DIWA 353 Alloyed steel plates for economic constructions of shell boilers

Transcription

1 DIWA 353 Alloyed steel plates for economic constructions of shell boilers 1

2 1. Introduction Due to the huge development of the Chinese economy the power demand is rising tremendously As many power plants have recently been installed and also a large number of projects is in preparation the demand for shell boilers has increased sharply. DILLINGER HÜTTE is the specialist in boiler plates e.g. for - unalloyed steel plates up to more than 200 mm like SA alloyed steel plates like DIWA 353 A large quantity of the shell boilers in China is constructed in DIWA 353 DILLINGER HÜTTE has a sales record of more than 20 years to supply such boiler plates to China In total more than tons of only boiler plates were delivered to the well recognised Chinese boiler manufacturers. 2

3 2. Design and material selection for boilers Following the design codes and the customer requirements different steel standards are normally used. Often steels according to ASTM/ASME, EN part2 or the VdTÜV-Data sheets are selected by the clients. DILLINGER HÜTTE supplies world-wide boiler steel plates mainly as: P355GH DIWA 353 (13MnNiMo5-4) DIWA373 (15NiCuMoNb5) A/SA 299 A/SA 302 B A/SA 516 Gr. 70 3

4 Currently required boiler grades and their tensile properties Y.S. / T.S. [MPa] ( ) R m R p0,2 R p0,2/350 C Specified values for thickness of 60 to 100mm ( ) For information only, not specified in the standard ( ) ( ) DIWA373 DIWA353 SA302 B SA299 P355GH SA

5 450 Hot tensile properties for current steel grade acc. to EN10028 and VdTÜV- data sheets 377 and 384) (plate thickness mm) 400 DIWA 373 Yield strength [MPa] Mo3 P235GH P355GH DIWA 353 P460NH SA 302-B SA SA Temperature [ C] 5

6 Cost- and thickness advantage Economic value compared using to DIWA353 DIWA353 at 350 C 120% 100% 16Mo3 P235GH Cost-Increase* 80% 60% 40% DIWA373 20% 0% DIWA353 P460NH P355GH -25% 0% 25% 50% 75% 100% 125% 150% 175% 200% * cost defined as material cost + welding cost thickness Based upon DIWA353 plate thickness of 100 to 150mm 6

7 3. DIWA353 base material properties DIWA 353 (13MnNiMo5-4) is defined by the VdTÜV data sheet 384. The plates are produced by the basic oxygen steel making process. The treatment leads to high cleanliness, low sulphur steel plates. Chemical frame analysis : C Si Mn P S Altot Mo Ni Cr Nb heat < < < > < product < < < > < Additions of Mo, Ni, Cr and Nb cause a steel with excellent elevated temperature properties. 7

8 Specified properties at room temperature: Plate thickness Yield strength Tensile strength Elongation ReH Rm A5 mm MPa, minimum MPa %, minimum < > 50 < > 100 < > 125 < Specified properties at elevated temperatures: Plate thickness Minimum yield strength Rp0,2 in MPa at test temperature mm 100 C 200 C 250 C 300 C 350 C 400 C < > 50 < > 100 < > 125 <

9 Actual tensile properties of DIWA yield strength [MPa] specified value at room temperature specified value at 350 C specified value at 400 C elongation [%] plate thickness [mm] Ref-No

10 Actual toughness properties of DIWA 353 Specified values: Impact test with ISO-V/Charpy-V transverse specimens test temperature in C 0 20 minimum impact value in J toughness values at 0 C Av [J] specified value at 0 C plate thickness [mm] Ref-No

11 4. DIWA 353 -Properties after cold forming Forming at maximum 580 C If no different rules are established by the design code following recommendations based upon AD-Merkblätter are given: strain in % heat treatment not exceeding 2 over 2 up to 5 exceeding 5 not required heat treatment adequate to PWHT (may be covered by the final PWHT after welding) Can possibly be avoided if impact tests carried out on strained and aged (0,5h at 250 C/480 F) specimens reveal sufficient toughness. Such tests have to be part of the order. normalizing + tempering 11

12 5. Welding of DIWA 353 Weld preparation By machining or flame cutting Minimum preheating before flame cutting: t < 30mm 10 C 30-50mm 70 C t > 50mm 120 C To avoid hardness cracks an area of 100mm parallel to the thermal cut has to be kept at the minimum preheating temperature Appropriate cutting parameters in respect to the plate thickness have to be applied to avoid flame cutting defects 12

