067 0.083 0.100 0.146 40 0.041 0.056 0.071 0.086 0.129

45 0.054 0.073 0.092 0.110 0.161 45 0.045 0.062 0.079 0.096 0.142

50 0.059 0.079 0.100 0.119 0.175 50 0.049 0.068 0.086 0.105 0.155

60 0.067 0.092 0.117 0.138 0.204 60 0.056 0.079 0.101 0.122 0.182

70 0.075 0.104 0.131 0.157 0.232 70 0.064 0.090 0.115 0.139 0.207

80 0.083 0.117 0.146 0.175 0.259 80 0.071 0.101 0.129 0.155 0.232

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Opening angle:180 ≥α ≥120°

Minimum wall thickness:s ≥ 12.5 mm


Window seating:

Di/Df≥ 1.02


p ≤ 170 bar

Minimum wall thickness /Inside diameter of seat s/Di


Inside diameter of seat s/Di

for α = 180° at

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

Designpressure

PR

[bar]

10°C 24°C 38°C 52°C 66°C

90 0.092 0.127 0.161 0.193 0.285 90 0.079 0.112 0.142 0.172 0.256

100 0.100 0.138 0.175 0.211 0.310 100 0.086 0.122 0.155 0.188 0.278

110 0.108 0.149 0.190 0.228 0.334 110 0.094 0.132 0.168 0.204 0.299

120 0.117 0.161 0.204 0.245 0.357 120 0.101 0.142 0.182 0.220 0.319

130 0.123 0.171 0.218 0.262 0.379 130 0.108 0.152 0.194 0.235 0.337

140 0.131 0.182 0.232 0.278 0.400 140 0.115 0.162 0.207 0.250 0.352

150 0.138 0.193 0.245 0.294 150 0.122 0.172 0.220 0.264 0.366

160 0.146 0.204 0.259 0.310 160 0.129 0.182 0.232 0.278

170 0.153 0.214 0.272 0.325 170 0.135 0.191 0.244 0.292

5.2 Acrylic windows of other shapes and sizes or for other ranges of pressure may be used on application ifapproved by the Society or if they are designed and manufactured to a standard recognized by the Society.Acrylic windows may be performed e.g. according to ASME PVHO-1-2012, Section 2.

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5.3 The design temperature to be assumed for acrylic windows shall be the mean value of the maximum externaland internal temperatures to be expected under design pressure conditions.

5.4 Windows subjected to pressure from both sides shall be designed for the maximum pressure applied,regardless of whether this pressure is external or internal.

5.5 Pressure may only be applied to the convex side of spherical shell windows.

5.6 The thickness of the window shall be everywhere equal to, or greater than, the minimum value determinedby reference to Table 4, Table 5 and Table 6. For intermediate temperatures linear interpolation may beapplied.

5.7 With flat windows having right-angled edge and an O-ring seal, the outside diameter of the disk shall bewithin + 0.00/–0.25 mm of the nominal value, or within + 0.00/–0.75 mm where flat gasket seals are used.

5.8 Because of stress increasing effects grooves for seals shall not be located in the acrylic window bearingsurface and also not in the window itself.

5.9 The greater diameter of the conical bearing surface of an acrylic window shall be within +0.000/–0.002 Do ofthe nominal value.The included conical angle (opening angle) of the seating surface of a window shall be within +0.25/–0.00degrees of the nominal value.

5.10 The concave or convex surface of the window shall not differ from an ideal spherical sector by more than +0.5 % of the nominal external spherical radius.

5.11 The surface roughness Ra of the window bearing surface shall be 0.75 μm or less.

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6 Window seats and installation of windows

6.1 Requirements for window seats

6.1.1 The window seat in the viewport flange shall be designed to give the window sufficient support at themaximum operating pressure. The seat dimensions for various standard windows are indicated in [4].

6.1.2 For flat windows having a perpendicular edge and an radially compressed O-ring, the seat diameterin the viewport flange shall be within + 0.25/–0.00 mm of the nominal value, or within + 0.75/ - 0.00 mmwhere flat gasket seals are used.

6.1.3 For spherical windows with a conical bearing surface, the major diameter of the conical seat cavity inthe viewport flange shall be within + 0.002 Do/–0.000 mm of the nominal value.The included conical angle of the window seat in the viewport flange shall be within + 0.000/–0.25 degreesof the nominal value.

6.1.4 The surface roughness of the window seat shall not exceed 1.5 μm.

6.1.5 The window seat shall be permanently protected against corrosion (e.g. by overlay welding usingcorrosion-resistant filler metals).

6.1.6 A soft gasket material can be used for the primary seal of standard windows in accordance with Table 4 to Table 6. This seal shall be sufficiently thick to enable it to absorb a reasonable degree of deformation without experiencing permanent setting.

6.1.7 In the case of flat windows with perpendicular edge, a secondary seal is required which is normallybonded to the flange seat with contact cement. This seal also acts as a supporting gasket for the window andmay not be more than 3 mm thick.

6.1.8 Sealing ring grooves are not allowed in the bearing surface of the window and in the metal flange seat.

6.1.9 Retaining rings shall be able to provide the necessary initial compression of the window seals.

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6.2 Installation

6.2.1 When fitting acryl glass pane windows, care shall be taken to ensure that all bearing surfaces arethoroughly cleaned. Where cleaning agents, window seat greases or adhesives for the window seals are used,these shall be tested for compatibility with acrylic plastic prior to use.

6.2.2 If the window seat is not made of corrosion resistant material, it shall be sufficiently preserved with asuitable agent. In addition window and window seat shall be carefully cleaned using only cleaning materialwhich is compatible with acrylic glass.

6.2.3 Conical window seats shall be treated with silicone grease or another suitable grease before theinstallation.

6.2.4 During installation of the window care shall be taken that the bolts of the fastening ring are preloadedaccording to the stipulations of the instruction/maintenance manual.

6.2.5 Windows mounted on PVHOs shall be protected to avoid damage by impacts and to prevent chemicals,which can deteriorate the acrylic plastic, to come in contact with the window.

Guidance note:Many solvents for paints, acetone and other agents will deteriorate the acrylic plastic and reduce the strength significantly.


7 In service inspectionIn service inspection and testing shall be carried out in accordance with requirements given in Pt.7 Ch.1 andASME PVHO-2 or equal.

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dnvgl-ru-uwt-pt4ch7 pressure vessels … · ship pt.4 ch.7, where applicable. 2 references the...

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