Bladder surge vessel- Freezing concern

[waterpipe]

For a water pipeline, The designer has proposed bladder surge vessels (5000 and 40000 liter each) for water hammer mitigation. He has also proposed a "standby" vessel. The vessels are outdoor with ambient temp of -10C while the water temp is specified 15C.

In my opinion, the water inside the connection piping and valves (from vessels to the main line)will ultimately become equal to the amb. temp. and so I am concern about freezing. Knowing that water freezing point is not changing with pressure and that there should not be a flow circulation in a surge vessel system, I am going to question the design.

Tips are needed here:
1- Am I thinking right?
2- Any experience with bladder type vessels especially with a large volume?
3- I am concern about the performance of the butyl rubber bladder under cold or freezing weather. any idea?
4- And finally, is there any need to have a "standby" surge vessel?

 

[BigInch]

If there is danger of freezing, the design could be questioned, if adequate provisions have not been otherwise taken in the design itself, or perhaps in the operating procedures, to prevent risk. Such as, The water entering the vessel would have to be drained within the freeze time.

The 15 deg water might be circulated around/near or incontact the vessel, rather than through.

The freezing vessle problem could also potentially be avoided by operational procedures, safety instrumentation, and a temperature alarm for water reaching 2C or so where an alarm would sound and/or an automatic discharge valve would open, for one example.

I would expect to see an operating procedure that required the surge vessel to be drained within some reasonable time, definately before another surge was expected, or I would expect to see a vessel with a volume large enough to accept all surges that could happen within the time needed to drain it.


You wouldn't normally need a standby surge vessel, unless there is a high likelyhood of the first vessel being out of service, due to maintenance, due to freezing(?), or some other condition present when another surge is experienced, or if two surges might be expected, before the first could be drained off within a reasonable amount of time.

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[waterpipe]

Thank you BigInch. You confirmed that the freezing issue should be seen and proper preventive measures should be taken.
Since I haven't seen any mention about this in the design and also there's no operating procedure (that I'm aware); I am going to check this and raise the issue.

The concern regarding the performance of the rubber bladder under cold temperature (0 to -10C) is still open for discussion. Any experience with bladder surge vessels?

 

[micalbrch]

-10 °C is not problem for a butyl rubber bladder.

I guess the surge vessel is installed on a T-piece. If so, the (nitrogen) charging pressure will press out the water when the system is stopped. The bladder will then fill the entire vessel.

The only reason for a stand-by vessel is a failure of the bladder in the first vessel. Make sure that the vessels you get have a bladder which can be exchanged. There are bladder vessels available which must be changed completely when the bladder fails.

 

[waterpipe]

Thank you for the tip. Bladders are mentioned to be changeable in the spec.
Just a point: bladders are air-filled not nitrogen. Any preference?

 

[micalbrch]

Usually nitogen filled as the oxygen in the air can pass through the bladder over a longer period. And that leads to a loss of charging pressure. I do not fully recall the reason for that but it has something the do with the molecule properties of oxygen and nitrogen under higher pressure. But have a look in the vessel's operating instructions. It is fore sure mentioned what gas shall be used.

 

[stanier]

Have you considered an alternative to bladder vessels to mitigate surge? I have been using flywheels on pumps to overcome the surge in pipelines in recent years.

They do not freeze, very reliable, require little maintenance, do not need spares and do not take up much additional space.

 

[chief]

You can insulate and heat trace your surge accumulator.

Offshore Engineering&Design