First off I don't know anything about oil analyis but I have a question.
My company takes oil samples from transformers on a yearly basis, but sometimes these collected samples may sit around for weeks or months before they are sent in for analysis. Does this hurt the sample?

Doble is one of the leaders in transformer oil analysis and they tell you not to let your transformer samples sit around any longer than necessary.

I'm not sure of the exact reason why they say that, but I have a few guesses. One thing is that the dissolved gas may separate. It should not be a problem if the container is airtight, but I suspect there is some loss, particularly of hydrogen which is a very small molecule that diffuses easily.

I have also heard that the oil undergoes some kind of slow decomposition of the hydrocarbon chains when exposed to sunlight, causing increase of certain gases, so those sample containers should be opaque

Ditto on pete's comments...

Why not just send it off after it is collected?

Transformers are typically critical pieces of equipment; they justify the extra diligence.

I would say if the samples are sitting around that long are they really relied upon. Sounds like oil analysis isn't taken seriously - just going thru the motions??

Paul,

There is a tier or sequence to be followed when sampling oil. I believe this sequence is not followed for off site laboratory or when you will send you sample to the laboratory. Your oil sample will fall in line with the rest of the samples that are ahead from you. Kindly take note that you are not their only customer.

To my knowledge the most sensitive test will be that of particulate contamination and water. If you are testing your transformer oil for moisture content. Then this must be prioritize in the sampling to get an accurate moisture content in ppm.

My Warm Regards,