PWHT / Stress reliving Procedure
1.0 Scope:-
This
describes the Procedures Provide information for heat treatment (Stress
relieving only) for Carbon steel, alloy steel.
2.0 Reference Codes & Specification:-
• ASME
Section VIII Div.1
• AWS
D1.1
• Railway
Specification.
•
Manufacturing Drawing.
3.0 Responsibilities & Duties:-
• To
ensure that all heat treatment in accordance with specified standards &
applicable quality control criteria.
• Heat treatment shall be performed by employees who are adequately qualified.
• Assures
facilities/equipment is properly maintained.
• Assures
equipment like Furnace, thermocouples, temperature recording & controlling
devices are calibrated.
4.0 Furnace loading:-
•
Material shall be loaded in the Furnace in a manner that provides sufficient
spacing to ensure that there is adequate furnace airflow & circulation.
• Material
shall not be placed on the furnace hearth (floor). Material shall be placed on
racks or supports. Long part to be supported, as needed to prevent sagging.
•
Complete furnace loads should be inspected to ensure that doors/openings are
properly sealed.
• Furnace atmosphere shall be controlled so as to avoid
excessive oxidation during heating & holding Period.
• During heating, no temperature variation exceeds 14 degrees C
• During holding no temperature variation between the highest
& lowest temperatures exceeding14 degrees C is allowed.
• The Heat treatment operation (Heating rate, holding time /
temperature & Cooling rate shall be in accordance with the Stress reliving / PWHT specification.
5.0 Thermocouple Placement:-
• Thermocouples Locations
attached in Rectangular furnace (Working Zone)
6.0 Inspection & Records:-
• Ensure the Heat treatment chart
shall indicate the Job identification / Joint Identification to be covered in the PWHT cycle & Chart shall be
endorsed by Authorized representative & Heat treatment Personal along with a date.
• Visual & dimensional Check for possible deformation & loss of
identification.
• Check there is no deformation or Visual defects on the structure being
Heat-treated.
• NDE on joints to be performed after 48 hours
PWHT / Stress relieving.
PWHT / Stress reliving
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Job no.
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Description
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Material Specification
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Nominal Thickness
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WPS no.
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Method of Heating
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Electric Furnace
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Loading & Unloading Temperature
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300oC Max
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Heating Rate
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80-120oC/Hr
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Cooling Rate
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80-120oC/Hr
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Soaking Temperature
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600 ± 20°C and Minimum holding time
shall be as per below mention table.
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Weld Metal Thickness in mm
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Holding Time
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≤ 6mm
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Above 6mm to 50 mm
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Above 50mm
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15 minutes
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15 minutes for each 6mm or fraction thereof
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2 hrs plus 15 minutes for each additional 25 mm or
fraction thereof over 50mm
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THERMOCOUPLE LOCATIONs