PREDICATION OF RESIDUAL LIFE TIME OF STEAM REFORMER TUBES

Transcription

1 PREDICATION OF RESIDUAL LIFE TIME OF STEAM REFORMER TUBES Prof. Bahaa Zaghloul Ex President of Central Metallurgical Research and Development Institute CAIRO, EGYPT

2 DIFFERENT APPLICATIONS OF REFORMER TUBES 40 Limit of tube Metal Applications Pre essure (Kg g/cm 2 G) H 2 NH 3 CH 3 OH 10 Town Gas D. R Gas Temperature ( O C)

3 LIMITATION OF OPERATION TEMPERATURE Inlet Cata alyst Tube Control to Prevent Carbon Formation Control the Max. Tube Skin Temperature Outlet Critical Portion

4 DIFFERENT DESIGNS FOR REFORMER FURNACE 1 3 Radiant Wall Type UP Firing Type Terrace Wall Type Down Firing Type 2 4

5 EFFECT OF FIRING SYSTEM ON TEMP. PROFILE I. UP II. Down III. DOWN & UP Preferable Profile IV. TERRACE WALL V. RADIANT WALL

6 IDEAL TEMPERATURE PROFILE Inlet Outlet Gas Temperature Heat Flux Tube Skin Temperature Solid Line : Ideal Profile Dotted line : Preferable Profile

7 REFORMER TUBES MATERIALS EVALUTION CHARTS Si HK40 high Si 25Cr 20Ni-high Si HK40 25Cr 20Ni Nb IN519 24Cr 24Ni Nb Ti IN519 mod. 24Cr 25Ni-Nb Ti HT 15Cr 35Ni HU 19Cr 39Ni Ti HI Ka1a 25Cr 20Ni-Ti MS HT mod. 20Cr 32Ni C Nb Nb BST Alloy 25Cr 20Ni Ti Nb Nb Manaurite 900 T52,PG20 32 CR32W,KHR32C 20Cr 32Ni Nb Low C Alloy Cr 32Ni HI Ka1b 25Cr 20Ni-Nb Ti MS MS: Mishmetal Manaurite 36X Su Paralloy H39W 25Cr 35Ni Nb Low C Manaurite 900B Paralloy CW39W 25Cr 35Ni Nb Low C HP 26Cr 35Ni Nb W Mo Re 1 25Cr 35Ni-W Ti W Nb Manaurite 36XM HP BST 25Cr 35Ni Nb Ti Manaurite 36XS 25Cr 35Ni-Nb W Mo Manaurite 900 T52,PG Cr 32Ni Nb Low C Co Su Paralloy H34CT 25Cr 35Ni-5W 2Co Co Supertherm 28Cr 35Ni-5W 15Co

8 REFORMER TUBES MATERIALS EVALUTION TABLES METALLURGY DEVELOPMENT DATE COMMON NAME Cr % Ni % Nb % OTHERS RELATIVE STRENGTH 1960s HK s IN Early 80s BST Ti 1.7 Mid 80s HP BST Ti 1.9 Late 80s HP Micro alloy Ti, Zr, W, Cs 2.2

9 CREEP RAPTURE STRENGTH OF COMMERCIAL MATERIALS 20 Str ress (Kg f /mm 2 ) BST - M 25 35Ni - Nb IN 519 HP HK Time to Rupture (h)

10 CREEP RAPTURE STRENGTH OF COMMERCIAL MATERIALS

11 CREEP RAPTURE STRENGTH OF COMMERCIAL MATERIALS Rapture Stress for Generic Tube Materials 35 Rapture St tress (N/ /mm 2 ) R HK40 IN519 BST HP BST HP Microalloy

12 FAILURE MODE OF REFORMER TUBE

13 CROSS SECTION OF FAILED REFORMER TUBE

14 PROGRESS OF CREEP FAILURE START GROWTH FAILURE Cracks 30% from inner wall Cracks grow to break inner wall Cracks progress to outer wall

