The Unsteady Static Frictional Behaviors Of Tensioner Rubber Material

Pipe laying by tensioner is a common standard industrial process for subsea pipeline installation.The dead weight of pipeline is sustained by static friction which is generated by contact between rubber blocks of tensioner and pipe out wall.So that the pipe line can be laying down into sea water with constant speed.The static frictional property of rubber-pipe contact system is of great importance for safety of tensioner.Therefore,it is necessary to investigate the static frictional behaviors of tensioner rubber material.In this paper,environmental conditions,normal load and tangential load were regarded as influence factors to the static frictional behaviors of rubber contact system.A series of experimental tests were carried out to identify their impact principles.The main study research are as follows.Firstly,three common environmental conditions had been concluded as dry condition,sea water lubricating condition and thin ice medium condition during pipe laying operation.Dry condition was seen as the fundamental condition,whereas the others were the extreme situations which should be avoided.The sea water lubricating condition could be divided into three parts due to the different relative locations of sea water medium,namely the central lubrication,the front part lubrication and the tail part lubrication.On the other hand,four identical models were set for the thin ice medium condition,the thin ice medium distributed at the whole contact area,the leading boundary,the front part and the tail part of contact.In addition,the forces analysis had been made for the rubber-pipe contact.Therefore,a series of contact models for tensioner pipe laying were established for the guide of experimental investigation.Secondly,a self-built frictional testing machine was set for experimental tests,and there types of rubber samples were manufactured in different cross link system.The frictional testing machine could simulate preliminary stage of pipe laying operation,where the pipe line was clamped and laying down into sea water with constant speed.Thirdly,the experimental investigations of static frictional behaviors of the three types of rubber were carried out to identify influences from loading conditions.The results indicated that normal load was the primary impact to level of static friction.The evolution of contact had been analyzed,as a consequence,two phenomena were observed which behaved in opposite influence to the maximum static friction.The fold phenomenon was verified that could improve the static friction,whereas the creep deformation accelerated separation between interfaces.The instability of coefficient of static friction was discussed and was pointed out depending on normal load.Fourthly,the experimental tests of rubber materials were carried out for sea water lubrication conditions.Obviously reduction(5%-35%)on the static friction were shown in results of tests.And the sequence of lubricating efficiency of different lubrication conditions was as follows: the central lubrication> the tail part lubrication> the front part lubrication.Their difference in efficiency of lubrication were discussed and conclude as a consequence that sea water lubricating medium formed at difference locations.Fifthly,the static frictional behaviors of rubber materials in low temperature conditions had been examined.The results showed that the level of static friction of contact system was restricted by thin ice medium more intensely than that in sea water lubrications.The sequence of reduction on the static friction was as follows: thin ice layer completely covering contact zone> the ice pellet at the tail part of contact> the ice pellet at the front part of contact> ice pellet at the leading boundary of contact.The sequence could be seen as a consequence that rubber contacted with thin ice medium in different positions with different scales.Moreover,the experimental temperature affected the level of the maximum static friction significantly.