If you have purchased one of our samples with a K number on the side we will honour these for many years, so its not like a voucher you have to spent in 1 year etc. In terms of sample validity most oil samples don’t have an expiry once taken, although if you hold onto them for a long time before sending the data is less current and valid. A couple exceptions are dissolved gases in transformers should be sent within 1 week and microbial testing equally should be done as soon as possible. Most other tests are fairly stable.