Help needed for a Hydro-Test
Help needed for a Hydro-Test
(OP)
I am "trying" to Hydro a 42" Pipe spool with 600# Flanges. We are now on our third set of gaskets and our second set of Blind Flanges.
We have been able to achieve a pressure of between 1500 and 1800lbs before it springs a leak at the joint.
Does anyone have any tips on Hydro-testing large bore spools.
I have to admit I have very little experiance of this size.
Thanks
We have been able to achieve a pressure of between 1500 and 1800lbs before it springs a leak at the joint.
Does anyone have any tips on Hydro-testing large bore spools.
I have to admit I have very little experiance of this size.
Thanks





RE: Help needed for a Hydro-Test
David
RE: Help needed for a Hydro-Test
Thanks
RE: Help needed for a Hydro-Test
Just to verify - the blind flange is one which has bolt holes in it - not a slip blind which gets sandwiched between two flanges, right?
jt
RE: Help needed for a Hydro-Test
RE: Help needed for a Hydro-Test
RE: Help needed for a Hydro-Test
Check the bolting. Spiral wound gaskets usually require high strength ASTM A193 Gr B7 alloy steel stud bolts. Ordinary steel A307 Gr B machine bolts could yield before the spiral wound gaskets are seated, or hydrotest forces could cause yielding of bolts.
You mention the spool is 42". What is the flange standard that is used for the dimensions? What is the thickness of the flange? Thickness of the blind flange? Number and dia of bolts? These could be 2.5" dia bolts, and how are bolts being torqued? Are these flanges weld neck or slip-on type? (ASME B16.5 has dimensions up to 24", so we need to know flange joint design)
Check that the gasket spiral winding area is comnpatible with the flange face dimensions. Some spiral wound gasket designs include an inner compression ring along with outer compression ring to prevent spiral winding inner bulging failure during compression by flanges. Use gasket vendor's torque specifications, torque by 2 or 3 stages usng crossing pattern on bolt circle to reach the final torque.
Check gasket sealing surfaces for flatness and the machined finish (usually 125-250 rms spiral pattern serrations). The welding heat could distort slip-on flanges so that flatness of sealing face is 'cupped'. Total flatness over the 42" dia must be limited to 0.020" or less? Mis-handling could damage the serrated finish and leave a groove or scratch across face for a leak path.
RE: Help needed for a Hydro-Test
... and (as queried above) which standard is the thickness determined by? Or have you run hand calc's to determine the required thickness?
Guess what I'm suspecting at the moment is that the temporary blind flange may be bending enough under pressure to both rotate the flange as well as scuff the gasket radially as it "sucks in" the perimeter as the center bulges out. Although restrained by the bolt holes, there will be some play between the holes and the studs. I suffered from this effect with some specialized testing I was overseeing a few years ago. Especially if you have several uses for a flange, I'd consider using a regular flange mated to a 2:1 SE head. Might be more expensive up front but less likely to see the problems a flat blind will when sealing.
jt
RE: Help needed for a Hydro-Test
Is this a machined raised face blind or a flat plate blind?
You can rent a proper blind from either one of the following companies.
http://
http://www.twincoindustrial.com/flanges.html
RE: Help needed for a Hydro-Test
The blind is a rented RF Blind.
We are using ASTM A193 Gr B7 bolts.
Thanks
RE: Help needed for a Hydro-Test
How are you torquing the studs?
Are you using the proper torquing pattern?
RE: Help needed for a Hydro-Test
Regards,
Bill
RE: Help needed for a Hydro-Test
The original Blinds had slight scratches on the face. We are torquing to 5000ft/lb.
RE: Help needed for a Hydro-Test
My tables give:
dry .223 15,331 ft lbs
lub .167 11,481 ft lbs
These values give a clamp load of 330,000 lbs.
RE: Help needed for a Hydro-Test
The torque values given are essentially the maximum usable values based on 95% of yield strength. You can calculate the needed values for your test which will be less that what I posted or you can use these values to give the maximum available clamp load.
Watch your friction factor on these studs.
RE: Help needed for a Hydro-Test
What you can do, not sure if it has been suggested, is apply a gasket sealant to both surfaces prior to bolting it up. This will help to remove micro leak paths.
Also, leaks are highly dependant on exactly how you torque the fasteners. It is best to use the star pattern approach after the nuts are put on hand tight. My practice is to put minor pressure to the assembly, say 150 psi, remove or neutalize the system and then redo the torque following a different star pattern along the perimeter of the flange. Nuts do back off under pressure and I would expect this to be a factor with your spool.
Also, rent a torque machine to get uniform compression of the blind on the RFWN RF of the spool.
Good luck with it.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada