La Edad del Bronce

NECK WELDING 135

B5. INSTRUCTIONS FOR CARRYING OUT CONDENSER PLATE AND NECK WELDING

1.1 GENERAL:

1.1.1 The welding of the condenser is performed by ‘step back seam method’ i.e. from tack weld to tack weld.

1.1.2 Subsequent filling welds after tack welding are always performed in the opposite direction. Welding to be carried out as per requirement envisaged in drawing / field welding schedule.

1.1.3 Condenser Erection Manual as well as instructions issued by manufacturing unit may also be referred in conjunction with this manual.

1.1.4 All the welding shall be carried out by qualified welders.

1.2 CONDENSER SHELL INTERNALS WELDING:

1.2.1 Tack weld the tube support plate sections aligned with the centre point to the slot profiles on the bottom plate and the side walls. After tack welding, verify that the holes in the support plates lie in the vertical and horizontal planes. Enter the actual measurements on the measurement data record provided.

The thin steel wires and alignment devices can now be removed, as they are no longer required for further assembly of the condenser shell internals.

Move the internals temporarily housed in the spaces in the tube support plate sections into their correct positions, align and tack weld them in accordance with the plant-specific drawing. Assemble the central fishing and the bracing assemblies such as flat irons and tubes.

NOTE:The steam baffles and bracing units must not be tacked to the tube plates of the water boxes. This operation is not performed until all internals have been welded to one another.

Then align the various sections of the air extraction line, weld them together to form one unit and tack weld to the tube support plates.

During alignment, ensure that the air extraction openings are directed towards the bottom plate and that therefore the connection holes for the connecting piping systems are necessarily in the correct positions. Pass out and fit the pipe work to the connecting piping system through the connection holes. Assemble the shields for the cooler tube nests. Set down the shields on the flat iron supports, align and tack weld.

may only be tack-welded, commence welding of all the condenser shell internals, the welding sequence being of up most importance.

NOTE: The feed water heater platform must be mounted and welded in place prior to the assembly of the condensate drain sheets as there is only a gap of approximately 200 mm between the feed water heater platform and the air cooler sheet.

Then weld the vertical slot profile strips to the side walls and tube support plates.

During this procedure, welders should as far as possible work simultaneously.

When the condenser shell internals have been completely welded together, tack and weld the steam baffle plates, the bracing assemblies and the air extraction line and the connecting piping system at the front and rear tube plates. When all welding work has been concluded, remove all weld residue from the weld seams and weld zones in the entire condenser shell.

NOTE:To prevent welding warpage, all welds must be performed simultaneously from both sides using the back-step method. Vertical joints must be welded from top to bottom, i.e. from the upper edge of the tube support plate to the bottom plate.

ATTENTION:- THE PERTINENT WELDING PROCEDURE SPECIFICATION AND WELDING INSTRUCTIONS MUST BE OBSERVED WHEN WELDING.

1. Steam space (top view) 2. Tube support plate 3. Vertical slot profiles 4. Welding locations

NECK WELDING 137

1.3 WELD CONNECTIONS BETWEEN CONDENSER AND LOW PRESSURE TURBINE

NOTE :- The assembly welding instructions given herein are of a general nature.

Please see also the assembly plans, drawings and other instructions for the plant in question.

1.3.1 In any weld connection, the cooling of the locally heated material in the weld zone will, by laws of physics cause transverse and longitudinal contractions, these giving rise to stresses in the material.

In order to keep these stresses as low as possible, it is imperative that the weld is prepared as specified in the drawings. Before welding is commenced the semi-circular structural profiles must be bolted to the dome end walls.

1.3.2 WELDING THE CONDENSER TO THE LOW-PRESSURE TURBINE

After the condenser has been brought to operating weight and the spring supports have been adjusted to compensate for welding contraction, prepare for welding the

condenser to the low-pressure turbine.

Erect scaffolding inside the condenser in accordance with applicable accident prevention regulations to facilitate access to the weld locations. Then fit the

intermediate, corner and web plates (as called for) and prepare the weld edges. Tack these parts to the condenser dome with welds with a tack length of three times the plate thickness at intervals of 25 times the plate thickness.

Weld the joint using the back-step method from tack to tack (see Fig.1). When the base layer has been completed, make the following filler weld layers, each in a single pass, and reversing direction for each layer (see Fig.2). After welding, clean the weld zone using suitable tools.

ATTENTION:- THE PERTINENT WELDING PROCEDURE SPECIFICATION AND WELDING INSTRUCTIONS MUST BE OBSERVED WHEN WELDING.

CHAPTER - B6

REPAIR PROCEDURE FOR ARRESTING THE LEAKAGE OF