15 EFFECT OF MACROSTRUCTURE ON CRACK PROPAGATION

16 TYPICAL CREEP DAMAGE MECHANISM IN REFORMER TUBES FRACTURE D reep Str rain C A B C I, II, III : Creep Ranges Exposure Time

17 Microstructure Evaluation of Cast Steel Tubes During Operation Time in Reformer Furnace Change In Tube Microstructure During Operation in Reformer Furnace MATRIX PRIMARY AND SECONDARY PHASES Chemical composition modifications & accompanied heterogenty in solid solution Change in primary inner dendritic austenite carbides eutectic Secondary carbides precipitationandand interactions with primary carbides Changes in dislocation structure and dislocation density growth Continuous carbides network Changes in austenite grain formationaround around austenitegrains boundary microstructure due to the carbides coalescence and voids formation Coalescence of sigma phase inside and around austenite grains

18 Effects Of Microstructural t Changes In Reformer Tube Decrees In Creep Resistance Deterioration On Mechanical Properties Microvoids Initiation On Interphase Boundaries Voids Propagation Voids Coalescence Into Fissures

19 COMMON DAMAGE MECHANISM IN REFORMER TUBES 1. Overheating (Cumulative) 2. Thermal Cycling ( cyclic operation ) 3. Tb Tube Bending ( improper counter weight balance bl for tube linear will increase stress on tube) 4. Thermal shock 5. Stress Corrosion Cracking

20 OVERHEATING Temperature Increase To Maintain Yield When Catalyst Becomes Less Active. Feedstock Or Steam Supply Failure The Absence Of Cooling Effect Of The Endothermic Reaction 4 Burner Misalignment Can Result In Over Temperature 5 Restricted Flow Of Process Due Catalyst Choking

21 EFFECT OF OPERATION TEMPERATURE AND PRESSURE ON TUBE LIFE

22 COMMON DAMAGE MECHANISM IN REFORMER TUBES 1. Overheating (Cumulative) 2. Thermal Cycling ( cyclic operation ) 3. Tb Tube Bending ( improper counter weight balance bl for tube linear will increase stress on tube) 4. Thermal shock 5. Stress Corrosion Cracking

23 THERMAL CYCLES 1 Through Wall Stresses are Temporarily Increased 2 TubeWall Temperature GradientsCan Be Significant 3 During Operation, The Stress Produced By Different Expansion Relaxes Through Creep Temperature Changes Up Or Down Will Reintroduce Some 4 Stress.

24 COMPARISON OF STRESS DISTRIBUTION IN CYCLIC OPERATION HK40 IN519

25 COMMON DAMAGE MECHANISM IN REFORMER TUBES 1. Overheating (Cumulative) 2. Thermal Cycling ( cyclic operation ) 3. Tb Tube Bending ( improper counter weight balance bl for tube linear will increase stress on tube) 4. Thermal shock 5. Stress Corrosion Cracking

26 THERMAL SHOCK Creates Extremely High Stresses As The Tube Attempts To 1 Contract tu Under Restraint t. 2 It Results In Circumferential Tearing Or Shattering Of The Tube. 3 Can Occur Through Boiler Water Carry Over On Inside The Tubes

27 EFFECT OF OPERATION TEMPERATURE ON MICROSTRUCTURE OF IN519 MATERIAL MICROSTRUCTURE OF IN519 CAST STEEL TUBE Non degraded d dsample after h after h Operation in Reformer furnace h

28 FAILURE ANALYSIS OF PRIMARY REFORMER TUBE OPERATION PERIOD = 6 Years Top Flange Rapture Zone Rupture Zone Top Flange

29 GENERAL AND ENLARGED VIEWS OF OUTER AND INNER SURFACES OF RUPTURE ZONE OF REFORMER TUBE. NOTE: NON UNIFORM WIDTH OF BRANCHED CRACK.

