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Metal BellowsMetal Bellows

Manual

WITZENMANN

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Labhard Verlag

The Metal BellowsManual with Design Examples andDescriptions

ISBN 3-926937-41-6

441E

Metal Bellows

WITZENMANNWitzenmann GmbHMetallschlauch-Fabrik Pforzheimstliche Karl-Friedrich-Strae 134D-75175 PforzheimPostfach 1280D-75112 PforzheimTelefon ++49 (0)7231-581-0Telefax ++49 (0)7231-581-820 or 581-824e-mail: [email protected]://www.witzenmann.com

Metal BellowsMetal Bellows

ManualPublished by

Witzenmann GmbHMetallschlauch-Fabrik Pforzheim

Labhard Verlag Konstanz

WITZENMANNWitzenmann GmbHMetallschlauch-Fabrik Pforzheimstliche Karl-Friedrich-Strae 134D-75175 PforzheimPostfach 1280D-75112 PforzheimTelefon ++49 (0)7231-581-0Telefax ++49 (0)7231-581-820 or 581-824e-mail: [email protected]://www.witzenmann.com

Publication no. 441 E1999 editionSubject to changes

Nominal charge 15,34 EURO

CIP-Titelaufnahme der Deutschen Bibliothek

Hrsg. Witzenmann GmbH, Metallschlauch-FabrikPforzheim. Konstanz: Labhard 1999NE: Witzenmann GmbH

Labhard Verlag, KonstanzLayout: Schindler, Parent & Compagnie GmbH, PforzheimSatz: Schindler, Parent & Compagnie GmbH, MeersburgDruck: Labhard Verlag, Konstanz

1999 Witzenmann GmbH / All rights reservedPrinted in Germany 441e 10 99

Flexible in Steel WITZENMANN 5

Table of Contents

1 The Company 7

2 Quality Assurance 9

3 The Structure of the Manual 18Materials 23Resistance to Pressure and Extreme Temperatures 26Resistance to Corrosion 32Thrust Force 33Springrate 34Types of Movement 36Cycle Life 38Affecting Factors 40

4 HYDRA Metal Bellows 44Metal Bellows (Corrugated) 46Applications 52Quality Tests and Control 56Details and Notes 58

Dimensional tables and Technical Data, Metal Bellows 84Stainless Steel Bellows longitudinally welded 86Stainless Steel Bellows seamless 100Bronze Bellows 102

5 HYDRA Diaphragm Bellows 104Details and Notes 111

Dimensional tables and Technical Data, Diaphragm Bellows 130Diaphragm Bellows of Stainless Steel Standard Profile 132 Narrow Profile 142 Special Series with Large Diameters 148

6 End Fittings and Connection Methods 150

Flexible in Steel WITZENMANN6

Table of Contents

7 Applications/Design Examples 162Metal Bellows with Intermediate Pipe for High Lateral Travel 164Torsional Stress to Metal Bellows 165Metal Bellows for Shaft Couplings (Table) 167Metal Bellows in a Chamber Type Expansion Joint 168Metal Bellows for Absorption of Vibrations 169Metal Bellows for Absorption of Vibrations (Table) 174Specific Applications of Metal Bellows 176

8 HYDRA Load Cells 184

9 Stainless Steel Pipes HYDRAWELD 186

10 Guidance for Enquiring and Ordering 194

Supplement A Materials 196General Information 197Types of Test Certificates Extract from DIN EN 10204 199Material Tables 203

Supplement B Corrosion Resistance TablesCorrosion Types 223Corrosive Media Tables 230

Supplement C Conversion Tables 261Temperature, Saturated Steam, Pressure (Conversion Diagrams) 262Steam Service Tables 263Physical Units (D, GB, US), Conversion Tables 265Greek Alphabet 269

Products of the WITZENMANN Group 270

1 The Company

7Flexible in Steel WITZENMANN

Specialist for Flexible Metal Components

Multiple Applications

Whenever pipes are subject to expansion caused by frequent changes in tempe-rature or pressure, when vibrations or movements occur in hose assemblysystems, when fluids are to be conveyed without leakage caused by pressure,when high loads must be sustained without danger or when a strong vacuum is tobe kept, there is a need for special products: flexible metal components. Thesecomponents include metal hoses, metal bellows, expansion joints, metal pipes,pipe hangers and roller supports.

The Origin: A Gem

It was the invention of the metal hose which created the basis for the developmentof these hose assembly components, unrenounceable in our technology. In 1885,the founder of our company, Heinrich Witzenmann, developed and produced thefirst metal hose, using a particurlarly flexible gem, the so-called (goose throatnecklace), as a model. Invention and introduction of the metal hoses were the basisfor the development of the metal hose and expansion joint industry. Heinrich Witzen-mann had also invented the metal hose expansion joint as far back as the beginningof the 20th century. In 1920, he applied for a patent for this invention. WitzenmannGmbH, the pioneer in this field of technology, is the only company that offers thecomplete range of products based upon the metal hose technology.

A Large Enterprise in the Branch

Our company employs over 1250 employees, the WITZENMANN group approxi-mately 2100 employees. Since 1854, when the company was founded, its mainplant has been located in Pforzheim. Besides this plant, there are nine productionsites in Germany. The WITZENMANN Group includes subsidiaries and companiesin which it has shares, mainly in Europe. All information based upon statistics as ofJanuary 1999.

Range of Products

We produce flexible metal components within a diameter range from 4 mm to 12 m.They are subject to operating pressures up to 1000 bar and to temperatures from270C to +1000C. Metal bellows as well as all our other products meet therequirements in respect to flexibility, operating safety, service life, tightness,resistance to mechanical stress and pressure; they are maintenance-free andresistant to temperature and corrosion at an extraordinarily high level.

1 The Company


Innovative Development

Our products are extremely appropriate for the solution of problems, but not justby chance. Their quality is the result of innovative research and development con-sidering the latest technological achievements, in combination with our custo-mers' requirements and experience gained in numerous practical applications.Precision in production and a wide-range of testing and inspection system for per-manent quality assurance guarantee high grade products in both technologicaland qualitative respect.

Main Plant in Pforzheim

2 Quality Assurance

Systematized Quality AssuranceThe quality assurance system of Witzenmann is continuously optimized. It guaran-tees both compliance with the high quality demands made on our products and anutmost level of service quality. Our quality assurance system which is organizedand structured according to the provisions of DIN EN ISO 29001, has beencertified by TV-CERT (certificate issued by the Technical Control Board ofGermany). Its efficiency is supervised by means of regular external and internalaudits. A Quality Assurance Manual and supplementary procedural and workinginstructions give a detailed and comprehensive description of the structural andprocedural organization as well as of the standards set for our QA System. One ofthe targets of our quality policy is the continuous improvement of the QA System.Thus, we can guarantee that not only our own quality demands but especiallythose of our customers are met.

9Flexible in Steel WITZENMANN

Besides certification by TV-CERT (certficate issued by the Technical ControlBoard of Germany) according to DIN EN ISO 29001, our QA System has also beeninspected and accepted by renowned customers from the business fields of auto-motive components and energy as well as the aoerospace industry. On thefollowing pages, there are tables giving a list of the most important customers.

Quality Assurance Manual ISO Certificate

2 Quality Assurance

Approvals

General Approvals/Qualifications

Quality Management System according to DIN EN ISO 29001

Technischer berwachungs-Verein Sdwest e.V.Producer Audits and Certification according to AD sheet HPO, WOand according to TRD 100

Approval of Metal Bellows for Special Fluids

S e w e r G a s / N a t u r a l G a s / L i q u i d G a s

DVGWGerman Association of Specialists in Gas and Water Engineering

COPZ Czech Cech Odbornk Plynovych Zarzen Republic

DGDanmarks Gasmateriel Prvning Denmark

VGWAssociation of Austrian Specialists in Gas and Water Engineering Austria

SVGWAssociation of Swiss Specialists in Gas and Water Engineering Switzerland

O t h e r s

Ministry of Labour, Health and Social ServicesBaden-Wrttemberg

BAMBAM Federal Institute for Material Research and Testing


Approval of Metal Bellows for Special Applications

N a v i g a t i o n

GLGermanischer Lloyd

ABSAmerican Bureau of Shipping USA

BVBureau Veritas Belgium

DNVDET NORSKE VERITAS Norway

LRSLloyds Register of Shipping Great Britain

PRSPolski Rejestr Statkw Poland

A v i a t i o nBWBFederal Office for Military Engineering and Acquisition

O t h e r A p p l i c a t i o n sVdSAssociation of Insurance Companies

Federal Office of Civil Defense

Applicability Inspections/Approvals from Producers have been carried out andgranted by many companies as e.g. Mercedes Benz, Opel/GM, Renault/P.S.A.,Siemens/Nuclear Power Supply (KWU) Germany, Atomic Energy of CANADA Ltd.(AECL), Framatome-France, ASEA-ATOM, Sweden

Final Inspections are carried out in respect to each order in cooperation with fur-ther inspection companies

2 Quality Assurance


2 Quality Assurance

anization of Quality-Assurance

Our quality assurance is organized on two levels. The central quality assurancedepartment is in charge of superior organizational and technological quality assu-rance measures. The quality departments of our product divisions deal withquality planning, quality management and documentation within the scope of theexecution of orders.In respect to its organization, the quality assurance department is independent ofthe production department. It has the authority of giving orders to all employees incharge of tasks which have an influence on quality.

