Inspection personnel and their qualifications and validation are the most important key for a good inspection to be done and a required output efficiency of the produced is highly influenced by this
This article will point on the simple aspect of a person involved in welding inspection for any kind of welding in a big or small component.
DUTIES OF A WELDING INSPECTOR:
To ensure all welding activities strictly comply with code, standards, and client specification, and can be classified into three main categories i.e. before welding, during welding, and after welding.
- Familiarization to applicable codes, standards or client specifications and also approved drawings.
- Check the welding documents such as approved WPS, PQR and check all information for all variables and range of approval for that procedure.
- Check the variables for welder qualification certificate and the position limits and the history of employment to avoid time lapse.
- Check and monitor joint preparation such as per WPS used and also the jig and fixtures for distortion control.
- Check the condition of welding machine and welding cables, electrode holder, welder tools and ensure all connections is correct.
- Check and review all the calibration certificate for all measuring devices such as caliper, oven, welding machine, and PWHT machine.
- Check the material size, type, and condition such as flatness and ovalness of pipe. Make sure receive the copy of mill certificate of the materials and must be genuine.
- Check the consumable size, type, and condition such as concentricity of the flux covering and the treatment or storage and handling of the electrode. In case of basic electrode need to be baked prior to use as per manufacturer recommendation, holding oven and quiver and make sure receive the batch certificate of the consumables.
- Check the requirements of preheating such as the methods, the minimum temperature and inter-pass temperature and the direction of preheating if using flame type. Make sure the heating rate is uniform and not localized heating applied.
- Check the safety requirements.
- Check the weather conditions and avoid welding during raining day and provide adequate protection during windy situation.
- Check welding position as per WPS used and correct welder identification.
- Monitor the preheat maintenance by looking at a minimum temperature as per WPS used.
- Check the welding parameter such as current, voltage and travel speed as per WPS used to avoid metallurgical effects on the weldment.
- Check the consumables condition and storage and stop welding if welder uses the different electrode that recommended by WPS or issues the NCR.
- Check the interpass temperature that recommended by WPS.
- Check the inter-run cleaning and cleaning method whether by brushing or grinding and the type of tools involved in cleaning.
- Perform visual inspection of the root to ensure the welder produce a sound root run before performing next weld run.
- Check the removal condition allowed for distortion control such as strong back, jig, and fixtures such as 50% after completion of the weld.
- Check safety during welding.
- Maintain the log book daily.
- Check cleanliness of the welded joint, must be free from spatter, oil or grease and also check the welder and joint identification.
- Perform visual inspections, observe any defects, record if there are such and compare the size of the defects with specified code or standards.
- Monitor or witness the NDT activities.
- Check or witness PWHT activities such as the heating rate, temperature attained, holding time and the cooling rate as per procedure used. Check also the calibration certificate for the equipment before working commenced.
- Collate all documents that involved during fabrication and submit to higher authorities.
In the event of repair:
- Report to the higher authorities regarding the extent and severity of the repair.
- Liaise with an engineer for the repair procedure.
- Marking of the defective area for repairing.
- Carry out the repair of welding as per procedure used and checks repeat all activities or duties before, during and after welding.
- Witness the NDT if any.
- Collect the data and result and submit to higher authorities.
Welding Process details
MMA (also known as SMAW)
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Characteristic
- MMA is an arc welding process that uses an arc between melting tip of the covered electrode to the base metal.
- Type of source characteristic is constant current or drooping arc.
- Type of welding machine: Transformer, Rectifier, Generator, and Inverter.
- Type of polarity: DC+ (reverse polarity) deep penetration, DC- (straight polarity), AC.
- MMA is a manual process and welder control directly arc length, angle electrode, travel speed.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Variables
Current, Arc Voltage, Arc Length, Travel Speed, Open Circuit Voltage (OCV), Polarity, Electrode Angle.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Material
SizeÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : 3.0~25.0mm
TypeÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : CS, SS, Ni
ConditionÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : some tolerances for surface preparation.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Consumable
SizeÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : 1.6~6.0mm.
TypeÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : Basic, Rutile, Cellulose (deepest penetration).
ConditionÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : crack, chip, concentricity.
TreatmentÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â : Basic ~ need to be baked at 300C for 2 hrs or as per manufacturer instruction, holding Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â oven at 150C quiver at 70~80C.
Rutile ~ dried at 120C for 1 hr.
Cellulose ~ never bake and what so ever.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Typical defect
All defects except cooper slag, tungsten and silica inclusion.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Function of flux
provide shielding, provide deoxidizer & stabilizer, improve weld meta properties.
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Process Diagram
Ã¢â€”ÂÃ‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Equipment Set-up
- SAW is an arc welding process that uses an arc between a melting tip of the bare wire to the base metal.
- Arc is shielded by fused or agglomerated fluxes.
- Types of static characteristic: Constant Voltage < 1000 Ampere, Constant Voltage > 1000 Ampere.
- The type of flux: Fused, Agglomerated, Mixed Type.
- The functions of flux: Provide shielding, provide deoxidant, produce slow cooling, improve properties of weld metal.
- Variables: Current, Voltage, Travel Speed, Flux Depth, Wire Size, Electrode Extension.
- Material: Size: 6.0-150 mm, Type: CS, SS, Non-Ferrous Alloy, Conditions: Moderate Cleaning.
- Consumable: S:2.0-4.0 mm, T: as per parent metal, C: store in a dry and clean area.
- Treatment: Fused: Baking is not required, Agglomerated: Must be bake at 400C for 1 hour.
- Typical Defects: Burnthrough, lack of rot penetration, porosity, slag inclusion, solidification crack.
- Advantages: High productivity, low ozone level, no visible arc light, low weld metal cost, easily automated.
- Disadvantages: Restricted welding position, shrinkage defect, arc burn on DC current, difficult root penetration control.
- MIG: Metal Inert Gas: Ar and He.
- MAG: Metal Active Gas: CO2, Ar+CO2, Ar+H2
- Also known as GMAW.
- MIG/MAG is an arc welding process that uses an arc between a melting tip of a solid wire to the base metal.
- The types of static characteristic are Constant Voltage or Flat Characteristic.
- The type of welding machine: Transformer/Rectifier, Inverter.
- The type of polarity: DC+
- The type of metal mode of transfer:
Short circuiting or Dip Transfer: I<200 Ampere, V<22 Volt, Thin Material, All position, Lack of side wall fusion, High spatter.
Spray Transfer: I>270 Ampere, V>27Volt, Thick Material (Al or Mg), No Spatter, Solidification crack, Ar >85% required, Flat and HV position.
Globular Transfer: In between SC and ST, High spatter.
Pulsed Transfer: Better Fusion, Low Heat Input, Low distortion.
- Variables: Current, Voltage, Travel Speed, Gas Flow Rate, Electrode Extension, Nozzle to work distance, Contact tube to work distance, Arc length.
- Material: S: 0.8-50mm T: CS, SS, Copper, Nickel, Al, Alloy C: Moderat Cleaning
- Consumable: S: 0.8-1.6mm T: as per parent metal, C: store in a dry and clean area.
- Gases: Ar, He, CO2, Ar+He, CO2, Ar+O2+CO2
- Equipment Set-up
- Advantages: High Productivity, low hydrogen (3ml/100gr), easy to be mechanized, deep penetration compared to MMA, less wastage of electrode.
- Disadvantages: Expensive, need gas for shielding, not suitable for restricted areas, not so portable, high ozone level.
- Typical Defects: Silica inclusion, copper inclusion, spatter, lack of side wall fusion, solidification crack, porosity.
- Safety: Fume, electric shock, burn skin, arc rays.
- Also known as GTAW
- TIG is an arc welding process that uses an arc between non-consumable electrode to the base metal.
- Need or no need filler metal to molten pool.
- The type of static characteristic is Constant current or dropping arc.
- The type of welding machine: Transformer/Rectifier, Inverter.
