47413_03

Design Guide for Steels at Elevated Temperatures and High Strain Rates

3 ELEVATED TEMPERATURE MATERIAL PROPERTY DATA

3.1 Introduction This chapter provides information on material property data to be used in the design of offshore structures against fires. Data is provided to enable the engineer to use both simplified code based methods and advanced non-linear system methods.

3.2 Methods to measure elevated

Material properties of steel at elevated temperature are obtained using one of two methods; these being termed the Steady State (Isothermal) and the Transient State (Anisothermal) test methods. It is important to distinguish between the two methods used as the properties are different.

temperature material properties

3.2.1 Steady state (isothermal) test

Steady state tests have been traditionally used for mechanical engineering applications where the tensile specimen is subject to constant temperature and further strain is applied at a steady rate. An unloaded specimen is brought into thermal equilibrium at a certain temperature and then it is strained at a uniform rate (rate of strain in the range typically 0.001-0.003 per minute) while the resulting loads experienced by it are recorded as a function of extension. Similar tests are then repeated at other temperatures to build up a family of load - extension curves from which the required strength-temperature data can be extracted. Until quite recently, this method was by far the most commonly used and standards exist in many countries for this test. In Europe this test is performed in accordance with EN 10002-5.

method

3.2.2 Transient state (anisothermal)

The transient-state test method was developed specifically for fire engineering purposes. In fire it is important to know how deformations will develop in a loaded steel component that is subjected to a change in temperature. For this reason tensile tests under transient heating conditions have been devised in which the load on the steel specimen is maintained constant,

test method

whilst its temperature is increased at a given rate. The data in BS 5950-8 and ENV 1993-1-2 are largely derived from transient state tests.

Currently there is no British, European or International standard on the procedures for carrying out transient state testing. However, an IS0 standard outlining the principles of transient state testing is being produced.

Results from a typical test comprise a series of strain-temperature curves as shown in Figure 3.1.

1b

9

8

.f ’ & + a

5

4

3

2

1

0

3

0 4

I 1” 10 I

Tmp.nu8 I‘CI

Figure 3.1 Elevated temperature transients state heating test curves for various stress ratios

There are two main models for predicting the behaviour of steel at high temperatures, one for carbon steel and one for stainless steel.

3.3 Carbon Steel Model The carbon steel model is based on both transient state (anisothermal) and steady state (isothermal) tests, derived from extensive testing and research conducted by numerous establishments. It is described in ENV 1993-1-2 and applies to grades S235, S275, S355, S240 and S460 of EN 10025 and all steel grades of EN 10113, EN 10155, EN 10210-1 and EN 10219-1.

For heating rates between 2 and 50”C/min, the strength and deformation properties of steel at

6 FABIG Technical Note 6 - September 2001


elevated temperatures are obtained from the 0 slope of linear elastic range, relative to

illustrated in Figure 3.2. Table 3.2 gives the strength reduction factors, relative to the appropriate value at 20"C, as follows:

0

stress-strain relationships given in Table 3.1 and slope at 20°C: kE,e = E%e/Ea

The variation of these three reduction factors with temperature is illustrated in Figure 3.3.

The mechanical properties of steel at 20°C are the characteristic values given in ENV 1993-1-1 for normal temperature design.

effective yield strength, relative to yield strength at 20°C: &,e = fY,eyy

proportional limit, relative to yield strength at 20°C: 4,e = fp,e/fy

0

Strain E

Figure 3.2 Stress-strain relationships for steel at elevated temperatures

FABIG Technical Note 6 - September 2001 7

Design Guide for Steels a t Elevated Temperatures and High Strain Rates

Table 3.2 Reduction factors at elevated temperatures for stress-strain profiles at elevated temperatures 0, relative to the value of f y or E, at 20 "C (given in ENV 1993-1-2 Table 3.1)

Steel Reduction Reduction Reduction temperature factor (relative factor (relative factor (relative

9, to f,) for to f,) for to E,) for the effective yield proportional slope of the

strength limit linear elastic range

100 200 300 400 500 600 700 800 900

lo00 1100

1 .Ooo 1 .Ooo 1 .ooo 1 .ooo 0.780 0.470 0.230 0.110 0.060 0.040 0.020

1 .Ooo 0.807 0.613 0.420 0.360 0.180 0.075 0.050 0.038 0.025 0.013

1 .Ooo 0.900 0.800 0.700 0.600 0.310 0.130 0.090 0.068 0.045 0.023

1200 0.Ooo O.OO0 0.Ooo NOTE; for intermediate values of the steel temperature, linear interpolation may be used.