Calculation, Design Engineering

The Product Development Department provides engineering expertise for thedesign and calculation of our products. Comprehensive theoretical investigationsare the basis of our activities. The individual divisions will finally apply the designrequirements in practice, taking specific product features and customers' require-ments into particular consideration.


FEM Structure of a Corrugated Part

2 Quality Assurance

Meticulous Supplier Audits

We only cooperate with qualified suppliers who give proof of an effective qualityassurance. For semi-finished products coils, sheet-metal plates, pipes, wires forbraidings etc., we demand inspection certificates according to the application ofthe parts. We make sure that the supplied products meet our order and accept-ance standards by inspections and testing in our goods inwards department andat our material testing laboratory.

Complete Production Supervision

We have supervisors who are responsible for the inspection and maintenance ofproduction equipment and the correct performance of production procedures inthe production process according to the provisions of the production plans pro-vided.

Monitoring of Welding Processes

Welding processes are carried out according to written procedures. The qualifica-tion of the welders is guaranteed by examinations according to DIN EN 287-1/ENISO 9609-4. The most important and frequently applied welding techniques arerecorded by certified procedures. The welding supervision meets the requirementsaccording to AD-Merkblatt HP3 (AD Instruction Sheet HP3).

Supervision of Measuring and Gauging Equipment

All testing and gauging equipments have been documented They are recheckedfor precision and reliability at regular intervals. The date of calibration can be takenfrom control marks.

Supervision of the Quality Assurance System

The quality assurance procedures in the QA System are monitored in all depart-ments dealing with Q.A-related duties and checked for efficiency by internal auditscarried out at regular intervals.


2 Quality Assurance

Quality Examinations

Product Audit

Comprehensive systematic audits carried out in the last few years have enabledus to transfer from empirical knowledge based on routine to the development ofsystematic knowledge. On one hand, this systematic knowledge is the preconditi-on for product development and optimization. On the other hand, it is necessaryto meet the increasing demand of the market for information about all aspects ofour products, especially for applications such as for the purpose of safety in aero-space and the automotive industry.

Material Audit

The demand for an economical production requires careful selection of appropriatematerials. A thorough knowledge of material properties is the precondition forboth this selection process and the demand for an increase in quality and safety.Semi-finished parts for our products are mostly thin high grade coils, wires forbraidings, sheet metal plates or thin-ply pipes. The high qualitiy requirements toour semi-finished parts are documented in our purchase and certification require-ments. Besides the provisions of national and international standards and regula-tions, the quality requirements also include specific internal procedures concern-ing production and documentation. In continuous goods inwards inspections, theparts are inspected for compliance with dimensional, mechanical-technologicaland chemical properties required in our order.Our material inspection laboratory is responsible for mechanical, technologicaland metallographic examinations for weld procedures and qualifications.

Qualification of welders and Welding Procedures

The welding methods applied in the production are documented in procedures.Continuous up-dating of procedures is one of the duties of the welding supervi-sion. This department is responsible for regular requalification of the welders(audits according to DIN 8560, DIN EN 287-1 and DIN 8561).


2 Quality Assurance


cycle testing device for large diameterhoses installed in U-bends with internalpressure and fluid temperature of up to300 C.

springrate test rig for metal bellows vibration test stand for simulation ofcomplex movements

cycle testing for expansion joint DN 200

2 Quality Assurance

For non-destructive testing of parts and weld seams, we use X-ray and ultrasonictesting devices.

Our material testing laboratory has been qualified from competent third partyinspectors and surveying bodies to perform destructive and non-destructive tests,and issue official test certificates.


Failure Analysis

Another duty of the material inspection laboratory is the failure analysis of pro-ducts after premature failure during testing or service. Metallographic checks arecarried out and the result is documented by photographs.More detailed examinations can be performed externally with electron beammicroscopy.

X-ray testing device.

2 Quality Assurance


Micrograph of fatigue crack of theouter ply in the root of multiply bellows

Fatigue crack shown in electron beam microscope

Quality of Metal Bellows

For the benefit of our customers, we make high demands on the efficiency, qualityand reliability of our metal bellows.

In addition, we also carry out inspections of the supplied materials used in pro-duction within the scope of our quality assurance, continuous production auditsand final inspections of the finished products before they leave our plant.

The use of high-grade materials, optimized production methods with low stress tomaterial, modern and efficient equipment and devices and last but not leastqualified personnel with a sense of responsibility are the most important factors toguarantee the quality of our products.


The Structure of the Manual

Objective

It is the objective of this manual to provide its user not only with information aboutthe product, i.e. with descriptions of the types of bellows available, but also withsolutions to problems, as required for the useful and adequate application ofmetal bellows.

The manual is to enable the user and engineer to make definite solutions for hisproject. It should be stressed however that this will not exclude the need of techni-cal consultation with us in complex and difficult cases.

Arrangement

This manual includes, in a revised and completely updated edition, all informationwhich has been provided in our yellow manual about

HYDRA Metal Bellows.

Furthermore, the explanations and dimensional tables for

HYDRA Diaphragm Bellows

have been amended and extended.

3 The Structure of the Manual



The main sections of this manual have been colour-coded to allow a faster andmore efficient use:

HYDRA metal bellowsdesign, material,application and propertiesof all HYDRA metal bellows

HYDRA metal bellows (corrugated)

HYDRA diaphragm bellows

HYDRAWELD stainless steel pipes

bellows end fittings, connection methods,special versions, special applications

supplement with material tables,extracts from standards, data sheets,conversion tables

inquiry questionnaire

wei

HKS 3N

HKS 8N

wei

HKS 73N

HKS 47N

HKS 64N

wei



Applications

In the whole field of modern engineering, there are many and a wide range ofapplications for flexible metal elements such as

HYDRA metal bellows

which are available in different types, as hydroformed corrugated bellows and asdiaphragm bellows.

Flexibility in all directions, combined with a long service life and high leakage resi-stance have secured access to an extraordinarily wide field of application; fromvalve industry measuring and control engineering and automotive industry to avia-tion and aerospace, from machine, apparatus and container construction to medi-cal instruments, from chemical plant engineering to cryogenic and nuclear power-stations, vacuum and solar technology to nuclear research.

Especially the techologically demanding applications call for metal bellows.

Within our product range, we supply bellows for all common diameters, pressurerequirement, temperature ranges and fluids for compensation of:

axial movements angular movements lateral movements corresponding combinations of movements

axial angular lateral


When correct selection is made and appropriate installation is carried out, HYDRAmetal bellows meet the following properties

pressure resistance vacuum tightness temperature resistance corrosion resistance high elasticity no maintenance long service life operational safety favourable economical properties

The elastic corrugations or diaphragm rings of the bellows absorb the movementsand need no maintenance.

The demands for high elasticity combined with high pressure resistance are cont-radictory. In a majority of applications, the pressure resistance does not allow forany compromises, whereas the flexibility requirements are complied with if suffi-cient space is available for installation.

Pressure resistance is given priority with HYDRA metal bellows.




The geometrical design of the HYDRA diaphragm bellows is the most obvious evi-dence for their extreme elasticity combined with low overall length. However thelower pressure load performance is limited to lower pressure ratings.

The range of dimensions and permissible pressures within the individual ranges ofour bellows types allow for an optimum application. The variable structure, single-ply or multi-ply, with corrugations or diaphragms, and a high variety of commonlyused materials form the whole range of bellows.

The applications of the two groups of bellows mentioned before overlap to a cer-tain extent. The colour-coded sections of this manual therefore specify the parti-cular advantages of the various types of bellows, thus allowing easy decisions forone or another version in standard cases.

We will be glad to give you advice in the case of doubt and ask you to contact usin such a case.



Materials

The materials appropriate for the manufacturing of metal bellows must guaranteethe following properties:

formability resistance to pressure thermal resistance corrosion resistance reliability of function

Especially a flexible element which is subject to elastic deformation under extremeconditions and which is to be extremely resistant to corrosion because of its thin-walled design, requires a diligent selection of materials.

There is, of course, no single material that complies with all requirements occuringin practical application. Austenitic stainless steels already cover a wide range ofrequirements. The material type 1.4571 (AISI 316 Ti) is a standard material, andparts made of this material are always held in stock in a sufficient quantity and inall dimensions.

Metal bellows made of other materials are special versions and are above allapplied if a high resistance to corrosion or to high temperatures is required.

Alternatives from the range of non-ferrous metals are metal bellows made ofbronze, material no. 2.1020 (CuSn 6).

All materials are cold-formed. A subsequent heat-treatment is not required ormight even have unfavourable effects. The work-hardening effect caused by theforming process is favourable for the elasticity and the service life of the bellows.



