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Reg. 562


Heat Treatment

 

1)

 All boilers constructed to class I or class II requirements shall be stress-relieved by heat treatment after completion of all welding and before hydraulic test if any plate is 20 mm thick or greater or carbon content of the steel exceeds 0.25% or the material used in the construction of boiler is alloy steel.

For Carbon steel a stress relieving heat treatment shall be performed by heating part to at least 600±20°C. When required by the characteristics of the material different temperatures may be necessary to obtain proper stress relieving. The part to be stress-relieved shall be brought slowly up to the specific temperature and held at that temperature for a period of proportionate on the basis of atleast 2 ½ minutes per milimetre of the maximum thickness of part (approximately one hour per 25 mm of thickness) and shall be left to cool in the furnace to a temperature which, for the parts with a thickness greater than 20 mm does not exceed 400°C. After withdrawal from the furnace the part shall be allowed to cool in a still atmosphere. A temperature-time diagram of the stress-relieving process shall be provided for a welded shell or drum and a similar diagram for other welded pressure parts when the Inspecting authority requires it. During heat treatment the official test plates shall be inside the boiler. Where the shell is subjected to a primary stress relieving treatment identical to the final heat treatment to be given to the boiler, the test plates may be placed inside the shell during primary treatment and thereafter cut up and tested without waiting for the final treatment of the boiler.

Where the shell is not subject to primary stress relieving treatment or is subjected to primary stress relieving treatment which is not identical with the final heat treatment, the test plates may be placed inside any other boiler of comparable dimensions which is to be heat treated in accordance with this chapter.

Temperature charts shall be submitted to indicate that the test plates and the boilers they represent have been subjected to identical heating, soaking and cooling treatment.

NOTE: -
Other stress-relieving heat treatment at a temperature as low as 550°C may be adopted, provided attention is given to the holding time in order to ensure a sufficient degree of stress-relieving.

2) Where the welding joint connects parts that are of different thickness, the thickness to be considered in applying the limiting thickness of 20 mm for carbon steel shall be the following nominal thickness including corrosion allowance:

i) the thinner of two adjacent butt welded component including shell to end connection;
ii) the thickness of the shell in connections to flats ends;
iii) the thickness of the shell or end in nozzle attachment welds;
iv) the thickness of the nozzle at the joint in nozzle to flange connections;
v) the thickness of the pressure part at the point of attachment where a non-pressure part is welded to a pressure part in case of butt welds;
vi)

the thickness of the fillet weld at the point of attachment where a non-pressure part is welded to a pressure-part, in case of fillet welds.

3) Notwithstanding anything contained in sub-regulations (1) and (2), if the thickness of a small component of boiler exceeds 20mm and the weld recess also exceeds 20mm, local stress relieving to the satisfaction of the Inspecting Authority shall be permitted.
4)

Notwithstanding anything contained in sub-regulations (1) and (2), post-weld heat treatment in weld joints of such equipment in carbon steel and low alloy steel may be exempted when heat treatment is not practical in some of such equipment, where inside is lined with special Stainless Steel which cannot be heated beyond 400C (due to the associated problem of reduction of corrosion properties of such lining during heating to the temperature), post weld heat treatment may be avoided in the weld joints of such equipment in carbon steel and low alloy steel when all the following conditions are satisfied:- 

(a) Built up overlay welding (buttering is performed on both the welding edge bevels of the parts of the closing joint to be welded together.  The buttering can be of :

(i)                   With Carbon Steel Electrode with low carbon (C) = 0.1 per cent max (Ex: E7018-1) in case of Carbon Steel parts.

(ii)                 With Stainless Steel Electrode E-309 or with Inconel electrode in case of low alloy steel parts.

(iii)                With low alloy steel electrodes, having carbon (C)=4.12 per cent max (Ex:9018G) or with Inconel electrode in case of high strength low alloy steel parts having UTS greater than 56 kg/mm2 such as WB36, SA533 Gr. B C 1.02:

(b)  Buttering thickness shall be 15mm minimum on the side where chip[ back is required to be done before re-welding and 8mm minimum on the other side.  Refer figure given below:-


       (c) Suitable pre-heat and other pass heating is applied during buttering;

(d) Individual parts shall be post weld heat treated after buttering if required as per applicable regulations prior to welding the special stainless steel corrosion resistant liner plate or prior to applying final weld overlay of special corrosion resistant stainless steel lining;

(e) The final layer on the internal liner side shall be compatible with liner material and final weld (carbon steel welding in carbon steel base metal, low alloy steel Inconel welding in case of high strength low alloy steel base metal and  E309  Inconel welding in case of other Low alloy steel base metals) on the base metal side shell be compatible with base metal in respect of mechanical properties.  The welding procedure shall be established taking care of adequate toughness and ductility and the procedure approved by IBR inspectors; 

(f)      Charpy -V Notch impact test shall be carried out at 0C for:

(i)                   base metal and heat affected zone;

(ii)                 weld metal in case of Carbon Steel welding; 

(g)     Non-destructive testing as below is recommended,-

(i)   Magnetic particle test of weld bevels prior to buttering.

(ii)  Dye- Penetrant test of buttering layer,

(iii) Dye Penetrant test of rest of weld,

(iv) Dye Penetrant test of final weld on internal liner side,

            (v) Ultrasonic test of final weld after hydro test of the equipment with the closing seam.

 

 
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