1.0 -

0.9 -

0.8 - L

c, 0 0.7 - 0 3 0.6 - C 0 0.5 -

0.4 -

0.3 j

.- c,

D

-Effective yield strength k y , O

- - - -Proport ional l imi t k,,,,

. . . . - - . S l o p e o f e last ic range k E , "

+ 0 200 400 600 800 1000 1200

Temperature O C

Figure 3.3 Reduction factors for the stress-strain relationship of carbon steel at elevated temperatures (ENV 1993-1 -2 Carbon Steel Model)

8 ~~

FABIG Technical Note 6 - September 2001


3.3.1 Stress-strain relationships at stress-strain relationships at different temperatures are illustrated in Figure 3.4 for steel grade S355. It should be recognised that the relationships predicted in Table 3.1, and the The stress strain relationship for the carbon steel

corresponding Figures and Tables, do not allow model of Table 3.1 is evaluated for steel grades for strain hardening. S355 and S460 in Appendix A. The resulting

elevated temperatures

1 .o 0.9

0.8

0.7

0.6

0.3

0.2

0.1

0 .o 0.000 0.005 0.010 0.01 5 0.020

Strain E

Figure 3.4 Variation of stress-strain relationship with temperature for Grade S355 Steel (Strain- hardening not included)

_ _ _ _ _ _ _ ~ _ _ _ _ _ ~

FABIG Technical Note 6 - September2001 9


3.3.2 Strain-hardening of steel at elevated temperatures

For temperatures below 400 "C, the stress-strain relationship for the carbon steel model of Table 3.1 may be extended by the strain-hardening option given in Annex B of ENV 1993-1-2. These relationships, however, should only be used if the proportions of the cross-section are such that local buckling does not prevent attainment of the increased strain and that the member is adequately restrained to prevent buckling.

For temperatures below 400 "C, the stress-strain relationship, allowing for strain-hardening, may be expressed as follows:

for 0.04 I + IO.15 ae = fu,e

where: f4e is the ultimate strength at elevated

temperature, allowing for strain- hardening, and should be determined as follows:

f,e = 1.25 fY,@ for 8 < 300°C

f4e = fy.e (2 - 0.00259 for 300°C I 6 < 400°C

fu,e = fy,e for 0 2 400°C

The stress-strain relationship for steel, allowing for strain hardening, is illustrated in Figure 3.5.

Stress 0 0

u . 0

f v , 11

f p.0

Strain E O

Figure 3.5 Stress-strain relationship for steel, allowing for strain hardening

3.3.3 Thermal properties The thermal elongation of steel A I / I may be determined from the following:

for 20°C I 6 < 750°C ~ i / i = 1.2 x 10-5 6 + 0.4 x 1 0 - 8 62 - 0.0002416

for 750"CI e < 860°C A l l 1 = 1.1 x I O - ~

for 860°C < e < 1200"~ Al/l = 2 x lo-' 8 - 6.2 x

where: I A1 is the temperature induced

e

is the length at 20°C;

expansion; is the temperature [ "C]

In simple calculation models the relationship between thermal elongation and steel temperature may be considered to be constant. In this case the elongation may be determined from:

AZ/l = 1 4 x W 6 (6-20)

The data supplied in ENV 1993-1-2 can be generally used for strength classes S235, S275, S355, S420 and S460 steels. However, i t must be appreciated that there are numerous different types of steel within each strength class with different compositions and different methods of processing (i.e. non-alloy, fine grain, normalized, thermo-mechanical1 y rolled,



quenched and tempered and precipitation hardened steels). Each of these steels will exhibit different behaviour under elevated temperatures. In the following section other sources, where additional research and testing have been performed, are reviewed.

3.4 Quenched and tempered steels There are greater variations as to the behaviour of quenched and tempered steels at elevated temperatures than the normalised, fine grained or thermo-mechanically rolled steels. These variations are due to differences in composition, quenching and tempering of the various grades.

To illustrate this, the variation in 0.2% proof strength with temperature for two different types of Corus RQT steels are shown in Figure 3.6"'. It can be seen that for temperatures in excess of 400°C, the Cows RQT 501 steel shows a

marked increase in strength reduction, whilst the BS 4360 Grade 55F steel maintains better strength properties.

It is important therefore not to attempt to generalise the behaviour of quenched and tempered steels at elevated temperature because the use of inappropriate data can lead to onerous results.

3.5 Thermo-mechanically Rolled Steel

3.5.1 Grade S355M Limited elevated temperature material property data is available for the steel in the form of data sheets. The data available for BS EN 10113-3:1993 Grade S355M steel is limited up to 500°C and is based on isothermal tests (data supplied by Dillinger). Figure 3.7 shows the tests results.

500 I I 1 450

400 8 t 2 350

0 ic

300

250

0 100 200 300 400 500

Temperature 'C

Figure 3.6 EfJect of composition on strength of RQT 501 steelo)

FABIG Technical Note 6 - September 2001 1 1


550

500

450

400

"E 350 E 2 300 5 p 250 2 ;j 200

+Yield strength 25mm pl

BYield strength 50mm pl

50mm pl

0 100 200 300 400 500 Temperature 'C

Figure 3.7 Elevated temperature material properties for S355 therm-mechanically rolled steel - (source, Dillinger Technical Department)

3.5.2 Grade S420M Research has recently been undertaken by Outinen, Kesti and Makelainen of Helsinki University of Technology''' to study the behaviour of BS EN 101 13-3: 1993 Grade S420M thermo-mechanically rolled structural steel under fire conditions. This is a grade of steel that is commonly used for Norwegian offshore structures. Transient state tensile tests were undertaken to develop simple formulae for calculating the mechanical properties at elevated temperatures and a comparison was made between the relationships specified in ENV 1993-1-2 using

(a) the reduction factors relationships in

(b) equations proposed by Outinen et al, based on test results.