Materials appropriate for application in temperatures of more than 500 C are theheat-resistant or high-temperature resistant austenitic steel types 1.4828 (AISI309) and 1.4919 (AISI 316H) as well as some nickle-based alloys, including forexample Inconel 625 and Incoloy, whose importance is steadily growing becau-se of their specifically favourable corrosion resistance properties.

Materials especially appropriate for application with corrosive media are HastelloyC-276 and Inconel 625.

Comprehensive material tables, including not only the standard bellows materi-als but also similar materials for comparison, can be found in the blue-coded sup-plement A to this manual (pages 196 to 222).

The materials specified in these tables are appropriate for the manufacturing ofbellows. Materials required for specific applications are either held on stock orcan, if required, be ordered.

Especially for high quantities, manufacturing of bellows from deep drawn tins isalso possible. The following chart shows the current range of bellows materials held in stock formetal bellows (corrugated) and for diaphragm bellows.If your service requires other materials, please send your inquiry to our engineers.



Bellows Materials held in Stock

Metal Bellows Diaphragm Bellows

Material Type of Material Material Type of Materialno. or Trade Name no. or Trade Name

1.4541 austenitic AISI 321 1.4541 austeniticstainless steel stainless steel

1.4571 austenitic AISI 316 Ti 1.4571 austeniticstainless steel stainless steel

1.4404 austenitic AISI 316 L 1.4404 austeniticstainless steel stainless steel

1.4828 heat-resistant AISI 309 1.4828 heat-resistantaustenitic stainless steel austenitic stainless steel

2.4816 Inconel 600 2.4816 Inconel 600

2.4856 Inconel 625 2.4856 Inconel 625

2.4819 Hastelloy C-276 2.4819 Hastelloy C-276

2.4610 Hastelloy C-4

2.4617 Hastelloy B-2

1.4876 Incoloy 800 H 1.4876 Incoloy 800 H

3.7025 Titanium 3.7025 Titanium3.7035

2.4360 Monel 400

2.4060 Pure Nickel AM 350



Resistance to Pressure and Extreme TemperaturesThe permissible pressure at ambient temperature 20 C for every bellows isquoted in the dimensional and technical data tables (pages 86 to 103 and 132 to149) as reference pressure pn in column 16. This value is unrestrictedly valid for:

externally pressurized bellows with axial movement for all overall lengths,externally pressurized bellows with angular and lateral movement for all overalllengths,internally pressurized bellows with all types of movements for bellows with a lownumber of corrugations, whose number (816) depends on the bellows diameterd1 (see the squirm reduction factor tables on pages 63 and 116).

For the calculation of the permissible operating pressure, the reference pressurepn is to be reduced if the bellows is subject to

thermal stress internal pressurization with long bellows without guide or external pressurization with long bellows and angular or

lateral movement.

The following paragraphs give a detailed description of these aspects.

The reference pressure pn is based upon both empirical knowledge and theoreticalinvestigations according to recognized design calculation methods.

Surveying bodies demand higher safety factors, it will often be necessary to redu-ce the reference pressure pn quoted in the dimensional tables. In such cases,please submit the respective specification for design layout purpose.



Reduction of resistance to pressure and elastic deformation at high temperatures

The reference pressure pn refers to the room temperature 20 C. If the operatingtemperature is higher, the reference pressure is to be reduced respectively,depending on the individual material.

The temperature-pressure-reduction factors kt on the pages 64 to 67 corre-spond approximately with the temperature-based lowering of the yield point of thematerials according to DIN, VdTV or ASME values.

Since the elongation values in the data tables (columns 17, 18 and 19) also refer to20 C, they are also to be reduced, to a lower rate, however, in the case of anincrease in temperature. In this respect, the movement reduction factors kw apply.

The factors kt and kw quoted in the tables are based upon the current level oftheoretical and practical knowledge. Applications for which the acceptancetesting authorities have specified particular provisions have to be treated separ-ately, if necessary.

Reduction of the Resistance to Internal Pressure of Long Bellows

The resistance of metal bellows and diaphragm bellows to internal pressuredecreases when the length of the bellows and the number of corrugation increase.Their behaviour is then similar to that of an EULERS bar of low diameter, clampedat both ends, which will squirm under excessive axial pressure.



On page 63 of this manual, factors ki, depending on the internal diameter d1 andthe number of corrugations, for metal bellows can be found. If such factors aremultiplied by the reference pressure pn from column 16 of the dimensional tables,the permissible internal pressure of the bellows will result. The ki factors for dia-phragm bellows can be found on page 116. Because of the slightly different geo-metrical profile of the corrugations, the diameter d1 has only little influence on dia-phragm bellows. For this reason it is not necessary to quote this parameter in thetable.

The pressure reduction factors ki with a decrease approximately in their secondpower will, in the case of higher numbers of corrugations, very rapidly cause verylow permissible internal pressures which may then fall below the required values.

In such cases, the application of externally or internally mounted pipe sleeves orof internally mounted stem with a narrow annular gap to serve as a bellows guidemight be useful. The danger of squirming will then cease to exist, and a reductionof the reference pressure pn is not necessary any more.

It is, however, necessary to verify the squirming length of the bellows. The follow-ing pictures show bellows with internally or externally mounted guides as well as abellows squirming because of internal pressurization.



If a bellows guide is not sufficient or if its installation is impossible - for examplesince the bellows also has to carry out angular or lateral movements - the onlysolution will be a change of the design to external pressurization or, if only angularor lateral movements occur, outer wire braiding of the bellows.

If bellows are subject to a pressure differential, the higher pressure should beapplied to the exterior surface of the bellows.

The two following examples show bellows subject to external pressurization.



Reduction of Outside Pressure Resistance of Long Bellowssubject to Angular or Lateral Movement

The angular bellows, whose neutral line is part of a circular arc when not beingpressurized, will be compressed under pressure. The deflection of the bellows willdecrease while the pressure to the center increases. The deflection at the fixedends of the bellows will increase accordingly.The unstable curved shape of the lateral bellows which already under atmosphericpressure does not equal an ideal circular arc will increase under pressure. For thisreason, the reference pressure pn is to be reduced when the outside pressureincreases. The factors ka, required for the formulae on the pages 62 and 115, arequoted in tables on page 63 for metal bellows and on page 116 for diaphragm bel-lows. The reduction factors for external pressure are less than with insidepressure.

Test Pressure

In general, 1.3 times the service pressure, with reference to room temperature orthe respective nominal pressure rate, is the pressure value provided for the verifi-cation of the mechanical strength.

A bellows for the design pressure (= pressure at room temperature 20 C) of, forexample, 20 bar has to be capable of "withstanding" a test pressure of 20 x 1.3 =26 bar. The values of the design pressures pn (in the dimensional and data tableson pages 86 to 103 and 132 to 149) have been determined at rates that guaranteea reserve covering a pressure excess of 30% in a short-time testing process. If acomplete system is subject to a testing pressure of this rate, there will not be aplastic deformation of the corrugation profile which will affect the service life of thebellows.

In certain cases, a pressure of 1.5 to 2 times the design or nominal pressure isrequired for the testing of a system. In such cases, a particular layout of the bel-lows is required.



High pressure resistance, requiring a thick wall, is counter productive to highelastic deflection requiring small wall thicknesses. This problem is solved by sub-dividing the total wall thickness of the bellows into several thin plies. This method,however, is subject to certain limitations in practice. For this reason, demands foradditional pressure resistance reserves, even if the only aim is the possibility ofapplying a higher testing pressure one time, will always cause a reduction offlexibility reserves. Since the number of cycles is another factor which is to beguaranteed, this fact has led to the development of longer bellows which iscertainly unfavourable from an economical point of view.

Test pressures higher than 1.3 x the design pressure (pn) should be resisted unlessthere are compulsory provisions, above all since the decisive factors for the safetyof a bellows are a long service life and high flexibility reserves and not a designthat allows utmost test pressures. The idea that high test pressure always meanshigh safety is therefore not correct in respect to bellows.

Another requirement is the burst pressure of a bellows. It amounts to at least threeto five times the design pressure and guarantees pressure reserves which arenecessary under extraordinary and, strictly speaking, impermissible servicepressures in a system under extreme conditions. Before a bellows will burst, anextreme plastic deformation occurs so that, after such an extreme stress, the bel-lows is no longer able to carry out his actual task of absorbing movements thoughit might still be tight. It will then have to be replaced.

If bellows are applied as basic pressure elements for measuring and controlequipment, they should not be subject to more than 70% of the calculated designpressure in order to obtain lower hysteresis, good reproducability and the preci-sion required in measurement engineering. Particular compliance with this restric-tion is required whenever high load cycle life in respect to alternating pressuresand movements are to be achieved.



Resistance to Corrosion

To this factor, the principle applies that the bellows material should have at leastthe same quality standard as the other components of the system or the pipe.

