On Oct 31, 2005, at 4:24 AM, RICK wrote:
> If you have a 300# system how much pressure can it take during
> hydrotest assuming all components in the system meets the 300# P-T
> rating under ambient temperature.
The question 'how much pressure can it take…' isn't really an
appropriate question. The hydrotest requirements are set by code, and a
properly designed system will have no trouble taking that pressure. If
you're trying to use a hydrotest prove something besides Code
compliance for the stated maximum allowable working pressure, that's a
non-starter.
Section VIII allows you to qualify a component for a particular service with a burst test, but only if there are no design rules for the component. You can't use the component for regular service afterward even if it didn't actually burst because there's no guarantee that the test didn't cause hidden damage, such as a weld crack that might compromise its strength.
In general a system designed for a particular pressure and temperature will have a burst pressure about 3x the pressure at which the primary stress is close to the Code allowable. The hooker is that most vessel failures don't involve bursting--the main structural cause over and above outright abuse (which I'll take to include corrosion caused by neglect) is fatigue or fracture. A properly located weld defect will cause rupture after relatively few cycles to yield, even when the high stress is localized. I learned this the hard way one evening when a vessel I was testing burst during a service test. The cause of the failure was a crack in a weld seam which split the vessel without warning at a stress level of about 3/4 yield. Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=Y5mGxAzG_yzS3xEGkOb4FE6A0GiPq3cHGcvB6NQqyldeYYJ11XyZBxtAI2fx3MCZV9grGChNKew3LQ">chrisw@skypoint.com</a> | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania1864)
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