CSWIP 3.2 Summary

CSWIP 3.2

HEAT TREATMENT

Temperature are divided in two groups follows
- Upper Critical Temperature ( 880 – 920 deg. C ): Annualizing; Normalizing; Quenching
- Lower Critical Temperature( <730 deg. C):  Preheat; PWHT; Tempering; Recovery

- PWHT, Term “ local” - heat treatment a partial equipment or weld joint; “ Global ” = heat treatment whole equipment

• PWHT soaking: decrease yield strength, decrease residual stress, and then increase yield strength (<100%).
• PWHT effect: toughness increase, hardness decrease, residual stress decrease, tensile decrease, not completely remove residual stress.
• Tempering: follows Quenching.

Note: purpose and effective heat treatment see in study book.

WELDING CONSUMABLE AND WELDING PROCESS

1. MMA (111) process

Electrode type: Cellulose (0, 1), Rutile (2,3,4) Basic (5,6,8).

• Cellulose never baking, 
• Rutile only drying at 90 – 120 degree C; 
• Basic shall be baked at 350 deg. C and then drying at 150 degree C before using (4hours).

2. TIG (141) process

• Lowest hydrogen content.
• Slope-in occurs tungsten inclusion, slope-out occurs crater crack (shrink crack).
• Zirconated electrode(non-consumable) suitable for Aluminum, only AC current; Thoriated electrode suitable carbon steel.

3. MIG/MAG (131/135) process

• Dip transfer for thin plate; give lack of fusion and spatters.
• Pulse transfer for small weld pool and all positions.
• Spray transfer for thick plate, flat, horizontal; give no spatter, less distortion.
• Globular transfer given high distortion, only with CO2

4. SAW (121) process

• Fusion: hydroscopic, restrict moisture, no baking
• Agglomerate: sensitive moisture, baking before use, easy add more elements, good quality.
• Given high deposit rate, less distortion, high dilution.

5. Current and Polarity 

• DC EP: MMA, FCAW, MIG/MAG, SAW prefer, given highest penetration, narrow weld bead, lowest deposited metal.
• AC: Balance 50:50, weld bead normal, deposit weld metal normal, suitable with Aluminum and aluminum alloy.
• DC EN: TIG process, avoid tungsten inclusion, Lower penetration, wide weld bead, highest deposit metal.

NOTES:

• Avoid arc below by changing DC to AC.
• Inverter changes DC to AC; Rectifier changes AC to DC.
• MMA welding process and welding consumables are most suitable application to compare with other process.
• MIG/MAG most used DCEP, MIG suitable with Al, Ni, its alloy, stainless steel.
• Flat characteristic = constant voltage, current = wire feed speed, for automatic, semiauto, MIG, MAG, SAW (less than 1000A).
• Drop characteristic = constant current, control arc length by welder, manual, for TIG, MMA.
• Arc length = arc voltage = arc gap, effect to weld profiles; increase arc length > increase weld bead, decrease penetration, unstable arc, susceptible hydrogen entrap.
• In SAW process: increase arc voltage > increase flux consumption; susceptible solidification crack (depth to width ratio >1.5), less dilution by change DCEP to DCEN (for cladding/surfacing).
• Remember welding process number of 111, 121, 131, 135, 136

WELD FRACTURE

1. Ductile

• Reduce area, plastic deformation (permanent deformation).
• Surface roughness, torn surface, 45 degree shearing slip.

2. Brittle

• Low temperature, occur at subzero temperature.
• Fast at the speed of sound.
• Flat, roughness, not torn.
• Crystalline appearance.
• Stress

3. Fatigue

• Cycle loading, load below yield stress, slow propagation.
• Chevron mark, initiation point.
• Surface smooth, beach mark, curve.
• Initial point from the defects.

DESTRUCTIVE TEST

• Understanding term of “quantitative test” and “qualitative test” has detailed in the study book.
• Definitions of each mechanical test such tensile, CVN, bending test …
• Which method use for WPS qualification, such transverse tensile test, CVN, macro, micro, bend test, hardness test.
• Which method use for welder qualification, such fillet weld fracture test, butt weld nick-break test (alternative RT).
• Which method use for welding consumables, such all tensile test.

Tensile test

• All tensile test for welding consumable to measure tensile, yield strength and elongation (gauge length 50 mm)
• Transverse tensile test to measure tensile strength of weld joint.
• Elongation determine using gauge length for all tensile test; reduced cross section for transverse test and Z through thickness test.
• Re, Rm, unit, elastic, necking, plastic statement should note from study book.
• Related TS, YS, Elongation and %C graphic should note from the study book.

Bending test

• Diameter of former (typical 4T), if former (OD) less than 4T may cause wrongly results.
• Bending test formed at 180 degrees.
• Side bend test for material >= 13 mm, face bend and root bend for material <13 mm (cap or root may be flushed to remove stress.

Hardness

• Why Rockwell diamond cone hardness test not allowed testing on product weld, because it made initiation point.

Impact test

• Transition range definition should note from study book.
• CTOD test measures material properties – toughness fracture (quantitative test type)

Macro and Micro test

• Marco test to detect the defects (5x-10x magnification).
• Micro test to detect defects and grain structure (100x – 1000x magnification)

OtherAdvantage and disadvantage should note from study book.


JOIN DESIGN

• Single sided preparation (V, bevel) gives high distortion, required high skill welder and more deposited weld metal.
• Double sided preparation (V, U, bevel) and single sided (U, J) give less distortion and less deposited weld metal.
• A U-, J-preparation susceptible solidification because of high depth to width ratio.
• Set-on nozzle: susceptible lamellar tearing (after welding), difficult to UT, limits access from outside.
• Set-out nozzle: not occur lamellar tearing, easy access both sides, easy UT
• SAW very hard to weld with opening root gap.
• Reduction of bevel angle may result in a risk of lack of fusion and would not compliant with the specification.

WELDABILITY (ISO 1011-2)

Solidification cracks

• Another name: is hot crack, hot shortness, centerline.
• Factor effect: high tensile stress, Sulphur, joint design (dept to width radio).
• Single-U preparation are susceptible to hot cracks
• Occur only on centerline of weld metal only, star crack (stop weld).
• NDT method detect solidification crack: visual and both surface/volumetric.

HICC

• Another name is cold cracking, HAZ crack.
• Factors: CEV, Temperature, Stress, Hydrogen = occur the same time.
• Occur on weld metal, HAZ (weld zone).
• Austenitic stainless steel does not occur HICC.

Lamellar tearing

• Other name is step line appearance, occur on base metal only, underneath or subsurface, can’t detect by MT/PT, least effect RT (due to perpendicular with the beam), good detect by UT with 0-degree probe (straight, zero, normal probe).
• Occur on T-Y-K or Conner joint only.
• Lamellar tearing occurs only on set-on joint.

Factor and avoid cracking see in study book.

REPAIR

• Do not confuse when weld joint subject to repair or cut-out.
• Cut-out: crack defect, second repair, exceed 25% circumferential weld length.
• Weld repair procedure must approve before commencing.