Our stainless steel standard type 1.4571 (AISI 316 Ti) is resistant to a high numberof aggressive media; it also has an optimum bending fatigue strength. Special bel-low materials, particularly corrosion-resistant nickle-based alloys are quoted in thematerial tables on pages 196 to 222.

Questions arising in connection with corrosion problems are discussed in theappendix to the manual on pages 223 to 260.

They are, in part, based upon our own research and findings, but to a great extentthey are a summary of research literature (DECHEMA) and do not claim com-pleteness. Furthermore, it is to be taken into consideration that even the qualitygrade 0 is not absolutely resistant to eroding corrosion.


Thrust Force

This property is not to be confused with the inherent rigidity or spring rate of abellows.

It is comparable with a piston force and is the product of the effective cross-sec-tional area of a bellows and the service pressure. Normally, the service pressure isthe pressure counteracting the atmospherical pressure and is to be considered asa positive pressure occurring during operation. If - for example in the field ofmeasurement engineering - the compression is counteracting a 100% vacuum,the service pressure will be corresponding with the the absolute pressure.

The effective cross-sectional area of a bellows specified in the dimension and datatables for every bellows dimension (under external pressure) in column 23, can becalculated according to the approximation formula:

a = (d12 + d1 d2 + d22) 102 [cm2]

d1 = internal bellows diameter [mm]

d2 = external bellows diameter [mm]

This formula applies to both metal bellows and diaphragm bellows in their neutralphase and provides results approximately equal to measured values.

The compression or its effect is of high importance in practically all bellows appli-cations. In the field of measurement and control engineering working with lowpressure differentials, the thrust is the effective force for the initiation of an axialmovement. In these cases, the spring rate of the bellows discussed in thefollowing chapter is to be considered as the counteracting force.

In higher pressure ranges, the thrust forces increase to considerable values. Forthis reason, adjacent pipe elements have to have an accordingly high mechanicalstrength or are to be equipped with special anchor points.

12




Spring Rate

Metal bellows and diaphragm bellows are elastic to a varying extent and can carryout axial, angular and lateral movements as well as combinations thereof underthe effect of external forces and moments.

Any of these enforced movements causes a specific counteracting resistance.This resistance to deformation is proportional to the load applied as long as thematerial stress is within the elastic deformation. The coefficient of proportionalityof this function is called spring rate.

The corresponding calculations are explained on pages 79 to 82 and 124 to 127.The scattering of the spring rate is about 30% for standard versions of metal bel-lows and about 20% for standard versions of diaphragm bellows.

The scattering values of precision grades available amount to only the half of thesevalues because of increased inspection efforts in respect to the basic materials(narrowing of the range of quality and dimensional tolerances) and to the manu-facturing process itself. The fact that differences in the wall thickness will affectthe spring rate in the third power, whereas a change in the height of corrugation orin the profile depth of the grooves of diaphragm bellows will cause a changeapproximately in the second power. An additional possibility of obtaining a satis-factory constancy of the spring rate of bellows is the use of pre-selected bellowswhich, however, is a matter of economical application.


As a functional precondition for many applications, especially in measurement andcontrol engineering, the inherent rigidity of the bellows should be as low as pos-sible. In many cases, diaphragm bellows with their typical high axial "softness" areto be preferred to metal bellows. The high elasticity required, however, reaches itslimits whenever intermediate and higher service pressures require stronger wallthicknesses. The only way of solving this problem is to verify whether there isenough space for an accordingly longer (i.e. proportionally softer) bellows.

If bellows are installed in a preset state, it is to be considered that the springloading at first occurs as traction and, after passing the neutral position, as com-pression (or vice versa) and this change of signs is to be considered in designcalculation.

Bellows should, if possible, not be used as elastic elements, i.e. as an energy sto-rage device. This effect can be achieved by incorporation of a spring which willreduce the scattering range of the coefficient of elasticity of the bellows.Hysteresis and bellows fatigue, depending on the number of movement or pressu-re cycles, can thus be reduced.



Types of Movement

The main elasticity of both corrugated metal bellows anddiaphragm bellows is in axial direction. For this reason,they are mostly used in applications requiring axial flexi-bility.

The longest service life can be achieved by exploiting theaxial flexibility in both directions, as elongation (+) orcompression ( ).

A symmetrical distribution of movements (50/50%) ofcorrugated metal bellows will achieve a maximum numberof stress cycles.

For diaphragm bellows, a stroke ratio of 20% elongation(+) and 80% compression ( ) is the most favourablesolution.

The same also applies accordingly to lateral and angularmovements, thus requiring an installation of bellows in apre-set condition.

Exceptions are bellows applied in measurement and con-trol engineering. They normally work axially and in onlyone direction.

Further details can be found in the yellow- and orange-coded pages of this manual.

Bellows are also able to transmit rotations i.e. torquemoments, combined with the ability of compensating axialmisalignment in lateral or angular direction, as can beseen in the marginal figures on this page. For furtherdetails see pages 165 and 167.


angular

angular

axial

lateral

lateral


If an element is subject to high angular movements or also lateral movementscombined with high internal pressure, the flexible element (in this case only thecorrugated metal bellows) is to have an outer wire braiding. This braiding, howe-ver, will cause a high decrease in the axial flexibility of the bellows, and only theangular and/or lateral flexibility will be dealt with in this manner.

It therefore is to be decided whether the annularly corrugated metal hose which isin most cases more economical and has been designed for such purposes, is tobe preferred (order HYDRA manual no. 301E, if required). Only if there is very littlespace for installation, a metal bellows whose angular and lateral elasticity is higherthan a metal hose should be used.



Service Life

The service life of a corrugated metal bellows or a diaphragm bellows is the num-ber of stress cycles endured until first leakage, with a total forward and returnmovement, i.e. return to the initial position, being one stress cycle.


The pressures and movements quoted in the data sheets have thus been speci-fied that in the case of cold stress (room temperature 2030 C) and expert instal-lation at least

10 000 stress cycles

will be endured. The number of cycles to fracture is, considerably higher in general.

Bewegungen whrend

eines Lastspielsoder

Nullage

movements duringone stress cyle

or

neutral position


The following survey gives a detailled presentation of the number of stress cyclesto be expected. They show that one load cycle per minute (with an operatingperiod of 8 hours per day) will make 105 stress cycles per year.


1 year has days hours minutes seconds

with an operatingperiod of 24 hours 365 9000 5 105 3 107

per day

with an operatingperiod of 8 hours 240 2000 105 7 106

per day

The figure 10 000 is a nominal stress cycle number which may change under theinfluence of the operating conditions in practice or of stress factors to be fixedaccordingly. The main affecting factors are

1. Temperature2. Elastic Deflection (Maximum Movement)3. Service Pressure Load4. Pre-Setting of Stroke5. Stroke Frequency

Factors of incalculable negative influence such as

6. Pressure Shocks, Pulsations7. Thermal Shocks8. Corrosion9. Inadequate Installation etc.

are to be taken into consideration.

When selecting the bellows type and dimension, the design engineer should atleast have an approximate idea of the number of stress cycles required. The moreprecise the information about the requirements of an application is, the better thepossibility of selecting the appropriate bellows.



Affecting Factors

TemperatureThe pressure and movement values specified in the dimensional tables are to bereduced with increasing temperatures. The reduction has to correspond with thedecrease in the mechanical strength of the material or the bending fatiguestrength; see table of factors kt and k, pages 64 to 67 and 74 to 77.

The design calculation example of a stainless steel bellows in the standard quality1.4571 (AISI 316 Ti), whose pressure resistance will be reduced to about 77% at atemperature of 200 C and whose movement will decrease to 78% of the value atroom temperature, shows that its service life is reduced from 10,000 to about2,000 stress cycles only because of the effect of high temperatures.

Since temperatures have a considerable effect on the pressure resistance and thenumber of stress cycles endured, it is recommendable to reduce the temperaturein the bellows area by means of appropriate design measures.

Movement and Pressure RateThe service life table on page 83 includes the affecting factors of pressure ratingand stress by movement. The numbers of load cycles quoted in the table showthat the influence of the movement rate (kn) is considerably higher than that of thepressure rate (kp).

Pre-SettingThe number of stress cycles to rupture quoted applies to symmetrical elasticstress (50%) with metal bellows and to an 80/20% distribution of movement withdiaphragm bellows.

If pre-setting is dispensed with, the permissible elastic deflection will have to bereduced to about 75% or a longer bellows will have to be applied; see formulae onpages 68 to 73.

Frequency of MovementThe frequency of movement is in most cases very low, far below the natural fre-quency of the bellows and has practically no influence on the number of stresscycles to be endured. Frequencies within the the range of natural frequencies ofthe bellows (in most cases >50 Hz) are to be avoided. With respect to high-fre-quency vibrations, we refer to the paragraph "Absorption of Vibrations", pages169 to 175.



Pressure ShocsThe permissible service pressure of a metal bellows should correspond with thehighest pressure peaks occurring. In case of doubt, we suggest the selection of astronger bellows for higher pressure. It is to be taken into consideration thatduring pressure shocks or pressure pulsation the pressure stress will be severaltimes higher compared to the pressure resistance for standard conditions.

