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INDUSTRIAL TRAINING PHASE- 1 AT LARSEN & TOUBRO LTD., HAZIRA COMPLEX HEAVY ENGINEERING DIVISION

A MINOR REPORT ON WELDING AND FABRICATION TECHNOLOGY ROYAL COLLEGE OF TECHNOLOGYINDORE,

PREPARED BY:

RAJNIKUMAR KOLADIYA ENR. NO: - 0836ME091019CERTIFICATE

This is to certify that MR. RAJNIKUMAR KOLADIYA . Enrolment no. 0836ME091019 of Dept. of Fabrication Technology has successfully completed his Minor report on WELDING during his training period of first phase 05/07/2012 to 20/07/2012 in L&T Hazira, Surat.

APPROVED BY: GUIDED BY :

Dr.SUJIT MEMON Dr.JAIRAJ GOHIL

(INCHARGE OF HFS-3A) (CO-ORDINATOR OF

HFS 3A)

Sr.NO. TOPIC

PAGE NO.1. Job Detail

42. P no. 5 Low Alloy Steel

63. Characteristics

64. Chemical composition

65. Effect of Chromium

66. Effect of Vanadium

77. Cr-Mo-V steels

78. Comparison

79. Comparison of reactor steels

810. Enhanced Tensile Strength

811. Creep

812. Temper Embrittlement

913. Hydrogen Embrittlement

914. Hydrogen Induced Overlay Disbonding1015. Weldability of Cr-Mo Steel

1016. Preheating

1117. Inter-Pass Temperature

1218. DHT (De-Hydrogenation Treatment) 12 19. Intermediate Stress Relieving (ISR) 1220. Why ISR??

13 21. ISR Requirement 1322. Critical Weldability issues 13 Reheat, or stress-relief cracking

Solidification, or hot cracking

Hydrogen-induced, or cold cracking

23. Welding Training 21 AIM: To investigation the slag inclusion in PETROBRAS job

JOB DETAILS:-

NAME OF JOB:- DIESEL HYDROTREATING REACTOR

PROJECT NO.:- 45537/2 CUSTOMER:

PETROLEO BRASILEIRO (PETROBRAS)

JOB DIMENSION:

4916 mm I.D., 23346 mm LENGTH, (150 mm THK+8 mm OVERLAY)

JOB MATERIAL:

FOR HEADS: SA 542M TYPE .D CL. 4a (Quenched + Tempered) + (SS 309 L+ SS 347 overlay - 8 mm THK.)

FOR NOZZLE: SA 336M GR. F22 V.

Y-RING : SA 336 GR. F22 V (Q+T)+(SS 309L +SS 347O/L-8THK).

MANHOLE: SA 542M TYPE .D CL. 4a (Quenched + Tempered)+(SS 309 L+ SS 347 overlay) BOLTING:SA193M Gr. B16/ SA 194 M Gr.4 GASKATE: SA182M Gr. F347 DESIGN TEMPERATURE (INT/EXT.)430/30 0C

DESIGN PRESSURE (KG/CM2)- INTERNAL: 134

- EXTERNAL: 1.05

SHELL: 9 shells + 2 D end. FABRICATED WEIGHT: - 560000 kg.

HYDRO TEST PRESSURE : 16.26 M pa horizontal

: 5.988 M pa vertical

HYDRO TEST TEMP. : 27 to 50 0C CHEMICAL COMPOSITION : Carbon 0.05 to 0.15

Manganese 0.30 t0 0.60

Phosphorus 0.035 max.

Sulphur 0.035 max.

Silicon 0.50

Chromium 2.00 to 2.50

Molybdenum 0.90 to1.10

CODE REFERENCE: ASME SEC: VIII, DIV: - 2 ED.-2007.P no. 5 Low Alloy SteelCharacteristics Used up to 650oC Operating Temp.

