Method to limit a creep of bolts and gaskets of bolted flanged connections

Abstract

A method to limit or exclude operational creep of the bolts and gaskets of Bolted Flanged Connections (BFCs) is disclosed. The method consists in the use of bolts and gaskets manufactured from the same Shape Memory Alloys (SMAs) having temperature intervals of reverse martensitic phase transformation close to operational temperatures of the BFCs. These bolts and gaskets of the BFCs are shape-memorized to the compression (bolts) and “swelling” (gaskets) during (1) the formation of stress-induced martensite under temperature of martensite state of the SMAs while bolt preload application, or (2) during the formation of stress-induced martensite while loading-unloading previously stretched bolts and previously compressed gaskets under temperature of martensite state resulting in residual bolt elongations and residual gasket contraction followed by bolt preload application. Constrained shape recovery of initial length of the bolts and initial thickness of the gaskets under operational temperatures of the BFCs is accompanying by appearance of reactive shape-recovering stresses having direction inverse to the direction of operational creep of the bolts and gaskets that limits or excludes their operational creep.

1 . A new sealing technology based on active intervention of bolts and gaskets of the Bolted Flanged Connections (BFCs) into technological processes of critical engineering structures by means of creep limitation or complete creep exclusion of bolts and gaskets. 
   
   
       2 . The new sealing technology according to  claim 1  wherein said creep limitation or complete creep exclusion of said bolts and gaskets results from bolt contraction and gasket “swelling” at operational temperature of said BFCs. 
   
   
       3 . A method to limit or exclude a creep of bolts and gaskets of the BFCs wherein bolts and gaskets are manufactured from the same SMAs having temperature intervals of reverse martensitic phase transformation close to operational temperatures of the BFCs. 
   
   
       4 . The method according to  claim 3  wherein said bolts and gaskets of said same SMAs are shape-memorized to the compression (bolts) and “swelling” (gaskets) during the bolt preload under temperature below than temperature of martensite state of the SMAs. 
   
   
       5 . The method according to  claim 3  wherein said bolts and gaskets of said same SMAs are shape-memorized in advance to said compression (bolts) and “swelling” (gaskets) when the bolts and gaskets, being previously stretched (bolts) and compressed (gaskets) under temperature below than temperature of martensite state of the SMAs, obtain some quantity of residual elongations and contractions after unloading. 
   
   
       6 . The new sealing technology and method according to  claims 1  and  3  wherein said bolts and gaskets manufactured from the same said SMAs and shape-memorized to said compression (bolts) and “swelling” (gaskets) display “negative creep” effect resulting from constrained recovery of initial length of said bolts and initial thickness of said gaskets followed by appearance of reactive shape-recovering stresses having direction inverse to the direction of operational creep of bolts and gaskets under said operational temperatures of the BFCs that are close to temperature intervals of reverse martensitic phase transformation of said SMAs from which said bolts and gaskets are manufactured.