Vent hole for carbon steel lined pipes
Vent hole for carbon steel lined pipes
(OP)
Dear All,
According to the client specifications of Thermoplastic Line Pipes, The vent hole size for carbons steel Pipe shall not be more than 3.0 mm Max. Basically A vent in a lined pipeline system is a hole that is drilled through the steel pipe to allow passage of any permeated gases or liquids or to monitor pressure build-up in the liner annulus.
However there is no detailed information in case of vent hole size is more than the requirement i.e > 3.0 mm, If a vent hole size is 6.0 mm or more what will be the implications during operation / technical justification for a HDPE lined pipelines? Shall we proceed for lining for such spools / pipelines or bound to the specifications? Seeking experts suggestions in this regard. Thanks in Advance - RAM
According to the client specifications of Thermoplastic Line Pipes, The vent hole size for carbons steel Pipe shall not be more than 3.0 mm Max. Basically A vent in a lined pipeline system is a hole that is drilled through the steel pipe to allow passage of any permeated gases or liquids or to monitor pressure build-up in the liner annulus.
However there is no detailed information in case of vent hole size is more than the requirement i.e > 3.0 mm, If a vent hole size is 6.0 mm or more what will be the implications during operation / technical justification for a HDPE lined pipelines? Shall we proceed for lining for such spools / pipelines or bound to the specifications? Seeking experts suggestions in this regard. Thanks in Advance - RAM





RE: Vent hole for carbon steel lined pipes
My guess is that 3mm is just a cautious approach to the issue of potential shear action on a cylinder of PE100 at your vent point. In reality a much larger hole would probably be ok, but too big and the liner could, over time, extrude into the hole or shear a plug off. How big and what the impact would depends on the internal pressure, thickness of the PE liner (often quite low), temperature of the fluid and the long term creep strength. That's one of the things with PE that is quite different to steel is that over long periods of stress which are lower than the SMYS, the material creeps very slowly.
So you could make the vent bigger, but I struggle to see the advantage of doing it and having to do all that work instead of using what is probably a tried and tested vent size.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Vent hole for carbon steel lined pipes
Thank you for the information and i missed in my question to mention that the vent hole is drilled by Pipeline contractor where as our's is lining activity. Sometimes It happens due to oversight by them or not giving importance on requirements. Your technical justification is similar to my thoughts considering long term effects on liner. It's always good to have second opinion from experts like you..
RE: Vent hole for carbon steel lined pipes
Vent holes in process pipe are in fact usually left open to vent, or sometimes the vents are captured to a vent system. In some services the vents will constantly release a small but significant quantity of gases which permeate through the liner even when it is 100% intact. In services where the permeating gases are corrosive when they contact the moist atmosphere, a half coupling is welded to the pipe OD around each weep hole to permit capture of the permeate or to permit the use of a sacrificial nipple to prevent the pipe shell itself from being corroded by the permeate/atmospheric moisture mixture.
If the vent hole is too large, the plastic liner has to span the distance of the hole unsupported. If the pipe is under a significant internal pressure and especially if the temperature is elevated, the liner will eventually extrude into a weep hole which is too large in diameter and this can lead to a liner failure. If this were my piping system and you drilled the weep holes too large, I would reject your pipe and make you re-do it to my specification. If the P/T combination is very modest, perhaps you can get away with it- but then, why didn't they just use thermoplastic pipe? Why bother lining carbon steel?
RE: Vent hole for carbon steel lined pipes
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Vent hole for carbon steel lined pipes
Don't think it would be advisable to put a larger hole without the concurrence of the lined piping manufacturer.
When Vent Extensions are required, a 10mm high 1/4” BSPT internally threaded boss is welded to pipes pools. For moulded fittings the injection boss is drilled and tapped with an appropriate BSPT female thread. A 65mm long vent extension is then supplied to fit to this, to provide a standard 75mm vent extension.
RE: Vent hole for carbon steel lined pipes
RE: Vent hole for carbon steel lined pipes