HI All,

I would like to ask some question..

1) Why do we need to do 2 processes (GTAW + SMAW) instead of one process?
    - Based on what I know that normally used two instead of one is to save the total of welding time when dealing with big pipe bore.

2) I heard that 3" and below only need one process (GTAW), why? Is it depending on the Thickness or NPS? (Any ASME Sec. Recommended?)

Dear Sir,
We would like to bring to your kind information that we have two crude oil tanks at Harega oil export terminal in Tabrouk.  We received inspection report of tank bottom of these tanks and found the recommendation that all of tank annular plate need to be replaced.
We have replaced all of the annular plates first time during year 1990. This will be the maintenance exercise of second times. In this connection we would like to get your expert opinion whether any special treatment is required for the shell plates or replace complete the first ring of shell plates due to that the area of carbon steel of shell plates connected with annular plates will be welded of the third times (one during contraction and the second during the previous maintenance and the third one will be during the in progress maintenance) 
Your earliest reply will be highly appreciated.
Best regards.