Gents

I work for a company which is interested in purchasing GT on very short notice. to make the deadlines, they are considering some GT engine cores and generators which have been lying idle in storage for 18 months.

What sort of problems are we letting ourselves in for?
The obvious one is deformation due to inadequate support.

Any pointers will be appreciated

I should have added that they are large (>100MW) industrial type machines

Blouwa,

Provided everything were properly "mothballed" when they were taken out of service I would not be too worried.  Thus the key questions you need to ask are the following:
1) How were they stored, specifically with respect to the following:
a) Moisture - there has to be some measurement data else you should not trust this.  This is the thing that kills all equipment.  I have seen many generator rotors standing just at the point where the roof seems to leak the worst...  
b) Were they stored in a still operating power plant?  What was the level of vibration in the area.  If there were vibration, check generator copper dusting.
c) What happened to the oil - was it left in service or left to rot.  Taking a sample from the oil tank can tell you a lot of things about how the machine was stored.  

2) NDT before comeback
a) Not really a gas-turbine man, but on a steam turbine I would make sure I have done a proper UT evaluation - specifically on the blade roots.
b) On the generator I would do capacitance mapping to make sure that there isn't too much moisture.  You may want to do a hi-pot test as well - get your OEM advise on the level to do it - the older the machine the lower value.

3) You seem to be worried about shaft deformation - I don't believe this would be an issue if it was properly shut down the previous time.  To make sure get the machine on barring for a while and measure the run-out.  For run-up you may want to have alignment and balancing guys stand by.

Good luck with this one!

Have the generators been stored with the heaters on?  Or has the equipment, especially the generator been stored with de-humidifying equipment attached?

In short, what are the storage conditions of the equipment you are looking at?

rmw

Check the bearings! During stand still, the last drop of lubrciant will eventually be squeezed out of the contact area, allowing metal to metal contact. Be sure to pre-lubricate for before rolling the thing.
If the turbines where stored in vincinity of other vibrating equipment, you may have additional problems due to fretting.
And as already said, be sure to measure vibrations and shaft displacements (orbits) during trial runs.

Gents

Thank you for the feedback received so far. Unfortunately I have very little info at this stage, only the sales guys have spoken to us and of course listening to them, the equipment is still perfect.

"The engine cores and generators were left unassigned when ____ recently terminated a production joint venture with a renowned Japanese turbine manufacturer. Those cores could be fitted with SB burners, gears, and plant auxiliaries to perfectly match the application, leading to total engine ex works times of 12 months or less."

The only worrying bit of further info I have(which ties up with the moisture problem) is that the GT's are said to be in storage in Rotterdam Harbour...

We are based at Rotterdam harbor. Perhaps we can be of assistance?

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