3.5.3 Stress-strain relationship The following empirical relationships were developed for grade S420M steel.

ENV 1993-1-2 and

Modulus of elasticity The modulus of elasticity E,,e is given by

where kE$ = - ~ . ~ X I O - ' ~ e3 - 1 . 9 ~ 1 0 ~ e 2 + 0.000288 + 1.0

for 20°C I 8 I 700°C

Proportional limit The proportional limit f,,e is given by

where kp,e = 9 x ~ o - 9 e3 - 2 . 9 ~ 1 0 " e2 - o.ooo64e + I .o for 20°C I 0 I 700°C

Yield strength The yield strength fy,e is given by

where

for 20°c I e I 4 0 0 " ~



and

b,e = 2.2 x lo-* e3 - o.oo0o38e2 + 0.01918- 2.09 for 400°C I B I 700°C

at temperatures up to 700°C is shown in Figure 3.8.

It shows that the ENV 1993-1-2 model is unconservative for this S420M steel.

3.5.4 Grade S460M Table 3.3 gives the strength factors, relative to Elevated temperature material property data is the appropriate value at 20"C, based on the available from Dillinger for above relationships. BS EN 10113-3:19!33 Grade S W M steel in the

form of data sheets limited to 500"C, and based A comparison of the yield strength reduction on isothermal tests. Figure 3.9 shows a factor for Grade S420M structural steel studied summary of this data.

Table 3.3 Strength reduction factors at elevated temperatures for Grade S420M steel

Steel Reduction Reduction Reduction temperature factor (relative factor (relative factor (relative

to f,) for to f,) for to EJ for the effective yield proportional slope of the

strength limit linear elastic range

"C k e ( =fY.elfv> k e (= fD.elfv> k e (= &e /&) 20 1 ,00036 0.98606 1 .W83 100 0.95300 0.90990 1.00865 200 0.91000 0.77920 0.97720 300 0.88500 0.62530 0.90355 400 0.87800 0.46560 0.78560 500 0.71000 0.31750 0.62 125 600 0.44200 0.19840 0.40840 700 0.20600 0.12570 0.14495

1.0

xz 0.9 b I3 0.8 c 5 0.7

0.6 E q

0.2

Makehinen et al

\h

0 100 200 300 400 500 600 700

Temperature "C

Figure 3.8 Yield strength reduction factor k,8 for the structural steel studies

FABlG Technical Note 6 - September 2001 13


0 1w 200 300 400 500

Temperature 'C

Figure 3.9 Elevated temperature material properties for S46Oh4 thernw-mechanically rolled steel - (source, Dillinger data sheets)

3.6 Tests on BS 7191 steels It was found that no elevated temperature data existed for the structural steels specified in BS 7191. Tests were therefore performed on BS 7191 Grade 355EMZ and Grade 450EMZ steels, the most commonly used grades for steels. Tests were performed to obtain stress- strain profiles appropriate for fire engineering purposes for temperatures in the range 20 - 700 "C. The details of the tests can be found in the report on the study carried out by the SCI on behalf of the HSE (OTO 200 1 /020(3)).

The material used in the work programme conformed to: BS 7191:355EMZ in the normalised and thermo-mechanically rolled condition and BS 7191:450EMZ in the quench and tempered condition. Elevated temperature tests were carried out under transient heating conditions using a laboratory procedure developed at Corus Swinden Technology Centre. There are currently no National or International standards covering this type of test. However, where appropriate, relevant clauses given in BS EN 10002-5 that describe test procedures for steady state tests, were followed. The results of these tests are presented in this section for Grade 355EMZ and in the next section for Grade 450EMZ.

The data obtained from the tests were plotted against the ENV 1993-1-2 carbon steel model (with strain hardening). In this manner, it was possible to determine values for reduction factors to be used in conjunction with the EC3 model, for representing the stress-strain behaviour of Grade 355EMZ and Grade 450EMZ steels.

3.6.1 355EMZ steels The 355EMZ steel in the normalised condition was supplied in three plate thicknesses of 12 mm, 30 mm and 60 mm, whilst the thermo- mechanically rolled steel was supplied in one thickness only of 11.5 mm. Coupons for machining into test pieces were taken from each plate parallel to the rolling direction. Specimens from each plate were tested over a wide range of stress ratios (stress applied/ambient temperature yield or 0.2% proof stress) using a specimen heating rate of 10 "C/min. The tests were terminated when strains of around 5 6 % were attained. At these levels of strain, 'runaway' (onset of instability) would have been achieved.

The results of the tensile tests at ambient temperature are presented in Table 3.4 and confirm that the plates supplied were within specification.