Pumps may cause pressure pulsations; quick-action valves create pressure peaksand vibrations, the re-starting of systems with steam-conveying pipes may causewater hammers due to spontaneous evaporation of residual condensates.

In these cases, multi-ply bellows have proven their particular efficiency, since inthese - often unpredictable - cases of excessive stress the bellows may be subjectto high deformation which will reduce the service life but will not burst anyway. Asa rule, the bursting pressure is many times higher than the operating pressure.

It is impossible to calculate the service life of components which are subject topressure pulsations or sudden movements. The influence of this parameter on thecycle life expectancy can only be roughly estimated and should therefore be veri-fied under real conditions in all cases. Test stands for most of the practical appli-cations are at your disposal. Please let us have your inquiry, if necessary.

Thermal ShocksFrequent spontaneous temperature changes, especially with high temperaturegradients, will accelerate the process of material fatigue.

In practice, this applies particularly to bellows in the exhaust system which aresubject to high stress caused by alternating tempera-tures due to the starting and stopping of the engine. Toincrease the service life, the selection of a temperatu-re-resistant material is recommendable, for examplethe stainless steel grade 1.4828 (AISI 309).Furthermore, design measures will be taken to avoidhigh bellows temperatures. An easy way of doing thisis to install an inner sleeve (see illustration below).



CorrosionThe service life is reduced by corrosion. This due to selection of unappropriatematerials and, in certain cases to the fact that corrosive rinsing fluids are used forthe cleaning of systems.Basically, the bellows material is of at least the same quality as the pipe material orthe system material, as already mentioned in the paragraph "corrosion resis-tance". In certain cases, however, the combination of different materials may causewelding problems in the connection of bellows and fittings. Mechanical connec-tion systems such as lap-joint flanges, will in most of the cases provide an appro-priate solution.

InstallationInadequate installation, perhaps the neglect of lateral misalignment or impermis-sible torsion, mechanical damaging of the corrugations etc. will not cause imme-diate destruction of the bellows but will reduce its service life expectancy. If thelateral misalignment already mentioned or a limited torsional stress is alreadytaken into consideration when designing the bellows, the designed service lifeexpectancy will be achieved.



Combination of Stress CyclesIn many systems, the bellows are subject to varying movements during their appli-cation. In control valves, for example, only a small number of stress cycles withlong axial travel, but a high number of medium-sized and small control cycles areto be expected.

The number of the additional corrugations required due to the frequent but in mostof the cases considerably shorter control movements particularly depends on therates at which the individual types of stress are combined. In most of the cases,only a small number of corrugations are to be added to the number calculated onthe basis of the maximum movement. Please send us a detailed inquiry for suchapplications.

Finally, it is to be mentioned that a bellows will practically never fail suddenly. Thisis a great advantage, especially with hazardous media or high pressures. Everyfailure caused by an inadequate selection of the bellows type or due to an installa-tion error, will reduce the number of stress cycles endured or the service life to asmaller or higher extent. Since, for example, an excessive pressure stress will firstcause a deformation of the bellows before its rupture, there will normally beenough time to eliminate the damage, i.e. to replace the bellows.

Flexible in Steel WITZENMANN 45Flexible in Steel WITZENMANN44

4 Metal Bellows

4 Metal Bellows


4 Metal Bellows

Metal BellowsThe manufacturing of metal bellows requires mastery in two decisive processingphases: forming of bellows and welding engineering.

The production of bellows begins with the manufacturing of thin-walled pipes. Inour company, such pipes are made of thin coils (0.1 to 0.5mm) by longitudinal wel-ding in a contiuous process (also see separate product range of pipes, pages 186to 193).Multi-ply bellows are made by inserting several pipe cylinders with slight differen-ces in diameter into each other to form multi-ply cylinders.

The transformation of the pipe cylinders or cylinder packages to bellows, whichincludes the forming of annular corrugations, is mostly carried out by means of ahydraulic forming process.

In this hydraulic process, a cylinder element separated by externally and internallyapplied tools is subject to high internal pressure exerted by a special hydraulicfluid. A corrugation is formed by the expansion of the cylinder element in circum-ferential direction due to the internal pressure applied. In this process, the materialis only subject to the elongation and workhardening corresponding to the changein geometry and does not require any heat-treatment.This process causes only little stress to the material. This principle also allows thesimultaneous forming of several corrugations which, as an economical process, isvery appropriate for higher production quantities.

In particular cases, the older process of mechanical disc-forming is applied. In thisprocess, rolling tools are "milling" the corrugations into the cylinder. This processis limited to 3 plies maximum.

The feature both production processes have in common is the subsequent form-ing of single corrugations, i.e. the material for the convolution forming can "flow"from the pipe length. A reduction in wall thickness, can thus be avoided to a greatextent.

4 Metal Bellows


4 Metal Bellows

It shows that the movement is above all due to the straight corrugation flanks(change of angle) and that both the external and the internal corrugation crests aresubject to bending stress (alternating bending). The internal or external pressureexerted on the bellows corrugation causes additional tensions which the bellowshas to sustain. The sum of these types of stress is, of course, included in the datatables (pages 86 to 103).

The following profile sketches show the wall structure of bellows for a high varietyof applications. Bellows with one or several plies are the basis for the corrugatedmetal bellows being the subject of this publication, whereas multi-ply bellows andbellows with massive walls are above all applied in expansion joints of high nomi-nal diameters as well as in high-pressure applications.

Special versions are metal bellows with oval cross-sectional areas (types anddimensions upon request).

Profile of a single-ply bellows Profile of a bellows with several plies

4 Metal Bellows

Besides the austenitic stainless steel type 1.4571 (AISI 316 Ti) mentioned before,other materials of a sufficient forming capacity are used in the production of bel-lows, depending on the application requirements. We have developed a compre-hensive know-how in the processing of these materials.

The flexibility of a metal bellows is based upon concentrically or parallely circum-ferential corrugations. Combinations of both corrugation types are also permissible.

c axialc angular andc lateral

The following figure shows the mode of function of a bellows corrugation.

+ elongation

compression


4 Metal Bellows

in the as expansion and tensionchemical industry compensators in pressure boilers

and reactors,for sealing purposes

in automotive engineering as vibration absorbers,in exhaust systems,as safety elements in steering columns

in nuclear technology according to the applicationsin reactor construction mentioned before, especially as

construction element in active circuits

in measurement as a primary element for the absorptionand control engineering of pressure and movements,

as shaft couplings and torquetransmissions

in vacuum engineering for the absorption of thermal expansions,for the absorption of vibrationsas a control element

in aerospace as an expansion joint for theabsorption of pipe expansions,for vacuum-tight passages(optionally made of titanium)

in medical engineering in medical equipment

4 Metal Bellows

ApplicationsThere are numerous applications of HYDRA metal bellows as elastically deforma-ble, pressure-tight construction elements.

They are most frequently and urgently required in modern technologies, especially if,besides other qualities of the bellows, absolute tightness is a function requirement.

HYDRA metal bellows are, for example, applied

in the for the sealing of valve spindlesvalve industry without packing

in aggregates with elastic for the absorption of vibrations,supports such as engines and for the relief of tensions,motors, pumps, compressors for noise-damping

in pipe line construction as expansion joint for theabsorption of thermal expansions,for the compensation ofmisalignments in installation andfor low-tension connections,as chamber expansion joint in jacketed pipes

in machine construction as a contact pressure element,as a piston,as a sealing element

in the manufacturing of boilers as compensation tank,for low-tension connection tosensitive fittings,for the absorption of expansions


4 Metal Bellows

Quality Tests and Control

Quality assurance is of outstanding importance for high-quality elements such asmetal bellows and diaphragm bellows.

Precondition for the faultless quality of our products are continuous audits andtests of basic materials, semi-finished and finished products. Statistical methodsof quality assurance are applied in the evaluation of the results of tests and audits.The products themselves, bellows and bellows units are subject to systematictests included in the standard range of supply.If individual customer applications require special tests, the execution of suchtests will be charged to the customer.

Additional tests also include acceptance audits and approvals by independentinstitutions (TV, Lloyds, etc.) as they are frequently required by, for example, thenuclear and the chemical industry.

A. Quality of the Basic MaterialWe only use materials (above all coils and pipes) which comply with high demands- in respect to both dimensional accuracy, surface quality, mechanical values andtheir detailed chemical composition. Tolerances which are permissible accordingto DIN-standard sheets and others have been, in certain cases, extended by furt-her restrictions and specifications which we are applicable to our materials.

All our bellows materials have been given certificates of approval according to EN 10204-3.1B which can be issued by the TV or other inspection authorities.

In our material test laboratory with its modern equipment, we continuously per-form resistance tests, determination of surface roughness as well as grain structu-re tests with samples taken at random, in the course of the inspection of incomingmaterials. We take and register an additional material sample per batch from anyincoming coil material.


The organization of the bellows production and the documentation system allowsthe traceability of any material batch to the finished product. Material certificatestherefore can be issued retrospectively.