30 SUMMARY OF MICROSTRUCTURE CHANGE THROUGH THICKNESS, ALONG REFORMER TUBE LENGTH S1: 30 cm from top flange S2: 114 cm from top flange 1000X 1000X S4: Rupture zone 320 cm from top flange S8: 1070 cm from top flange 200X 1000x S4: 1255 cm from top flange S12: 1330 cm from top flange 500X 1000x

31 FAILURE OF PRIMARY REFORMER TUBE OPERATION PERIOD S2 18 Years RUPTURE S1 S4 S3 RUPTURE A S5 S1 B C

32 X X 1000 X 1000 X 1000X 1000X Header 200 x 1000X Header 50x

33 PRIMARY REFORMER TUBE Tube: 135.6mm, 12.8mm Material: HP Nb 0.4C, 35Ni, 25Cr, 1.24Nb Pressure : 35.7 bar OPERATION PERIOD = 9 Years Skin Temp.: 917 o C Max 860 o C Min

34 Test Coupon 5 100X Inner Surface Outer Surface Test Coupon 3

35 TEST COUPON 5 100X TUBE WALL CENTER 400X TEST COUPON 3

36 RESULTS OF CREEP RUPTURE TEST OF USED PRIMARY REFORMER TUBE

37 Creep Rupture Strength Master Curve for Used & Unused Primary Reformer Tube Materials LMP = T ( C + t r ) 10 3 T: Test T ( O K), t r : Rup. time (hr) C: Constant This form of data plot is used to extrapolate short term test data to rupture stresses up to 100, hr

38 Working S is a function of mainly circum., long., and thermal S. The most critical one is the circum. S &itwasassumedtobe1.8kg/mm 2 based on the following equation. (ASME Section VIII Division 1) S = ( P R P t ) / E t S: Maximum allowable stress value. P: Internal ldesign P or max. allowable working P R: Inside radius E: Joint efficiency t: Min. thick Skin T was assumed to be 917 O C, Remaining life time is calculated from data of Larson Millar parameter of used reformer tube. The remaining life was estimated based on S & skin T. to be ~20,000 hr at 1.8 kg/mm2 working S. The life time will be increased at lower skin T

39 ESTIMATED RUPTURE TIME OF USED PRIMARY REFORMER TUBE UNDER DIFFERENT TEMPERATURES & STRESSES 1.8kg/mm 2 2.5kg/mm o C

40 NON DESTRUCTIVE TESTING METHODS FOR DAMAGE EVALUATION Dimensional changes; diameter and wall thickness due to creep Replica metalography; tl spot check for micro structural t changes due to overheating and some times creep damage Radiography; large voids and micro cracks Eddy current; chromium migration due overheating and conductivity changes Ultrasonic; attenuation and scattering New techniques such as LOTIS and IESCO H SCAN

41 CREEP DAMAGE EVALUATION METHOD

42 New Project for PREDICTION OF REMAINING LIFE OF REFORMER TUBES & Egypt PARTICIPATING COMPANIES Fraunhofer IWM Germany

43 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS Possible Industrial Partners: Egyptian Fertilizers Co., Ain El-Sukhna, EFC ALEXFERT Alexandria Fertilizers Co., Alexandria Delta Fertilizer Co.,Talkha Apu Quir Fertilizer Co.; Alex Schmidt + Clemens,Centrifugal Casting Div., Kaiserau UHDE Engineering Egypt, Cairo

44 LIFE ASSESSMENT REQUIREMENTS Requirements For Analysis To undertake a furnace life assessment the following input information is required Furnace design drawings / material records / Operation history (turn-around and process conditions) Process temperature and pressure records as available Tube samples for material specific assessment Appropriate NDT techniques data

45 Collection / Selection Of Tube Materials, Geometries, Plant, Connections And Process Conditions Development Of Test Set Up And Measurement Techniques For Specimens And Model Tubes. Continued Testing Of Specimens From Used Tubes And Failure Cases LIFE TIME PREDICTION OF REFORMER TUBES Testing Of Virgin Material Specimens In Tension, Creep And Thermal Fatigue Acc. To Service Repeated Examination Of Damage NDE E.G. Eddy Current, UT Hardness Metallography, Microstructure. Sem & Edx Material Description for deformation damage failure incl. overlapping effects Implementation In FE Code NDE Of Used Tubes Profilometry Visual UT, EC, X ray Evaluation Of Mechanisms And Degree Of Damage In Used Tubes Model Component Test And Simulation (Short Section Of Tube Exaggerated Loading, Shorter Times) Verification Comparison Of Calculation (Material Degradation Component Behavior) With Measurement Results Material / microstructure based life time prediction applied to a specific plant

