Control of stress corrosion cracking growth by operational pressure control

Abstract

A method of reducing stress corrosion cracking in a member made of metal, such as a pipe, comprises applying a load to the member to prevent stress corrosion cracking.

1 . A process for treating a metal member comprising: 
 a) applying a series of cyclic loads to the member; and,    b) subsequently apply a static load to the member.    
     
     
         2 . The process as claimed in  claim 1  wherein from 1 to 1000 cyclic loads are applied at a stress level R of from 0.1-1 wherein 
       R=minimum stress/maximum stress for each cycle. 
     
     
         3 . The process as claimed in  claim 2  wherein the cyclic loads are applied at a strain rate of from 10− 3  per second to 10 −6  per second.  
     
     
         4 . The process as claimed in  claim 3  wherein the maximum stress per cyclic is from 5% higher than the daily operating stress to 130% of the design hoop stress of the metal.  
     
     
         5 . The process as claimed in  claim 2  wherein the static load is applied for 1 to 24 hours.  
     
     
         6 . The process as claimed in  claim 2  wherein the static load is applied at from 5% higher than the daily operating hoop stress to 130% of the design hoop stress of the metal.  
     
     
         7 . The process as claimed in  claim 1  wherein from 40 to 1000 cyclic loads are applied at a stress level R of from 0.1-1 and the static load is applied at from 5% higher than the daily operating hoop stress to 130% of the design hoop stress of the metal.  
     
     
         8 . The process as claimed in  claim 7  wherein the cyclic loads are applied at a stress level R of from 0.5-1.  
     
     
         9 . The process as claimed in  claim 7  wherein the static load is applied at from 5% higher than the daily operating hoop stress to 110% of the design hoop stress of the metal.  
     
     
         10 . The process as claimed in  claim 9  wherein the cyclic loads are applied at a stress level R of from 0.7-1.  
     
     
         11 . A process for treating a metal member comprising applying a sufficient series of cyclic loads to the member at a severity and frequency which, together with a subsequent a static load which is also applied to the member reduce stress corrosion cracking in metal.  
     
     
         12 . A metal member treated by the process of  claim 1 .  
     
     
         13 . A pipe treated by the process of  claim 1 .  
     
     
         14 . A metal member which has been treated by applying a sufficient series of cyclic loads to the member at a severity and frequency which, together with a subsequent a static load which is also applied to the member, reduces stress corrosion cracking in the metal member.  
     
     
         15 . The metal member as claimed in  claim 14  wherein the metal member has been treated by applying from 0 to 1000 cyclic loads at a stress level R of from 0.1-1 wherein 
       R=minimum stress/maximum stress for each cycle. 
     
     
         16 . The metal member as claimed in  claim 15  wherein the metal member has been treated by applying the cyclic loads at a strain rate of from 10 −3  per second to 10 −6  per second.  
     
     
         17 . The metal member as claimed in  claim 16  wherein the metal member has been treated by applying cyclic loads which have a maximum stress per cyclic from 5% higher than the daily operating stress to 130% of the design hoop stress of the metal member.  
     
     
         18 . The metal member as claimed in  claim 14  wherein the metal member has been treated by applying a static load for 1 to 24 hours.  
     
     
         19 . The metal member as claimed in  claim 18  wherein the metal member has been treated by applying the static load at from 5% higher than the daily operating stress to 130% of the design hoop stress of the metal member.  
     
     
         20 . The metal member as claimed in  claim 14  wherein the metal member is a pipe.  
     
     
         21 . A process for treating a metal member comprising applying a static load which is in the range of from 5% higher than the daily operating stress to 110% of the design hoop stress of the metal to the member for 1 to 24 hours.  
     
     
         22 . The process as claimed in  claim 21  wherein the static load is applied at from 5% higher than the daily operating hoop stress to the design hoop stress of the metal.