can crack appear on valve body after pressure test?
can crack appear on valve body after pressure test?
(OP)
We have processed strict pressure test on a C.S ball valve with DN300,600#, during the test there's no leakage. While 6 months later on site customer find a crack with 20mm length. Believe us we did do all that need to do to prevent such thing, we wonder if the crack appear after pressure test? is it possible, do you have any similar experience? thanks for your help!





RE: can crack appear on valve body after pressure test?
RE: can crack appear on valve body after pressure test?
It is suspected that a minor defect in the casting at the crack location was quickly deteriorated due to particulates in the flow (the working fluid was raw water -strained but not heavily filtered).
I have pictures, but am on assignment at the moment and am unable to post them. Should have access to them again in a couple of weeks.
RE: can crack appear on valve body after pressure test?
RE: can crack appear on valve body after pressure test?
Compere to a crack in a car front window: an impact (stone or grit flying) can give an invisible, or almost invisible material damage, and because of internal stress and variation in stress (pressure and temperature) widen to be a crack across the complete window.
A crack in a valve body (or a ball) , without any other damage in the system, you wold strongly suspect to have started from some material imperfection and be widened from stress.
Metallurgic microscopic sample would probably be able to confirm the material fault.
A particular material imperfection may well have passed all previous inspections, even thorough different first-class types especially if they occur on 'non suspect' sections of the valve(cases seen personally).
RE: can crack appear on valve body after pressure test?
WCB is a fairly ductile matrial and as such, would be resistant to cracking. In the failure analysis, you should look at carbon content, verify proper heat treatment, and look for possible weld repair somewhere around the crack.
Also, there is a chance pipeline loads could have deformed the body and caused it to crack. Again, for a ductile material like WCB, when it is properly produced, would tend to yield and deform before cracking. But if the material is not processed correctly and is not ductile, it could crack if the valve body was used to jack mismatched pieces of piping together.
Other possible source of cracking is low temperature. If the material was not produced correctly (checmical composition, heat treament, and weld repair), the nil-ductility temperature could be up near ambient and the valve could crack when stressed. Doubt nil-ductility is the case, but should not be removed from the list of possible cuases until the inestigation data proves otherwise.
Best of luck in your root-cause analysis
RE: can crack appear on valve body after pressure test?
RE: can crack appear on valve body after pressure test?
Most of the cracks appear on 600# valve bodies, we seldom find cracks on valves with lower Class.
Obviously reqiurement for pressure test of API6D is higher than that of API598, but I wonder why? can any body help me?
RE: can crack appear on valve body after pressure test?
If you notice a pattern with similar leaks, you should conference with your foundryman and have him look at the sprues and risers in the pattern. It is entirely possible for the shrinking metal to tear as it begins to solidify, and skillful analysis of the pattern can correct this.
RE: can crack appear on valve body after pressure test?
We will check the root reason when the valve is sent back to us.