The monitoring of the operation and record keeping is of utmost importance to the effectiveness of any flushing operation. A dedicated log book for each flushed console should be maintained, and all entries should detail the condition of flushing screens and mode of operation. This log book can be extremely useful in determining the extent of the flushing operation and predicting the remaining flushing time. Samples of screens should be kept for review as the flushing procedure progress.
All unit piping should be flushed at high fluid velocities. This can be accomplished by operating both supply pumps, using a temporary high flow pump and/or installing temporary valves between each supply point and the drain header.
All critical equipment components (bearing, seals, etc.) should be initially bypassed unit supply piping is deemed to be clean.
One note concerning gaskets, those which are frequently used in flushing, particularly in remote operations, are not as specified and can deteriorate, thus leading to additional debris loading.
During the flushing operation, the use of mechanical vibration on piping to break debris loose at flange connections and/or any means of introducing turbulence into the pipe will significantly reduce flushing time. One specific means that has been found to significantly reduce flushing time has been the introduction of clean air or nitrogen into the system during flushing. This makes the system extremely turbulent and gives a scouring action that rapidly cleans all pipes. Care should be taken to only bubble downstream of the filters and only when the bearings are bypassed.
Filter cartridge assembly
Extreme care must be exercised when assembling filters to preclude the possibility of bypassing unfiltered oil. This action can significantly extend flushing time and result in the acceptance of a system that exposes the critical equipment to significant damage. After every filter cartridge change, the following checks should be made:
The final check of flushing acceptability is performed by using screens, usually 100-mesh or finer depending on the system. It is important to be sure that screens are not incorporated into the system until the system is deemed to be reasonably clean.
Initially 60-mesh or greater should be used. If this practice is not followed, screens can break, thereby causing long-term problems with the system. Anytime that 100-mesh screens are used, they should be backed by 60-mesh screens as a minimum to minimize the possibility of breakage.
The acceptance criteria should be based on a practical approach. Final acceptance should take into consideration that the drain side of most auxiliary systems is unpressurized and is vented to atmosphere. As a result, a small amount of debris can and will enter the system and will always be present. Once a consistent low debris load void of any hard, metallic particles is achieved, the drain side should be considered to be clean.
The supply side must be consistently free of all hard particles and debris. 100-mesh screens should be installed at each system final supply point to the equipment (note that all jumpers are removed at this point). A typical limit for soft (non-metallic) particles is 20 for a 2” schedule pipe.
The acceptance criteria should be mutually agreed by the vendor and the user in advance of issuing the flushing procedure. Note that metallic particles are not acceptable in any location during final flushing acceptance. Since many systems today utilize stainless steel piping and components, the use of a magnet does not conclusively prove the absence of metallic particles since stainless steel is non-magnetic.
Once the system is accepted, all screens should be moved. It is recommended that the system be kept running until critical equipment startup. Shutting down the system at this point will only expose it to the possibility of additional debris loads from the environment.
When one considers that this operation is the last significant pre-commissioning operation prior to the commissioning of new equipment, the tendency to rush and perform less than adequate flushing operations is surprising. It is strongly recommended that anticipated flushing times for each system are discussed frankly with management as early as possible in the project to ensure a clean auxiliary system.
The importance of effective flushing is essential to the final reliability of critical equipment. Therefore, the flushing procedure and acceptance thereof should be number one agenda item in the field pre-commissioning operation. User-contract or concurrence of this procedure should be obtained as soon as possible when commencing field construction. Once the procedure is accepted, supervisory means should be established to accurately monitor and implement this procedure.
A well thought-out flushing procedure, supplemented by equipment specifics, and performed by a dedicated crew of experienced individuals, will result in accurate, effective flushing operations that are accomplished in approximately two to three weeks. Any misconception that a flushing operation can be accomplished in a shorter time is exactly that – a misconception. The effective flushing of equipment will go a long way towards long term, reliable operation of critical equipment.
Photo Credit: FourQuest Energy