CORRECTIVE ACTION

Out of 888 welds 340 welds are clear in all aspects.

Radiographs of balance welds were examined jointly by site,

NTPC-CQA and BHEL-Tiruchy and all defects like porosity,

root mis-match, incomplete penetration and uneven surface

etc. which are not permissible as per codes were repaired.

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PREVENTIVE ACTION

For further projects like BELLARY, SIPAT etc.

Even though procedure had been qualified without backing gas

(purging), to achieve uniform smooth root weld, it was decided to

retain backing gas in future application also.

Welding Technology Centre, Trichy had been requested to

qualify a procedure using RT 21/4 Cr 1Mo filler wire for root

welding in the case of T91 welds and subsequent run by RT

9Cr1Mo filler wire i.e. matching filler wire of T91. Strength portion

also to be acceptable to Engineering.

If existing filler wire of T91 i.e. matching combination (9Cr1Mo) is

to be continued then,

Method of purging to be re-looked

Argon being heavier gas, if the entry is from bottom in a 2G

weld, it will ensure that the atmospheric air is completely

purged out through the root gap before starting welding &

welding can be continued with argon backing.

Argon entry can be at erection welds between RH front and

RH rear coils- i.e. 6 circuits above the roof (in pent house)

and 6 circuits below the roof.

This will ensure argon entry is from bottom in a 2G weld

and purging of air can be better in this case.

Trials can be conducted before starting the actual job.

Even though this is not maintenance friendly, this will definitely

improve the situation.

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� More number of welds simulating the actual weld condition are

to be test welded before qualifying the welder.

� 100% RT will be done till the welder performance is established

and consistently right quality welds are achieved.

� Location of weld is to be suitably modified for getting

consistently sound weld.

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