YQA Mission Critical Fuel System Design

11.01 What are the requirements for mission critical fuel system design?

The requirements of mission critical design is that failure of a single component is monitored by the fuel system, and the system responds with a redundant component to perform the required function. In short, the requirement is 2 of everything with the ability to monitor and switch.

In some instances, designers will use a single fuel supply and fuel return piping system aboveground to generators. The thinking is that welded steel aboveground pipe does not have a relevant failure mechanism. However many designers will provide dual parallel piping paths.

Underground piping systems, we believe should always have redundant parallel paths. The reason is that underground piping is continually subject to ground and surface loads, and that secondary containment test failure, whether real or a false positive, can triggure a shutdown of the piping system as a regulatory requirement.

11.02 Why are typical problems for fuel systems?

There are many problems with fuel systems that are based on the initial design of the system. Once a well designed system is commissioned, with any installation errors corrected, they operate as highly reliable systems.

Some of the typical post-commissioning problems for fuel systems are:

  • (a) pump or valve activation failure from loose wiring
  • (b) loss of prime in suction pump piping system
  • (c) leak in piping systems, sometimes due to overstress from thermal expansion
  • (d) solenoid valve leakage from seating surface debris or deterioration.
  • (e) failure of elements in relays or point sensing elements
  • (f) solenoid valve electrical failure
  • (g) submersible pump capacitor failure
  • (h) failures from line leak detection systems
11.03 What is fuel system commissioning?

Fuel system commissioning is a method of proving fuel system performance and accuracy, particularly in the event of failure of system components. The interaction of the fuel system with other building systems, such as building management systems is also demonstrated.

The first step in the process is development of a commissioning script document. This is a step by step procedure for testing that can range up to several hundred steps. The document is typically prepared in draft by the fuel system specialist, with review and approval by the design engineer and commissioning agent.

The commissioning procedure is typically performed by the fuel system supplier and installer, and observed by the commissioning agent and / or facility personnel.

11.04 What inspections and tests are required to assure ongoing reliability?

Fuel system inspections and tests can be summarized as follows:

  • daily inspection of the fuel system for leaks and observation of the control and monitoring system for alarm conditions.
  • Monthly or annual testing of secondary containment leak detection systems as required for state and local regulatory compliance
  • Annual, or more frequent testing, in accordance with the original commissioning script.

It is recommended that the systems be designed to facility ongoing testing. These details include:

  • pressure and vacuum gauges on piping system
  • day tank return flow pumps to lower tank levels and test refill
  • position indicators for actuated valves
  • quick disconnect wiring connectors for valves and sensors

In some instances, an automatic commissioning function is designed into the fuel system