14 FABlG Technical Note 6 - September 2001


Strength reduction factors, for use in conjunction with the ENV 1993-1-2 model defined in Table 3.1 and Figure 3.2, were derived using the following procedure:

stress-strain curves from test results presented in detail in Annex A in Tables A.3 to A.10. are plotted

0 different reduction factors are assumed until a conservative prediction, based on the EC3 model, is obtained

Tables 3.5 and 3.6 present the strength reduction factors, relative to the appropriate (minimum specified) values at 20°C for the Normalised and TMCR steels respectively. For simplified methods, it is sufficient to use the

strength reduction factors presented in Tables 3.5 and 3.6, while for advanced non-linear analysis, the strength reduction factors may be used together with the EC3 model (with strain hardening) to generate temperature dependent stress-strain curves.

It should be recognised that the strength reduction factors used in Table 3.5 are not dependent on steel thickness and are applicable for normalised steel plates supplied in all thicknesses up to 63 mm. Strength reduction factors for the TMCR steel are representative of plates up to 20 mm. A safety margin should be used for plate thicknesses greater than 20 mm.

Table 3.4 Ambient temperature tensile properties of the 355EMZ test plates

Material Yield or 0.2% Proof Tensile Strength Elongation Stress (N/mm2) (N/mm2) (%)

Measured Specified Measured Specified Measured Specified (Raw9

12 rnm (N) 408 355 524 460-620 27 20 30 rnm (N) 384 345 5 17 460-620 37 20 W m m ( N ) 392 340 499 460-620 39 20

12 mm (TMCR) 419 355 504 4 6 0 - 6 2 0 30 20

Table 3.5 Strength reduction factors at elevated temperatures for normalised Grade 355EMZ steel ~~~ ~

Steel Reduction factor Reduction factor Reduction factor temperature (relative tof,) for (relative to&) for (relative to E,) for the

effective yield proportional limit slope of the linear strength elastic range

100 0.820 0.750 0.900 200 0.750 0.550 0.800 300 0.720 0.450 0.750 400 0.650 0.350 0.700 450 0.620 0.350 0.650 500 0.550 0.300 0.450 550 0.450 0.200 0.400 600 0.320 0.150 0.250 650 0.210 0.100 0.130 700 0.130 0.050 0.075



Table 3.6 Strength reduction factors at elevated temperatures for TMCR Grade 355EMZ steel

Steel Reduction factor Reduction factor Reduction factor temperature (relative to&) for (relative to&) for (relative to E.) for the

effective yield proportional limit slope of the linear strength elastic range

"C k e (= f Y , e l f ) k e (= fp,e/fp) k , e (= E d E b 20 0.880 0.800 0.950

100 0.850 0.800 0.900 200 0.850 0.750 0.850 300 0.800 0.600 0.800 400 0.800 0.450 0.720 450 0.750 0.350 0.700 500 0.650 0.300 0.700 550 0.500 0.250 0.650 600 0.383 0.150 0.450 650 0.300 0.100 0.450 700 0.230 0.100 0.450

3.6.2 450EMZ steel (with strain hardening). In this manner, it was The quench and tempered 450EMZ steel was supplied in three plate thicknesses of 10 mm, 40 mm and 60 mm. Coupons for machining into test pieces were taken from each plate parallel to the rolling direction. For the 10 mm plate, full thickness test specimens were prepared, whereas for the 40 and 60 mm plates, specimens were machined so that their centre-line coincided with the plate quarter depth position.

possible to determine values for reduction factors to be used in conjunction with the EC3 model for representing the stress-stain behaviour of the 450EMZ steel. Table 3.8 presents the strength reduction factors relative to the appropriate (minimum specified) values at 20°C. For simplified methods, it is sufficient to use the strength reduction factors presented in Table 3.8, while for advanced non-linear analysis, the strength reduction factors may be used together with the EC3 model (with strain hardening) to generate temperature dependent stress strain curves. The strength reduction factors presented in Table 3.8 may be applied to all plates with thicknesses between 6 mm and 75 mm.

The results of the tensile tests at ambient temperature tests are presented in Table 3.7 and confirm the steel plates supplied were well within specification.

The data obtained from the tests were plotted against the ENV 1993-1-2 carbon steel model



Table 3.7 Ambient temperature tensile properties of the 4SOEMZ test plates

Plate thickness Yield or 0.2% Tensile Strength Elongation (mm) Proof Stress (N/mm2) (N/mII12) (%)

Measured Specified Measured Specified Measured Specified 10 484 450 564 550-700 28 19 40 478 415 553 550-700 20 19 60 448.5 415 544 550-700 31 19

Table 3.8 Strength reduction factors for normalised grade 45OEMZ steel

Steel Reduction factor Reduction factor (relative Reduction factor temperature (relative to f,) for to f,) for proportional (relative to E,) for

effective yield limit the slope of the linear strength elastic range

OC 4.0 (= f,.elfu) k e (= fp,elfU) k , e (= 4 , e / E & 20 0.85 0.80 0.95 100 0.82 0.75 0.90 200 0.80 0.70 0.80 300 0.80 0.65 0.75 400 0.80 0.65 0.65 500 0.75 0.60 0.65 600 0.70 0.50 0.55 700 0.62 0.40 0.50 800 0.48 0.30 0.35 900 0.32 0.20 0.20 lo00 0.20 0.10 0.10

~~

FABlG Technical Note 6 - September 2001 17


Strain range Stress

Ea,eEe

1 + aEe 6 B 5 k e

3.7 Stainless steel model As a consequence, another mathematical model

Tangent Modulus E, b Ea,e (1 + a E e - abEe )

(1+aEeb)’

is proposed, similar to the ENV 1993-1-2 model for carbon steel. The stainless steel model can be divided into two parts as shown in Figure 3.10‘3’. The significance and definition of different parameters are indicated in Figure 3.10

The stress-strain model for stainless steel is different from that for carbon steel in that the initial part of the curve becomes non-linear at an early stage and that there is no clear yield point.

and Table 3.9.

