Abstract: Analyzed here in the article are the reasons for the nonconformance of the percentage elongation of the hi-pressure boiler seamless steel pipe as made with the 3-roll Assel rotary rolling pipe mill.The percentage elongations of the specimens as taken from pipes with different inner spiral depths before and after straightening are compared.And applicable FEA software is used to analyze the percentage elongations of the specimens of the 12Cr1MoVG seamless steel pipes with inner spiral and without inner spiral which are under the same loading force.It is revealed via the analysis that one of the critical factors for the rather low or unqualified percentage elongation of the strip specimen of the steel pipe as rolled with the said Assel mill is the inner spiral thereof.Therefore it is suggested to adopt round bar specimen for the tensile test,when the sample has any inner spiral that is out of the requirement by applicable specification,and its thickness is up the requirement by applicable production specification.