B. Production SupervisionOur internal staff of supervisors and the personal responsibility of our employeesprovide a permanent supervision of our production. In addition, the permanentsupervision by our quality assurance department ensures that

the currently valid procedures and inspection instructions are available at theworking place

the parameters for the hydraulic forming of bellows are complied with the currently valid welding procedures for longitudinal weld seams and circular

weldseams are applied the correct filler materials are used the dimensional accuracy of components and assemblies is ensured.

If particular requirements are to be complied with, the quality assurance depart-ment will carry out inline examinations, also in presence of third party inspectors.

C. Standard Inspections of the Finished Products(without issue of inspection certificates)

The following minimum range of inspections is carried out:

1. Visual InspectionInspection of bellows, weld seams and, if required, connection fittings forvisible defects or damage.

2. Dimensional InspectionInspection of bellows and, if required, connection fittings, especially forinstallation and connection dimensions

3. Leakage or Pressure TestLeakage tests of metal bellows are carried out with nitrogen or air underwater at ambient temperature with 0,5 - 2 bar inside pressure and a hold-time of 2060 seconds. Bellows need to be equipped with connection fit-tings appropriate for sealing, for example weld ends. Test criterion: no visiblebubbles on the exterior surface, leakage rates exceeding about 103 mbarcan be detected in this test.

4 Metal Bellows


4 Metal Bellows

The standard method for the tightness testing of diaphragm bellows is thehelium/vacuum test.

Tests and acceptance inspections beyond this range as well as the respec-tive documentations are possible. The equipment required is at our disposal(see chapter 2, "The Quality Assurance"); the range of tests should belimited to tests really required in respect to the future application, since thetesting costs can be very high and can easily exceed the production costs.

D. Additional Requirements Tests(with issue of test certificates against payment)

1. Verification of the mechanical values of bellows and connection fittingmaterials

2. Internal, external or bursting pressure testUpon demand, pressure tests of bellows assemblies and expansion jointswill be carried out in a testing press.In this process, a testing pressure of 1.3 times the design pressure will beapplied in compliance with official provisions. For longer bellows and higherpressures we use a sturdy inner sleeve of special design to avoid squirmingduring inside pressure testing. The burst pressure is 35 times the test pres-sure and can be determinated at extra charge.

The criteria of these tests are:

Leakage and deformations giving reason for doubts about the safety of thebellows are impermissible.

3. Helium leakage test; this is the most sensitive leakage test. It is restrictedto corresponding applications with very high quality requirements as oc-curring, for example, in vacuum engineering and nuclear technology.

This test will cause a considerable increase in the specific costs of a bellowselement, especially if bellows which are bulky or difficult to be sealed willcomplicate the helium vacuum test or require the use of adaptors. The devi-ces at our disposal have a susceptibility of 1011 mbar l s1.


4 Metal Bellows

4. X-Ray tests are carried out - as it is customary in other cases - in respectto weld seams. Most frequently, these tests are carried out with the longitu-dinal butt-welding seams of bellows cylinders before convolution forming.If the testing of the bellows connection seams is required, the bellows andthe connecting element are to be of a special design. Due to their shape,standard bellows connection seams are not very appropriate for this process.

5. Ultrasonic tests are inadequate for the thin-walled basic material of the bel-lows and may only be used to restricted extent for the production of connec-tion fittings if these are to be supplied by us and a testing requirement exists.

6. Surface crack examination test or dye penetrant test can be applied forthe inspection of the weld seams and connection fittings. Inspection is carried out visually in the red-white process, and under UV lightin the fluorescence process.

7. The additional verification of the mechanical properties especially of those of the bellows materials is carried out by:

the high-temperature tensile testthe deep-drawing testhardness tests

8. Metallurgical inspections are

tests for corrosion resistancethe ferrite determinationthe grain-size analysismicrographs and macrographs

If inspections are required which are beyond our facilities, we will have themcarried out by external institutions as, for example, the German institute formaterial testing, Stuttgart (MPI).

9. Service life and cycle tests of bellows and bellows assemblies are destruc-tive tests and are carried out with additionally produced specimen of identi-cal material batch.

These tests can - at the respective expense - be carried out at ambient orservice temperature under service pressure. For further details, please seethe foregoing chapter "service life".


Additional tests according to section C are only to be carried out if they arerequired due to compulsory provisions.

The costs for such tests will often exceed the actual price of a bellows bymany times.

Our continuous basic material tests (section A) and obligatory inspections ofthe bellows (section B) will guarantee the quality of our products. The techni-cal data of pressure, elasticity etc., quoted in the bellows tables are not onlycovered by empirical tests but are also based upon acknowledged designcalculation processes.

E. DocumentationThe tests mentioned in sections A, B, C and D can either be certified by uswith a

certificate of approval according to EN 10204 3.1B

or by third party inspectors or external surveying bodies by means of a

certificate of approval according to EN 10204 3.1A or C

or surveying inspection authorities whose experts are allowed to issue 3.1Ccertificates are, for example

TV (German technical inspection authority)Germanischer LloydLloyds Register of ShippingBureau VeritasDet Norske VeritasInspection authority of the German railroad company(Bundesbahn-Abnahmeamt)Dienst voor het stoomwezen (Netherlands)

The range of acceptance inspections also includes procedures and homo-logation. Standard types of weld seams and material combinations have beencertified in

welding procedures

for both longitudinal seams of bellows cylinders and for circular weldsbellows/connecting element. For each type of weld seam, the most appropriate

4 Metal Bellows


and most economical procedure is applied. This includes Plasma, TIG andLaser welding which have been automated to a great extent. The efficiency ofthese procedures has been verified in many applications and most of thewelding connection have been standardized in procedures. Welding is per-formed only by approved welders according to written procedures.The welding supervisors comply with qualification sheet HP 3.

Furthermore, we have been given a series of certificates of approval andregistration issued by domestic and foreign independent surveying bodies.Finally, the actual quality criterion of bellows is the number of stress cyclesendured. It depends, above all, on the operating conditions. Our design calcu-lation instructions and the service life table on page 83 show that even with asmall reserve in respect to the elastic elongation of the bellows an over-propor-tional increase in service life will be obtained. If, for example, the theoreticalrequirement for a bellows is 10 corrugations and one further corrugation isadded (a 10% increase in quantity) this will provide an increase in service life ofabout 50%. This shows that additional corrugations, if there is enough space,will make any service life test obsolete. The costs for these additional corruga-tions are lower than the costs for a cycling test.

4 Metal Bellows


Explanations

Column The number of plies required is determined,6 by the pressure resistance required.

Number Furthermore, bellows subject to corrosive media and valve seal bellows of Plies shall be of multiply design.

In measurement and control engineering, the mainrequirement is a low spring rate. Single-ply bellows are most appropriate due to low service pressures.

Column The pitch of one corrugation is the distance from the center of one 7, 8 crest to the center of the next crest.

length of thecorrugated

section

Due to the various end types (colums 9 to 15) the corrugated length is not exactly the pitch multiplied by the number of corrugations.In practice, however, it makes sense to determine the corrugated lengthas the sum of the individual corrugations, regardless of the selected cufftype. The calculation is based upon the number of the corrugations to sim-plify matters. The order forms are also based upon this method.

nw = lg / lw; l g = nw lwl g = length of the corrugated bellows (active length) (mm)

lw = length of one corrugation (mm)

nw = number of corrugations

The maximum length of a bellows depending on the production process is quoted in column 8. If longer bellows are required, up to four individual bellows will be welded to form one longer bellows train.

4 Metal Bellows

lw

4 Metal Bellows

Explanations

Column In inquiries and orders, it is sufficient to quote1 the bellows type, the number of corrugations

Bellows (or Type the length of the corrugated section) and the end cuff type.

Example:10 HYDRA metal bellows, type 334220-J10

This brief form means:10 HYDRA metal bellows made of stainless steel, material no. 1.4571

double-ply versioninternal diameter 34 mmexternal diameter 50 mm20 corrugations = 84 mm length of the corrugated sectionend type Jlength of end 10 mminternal end diameter 34 mmoverall length 104 mm

Column The bellows diameter d1 and d2 are normally2 5 subject to the tolerances quoted.

Bellows With the "high-precision" version, theDiameter tolerances are reduced by half (additional charge).

Details and Notesto the dimensional and data tables for metal bellows, pages 86 to 103.This chapter gives explanations in respect to the terms and informations given inthe individual column of the dimensional and data tables.


4 Metal Bellows

special cuff type for stainless steelbellows with four to eight plies whichwill be welded with outerreinforcing rings.

special cuff type for seamless bellowspages 100 to 103column 10 and 11

Ja

E

lg l2

lg l2 lg l2

Explanations

Columns These columns quote the dimensions of the basic cuff types.9-15 See page 156 for information relevant for welding.cuff The cuff diameter tolerances are about half of the

types internal bellows diameter tolerances quoted incolumn 3. With high-precision versions (extra charge), further reduction of tolerances is possible.