Figure 3.10 temperatures

Definition of parameters for stress-strain relationships of stainless steel at elevated

where:

with Ec,e = fo.2p,e/E,e + 0.002 and fo,zp,e is the 0.2 proof stress of stainless steel.



In the stainless steel model, the parameters for behaviour at elevated temperatures are:

Ea,e

Ea elastic modulus factor kE.0 = -

0.2% proof strength k,,,e factor - f o . z p , e

f 0.2p

- -

2% absolute strain strength parameter k2943

ultimate tensile strength factor k,,,e - f u.e

f u - -

critical elastic modulus factor kEct,e

The 2% absolute strain strength, fi*/o,e is particularly relevant for stainless steel member design. It is equivalent to parameter k,,,e in the carbon steel model. This parameter is apparently related to two specific strengths of stainless steel, that is fozp,e and fu,e. Because in the proposed mathematical model, these two strengths are considered to be independent from each other, then a special parameter k2%,e can be used for calculating the 2% absolute strain strength with following expression:

In a more inconvenient way, it can be written as:

Compared to the carbon steel model, this model uses a non-linear branch for the first part and the second part remains unchanged.

Using values of the parameters for various stainless steel grades in the following sections, a very good estimation can be made of the stress- strain relationships of stainless steel at elevated temperatures.

For simplified methods, i t is sufficient to use the strength reduction factors presented in the tables below, while for advanced non-linear analysis, the strength reduction factors may be used together with the stainless steel model to generate temperature dependant stress-strain curves.

3.8 Stainless steel grades 3.8.1 Grades 1.4301 (304) stainless

Determination of the elastic modulus at elevated temperature is extremely difficult, since even the smallest inaccuracy in the measured stress- strain curves has a very significant influence on the modulus.

steel

Data from BS EN 10088, Avesta Sheffield, Ugine, Thyssen and Inco are a~ailable‘~’. In addition to these data, recent work has been performed by Nordberg‘” for Avesta Sheffield Research Foundation. Data from various sources have been analysed and the variation in elastic modulus with temperature has been represented by the relationship:

E,e = 200.0 - 0,0838

where Ea,e is the elastic modulus at 0, and 8 is the temperature in degrees centigrade

This relationship is valid up to 800°C.

The data from referen~e‘~’ has been processed to provide strength factors at elevated temperatures. These are shown in Table 3.10.



Table 3.10 Parameters for stress-strain relationships of grade EN I .4301 stainless steel at elevated temperatures.

20 100 200 300 400 500 600 700 800 900 lo00

1 .00 0.96 0.92 0.88 0.84 0.80 0.76 0.71 0.63 0.45 0.20

1 .oo 0.82 0.68 0.64 0.60 0.54 0.49 0.40 0.27 0.14 0.06

0.11 0.05 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02

1 .oo 0.87 0.77 0.73 0.72 0.67 0.58 0.43 0.27 0.15 0.07

0.40 0.40 0.40 0.40 0.40 0.40 0.35 0.30 0.20 0.20 0.20

0.26 0.24 0.19 0.19 0.19 0.19 0.22 0.26 0.35 0.38 0.40

Table 3.11 Parameters for stress-strain relationships of grade EN I .4401 /EN 14404 stainless steel at elevated temperatures

20 100 200 300 400 500 600 700 800 900 lo00

1.00 0.96 0.92 0.88 0.84 0.80 0.76 0.71 0.63 0.45 0.20

1 .OO 0.88 0.76 0.71 0.66 0.63 0.61 0.51 0.40 0.19 0.10

0.05 0.049 0.047 0.045 0.03

0.025 0.02 0.02 0.02 0.02 0.02

1.00 0.93 0.87 0.84 0.83 0.79 0.72 0.55 0.34 0.18 0.09

0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.3 0.2 0.2 0.2

0.24 0.24 0.24 0.24 0.21 0.20 0.19 0.24 0.35 0.38 0.40

3.8.2 Grade 1.4404 (316L) stainless

Data on the elastic modulus is available from BS EN 10088, Avesta, Ugine, Thyssen and Inco'" In addition to these data, recent work has been performed by N~rdbe rg '~ ,~ ' for Avesta Sheffield Research Foundation. The relationship proposed by Nordberg is the same as for grade 304 steel 1.e.:

steel

E,,e = 200.9 - 0.0838

where

Ea,e

8

is the elastic modulus at temperature 6 is the temperature in degrees centigrade

This relationship is valid up to 800 "C.

Data is taken from recent transient state tests performed by Corus Swinden Technology Centre for the Steel Construction Institute, as part of an ECCS project(6). The reduction factors are presented in Table 3.1 1.



