The penstock pipe for the hydroelectric power plant is 2400mm in diameter and the thicness varies from 12mm to 30mm, total head ise 288mt. The pipe material was selected as St-52 (S355JR). As we had hard time to find the 26 and 30mm thickness pipe in the local market. We decide to switch to API 5L X70 for those sections and the thickness dropped to 20 and 22mm.

Now at some point we will have to weld the St-52 pipe to API 5L X70 pipe. Will there be any consequences of welding different materials? Is there a suitable electrode in the market for such application. What would you recommend from practise?

St-52 Chemical Analysis is;
C  (max)% 0,27
Mn (max)% 1,70
P  (max)% 0,045
S  (max)% 0,045

X70 Chemical Analysis is;
C  (max)% 0,22 (0,12 According to Local Steel Manuf.)
Mn (max)% 1,65 (2,00 According to Local Steel Manuf.)
P  (max)% 0,025 (0,020 According to Local Steel Manuf.)
S  (max)% 0,015 (0,010 According to Local Steel Manuf.)

Regards,

No. You will need to select a filler metal capable of meeting the yield strength of the lesser strength material. You will need to preheat at 200F min for the thicker sections. I would suggest welding with a filler metal similar to E8018-C3.