Column9

4 Metal Bellows

The most economical cuff typefor weld connections.It can be made of longer bellows by individual.cutting process 1-8 pliespossible.

End cuff for individual pieces,especially for test bellows.

The cuff length (l2) is limitedto a few mm. The production oflonger cuffs is not possible.

Economical cuff type for largerseries.

Standard cuff lengths (l 2)optional cuff lengths are availabein preferable dimensions5, 6, 8 and 10 mm as well as withany length 10 mm.

cuff designtype

Column12

13

Column14

15

bb

S

J

lglg

lg lg l2

lg l2

Special Cuff Types

cufftype


number of corrugations nw factorfor internal bellows B d1 in millimeters

d1 % 24 25 to 42 43 to 65 66 to 125 ka k i

8 10 12 16 1

9 11 13 181

0,85

10 12 14 19 0,70

11 13 16 21 0,60

12 14 17 22 0,50

13 15 18 240,9

0,45

14 16 19 26 0,40

15 17 20 27 0,35

16 18 22 29 0,30

17 19 23 300,8

0,28

18 20 24 32 0,25

19 22 26 35 0,20

20 24 29 38 0,18

21 26 31 420,7

0,15

22 28 34 45 0,13

24 30 36 48 0,11

28 35 42 56 0,08

32 40 48 64 0,6 0,06

40 50 60 80 0,04

Squirm Reduction Factors for Long Metal Bellows

4 Metal Bellows

Column Explanations

The permissible pressures are calculated as follows:

type of thermal pressure stress to the bellowsmovement stress

externally internally

20 C paz = pn p iz = pn k i

.20 C paz = pn k t p iz = pn k t k iaxial

20 C paz = p iz =

.20 C paz = p iz =

angular

20 C paz = p iz =

.20 C paz = p iz =

lateral

paz = permissible external pressure (bar)p iz = permissible internal pressure (bar)pn = design pressure according to dimensional tables (bar)all three types of pressures are positive pressuresab = required angularity of the bellows, ()

the value is to be inserted, e.g. with 17 = 34 the value 17lb = required lateral movement of the bellows (mm)

the value is to be inserted, e.g. with 4 mm = 8 mm the value 4lg = corrugated length (active length) of the bellows (mm)nw = number of corrugationskaki = squirm reduction factors see page 63kt = squirm reduction factors see page 64 to 67

16designpres-sure

pn ka 5050 + ab

pn k t ka 5050 + ab

pn ka l gl g + lb

pn k t ka l gl g + lb

pn k t k i l gl g + lb

pn k i l gl g + lb

pn k t k i 5050 + ab

pn k i 5050 + ab

4 Metal Bellows


material material short term material temperature in Cgroup number 20 50 100 150 200 250

non-corroding 1.4301 X5 CrNi 18-10 0,96 0,83 0,75 0,67 0,62 0,57austenitic 1.4306 X2 CrNi 19-11 0,92 0,79 0,71 0,64 0,58 0,54steel

1.4541 X6 CrNiTi 18-10 0,92 0,87 0,82 0,77 0,73 0,691.4401 X5 CrNiMo 17-12-2 1,00 0,90 0,83 0,75 0,69 0,651.4404 X2 CrNiMo 17-12-2 1,00 0,85 0,78 0,71 0,65 0,621.4571 X6 CrNiMoTi 17-12-21,00 0,92 0,85 0,81 0,77 0,731.4435 X2 CrNiMo 18-14-3 1,00 0,85 0,78 0,71 0,65 0,60

heat-resistant 1.4828 X15 CrNiSi 20-12 1,00 0,90 0,83 0,81 0,76 0,71steel 1.4876 X10 NiCrAlTi 32-20 0,94 0,86 0,80 0,75 0,71 0,68

INCOLOY 800

1.4958 X5 NiCrAlTi 31-20 0,78 0,73 0,63 0,57 0,53 0,49INCOLOY 800H

austenitic steel 1.4948 X6 CrNi 18-11 0,88 0,80 0,75 0,68 0,62 0,58with hightemperature 1.4919 X6 CrNiMo 17-13 0,96 0,87 0,82 0,74 0,69 0,65resistance

nickle-based 2.4858 NiCr 21 Mo 1,04 0,96 0,92 0,86 0,80 0,78alloys INCOLOY 825

2.4816 NiCr 15 Fe 0,86 0,84 0,83 0,80 0,78 0,76INCONEL 600 / 600H

2.4856 NiCr 22 Mo 9 Nb 1,26 1,25 1,24 1,21 1,14 1,10INCONEL 625 / 625H

Temperature in C TemperatureDocumentation300 350 400 450 500 550 600 650 700 Limit [C]

0,53 0,51 0,49 0,48 0,47 0,47 - - - 300 DIN 17441

0,50 0,47 0,45 0,44 0,43 0,42 - - - 350 DIN 17441

0,65 0,63 0,61 0,60 0,58 0,58 - - - 400 DIN 17441

0,61 0,59 0,56 0,55 0,55 0,54 - - - 300 DIN 17441

0,57 0,55 0,53 0,51 0,50 0,50 - - - 400 DIN 17441

0,69 0,66 0,64 0,63 0,62 0,62 - - - 400 DIN 17441

0,57 0,55 0,53 0,51 0,50 0,50 - - - 400 DIN 17441

0,66 0,64 0,61 0,44 0,43 0,27 0,20 0,10 0,05 1000 SEW 470

0,65 0,62 0,59 0,58 0,57 0,55 0,53 - - 600 SEW 470VDTV-W

412

0,45 0,43 0,41 0,40 0,39 0,37 0,37 0,36 0,23 900 SEW 470VDTV-W

434

0,54 0,52 0,50 0,48 0,46 0,44 0,42 0,40 0,38 700 VDTV-W313

SEW 640

0,61 0,59 0,56 0,55 0,55 0,54 0,50 0,48 0,46 700 VDTV-W312

SEW 640

0,76 0,75 0,73 0,71 - - - - - 450 VDTV-W432

SEW 640DIN 17744

Reduction Factor k t for Determination of the PermissiblePressure in Dependance of Temperature1)

1) applied to pn values of stainless steel bellows made of 1.4571 (AISI 316Ti)

4 Metal Bellows 4 Metal Bellows


material material short term temperature in Cgroup number 20 50 100 150 200 250

nickle-based 2.4610 NiMo 16 Cr 16 Ti 1,33 1,27 1,24 1,18 1,12 1,08alloys HASTELLOY C4

2.4819 NiMo 16 Cr 15W 1,29 1,24 1,20 1,14 1,08 1,02HASTELLOY C276

2.4360 NiCu 30 Fe 0,90 0,88 0,86 0,84 0,82 0,78MONEL

copper tin 2.1020 2) CUSn 6 1,00 0,95 0,90 0,80 0,75 0,70alloys Bronze

pure nickle 2.4068 LC-Ni 99 0,41 0,39 0,37 0,36 0,35 0,27

titanium 3.7025 Ti 0,78 0,75 0,71 0,59 0,43 0,35

tantalum - Ta 0,55 0,51 0,47 0,43 0,39 0,35

Reduction Factor kt for Determination of the PermissiblePressure in Dependance of Temperature1)

1) applied to pn values of stainless steel bellows made of 1.4571 (AISI 316Ti) except 2)2) applied to pn values of bronze bellows

Temperature in C TemperatureDocumentation300 350 400 450 500 550 600 650 700 Limit [C]

1,06 1,04 1,02 - - - - - - 400 VDTV-W

424DIN 17744DIN 17750

0,96 0,93 0,90 - - - - - - 400 VDTV-W400

0,75 0,73 0,71 - - - - - - 425 VDTV-W263

DIN 17743DIN 17750

- - - - - - - - - DIN 17662DIN 17670

0,24 0,23 0,22 0,20 0,17 0,12 0,07 - - 600 VDTV-W

4 Metal Bellows 4 Metal Bellows

paz = permissible external pressure calculated values (bar)piz = permissible internal pressure according to column 16 (bar)pb = service pressure (bar)kl = reduction factor (elastic deflection)

for service pressure at 10000 stress cycleskn = corrective factor (elastic deflection) at higher design than service

pressure conditions, see table page 83


or k l

1 10,8 1,050,6 1,080,4 1,10,2 1,130 1,15

or + 1

axial movement

1 corrugation nw corrugations

z = n k l g = n k l nw nw =

z = n k l 1,5 g = n k l nw 1,5 nw =

z = n k k l g = n k k l nw nw =

z = n k k l 1,5 g = n k k l nw 1,5

nw =

z = n kn g = n kn nw nw =

z = n kn 1,5 g = n kn nw 1,5 nw =

z = n k kn g = n k kn nw nw =

b n

b n k l b

n k b

n k k l b n

b n kn

b n k

b n k kn

pbpaz

pbpaz

pbpiz

pbpiz

number of corrective factorstress cycles kf

107 0,055 106 0,12 106 0,28 105 0,34 105 0,42 105 0,5

105 0,650 000 0,725 000 0,814 000 0,910 000 1,04 000 1,21 700 1,41 000 1,6

kf = kn (also see page 83)

kl = kn (also see page 83)

If the length of the corrugated sec-tion has been increased in these cal-culations, the pressure resistancewill have to be verified again acc. tocolumn 16 (squirm reduction factor).The calculation of the axial move-ment is to be repeated, if necessary.This will also apply in calculationswhere mandatory spring rates influ-ence the corrugated length.