3.8.3 Gradel.4462 (2205) Duplex

Elevated temperature material properties data for grade 1.4462 (2205) duplex steel are available from a number of sources.

Stainless Steel

Transient state tests have recently been performed by RWTH for the SCI ECCS(6) project for Grade 1.4462 (2205) duplex steel. A summary of the data consisting of strength factors at various strains for temperatures up to 10oO"C are presented in Table 3.12, where it can be seen that this grade of duplex steel does not retain its elastic modulus as well as austenitic stainless steels at temperatures above 500°C.

3.8.4 Grade 1.4362 (SAF 2304)

No elevated temperature material properties data is available in the Standards. Limited data is available from stainless steel manufacturer Avesta SheffieIdO).

Duplex Stainless Steel

The data was used to generate strength reduction factors to be used with the stainless steel model. The strength reduction factors are given in Table 3.13.

Elastic modulus Elastic modulus elevated temperature data for Grade 1.4362 (SAF 2304) stainless steel is given in BS EN 10088 -1 up to 300°C. Table 3.13 shows the reduction in elastic modulus with temperature.

Table 3.12 elevated temperatures.

Parameters for stress-strain relationships of grade EN I .&62 stainless steel at

Temperature "C) kE.0

, I

20 100 200 300 400 500 600 700 800 900 loo0

1 .OO 0.96 0.92 0.88 0.84 0.80 0.76 0.71 0.63 0.45 0.20

ko.2p.e

1 .00 0.91 0.80 0.75 0.72 0.65 0.56 0.37 0.26 0.10 0.03

kEct,B

0.100 0.070 0.037 0.035 0.033 0.030 0.030 0.025 0.025 0.025 0.025

ke 1 .oo 0.93 0.85 0.83 0.82 0.71 0.57 0.38 0.29 0.12 0.04

Eu.8

0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15

k2./4e

0.35 0.35 0.32 0.30 0.28 0.30 0.33 0.40 0.41 0.45 0.47



Table 3.13 stainless steel.

Parameters for stress-strain relationships of grade EN I .4362 (SAF 2304) duplex

~

Temperature ( "C) kE.0 ko 2p.e k w e ke &U,O kzo/,,e

20 1 .Ooo 1.000000 0.100 1.000000 0.200 0.350 50 0.902893 0.948980 0.330 100 0.960 0.820248 0.070 0.865889 0.330 0.350 150 0.76033 1 0.8 19242 0.340 200 0.920 0.681818 0.037 0.78 134 1 0.300 0.320 250 - 0.665289 0.774052 0.330 300 0.880 0.632231 0.035 0.776968 0.290 0.300 400 0.840 0.605372 0.033 0.744898 0.260 0.280 450 - 0.683884 0.760933 0.330 500 0.800 0.609504 0.030 0.68226 1 0.330 0.300 550 0.4566 12 0.52478 1 0.330 600 0.760 0.36 1570 0.030 0.440233 0.430 0.330 650 - 0.316116 0.403790 0.330 - 700 0.710 0.25oooO 0.025 0.327988 0.500 0.400 750 - 0.183884 0.196793 800 0.630 0.148760 0.025 0.163265 0.410 900 0.450 0.065083 0.025 0.0962 10 - 0.450 lo00 0.200 0.024587 0.025 0.051020 0.470 1100 0.008884 0.027697

3.9 Pressure Vessel steels (BS EN 10028)

In all cases the elevated temperature material property data presented in the Standards are based on isothermal tests only and are minimum guaranteed values. Data is restricted to 0.2% proof strength values. In the following sub-sections, tables are given that list a selection of the most appropriate steels specified in BS EN 10028, and where applicable, the equivalent BS 1501 steels.

There are no models for the behaviour of pressure vessel steels comparable to that of the carbon steel model in ENV 1993-1-2.

3.9.1 BS EN 10 028-2 steels BS EN 10 028-2 : Non-alloy and alloy steels with specified elevated temperature properties covers the steels listed below in Table 3.14. Two types of steels are covered; non-alloy

steels and alloy special steels. As the high strength steels fall into the alloy special steel class, only data on these steels are presented here.

Elevated temperature material properties are given in Tables 3.15 and 3.16.

3.9.2 BS EN 10 028-3 steels BS EN 10 028-3: Weldable fine grain steels, normalized covers the steels given in Table 3.17 Grades P355N,

P355NH and P355NL1 are non-alloy quality steels, P355NL2 are non-alloy special steels, whilst the P460 ... steels are alloy special steels. The P355 No. series steels are the carbon steels that are commonly used for process equipment on offshore facilities.

Elevated temperature material properties are presented in Table 3.18.



