Testing and Inspection
Fire Sprinklers

What are the testing and inspection requirements?

NFPA 25 requires that each fire sprinkler system be visually inspected each year to verify that it appears to be in good operating condition and free of physical damage.  Water flow must also be conducted annually to verify water supply and to check for proper operation of alarm devices.  Electronic interfaces such as water flow and tamper switches are required to be tested semi-annually.  There are many items that have special requirements such as testing dry pendent sprinklers, high temperature sprinklers, interior inspections of valves and piping and recalibration or replacement of gauges.  Pre-action, Dry and Deluge sprinkler systems also have special testing and inspection requirements that extend past annual tests.
Internal Obstructions

It may look fine on the outside, but what about the inside?

NFPA 25 requires that each fire sprinkler system (with steel piping) be internally inspected to verify that piping, valves and sprinklers are free of internal obstructions.  This internal inspection is required every 5 years.  There are many conditions however, when present, would require an internal inspection be conducted immediately.  Below is a list of conditions, or early warning signs, which may indicate you have an obstruction issue.
     1. Seeing debris or heavy discoloration during routine main drain tests or hydrant tests.
     2. Finding debris inside Dry pipe valves, pre-action valves, check valves, pumps, etc during maintenance.
     3. Inspectors test connections being plugged with debris.
     4. Plugged sprinklers.
     5. Finding plugged piping during an alteration.
     6. Underground piping not flushed prior to new service.
     7. History of broken water mains in the area.
     8. Returning a system to service after long periods of not in service.
     9. Multiple pin-hole leaks.  
     10. 50% decrease or more in a dry pipe systems trip test.

Microbiologically Influenced Corrosion

MIC is corrosion caused by the presence of micro-organisms in the water supply. In steel pipe, MIC usually manifests itself in pin-hole leaks in the bottom of pipe. The interior often has deposits on the bottom of the piping. This is typically a function of the quality of the water supply as opposed to the quality of the piping or type of system however all have a factor in the process.
Nitrogen generators and MIC monitoring stations have come onto the market in the last few years to help reduce the effect of MIC in Dry pipe systems and Pre-action sprinkler systems.  MIC monitoring stations provide an accessible and efficient point in which presence of MIC can be detected. 
Here is a link to a very good article for more information.  
MIC PAPER Download