4 Metal Bellows

The values for an increase or decrease in length are always to be inserted into the formulae on this double page for the axial movements b, g, n, zi.e. from, e.g., b = 10 = 20 mm the value 10and from, e.g., b = +20 mm the value 20.

These formulae will convey general results.

with orwithoutpre-setting or ' 1

axial movement


20 C

z = n g = n nw nw =

z = n 1,5 g = n nw 1,5 nw =

.20 C

z = n k g = n k nw nw =

z = n k 1,5 g = n k nw 1,5 nw =

20 C

z = n kf g = n kf nw nw =

z = n kf 1,5 g = n kf nw 1,5 nw =

.20 C

z = n k kf g = n k kf nw nw =

z = n k kf 1,5 g = n k kf nw 1,5 nw =

b = required axial movement for the whole bellows (mm) g = permissible axial movement for the whole bellows also see (mm) n = nominal axial movement per corrugation according to of page 69dimensional tables (mm/corr.) z = permissible axial movement per corrugation (mm/corr.)nw = number of corrugationsk

= reduction factor for the bellows movement (elastic deflection) at temperatures > 20 C according to tables on pages 74 to 77

kf = reduction factor (elastic deflection) for stress cyclesunder maximum service pressure conditions

Explanations

Column17

axialdeflec-

tion

b

b n b n

b n k b

n kf b

n kf

b n k kf

b n k

pbpaz

pbpiz

The values of the elastic deformation in axial direction quoted in the dimen-sional tables apply to one corrugation. They guarantee that under the refe-rence pressure quoted, 10000 stress cycles at ambient temperature (20-30C) can be expected. Under thermal stress, the permissible elasticdeformation will decrease. Furthermore, it is to be reduced if cycle lifeexpectancy is raised, and vice versa.The permissible axial movements are calculated from the following table;according to the service conditions, only one formula is to be selected foreach individual case.axial

10 000

otherloadcyclenum-bers

4 Metal Bellows

with()

without (+)or ()

with()

without (+)or ()

with()

without (+)or ()

with()

without (+)or ()

cyclelifeexpect-ancy

thermalstress

At total or almost total permissibleservice pressure rate according to column 16

number of corruga-tions for the total

movement (round offto higher number)



With only partial application without excess of the permissiblepressure according to calculation in column 16


for service pressure at 10000 stress cycles

kn = corrective factor (elastic deflection) at higher design than servicepressure conditions, see table page 83


or k l

1 10,8 1,050,6 1,080,4 1,10,2 1,130 1,15

or + 1

bending angle


z = n k l g = n k l nw nw =

z = n k k l g = n k k l nw nw =

z = n kn g = n kn nw nw =

z = n k kn g = n k kn nw nw =

b

b

n k k l

b

n kn

b

n k kn

pbpaz

pbpaz

pbpiz

pbpiz


107 0,055 106 0,12 106 0,28 105 0,34 105 0,42 105 0,5

105 0,650 000 0,725 000 0,814 000 0,910 000 1,04 000 1,21 700 1,41 000 1,6



If the length of the corrugated sec-tion has been increased in these cal-culations, the pressure resistancewill have to be verified again acc. tocolumn 16 (squirm reduction factor).The calculation of the angular move-ment is to be repeated, if necessary.This will also apply in calculationswhere mandatory spring rates influ-ence the corrugated length.

4 Metal Bellows

or ' 1

bending angle


20 C z = n g = n nw nw =

.20 C z = n k g = n k nw nw =

20 C z = n kf g = n kf nw nw =

.20 C z = n k kf g = n k kf nw nw =

b = required bending angle for the whole bellows the value ( )g = permissible bending angle for the complete bellows for one direction ( )n = nominal bending angle per corrugation according of movement

to dimensional tables is to be ( /corr.)z = permissible bending angle per corrugation inserted ( /corr.)nw = number of corrugationsk



Explanations

Column18

angulardeflec-

tion

b

b

n k

b

n kf

b

n k kf

pbpaz

pbpiz

The values of the elastic deformation for the bending angles quoted in thedimensional tables apply to one corrugation. Due to their selection, 10000stress cycles at ambient temperature (20-30C) and under the referencepressure quoted can be expected. Under thermal stress, the permissible ela-stic deformation will decrease. Furthermore, it is to be reduced if cycle lifeexpectancy is raised, and vice versa.The permissible bending angles are calculated from the following table;according to the service conditions, only one formula is to be selected foreach individual case.angular

10 000

4 Metal Bellows


thermalstress


number of corruga-tions for the totalangle (round off

to higher number)

number of corruga-tions for the totalangle (round off

to higher number)




or + 1

lateral movement


z = n k l g = n k l nw2 nw =

z = n k k l g = n k k l nw2 nw =

z = n kn g = n kn nw2 nw =

z = n k kn g = n k kn nw2 nw =

b

or k l

1 10,8 1,050,6 1,080,4 1,10,2 1,130 1,15b

n k k l

bn kn

bn k kn

pbpaz

pbpaz

pbpiz

pbpiz


107 0,055 106 0,12 106 0,28 105 0,34 105 0,42 105 0,5

105 0,650 000 0,725 000 0,814 000 0,910 000 1,04 000 1,21 700 1,41 000 1,6



If the length of the corrugated sec-tion has been increased in these cal-culations, the pressure resistancewill have to be verified again acc. tocolumn 16 (squirm reduction factor).The calculation of the lateral move-ment is to be repeated, if necessary.This will also apply in calculationswhere mandatory spring rates influ-ence the corrugated length.

4 Metal Bellows


for service pressure at 10000 stress cycleskn = corrective factor (elastic deflection) at higher design than service

pressure conditions, see table page 83

or ' 1

lateral movement


20 C z = n g = n nw2 nw =

.20 C z = n k g = n k nw2 nw =

20 C z = n kf g = n kf nw2 nw =

.20 C z = n k kf g = n k kf nw2 nw =

b = required lateral movement for the whole bellows the value (mm)g = permissible lateral movement for the whole bellows for one direction (mm)n = nominal lateral movement per corrugation according of movement

to dimensional tables is to be (mm/corr.)z = permissible lateral movement per corrugation inserted (mm/corr.)nw = number of corrugationsk



Explanations

Column19

lateraldeflec-

tion

b

bn k

bn kf

bn k kf

pbpaz

pbpiz

The values of the elastic deformation in lateral direction quoted in the dimen-sional tables apply to one corrugation. Due to their selection, 10000 stresscycles at ambient temperature (20-30C) and under the reference pressurequoted can be expected. Under thermal stress, the permissible elasticdeformation will decrease. Furthermore, it is to be reduced if cycle lifeexpectancy is raised, and vice versa.The permissible lateral movements are calculated from the following table;according to the service conditions, only one formula is to be selected foreach individual case.lateral

10 000

4 Metal Bellows


thermalstress









material material short term Temperature in Cgroup number 20 50 100 150 200 250

non-corroding 1.4301 X5 CrNi 18-10 1,00 0,97 0,90 0,85 0,80 0,75austenitic steel 1.4306 X2 CrNi 19-11 1,00 0,97 0,90 0,85 0,80 0,75

1.4541 X6 CrNiTi 18-10 1,00 0,97 0,90 0,85 0,80 0,751.4401 X5 CrNiMo 17-12-2 1,00 0,97 0,90 0,82 0,78 0,721.4404 X2 CrNiMo 17-12-2 1,00 0,97 0,90 0,82 0,78 0,721.4571 X6 CrNiMoTi 17-12-21,00 0,97 0,90 0,82 0,78 0,721.4435 X2 CrNiMo 18-14-3 1,00 0,97 0,90 0,82 0,78 0,72

heat-resistant 1.4828 X15 CrNiSi 20-12 1,00 0,98 0,95 0,92 0,90 0,88steel 1.4876 X10 NiCrAlTi 32-20 1,00 0,97 0,90 0,87 0,84 0,80

INCOLOY 800

1.4958 X5 NiCrAlTi 31-20 1,00 0,97 0,90 0,87 0,84 0,80INCOLOY 800H

austenitic steel 1.4948 X6 CrNi 18-11 1,00 0,97 0,90 0,87 0,84 0,80with hightemperature 1.4919 X6 CrNiMo 17-13 1,00 0,97 0,90 0,87 0,84 0,80resistance

nickle-based 2.4858 NiCr 21 Mo 1,00 0,98 0,95 0,92 0,90 0,88alloys INCOLOY 825

2.4816 NiCr 15 Fe 1,00 0,98 0,95 0,92 0,90 0,88INCONEL 600 / 600H

2.4856 NiCr 22 Mo 9 Nb 1,00 0,97

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