Table 3.14 BS EN 10 028-2 alloy steels and equivalent BS 1501 steels

BS EN 10 028-2 Equivalent grade in BS 1501 (withdrawn) PART 1 PART 2

P355GH - 11 Cr Mo 9-10 - 622 - 515 B

Table 3.15 Elevated temperature material properties for BS EN 10 028-2 alloy steels

Thickness Minimum 0.2% Proof strength (N/mm2) at temperature ("C) 50 100 150 200 250 300 350 400

N/lIlm2 P355GH 160 318 290 270 255 235 215 200 180

> 6 0 I 1 0 0 298 270 255 240 220 200 190 165 > 100 5 150 278 250 240 230 210 195 175 155

Table 3.16 Elevated temperature material properties for BS EN I0 028-2 steels

Steel Thickness Minimum 0.2% Proof Strength (N/mm2) at temperature

Type (-1 100 150 200 250 300 350 400 450 500 550 ( "C)

N/IlUl12 27 1 I 25 420 406 398 389 374 363 351 347 314 -

> 25 S 75 402 389 380 372 354 343 332 329 301 - > 75 I 150 363 349 341 332 310 301 292 289 266 -

28 1 1 25 420 406 398 389 374 363 351 347 314 - > 25 I 7 5 402 389 380 372 354 343 332 329 301 - > 75 I 150 363 349 341 332 310 301 292 289 266 -

62 1 5 25 315 305 291 280 266 255 251 245 238 227 > 25 I 75 300 290 277 265 250 238 234 228 221 211 > 75 I 150 290 280 268 256 239 227 222 217 211 201

Table 3.17 BS EN 10 028-3 weldablefine grain normalized steels and equivalent BS 1501 steels _ _ _ _ _ _ _ _ ~ ~

BS EN 10 028 - 3 B S 1501 rl P 355 N P 355 NH P 355 NL1 P 355 NL2

225 - 490 A LT 20 225 - 490 B LT 20 225 - 490 A LT 50 225 - 490 A LT 50

P 4 6 0 N P460NH - P 460 NLl P 460 NL2



Table 3.18 Elevated temperature material properties for BS EN I0 028-3 weldable fine grain normalized steels and equivalent BS 1501 steels, as given in Table 3.1 7

Thickness Minimum 0.2% Proof Strength (N/mm2)

50 100 150 200 250 300 350 400 N/IIUn*

(mm) At Temperature (“C)

BS EN 10 028-3 P355 I 3 5 336 304 284 245 226 216 196 167 > 35 I 7 0 313 294 275 245 226 216 196 167 > 701 100 300 275 255 235 216 196 177 147 > 100 I 150 280 255 235 216 196 177 157 127

BS 1501-1 225-490 I 1 6 - 284 258 240 220 206 195 > 1 6 I 4 0 - 284 258 240 220 206 195 > 40 I 6 3 - 284 258 240 220 206 195

100 - 261 237 221 202 190 179 150 - 233 212 197 180 169 160

BS EN 10 028 P460 I 3 5 - 402 373 333 314 294 265 235 > 35 I 70 - 392 363 333 314 294 265 235 > 70 I 1 0 0 - 373 343 324 294 275 245 216 > 100 5 150 - 353 324 304 275 255 226 196

BS 1501-1 No grade corresponding to P460

3.9.3 BS EN 10 028-4 steels BS EN 10 028-4: Nickel-alloy steels with spec@ed low temperature properties are for low temperature use and as such no elevated temperature material properties are given.

The equivalent international standard to BS 10028-4 is IS0 9328-4. Limited elevated temperature material properties data is given in this IS0 standard. Table 3.19 presents a selection of the higher strength steels. Data consists of minimum guaranteed 0.2% proof strength based on steady state isothermal tensile tests up to a temperature of only 400°C.

3.9.4 BS EN 10 028-5 steels BS EN 10 028-5: Weldable fine grain steels, thermo-mechanically rolled does not contain elevated temperature material properties.

3.9.5 BS EN 10 028-6 steels BS EN 10 028-6: Weldable fine grain steels, quenched and tempered gives elevated

temperature material properties. The elevated temperature material properties are presented in Table 3.20.

Data consists of minimum guaranteed 0.2% proof strengths based on steady state isothermal tensile tests up to a temperature of only 300°C. The equivalent international standard to BS EN 10028-6 is IS0 9328-4. Limited elevated temperature material properties data is given in this IS0 standard. Table 3.21 presents proof strengths for a selection of the higher strength steels. The strengths are minimum guaranteed 0.2% proof strengths based on steady state isothermal tensile tests up to a temperature of only 400°C.

3.9.6 BS EN 10 028-7 steels BS EN 10 028-7: Stainless steels has recently been published. Table 3.22 presents elevated temperature material properties.



Table 3.19 Elevated temperature material properties for I S 0 9328-4 weldable fine grain steels with high proof stress supplied in the nonnalised or quenched and tempered condition

Minimum 0.2% Proof Strength (N/mm2) At Temperature ("C) 150 200 250 300 350 400

PH/PLH 355 TN 284 245 226 216 196 167 PH/PLH 390 TN 314 275 255 245 216 186 PH/PLH 420 TN 340 304 275 265 235 206 PH/PLH 460 TN 373 333 3 14 294 265 235

Table 3.20 quenched and tempered steels

Elevated temperature material properties for BS EN 10 028-6 weldable Pne grain

Minimum 0.2% Proof Strength (N/mmz) At Temperature ("C)

