Piping

Piping covers the pipes, fittings, valves and supports that convey water, air, oxygen and sludge through the facility. It is the physical realisation of the hydraulic design, and it determines how much of that design survives contact with the building.

• Pipe diameter sets friction loss, and friction loss is paid in pumping energy every hour for the life of the plant.
• Joints are the usual location of leaks, and a leak in a recirculating loop is a loss of water, of head and sometimes of level protection.
• Valve position and type determine whether a section can be isolated for maintenance without draining the system.
• Material selection determines service life in a wet, saline, ozonated or chemically treated environment.
• Layout determines whether pipes can be inspected, cleaned and replaced, or whether they are buried behind equipment.

The isolation principle is that every item requiring maintenance should be removable without draining the loop or interrupting life support to the fish. That means isolation valves either side of pumps, filters, heat exchangers and instruments, and it means deciding this at design because retrofitting a valve requires the shutdown it was meant to avoid.

• Size for velocity, not for the fitting that happens to be on the pump. Excessive velocity produces friction loss, noise and erosion; very low velocity allows solids to settle in the line.
• Minimise fittings. Every bend, tee and reducer adds loss, and long-radius bends cost less head than sharp ones.
• Design gravity lines with continuous fall and no local high points, since a high point collects air and throttles the line.
• Provide air release at unavoidable high points and drain points at low points.
• Support pipework properly. Unsupported plastic sags with temperature and time, creating low points and stress at joints.
• Allow for thermal expansion, particularly in long plastic runs and where water or air temperature varies.
• Keep solids-bearing lines short, straight and steep, and give them rodding or flushing access.
• Label every line and valve, so isolation during an incident does not depend on tracing pipes.

• Route pipework where it can be reached, inspected and replaced, rather than where it is tidiest.
• Keep pipe runs short by placing the plant room close to the tanks it serves.
• Separate clean and dirty lines physically, and never cross-connect them, so that a valve error cannot route sludge into culture water.
• Provide sampling points where water quality actually needs to be measured.
• Provide spool pieces or removable sections at equipment, so a unit can be lifted out without cutting pipe.
• Consider oxygen service separately, since oxygen lines require compatible materials, cleanliness and dedicated fittings.
• Design for the flushing and cleaning regime the lines will need, rather than assuming they stay clean.
• Record the as-built layout with line sizes, materials and valve numbers.

• Exercise valves periodically, since a valve never operated is frequently seized when it is finally needed.
• Flush solids-bearing lines on schedule rather than when they block.
• Watch for rising pump power at falling flow, which indicates progressive fouling or partial blockage in the pipework.
• Inspect joints and supports for movement, weeping and stress marks.
• Keep the valve schedule and line labelling current when anything changes.
• Hold spares for the fittings and valve types actually installed, since a failure at night is repaired with what is on site.

• Inspect joints, flanges and supports on a schedule, looking for movement and weeping before failure.
• Exercise and lubricate valves, and record which ones were found stiff.
• Flush and rod solids-bearing lines before they restrict.
• Check air release and vacuum breaker devices, which fail silently.
• Inspect any pipework exposed to sunlight for ultraviolet degradation.
• Update the as-built drawing and valve schedule after every modification.

• Sizing pipework down to save capital and paying the friction in energy indefinitely.
• Using the pump's connection size as the pipe size for the whole run.
• Omitting isolation valves, so any maintenance requires draining the loop.
• Creating high points with no air release, then treating the resulting flow loss as a pump problem.
• Leaving flexible hose in place as permanent process pipework.
• Using sharp elbows throughout where long-radius bends were available.
• Failing to label lines and valves, so isolation during an incident depends on guesswork.
• Cross-connecting clean and waste lines for convenience.

Surge and water hammer deserve attention wherever a valve can close quickly or a pump can stop suddenly on a long line. The pressure transient can exceed the steady operating pressure substantially, and it acts on joints and fittings rather than on the pipe wall. Slow-acting valves, soft starting and stopping, and surge protection where the geometry warrants it are the usual responses.

Biofouling inside pipework is a slow, cumulative process that reduces effective diameter and raises head continuously. It is one of the reasons pump power trended against flow is such a useful maintenance indicator: the pipework degrades before anything visible happens, and the energy record shows it first.

Pipework converts hydraulic design into a working plant. Size generously because friction is a permanent cost, select materials against the actual service, provide isolation so maintenance does not require a shutdown, avoid high points without vents, support the pipe rather than the joints, and label everything. Most failures are workmanship and access, not material.