Investigation on Different Tightening Sequences on Several Bolted Flange Types, Dimensions and Their Associated Gasket Types

In the last years, several projects have been performed on alternative tightening sequences in the US and in Japan. This work has led to the publication of documents introducing alternative tightening procedures as JIS B 2251:2008 / HPIS Z 103 TR (JAPAN) and the new revision of ASME PCC-1:2010. In this study, the required bolt torque is calculated according EN1591-1 [1] (EN standard for bolted flange calculation according to a given tightness class) to achieve a given tightness class for each investigated gasket (6 types) and flange type (CLASS/PN)/dimension (from 4″/DN100 to 16″/DN400). The calculated bolt torque is then applied using a hydraulic torque wrench following three tightening sequences based on Legacy cross-pattern of ASME PCC-1:2010, alternative pattern #1 of ASME PCC-1:2010 and HPIS Z 103 TR. The bolted flange connection is then pressurized with Helium. The load for each bolt is continuously monitored using strain gauges, through the bolt-up phase and during pressurization. The average obtained bolt load, the bolt load scatter, the evolution of bolt load versus passes and elapsed time are compared for all the tested configurations (tightening sequence/ bolted flange type & dimension/ gasket type). A “Quality factor” is defined enabling comparison between the tightening quality (according to several criteria) of the different investigated tightening sequences in the tested configurations.