One of the methods of eliminating residual stress is by heat treatment i.e. stress relieving, done at about 650 ºC (1202 ºF) for about one hour or till the whole part reaches the temperature then air cooled in still air. This removes more than 90% of the internal stresses.
To increase resistance to brittle fracture or in another word increasing mechanical properties such as ductility, can be done in several methods in metallurgical stand point of view. One of them is by cold working, such as rolling etc., the reason for this is strain hardening where dislocation density increases with plastic deformation.
The point is, hydrotest will not allow material to undergo plastic deformation not even reach yield strength. And hydrotest is not involving high temp either, thus such strengthening mechanism or eliminating residual stress will not occur.
fyi and ref
ADW - Indonesia
May 31, 2009
Indirectly the material is cold drawn very slightly during hydrotest at high pressure (90% - 95%SMYS) and becomes stronger. It also follows that there is reduction in the residual stress.
SAVE TREES - THINK BEFORE YOU PRINT
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Shank Vagal
Sent: Sunday, May 31, 2009 1:36 PM
Subject: [MW:2286] Re: hydro test
This is a very unusual query; hydrotest is an integrity test. All other things - where did you get them from?
--- On Sun, 31/5/09, Ali Asghari <email@example.com> wrote:
can every body answer two follwing questions?
how hydro test increase the resistance to brittle fracture or failure by crack like flaw?do hydro test decrease residual stress?
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