ad 2000-mb - s6 -02-2010

AD 2000-Merkblatt ICS 23.020.30 February 2010 edition

Special cases Creep stress for steels AD 2000-Merkblatt

S 6

The AD 2000-Merkblätter are prepared by the seven associations listed below who together form the “Arbeitsgemeinschaft Druck-behälter” (AD). The structure and the application of the AD 2000 Code and the procedural guidelines are covered by AD 2000-Merk-blatt G 1.

The AD 2000-Merkblätter contain safety requirements to be met under normal operating conditions. If above-normal loadings are to be expected during the operation of the pressure vessel, this shall be taken into account by meeting special requirements.

If there are any divergences from the requirements of this AD 2000-Merkblatt, it shall be possible to prove that the standard of safety of this Code has been maintained by other means, e.g. by materials testing, tests, stress analysis, operating experience.

Fachverband Dampfkessel-, Behälter- und Rohrleitungsbau e.V. (FDBR), Düsseldorf

Deutsche Gesetzliche Unfallversicherung (DGUV), Berlin Verband der Chemischen Industrie e.V. (VCI), Frankfurt/Main

Verband Deutscher Maschinen- und Anlagenbau e.V. (VDMA), Fachgemeinschaft Verfahrenstechnische Maschinen und Apparate, Frankfurt/Main

Stahlinstitut VDEh, Düsseldorf

VGB PowerTech e.V., Essen

Verband der TÜV e.V. (VdTÜV), Berlin

The above associations continuously update the AD 2000-Merkblätter in line with technical progress. Please address any proposals for this to the publisher:

Verband der TÜV e.V., Friedrichstraße 136, 10117 Berlin.

Contents

Page

0 Foreword.................................................................................................... 2 1 Scope......................................................................................................... 2 2 General ...................................................................................................... 2 3 Symbols and units ..................................................................................... 2 4 Design in the creep range.......................................................................... 2 5 Loads......................................................................................................... 4 6 Component design requirements............................................................... 5 7 Information on operation of plant in the creep range ................................. 6 8 Bibliography ............................................................................................... 6

Supersedes May 2007 edition; | amendments to previous edition

AD 2000-Merkblätter are protected by copyright. The rights of use, particularly of any translation, reproduction, extract of figures, transmission by photomechanical means and storage in data retrieval systems, even of extracts, are reserved to the author. Beuth Verlag has taken all reasonable measures to ensure the accuracy of this translation but regrets that no responsibility can be accepted for any error, omission or inaccuracy. In cases of doubt or dispute, the latest edition of the German text only is valid.

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AD 2000-Merkblatt AD 2000-Merkblatt S 6, 02.2010 edition

0 Foreword

The AD 2000 Code can be applied to satisfy the basic safety requirements of the Pressure Equipment Directive, principally for the conformity assessment in accordance with modules “G” and “B F”.

The AD 2000 Code is structured along the lines of a self-contained concept. If other technical rules are used in accordance with the state of the art to solve related problems, it is assumed that the overall concept has been taken into account.

The AD 2000 Code can be used as appropriate for other modules of the Pressure Equipment Directive or for different sectors of the law. Responsibility for testing is as specified in the provisions of the relevant sector of the law.

1 Scope

1.1 This AD 2000-Merkblatt contains criteria for handling creep-stressed steels. It shall be used when a creep-induced change in the material characteristics is to be expected as a result of the effect of temperature. The following lower limit temperatures apply here:

approximately 380 °C for alloyed steels,

approximately 440 °C for low-alloy steels,

approximately 525 °C for high-alloy steels (austenitic, ferritic, martensitic steels).

1.2 The exact limit temperatures shall be determined on the basis of the relevant harmonized material standard. The use of other materials is possible but the suitability has to be established in the form of an appraisal according to 4.2 of Annex I of Directive 97/23/EC from a notified body for each case.

