TABLE OF CONTENTS | ||
Sl. No. | DESCRIPTION | PAGE NO |
1.0 | INTRODUCTION AND GENERAL DESCRIPTION | |
2.0 | JOB SPECIFICATION | |
3.0 | REFERENCED DOCUMENTS | |
4.0 | POST WELD HEAT TREATMENT SPECIFICATION | |
5.0 | EQUIPMENT | |
6.0 | TEMPERATURE CONTROL | |
7.0 | SITE ELECTRICAL SUPPLY REQUIREMENTS | |
8.0 | TEMPERATURE RECORDING | |
9.0 | STRESS RELIEVING PROCEDURE | |
10.0 | RESOURCE AND PERSONNEL PLAN | |
11.0 | DOCUMENTATION AND RECORDS | |
12.0 | SAFETY | |
REFERENCED DRAWING: | ||
13.0 | GA DRAWING FOR EQUIPMENT | |
14.0 | THERMOCOUPLE LOCATION DRAWING | |
15.0 | BASE SUPPORT PLATFORM FOR PWHT OF TANK | |
1.0 INTRODUCTION AND GENERAL DESCRIPTION
This procedure relates to the application of high velocity oil fired technique for stress relieving of thin walled tanks by in-situ heat treatment to achieve stress relief temperature of 620 °C. The mode of heating will be by using high velocity burner.
The heat treatment specifications and temperature constraints as per API 650 10TH Edition Add-4 will be applicable for entire thin walled tank shell during the stress relieving operation.
The thin walled tank should have provision to enable free expansion & contraction of the vessel. The tank shall be placed on a platform 500 mm above the foundation or shall be placed on the ground level (uniform flat surface).
Uniform flat surface is very essential to ensure smooth expansion/contraction of the tank during heating/cooling.
For 5 mtrs. Ø x 7 mtrs. ht. and 6 mtrs. Ø x 7.2 mtrs. ht
The tanks shall be supported with minimum 10” Ø with 03 nos. radial supports.
For 8 mtrs. Ø x 11.6 mtrs. ht. tank only
The tanks shall be supported with minimum 12” Ø with 04 nos. radial supports, and External Stiffener for the Top Shells Coarse during the PWHT Operations as directed by our Supervisor.
The tank is insulated with 100 mm thick mineral wool insulation material having a density of 100 kg/m3 on its exterior surface. Before final placement of the tank either on platform/supports, 1 layer of mineral wool shall be laid on ground/support, so that the base of the tank rests on the insulated ground/support.
The high velocity burner with angled/straight cones will be inserted from the bottom manhole / nozzle opening. The products of combustion are exhausted through nozzles. The burner position across the tanks is such that circular of hot flue gases is created inside the tank, which ensures excellent temperature uniformity across the tank. The high velocity of the burner produces a scrubbing action on the shell surface, increasing the temperature uniformity. Care is taken to ensure that there is no flame impingement on any part of the tank.
The high velocity burner will be controlled manually by continuous monitoring of temperature recorder. Control of temperature will be done by manual adjustment of Oil flow/pressure and by butterfly valves of blower (combustion air). The turndown ratio of the high velocity burner is to the tune of 20:1 that gives high degree of control at all stages of firing. As the primary flame of the burner is enclosed in the main combustion chamber, at no time, the flame impinges on the vessel surface, totally avoiding hot spots. Exhaust gases will be taken out from the top manway & through other nozzle openings at the top.
Calibrated thermocouples will be located at suitable locations as per the code requirement & connected to the multipoint calibrated ‘K’ type temperature recorder through colour coded compensating cables. The thermocouple to be attached to the shell with the help of T/c.’s nut are from the Roll of 100 mtrs. which is calibrated per 100 mtrs. roll.
Temperature will be monitored & recorded at regular intervals of time & the heat treatment cycle will be controlled accordingly. After completion of heat treatment cycle, duly certified time –temperature chart will be submitted to the client.
This procedure is to be used at Spent Caustic Equalisation Tanks of under fabrication and erection by Ahmadia Contracting for KNPC/Kuwait
2.0 JOB SPECIFICATION
The heat treatment described within this procedure is based on following dimensional details:
3.0 REFERENCED DOCUMENTS
As per API 650 10th Edition Add-4
4.0 POST WELD HEAT TREATMENT SPECIFICATION
Unrestricted heating rate up to 300°C.
Heating rate of maximum 100°C/Hr. with a temperature differential of not more than 80°C between thermocouples.
Soaking temperature of 620°C +/- 20°C.
Soak Duration 1hr
Cooling rate of maximum 80°C/Hr. with a temperature differential of not more than 80°C between thermocouples.
Unrestricted cooling rate from 300°C.
Temperature constraints
Based on the above heat treatment specification, the temperature constraints, applicable as per API 650 will be followed as under:
Maximum Temperature Differential | ||
4.2.1 | Constraint 1 All Thermocouples below 300 °C | Unrestricted |
4.2.2 | Constraint 2 All Thermocouples above 300 °C | +/- 30 °C |
4.2.3 | Constraint 3 All Thermocouples during soak period | 620 °C +/- 20 °C as described at 4.1& 4.2. |
4.2.4 | Constraint 4 All Thermocouples below 620 °C | +/- 30 °C |
4.2.5 | Constraint 5 All Thermocouples below 300 °C | Unrestricted |
5.0 EQUIPMENT
Combustion Equipment Details For Internal Oil Firing Method :
Burner Type : 1 no. / 02 nos. High Velocity Burner.