46 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 1 : COLLECT & SELECT INPUT DATA - Tube material (properties, behaviour), -dimensions - Plant design: inlet/outlet pigtails,firing system, welds, - Operational conditions: feedstock rate pressure fluid temperature skin temperature through wall temperature start up/shut down cycles process upsets - service experience

47 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 2 : DEVELOP TEST SET UP AND MEASUREMENT TECHNIQUES FOR ROUND BAR SPECIMEN TESTS ON REFORMER TUBE MATERIALS Cyclic strain- and temperatures tests

48 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 3 : DEVELOP TEST SET UP AND MEASUREMENT TECHNIQUES FOR MODEL REFORMER TUBE TESTS Optical Strain Measurement HAZ T mm HAZ T mm NiCr20Nb Austenite 5 mm 10 mm

49 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS g in MPa Spannun STEP 4 : TESTING OF VIRGIN AND USED Grobkorn-WEZ 625 C REFORMER TUBE MATERIAL SPECIMENS Grobkorn-WEZ 550 C 300 LCF tests at RT up to service temp. (950 C) cyclic hardening/ softening Grobkorn-WEZ 650 C hystereses life time 100 interkritische WEZ 625 C interkritische WEZ 650 C 50 WEZ3 GK WEZ2 FK WEZ1 IK GW FZJ T in C GW MFI F Zeit in h TMF with realistic T e cycles Creep tests in/out of phase hold times heating and cooling times

50 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 5 : MEASUREMENT OF DEFORMATION, DAMAGE & FAILURE; EVALUATION OF MECHANISMS IN THE TUBE MATERIALS NDE: dimensional measurements, UT, EC, Hardness Metallography, microstructure, replica techniques Cyclic Plastic Deformation SEM & EDX Micro/Macro Cracking Creep Damage Corrosion

51 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 6 : MATERIAL DESCRIPTION FOR DEFORMATION, DAMAGE AND FAILURE INCL. OVERLAPPING EFFECTS Material models for cyclic plastic deformation (Chaboche, Jiang) - IWM Software FITIT 950 C Damage parameter D TMF 2 2 σ I, eff 2,4 σ I = 1,45 + ε e σ cye 1+ 3N σ cy σ e pl F ( T, t )

52 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 7 : IMPLEMENTATION OF NEW MATERIAL STRUCTURAL (FE) MODELS (EVALUATION OF SPECIMEN TEST RESULTS) Application Of Damage Parameter D TMF To LCF and Tmf tests

53 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 8 : VALIDATION BY Post evaluation of well documented failure cases from fertilizer plants (parameter studies!) Model component tests and FE simulation (short tube section, exaggerated loading, shorter times, ) Tube Tests FE - Simulation Of Stresses & Strains essure, pressure in bar, oad, load in kn kn Internal p axial Intern. Pre Axial lo Internal pressure: 480 bar Axial load 41.8 kn Temp peratur [ C] Temperatur re [ C] Cycles 0 Cycles

54 LIFE TIME PREDICATION FOR STEAM REFORMER TUEBS STEP 9 : APPLICATIONS Material tests/ microstructural analysis and FEM simulation based Validated d Procedure to assess component behavior under transient t severe service conditions Ready To Be Used For Life Time Management of catalyst steam reformer tubes Process Optimisation Inspection Strategy development Reconsidering plant Design and Operating Conditions

55 YOUR KIND PARTICIPATION IN THE PROJECT WILL BE HIGHLY APPRECIATED Many Thank For EFC Who Invited Me For This Presentation & THANKS FOR YOUR ATTENTION