1.3 This AD 2000-Merkblatt applies only in conjunction with the AD 2000-Merkblätter of the B Series. For the AD 2000-Merkblätter S 3 and S 4, a special stress assessment concept is required.

2 General

When the stress limitation criteria contained in this AD 2000-Merkblatt are met, the following types of failure are taken into consideration: creep fracture,

creep deformation,

creep fatigue.

The possibility of other types of failure shall be checked in addition, if relevant (e.g. embrittlement, high-temperature attack, elastic instability, stress corrosion cracking, corrosion fatigue).

3 Symbols and units

The following apply in addition to the requirements of AD 2000-Merkblatt B 0:

f normal design stress under static loading

se final wall thickness

Rm minimum tensile strength at 20 °C

Rm 100 000 mean creep rupture strength for 100 000 h at design temperature

Rm 200 000 mean creep rupture strength for 200 000 h at design temperature

4 Design in the creep range

4.1 Design pressure

The design pressure is at least the maximum allowable pressure (PS) of the relevant pressure equipment. In addition, if static pressures are present, their full value shall be taken into account.

4.2 Design temperature

The design temperature comprises the maximum allowable temperature (TS) and a temperature allowance. The following Table 1 applies for the water/steam and superheated steam ranges, otherwise clause 5 of AD 2000-Merkblatt B 0 applies.

4.3 Normal design stress

4.3.1 General

Time-dependent design strength values generally cover the ranges from 10 000 h upwards. Indication of these shall generally give the source. Time-dependent design strength values shall preferably be taken from harmonized standards. If other sources are used, the materials’ suitability shall be verified in accordance with 3.2.1 of AD 2000-Merkblatt W 0.


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Table 1 — Temperature allowances in the water/steam and superheated steam ranges

Temperature allowances

Heated components**)

Heated mainly through Unit condition

Reference temperature Unheated

components**) radiation*) convection

Shielded against radiation

Water and water/ steam mixture

Saturation tempe-rature at maximum allowable pressure (PS) (incl. hydro-static head)

0 K 50 K for headers***) (30 3 se) K at least 50 K

(15 2 se) K, max. 50 K

20 K

Superheated steam

Superheated steam

15 K****) 50 K 35 K 20 K

*) Compartmentalized superheaters are dealt with like convection heaters.

**) For definition of heating types, see FDBR/VGB/VdTÜV Agreement 1988/1 (VdTÜV-Merkblatt 451-88/1).

***) Regardless of the flow, headers are considered to be pipe-shaped hollow parts with an outside diameter 76,1 mm, into which three or more pipes discharge, not axially.

****) In the case of unheated components carrying superheated steam, the temperature allowance may be reduced from 15 K to 5 K (measuring tolerance), if it is ensured that the superheated steam temperature specified in the design cannot be exceeded. This can be achieved by:

(1) temperature control upstream of these components,

(2) arrangement of cooling or mixing points (e. g. by headers with longitudinal flow through them) upstream of these components or

(3) circuitry measures or similar upstream of these components.

4.3.2 Normal design stress on the basis of Rm 100 000

The smallest of the following values applies:

tensile strength at room temperature with a safety factor of 2,4,

minimum yield point value and 0,2 % proof stress value or — if relevant — 1 % proof stress value at design temperature with a safety factor of 1,5 for internal gauge pressure and 1,8 for external gauge pressure. If the yield point is not pronounced, the 0,2 % proof stress determined according to DIN EN 10002-1 shall be inserted.

mean creep strength for 100 000 h at design temperature with a safety factor of 1,5 for internal gauge pressure and 1,8 for external gauge pressure.