- The type of polarity: DC+ (steel), DC- (Steel), AC (Al).
- The type of tungsten: Thoriated DC, Zirconiated AC, Lanthanum DC or AC, Ceriated DC or AC.
- Variables: Current, Voltage, Travel speed, Electrode Extension, Gas Flow Rate, Polarity, arc length.
- Material: S: 1-15mm, T: Suitable for most material including reactive material, C: Must be very clean.
- Consumables: S: 1.6-4.0mm, T: as per metal, C: Store in a dry and clean area.
- Gases: Ar, He, Ar+He, Ar+O2
- Advantages: High quality, Suitable for thin material,
- Disadvantages: – Typical defects: Tungsten inclusion, porosity, undercut – Safety: Electric shock, arc rays, burn skin, fire.
- Also known as SMAW.
- MMA is an arc welding process that uses an arc between a melting tip of the covered electrode to the base metal.
- The type of static characteristic is constant current or dropping arc.
- The type of welding machine: Transformer AC, Rectifier DC, Engine Driven, Inverter.
- The type of polarity: DC+ deep penetration, DC- higher deposition rate, AC.
- The type of Flux: Basic High strength material, Rutile General purpose, Cellulose deep penetration.
- Functions of flux: Slow cooling, Deoxidizer, Shielding, Improve weld metal properties.
- Variable: Current, Voltage, Travel speed, OCV, Polarity, Arc length.
- Material: S: 3-25mm, T: CS, SS, Copper, Nickel.
- Consumable: S: 1.6~6.0mm, T: Basic, Rutile, Cellulose, C: Crack, chip, concentricity.
- Treatment: – Basic: baked 350C for 2 Hrs, Holding Oven 150C 1Hr, Quiver 70- 80c. – Rutile: Dried 120C for 1 Hr Cellulose: No baked and dried and whatsoever.
- Typical Defects: Porosity, slag inclusion, undercut, solidification crack, lack of fusion.
- Advantages: All position, easy to operate, versatile, suitable for restricted areas, cheap, no need gas for shielding.
- Disadvantages: Low productivity, not easy to be mechanized, high skill required, high wastage of consumable, critical cleaning to avoid slag between weld passes.
- Safety: Fume, Electric Shock, Burn skin, Fire, Arc Rays.
- Uses: surface inspection of any non-porous material.
- Advantages: Cheap, simple to use, rapid result, more sensitive than visual inspection, low operator skill required.
- Disadvantages: Inspections of accessible surfaces only, surface breaking defect only, penetrant may contaminate component, in most circumstance post cleaning required, surface preparation critical, very little indication of depth.
- Uses: Surface/slight subsurface inspection of magnetic materials.
- Advantages: Little surface preparation.
- Disadvantages: Inspection of accessible surface, no indication of depth, magnetic material only, only suitable for a linear defect, surface or near surface defect only detected.
- Uses: Surface inspection of any nonporous materials.
- Advantages: Cheap, rapid result, more sensitive than visual inspection, low operator skill required, simple to use.
- Disadvantages: Inspection of accessible surface only, surface breaking defect only, penetrant may contaminate component, surface preparation critical, very little indication of depth, in most circumstance post cleaning required.
- Uses: Surface/slight subsurface inspection of magnetic materials.
- Advantages: Inspection of accessible surface, no indication of depth, magnetic material only, only suitable for a linear defect, surface or near surface defect only detected.
- Require susceptible grain structure, stress, and hydrogen and low temperature is reached.
- Most likely occur in haz for carbon manganese steel and weld metal for hsla.
- Also known as hicc, delayed crack, under-bead crack or chevron.
- Type of crack is intergranular along grain boundaries or transgranular.
- H2 is absorbed by weld pool from the arc atmosphere.
- During cooling, h2 escape from solidified bead but some also diffuses into the heat-affected zone of parent material.
- H2 is major influence in this type of crack.
- The source of h2 may be from moisture or hydrocarbon such as paint, grease on the parent metal, damp welding fluxes or from the condensation of parent metal.