Fuel : HSD
Mounting of Burner : Will be fired through bottom manholes with appropriate straight or angle cones per nozzle orientation.
Combustion Air
Blower : 3500 N Cu. M at 600 mm WC
Ignition : With the help of spark ignition and LPG pilot burner that is integral part of burner.
Flame Length : 300 mm Max. at high temperature
Burner Management Train : Comprises of HSD flow control valve, Oil Pressure regulator Ignition transformer. Compressed Air line with FRL & control valve unit & LPG pilot ignition system line.
6.0 TEMPERATURE CONTROL
6.1.1 The High velocity burners will be controlled manually by continuous monitoring of temperature recorder.
6.1.2 Control of temperature will be done by manual adjustment of HSD flow/pressure and by butterfly valves of blower (combustion air).
6.1.3 The turndown ratio of the high velocity burner is to the tune of 20:1 which gives high degree of control at all stages of firing, as the primary flame of the burner is enclosed in the main combustion chamber & at no time, the flame impinges on the vessel surface, totally avoiding hot spots.
7.0 SITE ELECTRICAL POWER REQUIREMENTS
The electrical power requirement within 3 metres of our equipment at site is 415 volts, 3 phase, 4 wire, 50 Hz supply of following capacity:
1. Combustion Air Blowers (15 Kw X 2 Nos) = 30.00 kW
2. Pump & Other Accessories (Approx.) = 4.00 kW
3. Lighting and others (1kW) = 1.00 kW 35.00 kW
8.0 TEMPERATURE RECORDING
8.1.1 The thermocouple wire (T/C) will be of CR-Al i.e. K type of 21/22 SWG, which will be attached to the shell by means of Thermocouple nuts.
8.1.2 Copper constantan compensating cables will be used for the connection between T/C wire and temperature recorder. The copper lead (+ve) will be connected to the Cr-Al conductor (non magnetic) and the constantan lead (-ve) lead to the Ni.Al conductor (magnetic).
8.1.3 Each thermocouple will be connected to a calibrated continuously monitoring temperature recorder, thus providing temperature chart print out giving information on temperature variations and trends during the SR cycle.
8.1.4 The chart will be presented as a record of the heat treatment cycle. The recorder will be adjusted for a range of 0 °C – 1200 °C with appropriate chart speed.
8.1.5 Latest Calibration certificate of the thermocouple wire & temperature recorder will be submitted before start of the SR cycle.
8.1.6 The temperature recorder will be calibrated at intervals not exceeding 6 months.
8.1.7 The thermocouple location on the vessel will be as per Drg. No.
9.0 STRESS RELIEVING PROCEDURE
9.1.1 Before final placement of the tank on ground supports or on platform, 1 layer of mineral wool, 100 mm thk. insulation material of density of 100 kg/m3 shall be laid on ground/support, so that the base of the tank rests on the insulated ground/support. Then the entire vessel shell and roof will be externally insulated with one layer 100mm thk. insulation material of density of 100 kg/m3. The insulation mats will be enmeshed in chicken wire mesh. All the gaps between the insulation mats will be plugged before SR.
9.1.2 Thermocouples will be located circumferentially as per codes requirement & staggered. Thermocouples will be attached to the vessel as described above.
9.1.3 01 no. High Velocity burner (HSD fired) will be inserted from bottom manhole openings available on the tank. The approx. amount of HSD required for stress relieving shall be +/-55 liters per ton weight of the tank.
9.1.4 The combustion equipment will comprise of burner, blower, pilot burner with spark ignition system, flexible hoses, control station.
9.1.5 The HT cycle will be conforming to API 650 as detailed in section 4 above.
9.1.6 Heat cycle profile control will be achieved by controlling fuel flow and combustion airflow through regulating valves.
9.1.7 The placement of equipment will be as per GA Drawing
10.0 RESOURCES AND PERSONNEL PLAN
10.1 Site Organisation & Manpower Planning
Project Manager
Site Heat Treatment Supervisor (Site)
Heat Treatment Technicians Cum Operators(Site)
Insulation Lagers
Helpers as and when required
10.2 Equipment List
For above work we will mobilize 2 sets of High Velocity Burner system along with sufficient spares and accessories as listed below.
High Velocity Burner set comprising of
Burner complete with Injector, pilot burner
Combustion Air Blowers with starters
Spark Plugs
Oil Station
Ignition Panel
24 Point Temperature Recorders
Wire type thermocouples As Required
Flexible hoses from Oil station to burner As Required
Compensating cables As Required
Thermal insulation supply and application may be subcontracted to an independent agency for faster work under our direct supervision & control.
11.0 DOCUMENTATION AND RECORDS
11.1.1 A site supervisor will be appointed to liase with the client site representative and ensure compliance of procedural requirements. The site supervisor will be responsible for all documentation.
11.1.2 The documentation will comprise of the following:
1) Approved Specific Heat Treatment Procedure
2) Details of thermocouple layout
3) Heat Treatment Record Sheets as applicable
4) Time Temperature Chart with details of heat treatment specifications, job specifications, chart speed, date of operation etc.
5) Recorder and thermocouple calibration certificates
12.0 SAFETY
12.1.1 All burner and associated equipment will be checked and test fired prior to dispatch to site.
12.1.2 The site engineer will be designated as the safety officer on site to ensure that all site operation is carried out in accordance with accepted safe working practices. He will be responsible to ensure that all site safety requirements are fully met and complied with
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