Resistance to H2 attack

Better creep ruptures properties and high temp. strength than carbon steels

Resist oxidation and sulphidation

High hardenability

Chemical composition A: 2.25Cr 1Mo SA 508 Gr. 22, CL. 3 Forgings SA 541 Gr. 22 CL.3 Forgings SA 542 TYPE B CL.4 Forgings

B: 2.25Cr 1 Mo -2.25V (LAS) SA 336 Gr. F22V Forgings SA 182 Gr. F22V Forgings

SA 541 Gr. 22V Forgings

SA 542 TYPE D CL.4a plates SA 832 Gr.22V plates. C: 3Cr 1Mo V-Ti-B (LAS) SA 182 Gr. F3V Forgings

SA 542 TP C CL. 4A Plates

SA 832 Gr.21V Plates

SA 541 Gr.3V Forgings SA 508 Gr.3V Forgings SA 336 Gr.F3V Forgings CODE:- ASME SEC.8, DIV.-2, PART:3, Material requirements part content table-3.18.Chromium Increases resistance to corrosion and oxidation

Increases hardenability

Adds some strength at high temperatures

Resist abrasion and wear (with high carbon)

Molybdenum Molybdenum is a potent hardenability agent and is a constituent of many heat treatable alloy steels.

It raises grain coarsening temperature of austenite

It retards softening at elevated temperatures and is therefore used in boiler and pressure vessel steels, as well as several grades of high speed and other tool steels. Vanadium Enhance tensile strength at elevated temperatures (above 400oC)

Enhance creep rupture strength

Improve resistance to in-service degradation like temper embittlement, high temp. hydrogen attack, hydrogen embrittlement, hydrogen induced overlay disbonding

Lower unit weight of the reactors at a comparable cost by increase of steel strength.

Cr-Mo-V steels 2.25Cr - 1Mo - 0.25V

ElementCMnPSSiCrMoV

% Composition0.11 0.150.30 0.600.0150.0100.102.00 2.500.90 1.100.25 0.35

Tensile StrengthYield StrengthElongation in 2Brinell hardness no.

585 780 MPa415 MPa18.0%174-237

ComparisonMaterialTensile StrengthYield StrengthElongation in 2

C.S (SA 516 Gr. 70)485 620 MPa260 MPa21.0%

SA 387 Gr. 11415 585 MPa242 MPa22.0%

SA 182 Gr. F22V585 780 MPa415 MPa18.0%

Comparison of reactor steels

Steel Grade2.25Cr-1Mo2.25Cr-1Mo-0.25V

Max. allowed temp. ASME VIII 2482oC482oC

Min. Tensile Strength517586

Min. Yield Strength 310414

Design Stress Intensity Value, ASME VIII-2At 454oC 150 MPaAt 454oC 169 MPa

At 482oC 117 MPaAt 482oC 163 MPa

Wall ThicknessAt 454oC 338mmAt 454oC 298mm

At 482oC 442mmAt 482oC 310mm

454oC Design Reactor Weight; Typical Cost1038MT

Rs 45.2x107916MT

Rs 44.0x107

482oC Design Reactor Weight; Typical Cost1359MT

Rs 59.1x107953MT

Rs 45.7x107

Enhanced Tensile Strength In service behavior of steels strongly depend on the type and morphology of carbide phase

Vanadium modification provides fine, vanadium rich carbides, evenly distributed in the metal matrix

Four types of carbides formed: M7C3, M23C6, M6C and M2C

All contained vanadium with differentiated amounts of Cr, Fe and Mo

Thermodynamic stability of carbides is much greater than V free precipitates Creep Creep is defined as the process by which plastic flow occurs when constant stresses are applied to metal for prolonged period of time at high temp.

It occurs at all stress levels at higher temp.

Creep rate with stress at given temp.

Effect of Vanadium on creep resistance Heat application leads to carbide growth

Coarse carbides distort the grains and lead to smaller grains

More Sliding & Dislocations in smaller grains

Vanadium resist carbide growth at elevated temperature

Temper Embittlement Caused by:

Grain boundary segregation of impurities and tramp elements

Watanable No. (J Factor)

To limit the impurity /tramp elements content in reactor steels

J factor = 104(P+Sn)(Mn+Si)

Resistance of steel to temper embrittlement will be sufficient when J factor is limited to a value of less than 100

Carbide formation is accompanied by microstructural and microchemical change.

The addition of Cr in steels enhances the impurities, such as P, Sn, Sb, and As, segregating to grain boundaries and induces temper embrittlement.