50 100 150 200 250 300 N/DUXlZ

BS EN 10 028 P 355 QH 340 310 285 260 235 215 BS EN 10 028 P 460 QH 445 425 405 380 360 340 BS EN 10 028 P 500 QH 490 470 450 420 400 380 BS EN 10 028 P 690 QH 670 645 615 595 575 570

Table 3.21 Elevated temperature material properties for I S 0 9328-4 weldable fine grain steels with high proof stress supplied in the nonnalised or quenched and tempered condition

Minimum 0.2% Proof Strength (N/mmz) At Temperature ("C)

150 200 250 300 350 400 N/mm2

PH/PLH 460 TQ 364 347 338 328 315 29 1 PH/PLH 500 TQ 415 398 388 379 354 339 PHIPLH 550 TQ 466 449 439 429 413 387 PH/PLH 620 TQ 537 520 5 10 500 48 1 453 PH/PLH 690 TQ 587 570 560 550 530 500

FABIG Technical Note - August 2001 25


Table 3.22 Elevated temperature material properties for BS EN 10 028-7: Stainless Steels

Minimum 0.2% Proof Strength (N/mm2) at temperature ("C) Grade

20 100 150 200 250 300 350 400 450 500 550 600 1.4318 330 265 200 185 180 170 165 - 1.4307 1.4306 1.4311 1.4301 1.4315 1.4948 1 ,4950 1.495 1 1.4541 1.4941 1.4404 1.4406 1.4401 1.4571 1.4432 1.4435 1.4439 1.4539 1.4958 1.4959 1.4910 1.4335 1.4550 1.4961 1.4466 1.4580 1 A429 1.4436 1.4434 1.4563 1.4537 1.4547 1.4529 1 A 3 8

200 200 270 210 270 190 200 200 200 200 220 280 220 220 220 220 270 220 170 170 260 200 200 200 250 220 280 220 270 220 290 300 300 220

147 147 205 157 205 157 140 140 176 162 166 21 1 177 185 166 165 225 205 140 140 205 150 177 175 195 185 21 1 177 21 1 190 240 230 230 172

132 118 108 100 94 132 118 108 100 94 175 157 145 136 130 142 127 118 110 104 175 157 145 136 130 142 127 117 108 103 128 116 108 100 94 128 116 108 100 94 167 157 147 136 130 152 142 137 132 127 152 137 127 118 113 185 167 155 145 140 162 147 137 127 120 177 167 157 145 140 152 137 127 118 113 150 137 127 119 113 200 185 175 165 155 190 175 160 145 135 127 115 105 95 90 127 115 105 95 90 187 170 159 148 141 140 130 120 115 110 167 157 147 136 130 166 157 147 137 132 170 160 150 140 135 177 167 157 145 140 185 167 155 145 140 162 147 137 127 120 185 167 155 145 140 175 160 155 150 145 220 200 190 180 175 205 190 180 170 165 210 190 180 170 165 157 147 137 127 120

89 89 125 98 125 98 91 91 125 123 108 135 115 135 108 108 150 125 85 85 134 105 125 128

135 135 115 135 135 170 160 160 115

85 85 121 95 121 93 86 86 121 118 103 131 112 131 103 103

115 82 82 130

121 123

131 131 112 131 125

153 130 112

81 81 119 92 119 88 85 85 119 113 100 128 I10 129 100 100

110 80 80 127

119 118

129 129 110 129 120

148 120 110

-

80 - 80 - 118 - 90 - 118 - 83 78 84 82 84 82

108 103 118 -

98 - 127 - 108 - 127 - 98 - 98 - 105 - 75 75 75 -75 124 121

118 - 118 113

127 - 127 - 108 - 127 - 115 -

105 - 108 -

1.4958+R4 210 180 170 160 152 145 137 130 125 120 115 110

3.9.7 Commentarv on vessel steels structural steels, but the high temperature properties quoted in the standards for in-service design are appreciably more conservative than the properties of the common structural steels used for fire engineering. The available data is in the form of 0.2% proof stress minimum guaranteed values.

Elevated temperature material properties for vessel steels are required for in-service design. Hence only temperatures up to 550°C are quoted. For certain steels, data is only available for temperatures up to 300°C.

The carbodmanganese pressure vessel steels (P355GH) are broadly similar to the common The alloy steels (P-oNH series) have much

better performance at high temperature, but



appear to have poorer performance below about 200°C. This is because the data is 0.2% proof data and the values are minimum guaranteed values. At high temperatures the alloy steels have very good performance and in particular, Grade 271 "Ducol", can be classified as fire-resistant steel. Although alloy steels perform well, the properties at high temperature are product-specific and data used must relate to the specific steel being used.

With the introduction of quenched and tempered steels (P-oQH series), yield strengths of up to 690 N/mm2 can be specified. Elevated temperature material properties for these steels, however, are only given up to 300°C in the European standards and up to 400°C in international standards.

3.10 Piping steels There are no elevated temperature material properties data for the steels specified in API Specification 5L Specifcation for Line Pipe and BS EN 10208 Steel pipes for pipelines for combustible fluids.

An on-going project financed by HSE and FABIG is looking at structural integrity of piping and will address elevated temperature material property data of piping steels used offshore. It is expected that the results will be published by February 2002 and disseminated as FABIG Technical Note 8.


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