Operation of radial blower without compensators in gas pipeline

[MartinLe]

The situation is this: At a current project, there's a pair of (parallel, redundant) radial blowers to raise the gas pressure for the downstream consumers (CHP, gas burner). All vibrating machinery should be isolated from the pipeline by compensators.

Now, the installed compensators leak. New, better (stainless steel vs. thin rubber) ones have been reordered but will take a few weeks. We need to commission other machinery that depends on the blowers. So the contractor suggested the following interim workaround: Weld pieces of pipe so that the blowers are connected without compensators, install the compensators in a few weeks when they arrive.

The problem is, everybody knows that machinery needs compensators, but nobody I've asked so far has seen a blower operate without. So no one knows for sure what the problems are, and how grave.

Here's my thoughts on possible risks:

The vibrations could damage welds
The vibrations could damage gaskets

I think both are unlikely. Nevertheless, here's the mitigation so far:

[ul]
[li] The blowers are equipped with variable frequency drives, ramp up will be done slowly to avoid startup-shakiness[/li]
[li] If there's massive vibration with the blowers running, we'll reconsider[/li]
[li] After the provisional pipeworks are done, and again after the compensators are installed, there will be a pressure test[/li]
[li] Further down the road, 10% of the welds will be X-rayed. I will make sure that many of those checks will cluster near the blowers[/li]
[li] I'm thinking about having someone check the gaskets of the flanged connections near the blowers with leak detection spray after every or every few operation days[/li]
[/ul]

My question is: Did I miss a risk that's not covered by the mitigation mentioned above?

Here's some more facts and considerations:

[ul]
[li] pipeline upstream and downstream is stainless steel with welded and flanged connections[/li]
[li] upstream and downstream, there's an arch after the compensator[/li]
[li] downstream, the pipe can move a few cm (not mounted to the wall or anything for 2m)[/li]
[li] upstream, the pipe is bolted to the floor shortly before the blowers[/li]
[li] We are talking relatively small radial blowers - 120Nm3/h @ 20mbar ΔP [/li]
[li] Max. pressure in the pipeline will be 40-50mbar over pressure [/li]
[li] The room this is happening in is Ex-Zone 1 or 2, all equipment (including the blowers) is Atex rated and there's a gas warning installed [/li]
[/ul]

 

[LittleInch]

Probably terminology, but can you explain a bit further what you mean by "radial gas blower" There are many different types and some would seem to be less prone to pulsation and vibration issues than others.

"compensator" can also mean different things to different people. Do you mean a pulsation damper which is attached to the machine outlet pipe and has some sort of bladder inside or do you mean a flexible coupling such that the mechanical vibrations of the machine don't transmit into the pipework?

Have these machines been balanced and aligned correctly?

What size and wt of stainless pipe are we looking at?

It seems mechanical vibration is your issue? - This could lead to reduction in fatigue life for pipe or welds.

For the initial duration it might be an option to mount the blowers on solid foundations and remove any flexible mountings, or it could make it worse - difficult to know without trying.

Do you have a picture?

I don't like the idea of running anything in hydrocarbon service without weld examination done first, not after. That should be non negotiable IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MartinLe]

radial gas blower - this device:

http://www.elektror.de/en/product/HRD1TFU_FUK

Compensator, or rather flexible coupling:

http://www.elektror.de/en/accessory?groupno=Kompensatoren&productno=HRD1TFU_FUK

(rubber hose with spiral steel wire, attached to pipe stubs with hose clamp)

Picture:

Pipes are DN65

For the initial duration it might be an option to mount the blowers on solid foundations and remove any flexible mountings, or it could make it worse - difficult to know without trying.
This is one of the things I'd like to know. We've also discussed loosening some screws where the suction pipes are bolted to the ground, so they have more leeway (IMO the pipes on the pressure side have plenty).
The logic beeing that if we allow the pipes a longer 'lever' (= more movement near blower at lower deflection angle near where they are fixed) the stress should be lower.

I don't like the idea of running anything in hydrocarbon service without weld examination done first, not after. That should be non negotiable IMHO.
You raise a good point. Standard procedure here seems to be to do weld inspections as part of the final tidying up package, often after commissioning. (Pressure tests come before commissioning).

 

[LittleInch]

This is really no more than a slightly jumped up hair dryer (750W), so I think you're overthinking this. I can't see why this should vibrate at all.

The flexible is probably a good idea to remove any vibration and also to remove any stress on the blower from pipe expansion, but could almost certainly function without it without any issue.

Just hard pipe it and get on with it. If the pipe starts vibrating, clamp it down to get rid of long unsupported lengths.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MartinLe]

Hopefully/probably you're right. I'll know more tomorrow when we start them.

 

[georgeverghese]

Dont see any auto remote operable emergency shutdown valves upstream or downstream of each radial blower. This is in flammable gas service. Also no check valve d/s each blower (or is this the wafer style device on the d/s side?). How will you auto stop ( from control room) and isolate this unit in case of a large gas leak in this room due to a failure of the flexible expansion bellows (regardless of whether this is made of some rubber or metal )?

 

[MartinLe]

the wafer style devices are the check valves.

There's no way to automatically isolate the room in ase of leak.
This is up to code here* (Germany) though newer installations get automatic shutoff valves. These are refurbishment works in an existing plant.

The (not many) risk assessments I've seen so far assumed no spontaeous failures in pipework. The room is calssified an explosion hazard zone because some equipment there needs anual service and then some (50l?) gas will escape.

Not trying to defend this, just pointing out the guidelines and codes etc. I work within.

* It's a wastewater plant. Where it a biogas plant, an automatic and a manual shutoff valve outside of an engine room (so the fire brigade can turn off the gas before entering) would be mandatory.

 

[LittleInch]

"I'll know more tomorrow when we start them. "

Now is tomorrow. Any vibration??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MartinLe]

Postponed by a day (other reasons). I'm on site again tomorrow and will know more.

 

[MartinLe]

Finally been on site. At least at low power, the vibrations (in the pressure pipe) are noticable but weak.