A delay in carbide formation, precipitation or thickening usually leads to delay in embrittlement

Hydrogen Embrittlement At typical hydro processing temperatures and hydrogen partial pressures, hydrogen diffuses easily through reactor walls

When reactor is cooled down rapidly, delayed hydrogen cracking may occur

Fine, evenly distributed vanadium rich carbides trap the diffusible hydrogen in steel

So lesser hydrogen is available at the tips of the crack

High Temperature Hydrogen Attack Diffused hydrogen reacts with carbides to form methane

Leads to decarburization of the material with formation of cavities, fissures or cracks

Higher thermodynamic stability of carbides leads to reduced methane pressure

Precipitation of vanadium rich carbides in the modified steel enhances the resistance to hydrogen attack.

Hydrogen Induced Overlay Disbonding Hydrogen reactors must be protected from high temperature sulphide corrosion caused by hydrogen sulphide present in processed steam.

Hydrogen concentration increases at the interface of both the steels.

Hydrogen is trapped in the fine vanadium containing carbides

So, Hydrogen has low diffusivity in vanadium steels

Weldability The capacity of a metal to be welded under the fabrication conditions imposed into a specific, suitably designed structure, and to perform satisfactorily in the intended service

Depends on,

- Composition of weld metal

- Circumstances in which weld freezes

Weldability of Cr-Mo Steel Hardened when Quenched from Austenitizing temperature

Sensitive

-Hydrogen Induced Cracking

-Solidification Cracking

To avoid Cracking

-Preheat Maintenance

-Use of appropriate Welding Consumables

-Heat Treated to improve Toughness

-Carbon Content of weld Metal Ultra High Strength material

Air Hardenable

Form Hard Martensite when quenched from Hardening temperature of around 1000 C

Hard Martensite will form unless proper Preheat and PWHT procedure is followed

HAZ portion Highly susceptible Under bead Cracking

To avoid Cracking: Proper Preheat is required

Preheat Temperature: above Ms temperature

Preheating Preheating promotes slow cooling of weld and HAZ

Slow cooling softens or prevents hardening of weld and HAZ

Soft material not prone to crack even in restrained condition

Removes moisture, oil, etc. Temp = 35 X [CE(1 + 0.5t) 0.25]^0.5

Where t = thickness

CE = carbon equivalent

CE = C + Mn/6 + (Cr+Mo+V)/5+ (Ni+Cu)/15 Width of preheating material should be equal to plate thickness or 75mm whichever is less on each side (but not less than 25mm)P-NUMBERS

PREHEATING TABLEMaterial/ P.No.Groove & Fillet (Preheat)

Base Metal Thickness (mm)

=100

C-MnP1 Gr 1& 220100125150

C-1/2 MoP3 Gr1 & 2100125150175

P3 Gr 1100150175200

11/4Cr-1/2MoP4 Gr1 & 2150200

21/4Cr-1 MoP5A Gr 1150200

5Cr-1/2 MoP5B Gr 1200

21/4Cr- 1Mo -1/4VP5C Gr 1200

Q & T SteelP11 AS150

Inter-Pass Temperature Control on inter pass temperature avoids over heating, there by

Refines the weld metal with fine grains

Improves the notch toughness properties

Minimize the loss of alloying elements in welds

Reduces the distortion

Inter-Pass required for Cr-Mo-V is about 250OcDHT (De-Hydrogenation Treatment) SMAW introduces hydrogen in weld metal

Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature

Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld

Material/ P.No.Groove (DHT)Fillet (DHT)

Base Metal Thickness (mm)Fillet Size

=100

C-MnP1 Gr 1& 2----------

C-1/2 MoP3 Gr1 & 2------300-350oC /3 hrs(>=50 CFW)

300-350oC /3 hrs

P3 Gr 1----300-350oC /3 hrs(>=35 CFW)

300-350oC /3 hrs

11/4Cr-1/2MoP4 Gr1 & 2----300-350oC /3 hrs(>=35 CFW)

300-350oC /3 hrs

21/4Cr-1 MoP5A Gr 1--350-400oC /4 hrs(>=15 CFW)

350-400oC /4 hrs

5Cr-1/2 MoP5B Gr 1--350-400oC /4 hrs(>=10 CFW)

350-400oC /4 hrs

21/4Cr- 1Mo -1/4VP5C Gr 1350-400oC /4 hrsALL

350-400oC /4 hrs

Intermediate Stress Relieving (ISR) Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness Applicable to

-Highly restrained air hardenable materialWhy ISR?? Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.

