BoQ Contingency rules

This is a very good question and one that does (or should) come up on every project. We at Fluor use to refer to this as the "Bump" quantities.
The "Bump" quantity philosophy was an item we discussed with the Client early in the project and made it a part of our overall procurement planning. Remember it not only effects Piping Material but most other bulk materials also.

Things that you and the Client need to consider include:
- Job Site location
- Item source location(s)
- Material Type (common vs high cost alloy)
- Are these Construction spares or Operational Spares?
- Frequency of use or consumption (Example: Gaskets)
- Logistics & Time for replacement
- Actual quantity required vs spare
- Logic of spares for each item
- Type of warehouse Space (Secure vs open storage)
- Cost of warehouse space
- Method & Cost of inventory control

I am sure that others can add other issues worth consideration.