Abstract: After canceling telescopic joint of penstock in the hydropower station at dam toe, the closure weld has two types including butt joint and lapped joint, two joint types are studied by experiment, the results showed that this two joint types have their characteristics respectively, butt weld has more advantages than lapped joint, adopting some technology methods, constraint stress by welding can be reduced and cracks can be prevented, it’s evident that penstock can run safely using butt weld.

Key words: Constraint stress, Butt joint, Closure weld, Lapped joint