Cracks due to entrapped hydrogen and built in stress

Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone

ISR Requirement For 2.25Cr-1Mo-0.25V material,

all L/S & C/S having thickness >100 mm,

all nozzle # Shell/head welds and support ring/nub attachment to shells, shall undergo an ISR at 690oC for minimum 1hr or 650-670oC for 2hrs.

Critical Weldability issues Hydrogen-induced, or cold cracking

Reheat, or stress-relief cracking

Solidification, or hot crackingHydrogen-Induced Cracking (HIC) Hydrogen dissolved in molten weld pool (e.g., wet coatings, poor gas shield, grease/rust on component surface) high solubility in liquid

During rapid solidification of weld deposit, some hydrogen is trapped supersaturated condition

In Cr-Mo/Cr-Mo-V steels, greater hardenability increases the risk of lower bainite/martensite formation in the weld and HAZ

Hydrogen diffuses preferentially to these highly stressed regions of the weldment structure e.g., the coarse-grained HAZ increasing the risk of crackingNecessary Components for HIC to Occur Sufficient quantity of trapped hydrogen in weldment

-Total vs diffusible hydrogen (residual hydrogen remains)

Susceptible microstructure

-Structures with high internal stress/lower transformation products

Stress-Residual stresses, influence of stress concentrators

Temperature of susceptibility

-Limited range of susceptibility reflecting the influence of hydrogen mobility (must be high enough to allow concentration, but not so high to allow escape)

Potential Sources of Hydrogen in Weld Metal Welding consumable

-Coatings and fluxes (cellulosic vs basic)

Atmosphere

-High humidity

-Ineffective gas shield

Base metal

-Trapped hydrogen in heavy sections

-Surface moisture, grease, oil, etc.

-Rust, other surface corrosion productsSolubility of Hydrogen in Weld Metal

Typical Features of Hydrogen-Induced Cracking Can occur in weld metal or HAZ

Can occur at weld root, weld toe, sub-surface (underbead)

Can show features of intergranular, transgranular, or ductile fracture

Can occur hours after welding is complete controlled by diffusion rates

Exacerbated by restraint

Can propagate in service and lead to failure

Hydrogen-Induced Cracking In HAZ

Hydrogen-Induced Cracking in Weld Deposit

Prevention of HIC Minimize hydrogen in the weld metal

Low hydrogen electrodes (proper storage, baking)

Steel cleanliness

Preheat

Match temperature to alloy

Allow sufficient time for diffusion

Microstructure control

Isothermal transformation

Use austenitic or nickel base filler metal

Hydrogen sink & residual stress mitigationReheat Cracking Reheat Cracking is defined as cracking that occurs in the heat-affected zone (HAZ) or weld metal during the exposure of a welded assembly to PWHT or elevated temperature service.

Reheat cracking is also referred to PWHT cracking or stress-relief cracking.

Common in Cr-Mo steels containing less than 3%Cr.

Characteristics Of Reheat Cracking Low rupture ductility.

Intergranular fracture along prior austenite grain boundaries..

Heat-to-heat crack susceptibility varies ( dependent on residual elements

Bulk chemistry of a material may not be reliable predictor of cracking susceptibility

The time-to-failure exhibits a C-curve behavior as a function of temperature. Reheat Cracking --- C-Curve Behavior

Mechanism of Reheat Cracking A balance of intergranular and intragranular carbide precipitation controls the reheat cracking susceptibility.

Cracking can initiate at prior austenite grain boundaries by cavitation on incoherent, Fe-rich M3C carbides.

The grain matrix is resistant to plastic deformation due to precipitation strengthening by alloy carbides. Impurities have significant effect on susceptibility to reheat cracking.

Reheat Cracking Susceptibility Parameters G parameter:

- G = Cr + 3.3Mo + 8.1V 2

- If G > 0, the material is considered to be susceptible.

