HEAT TREATMENT PROCEDURE

PROCEDURE FOR POST WELD HEAT TREATMENT BY ELECTRIC RESISTANCE METHOD

SCOPE

This procedure is for heat treatment or stress relieving of dish ends and may be used for other parts.

INTRODUCTION & METHODOLOGY

·         We propose to carry out the heat treatment of Dished Ends by Electrical resistance method.

·         Firstly insulation will be placed on the ground.

·         On Insulation proper supports shall be placed in such a way that dish ends are stable on those supports.

·         On support dished ends shall be placed.

·         Thermocouple shall be attached to sense the temperature.

·         This temperature will be recorded into the temperature recorder.

·         Electrical coils element shall be placed below the dished ends.

·         The whole assembly will be covered with ceramic fibre.

·         All connection will be check.

·         All Electrical coils shall be controlled by electrical panel to follow the proper heating cycle as per client requirement.

 

NORMALIZING STEPS

·         To shape the coil properly as per requirement. 

·         To mark thermocouple positions and attached the thermocouple.

·         To cover the thermocouple base with insulation piece to avoid the detection of coil temperature. 

·         To Place the coil on the job area to be heat treated. 

·         To insulate the job area with ceramic fibre.

·         To connect to the panel via feed cable. 

·         To connect panel to the main supply. 

·         To connect thermocouple to the Temperature recorder via compensating  cable. 

·         On the Recorder.

·         On the main connection. 

·         To set the energy regulator/pid of panel as per temperature cycle to follow.

·         The temperature distribution obtained by this method of heat treatment is within standard codes.

·         The client presented certified/approved temperature graph chart of the heat

treatment.

 

REFERENCE DOCUMENTS

·         ASME SEC VIII DIV 1

POST WELD HEAT TREATMENT SPECIFICATION

·         Unrestricted loading temperature (°C) :  300

·         Rate of heating (°C/hr) : 100 °C/hr

·         Soaking temperature (°C) : 910 °C ± 10°C

·         Soaking time (Min) : 30 Min

·         Cooling media :   Air

Note: Above all data is related to dish ends, this may vary with the requirements and product specification and material.

HEATING SYSTEM

·         Type of electrical resistance heater which would be used as per requirements.

·         Heaters may be straight coil heater or shaped coil heater.

·         Power is supplied from the main switch to Heat-welds control panel and from panel to the heating elements (415 - 3 phase).

THERMAL INSULATION

·         A 50 mm thick layer of ceramic fibre /Rock wool used for insulation to job.

·         This insulation having 96 Kg/m³ (density may vary as per heating required) density will be applied to the entire Peripheral outer surface of the job.

·         The insulating material shall be fitted with binding wire in such a way that no gap is left so that no heat is lost.

·         It helps to achieve the desired temperature with minimum power input.

·         Prior to heat treatment all gaps in the insulation plugged with loose insulation material.

TEMPERATURE CONTROL

·         The heating shall be grounded into independent control zones.

·         Each controlled and monitored by respectively numbered thermocouple so as to provide the required temperature profiles.

·         We will use PID controller to control the rate of heating and cooling as per heating cycle.

THERMOCOUPLES AND COMPENSATING CABLES

·         Thermo-couple shall be made up of nickel-chromium / nickel- aluminium wire or other approved equivalent.

·         The thermocouple shall be attached to the work pieces by Copper/ constantan compensating cable shall be used for extension of the thermocouple to recording instrument.

·         Copper positive (+ve, Nonmagnetic) shall be connected to the nickel chromium conductor of the thermocouple and the constantan lead (-ve, magnetic) shall be connected to the nickel aluminium conductors.

·         6 no’s thermocouple will be used.

TEMPERATURE RECORDING

·         Temperature recorders shall be of the potentiometer self-compensating type, calibrated in degrees cellists with respect to a nickel-chromium/nickel-aluminium thermocouple, type K.

·         In temperature recorder, recording points are connected to the each thermocouple by compensating cable .The temperature is recorded in the recorder.

·         Temperature recorders shall be calibrated at intervals not exceeding 6 months.

·         If the calibration checks yield information that the temperature recorder is not within the manufacturers specified tolerances, re-calibration will be performed.

·         The calibrations shall be recorded and evidence to this is kept with the instrument by attaching sticker of date of calibration.

·         A clear print out of data shall be demonstrated before commencement of a heat treatment.

DOCUMENTS

·      Temperature chart with specification, thermocouple locations etc. 

·      Recorder test certificate. 

·      Thermocouple test certificate-one certificate for 100 Meter TC Wire. 

SAFETY PRECAUTION

It is mandatory to follow the following safety instruction. 

·      To wear safety shoes.

·      To provide earthing to the job.

·      To avoid coil from touching to the job by proper tightening the beads.

·      To provide MCB in the panels.

·      To assure the job is free from current.

·      The connectors are used for connection or connections are covered with glass tape.

·      If any problem occurs first switch off the main switch.

·      If any accident occurs, victim is first aided and moved to the hospital for further treatment. 

 

 

 

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