Internal gauge pressure

1,5;

1,5;

2,4min

000100m2,0pm RRRf

External gauge pressure

1,8;

1,8;

2,4min

000100m2,0pm RRRf

4.3.3 Normal design stress on the basis of Rm 200 000

The smallest of the following values applies:

tensile strength at room temperature with a safety factor of 2,4,

minimum yield point value and 0,2 % proof stress value or — if relevant — 1 % proof stress value at design temperature with a safety factor of 1,5 for internal gauge pressure and 1,8 for external gauge pressure. If the yield point is not pronounced, the 0,2 % proof stress determined according to DIN EN 10002-1 shall be inserted.

mean creep strength for specified operating time (up to 200 000 h) at design temperature with a safety factor of 1,25 for internal gauge pressure and 1,5 for external gauge pressure.

Internal gauge pressure

1,25;

1,5;

2,4min

000200m2,0pm RRRf


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External gauge pressure

1,5;

1,8;

2,4min

000200m2,0pm RRRf

4.4 Wall thickness allowances

The full value of the wall thickness allowances shall generally be taken into account in the design according to the specific tolerance indication (c1) or the wall thickness reduction (c2).

4.5 Quality of the weld joint

4.5.1 In the case of fully loaded welds, the normal design stress determined in 4.3 shall be multiplied by a factor of 0,8, except for those welds and heat affected zones for which already confirmed values exist.

4.5.2 If the maximum stress component normal to the direction of the weld exceeds 80 % of the normal design stress determined in 4.3, design changes are necessary to maintain the set 80 % limitation.

4.5.3 The weld factor determined according to AD 2000-Merkblatt HP 5/3 shall be included in the observations if this only allows 85 % utilization of the weld joint. In this case, this results in the normal design stress determined in 4.3 being limited to 68 %.

4.5.4 For weld-on parts, the weld quality is determined and ensured following agreement with the notified body involved.

5 Loads

5.1 Principally static loads

5.1.1 If the requirements of B 1 to B 9 are met, the dimensioning is adequate to withstand principally static loads.

5.1.2 The limits for alternating loads shall be taken from the AD 2000-Merkblätter of the S series.

5.2 Operating regime and accumulation of damage

5.2.1 General requirements for the operating regime are contained in TRD 508 [1] and DIN EN 12952-4 [3].

5.2.2 The accumulation of damage is made up of both creep fatigue and alternating loading fatigue. Determination of the creep fatigue is based generally on automatic acquisition and totalling of different loads on highly-loaded components, formed from pressure or assigned temperature above the creep limit. Alternating loading results from mechanical and thermal loads (above and below the creep limit) and may be determined in the form of a degree of fatigue using AD 2000-Merkblatt S 2 or according to Annex 1 of TRD 508 [2]. The resulting total fatigue is the sum of the two fatigue values determined.


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6 Component design requirements

Table 2 — Acceptable loadbearing weld joints in the creep range

A) Butt welds

B) Nozzle welded on both sides

C) Nozzle welded on one side

D) Set-on nozzle with drilled out root


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Table 3 — Acceptable non-loadbearing weld joints in the creep range

A) Welded-on block

7 Information on operation of plant in the creep range

Lifetime monitoring for plants in the creep range is recommended as a rule.

For pressure equipment without lifetime monitoring, the service life is generally limited to 100 000 hours of operation. If proof of operating already completed is not to be provided, the 100 000 hours start from the beginning of the year of manufacture of the pressure equipment in question.

The procedure for pressure equipment with lifetime monitoring is according to the measures in Annex 1 of TRD 508 [2] and DIN EN 12952-4 [3].

8 Bibliography

[1] TRD 508, Additional tests on components, calculated with time-dependent design strength values

[2] TRD 508 Annex 1, Additional tests on components — Methods for the calculation of components having time-dependent design strength values

[3] DIN EN 12952-4, Water-tube boilers and auxiliary installations — Part 4: In-service boiler life expectancy calculations; German version EN 12952-4


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Publisher: Source of supply:

Verband der TÜV e.V.

E-Mail: [email protected] http://www.vdtuev.de

Beuth Verlag GmbH 10772 Berlin Tel. 030 / 26 01-22 60 Fax 030 / 26 01-12 60 [email protected] www.beuth.de


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ad 2000-mb - s6 -02-2010

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