PSR parameter:

- PSR = Cr + Cu + 2Mo + 10V + 7Nb + 5 Ti 2

- If PSR > 0, the material is deemed to be susceptible

Effect of Cr and Mo According to G & PSR, Cr increases reheat cracking susceptibility.

According to Nakamura & Ito, steels containing >1.5Cr are not susceptible.

According to Tamaki, effect of Cr varies with Mo content (right figure)

Molybdenum:

Mo increases reheat cracking susceptibility

In early stage of tempering, Mo2C carbides precipitate first and cause hardening in grain matrix

In presence of V, Nb & Ti (more affinity for C than Mo), there exists a tendency to form more stable carbides.

Effect of Vanadium Vanadium

V increases reheat cracking susceptibility.

V forms uniform and fine V4C3 carbide in the matrix.

At temperatures of 930-1020 F, coherent precipitates of V4C3 occur in ferrite lattice similar to M2C formation.

z

Solidification Crack Cracking that forms during solidification of the molten weld pool hence the term hot cracking

Lack of sufficient feed of hot metal into the area of final solidification (e.g., crater cracking)

Unfavorable orientation of the final freezing zone relative to the direction of solidification

Factors Promoting Solidification Cracking Composition

Long freezing range

High levels of carbon, sulfur, phosphorus, etc.

Bead Shape

High depth : width ratio

Joint Profile

Root condition

Thickness mismatch

Influence of Composition on Solidification Cracking

Long freezing range:

The risk of cracking is a direct function of the magnitude of the difference in solidification temperature between the solvent-rich and solute-rich components of the molten weld metal

Stresses that develop during solidification due to contraction must be borne by the solute-rich metal that solidifies last

Elevated levels of impurities and some alloying elements:

Elements that promote low-melting eutectics, such as S, B, and Cb, increase the risk of solidification cracking

Differences in solubility of certain elements, such as sulfur, in austenite vs ferrite can have a potent effect on susceptibility: Carbon and other austenite formers that promote solidification as austenite increase the risk of solidification cracking

Role of carbon can be critical, particularly weld roots and when using high dilution processes, such as SAW

Bead Shape Depth:Width ratio affects solidification pattern

High depth:width ratio

promotes concentration of lowest melting material at the centerline (by heat extraction) of the weld deposit

Shape of the weld bead will be influenced by:

Welding current (lower current reduces depth:width ratio)

Welding speed (lower speed reduces depth:width ratio)

Polarity (dc positive vs ac/dc negative)

Reducing Susceptibility to Solidification Cracking Change bead shape (depth:width ratio) by reducing penetration

Reduce dilution, particularly in root pass (lower C and S)

Buttering of higher carbon steels

Reduce length of molten weld pool (easier fill of final solidification zone with hot metal), use backfill techniques

Control weld metal chemistry within specification

Reduce root gaps; maintain gap dimension along full length of long weldsWelding Training

Welding training includes the training given to welders, L&T Supervisor & Contractors Welding Engineer by Welding Engineering.

1. Welding parameter understanding

Preheating Temperature

Interpass Temperature

DHT Temperature & Time

Checking of Preheating on Base Metal

Checking of Interpass Temperature on Bead

Maintenance of preheat temperature until DHT

SMAW Welding Parameters: Current, Voltage, Bead Length

GTAW Welding parameters: Current, Voltage, Travel Speed

Temper Bead understanding

Interpass Cleaning

Understanding of Detrimental effect due to Arc Strike, Precautionary actions to avoid Arc-Strike on base metal.

Critically of Cr-Mo-V with respect to welding, handling, etc.

Practical Training: Before Starting on job- SMAW Bead on Practice to achieve required bead length in various positions.

Position of Curve Dependant on Alloy And Heat Chemistry.

PAGE 22

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P-NUMBERSTypes of material

1Carbon-Manganese steel

2Carbon-1/2%Mo

31%Cr-0.5%Mo

42.25%Cr-1%M

5Ferritic stainless steel.

6Martensitic stainless steel.

7Austenitic stainless steel.

8Nickel steel.

9 to 11Quenched & Tempered steel

21-25Al & Al base alloys

31-35Cu & Cu base alloys

41-45Ni & Ni base alloys

51-53Ti & Ti base alloys

61-62Zr & Zr base alloys