13 Welding process Weld seam has to be free of rust, moisture, grease, paint or other impurities impairing the weld process or leading to elevated hydrogen level in the weld metal. Welding techniques: In case of ESW welding the normalisation of the welded shell is normally requested in order to achieve the mechanical properties in the HAZ. Ohterwise SMAW, GMAW, FCAW and SAW can also be applied. If ESW is not used, heat input should be chosen to achieve a cooling time t 8/5 between 10 and 30 seconds. If ESW is not used, preheating of the material for welding. thickness (mm) minimum temperature *) ( C) < > *) For low constraint, very low hydrogen (HDM < 5ml/100g) and higher heat input, lower limit shall be applied; for elevated constraint, low hydrogen, and lower heat input, upper limit shall be applied. 13

14 Welding process (continued) only low hydrogen consumables shall be used to avoid cold cracking high heat input may lead to reduced tensile properties and weld metal toughness if no new heat treatment is applied to reduce hydrogen content a effusion treatment at C should be done after welding. Holding time 1 hr (t<30mm) up to 6 hrs for high thickness. Hydrogen effusion treatment is also recommended if incomplete weld cooled down below minimum interpass temperature 14

15 Electroslag welding of DIWA353 test weld with a 95mm plate was carried out after welding N+A treatment is required different heat treatments were applied to the weld tensile properties at room temperature and elevated temperatures are generally good with the chemical analysis of actual production single values of toughness might be slightly reduced due to higher carbon content in the base metal best results were obtained with annealing temperature of 640 C after normalising filler material used in the test weld was Oerlikon s Fluxocord 43.1 Chemical analysis: C Mn Si Ni Mo V 0,05 1,40 0,10 1,80 0,35 0,12 Chemical analysis of base metal: C Si Mn P S Altot Mo Ni Cr Nb 0,12 0,39 1,45 0,016 0,001 0,049 0,32 0,83 0,33 0,01 15

16 Tensile properties of DIWA 353 at room temperature - ESW plus N+A Maximum specified tensile strength 700 YS,TS [MPa] Minimum specified tensile strength 450 Rp0,2 weld metal Rm weld metal Minimum specified yield strength 400 Rp0,2 base metal Rm base metal annealing temperature [ C] 16

17 Tensile properties of DIWA 353 at 350 C - Electro slag weld, condition N+A YS,TS [MPa] Minimum specified yield strength at 350 C annealing temperature [ C] Rp0,2 weld metal Rm weld metal Rp0,2 base metal Rm base metal 17

18 Weld metal - Impact test at 0 C - Electro slag weld, condition N+A DIWA 353 3mm subsurface mid thickness Charpy-V values [J] Minimum specified value acc. TRD annealing temperature [ C] 18

19 Base Metal & HAZ - Impact test at 0 C - Electro slag weld, condition N+A DIWA 353 Charpy-V values [J] quarter thickness, base metal 3mm subsurface, fusion line Minimum specified value acc. TRD annealing temperature 19

20 Consumables for SMAW, SAW and FCAW Welding process SMAW SAW FCAW condition Esab Oerlikon Böhler as welded OK Tenacito 65R stress relieved normalized+ tempered as welded stress relieved normalized+ tempered as welded stress relieved normalized+ tempered OK OK Autrod OK Flux OK Autrod OK Flux manufacturer Tenacito 65R tenacito 75M Fluxocord 41 OP121TT Fluxocord 41 OP121TT Fluxocord 43.1 OP121TT Fluxofil 41 CO2 Fluxofil 41 CO2 Fox EV 65 Fox DMOKb Fox EV 65 Fox DMOKb 3NiMo1-UP OP41TT"LH" 3NiMo1-UP OP41TT"LH" 20

21 6. Non Destructive Testing, Post Weld Heat Treatment Final NDT shall be carried out at least 48hrs after welding if hydrogen effusion or stress relieving treatment is not performed directly after welding. PWHT shall be performed at C at a max. holding time of 2,5hrs. If holding time exceed 1,5 hrs or several cycles are required the lower range of recommended temperatures shall be applied. Longer holding times or higher stress relief temperatures have to be agreed upon at the state of inquiry. 21

22 7. Conclusion DIWA 353 is an optimal choice for boiler drums: big wall thickness reduction (compared to the other grades) reasonable material cost (also compared to DIWA 373) uncritical fabrication properties well accepted by the Chinese fabricators and end-users 22