Martensitic stainless steel welded pipe

A martensitic stainless steel welded pipe which comprises a base metal which is a stainless steel containing, on the mass % basis, not more than 0.05% of C and 9-20% of Cr and having a metallurgical microstructure comprising a full martensite phase or a martensite phase as the main constituent with a ferrite phase contained therein, and a seam weld metal which is a stainless steel containing, on the mass % basis, not more than 0.1% of C and 7-20% of Cr and having a metallurgical microstructure comprising a martensite phase as the main constituent with an austenite phase contained therein, a seam weld bead on the inside surface satisfying the following relation (1):

• L≦0.2×W (1)
• where
• L:
• the length of the portions of the seam weld bead which show a value of h exceeding 1.25 as calculated by the expression (2) shown below:
• h={1+(2×H/W)}×(YSB100/YSw100) (2)
• where
• H:
• the height of the bead from the pipe inside surface (mm),
• W:
• the width of the bead (mm),
• YSB100:
• the yield strength of the base metal at 100° C. (MPa),
• YSw100:
• the yield strength of the weld metal at 100° C. (MPa).