SOLAS Pipefitting key terms

A formal written authorization that defines the scope, hazards, isolations and controls for a specific task before work starts, signed by the responsible issuer and accepted by the person doing the job.

A step-by-step breakdown of a task that identifies hazards at each stage and records the controls to be applied, completed with the crew before work begins.

A short pre-shift briefing where the supervisor covers the day's tasks, hazards, controls and any lessons learned, giving workers a chance to raise concerns.

The procedure of closing, blinding or disconnecting energy sources, then applying personal locks and tags so equipment cannot be re-energized or pressurized while work is in progress.

Opening a pipe, flange or fitting that has contained fluid, done only after isolation, depressurization, draining and verification that the line is empty and safe.

A specific authorization required for welding, cutting, grinding or any activity producing sparks or flame, listing fire watch, gas testing and area-clearing conditions.

A document confirming that an enclosed or confined space has been tested and found to contain breathable air with flammable and toxic gases below specified limits.

Entry into a space with limited access that is not designed for continuous occupancy, requiring gas testing, ventilation, a standby person and a rescue plan.

The International Convention for the Safety of Life at Sea, an IMO treaty that sets minimum safety standards for ship construction, equipment and operation, including piping for essential services.

A private body such as ABS, DNV or Lloyd's Register that publishes rules for hull, machinery and piping and issues certificates confirming a vessel meets those rules.

The International Maritime Organization, the United Nations agency that develops and adopts conventions such as SOLAS and MARPOL governing ship safety and pollution prevention.

The International Convention for the Prevention of Pollution from Ships, which controls discharges and imposes requirements on piping such as oily water separators and overboard connections.

A formal inspection by a classification society or flag state to verify a vessel and its systems, including piping, remain compliant with applicable rules and certificates.

A dimensionless size designation for pipe used in North America, where NPS 2 corresponds to approximately two inches outside diameter but is not the actual inside or outside diameter.

A designation such as Sch 40 or Sch 80 that indicates pipe wall thickness relative to nominal size; higher schedules mean thicker walls and higher pressure ratings for the same NPS.

The measured thickness of the pipe wall, often specified in millimetres or as a schedule, which determines pressure containment capability and weld preparation geometry.

A fitting with ends prepared for full-penetration welding to pipe, commonly supplied to ASME B16.9 dimensions in long-radius elbows, tees, reducers and caps.

A butt weld fitting that changes flow direction by 45 or 90 degrees, with a centreline radius of 1.5 times nominal pipe size for a long-radius pattern.

A fitting that reduces pipe size with a common centreline, used where flow conditions matter and the line remains on the same axis through the reduction.

A size-reduction fitting with one flat side, installed flat-side down in horizontal liquid lines to avoid trapping gas or flat-side up in vapour lines to avoid liquid pockets.

A class designation such as 150, 300 or 600 that sets the pressure and temperature limits a flange, valve or fitting may be used at, per standards like ASME B16.5.

A valve with a sliding gate that gives low resistance when fully open and is intended for on-off isolation, not throttling, because partial opening erodes the seat.

A valve with a plug and seat that forces flow to change direction, giving good throttling control at the cost of higher pressure drop than a gate valve.

A valve that permits flow in one direction only and closes automatically to prevent backflow, protecting pumps and preventing reverse rotation of equipment.

A mechanical device installed in piping to start, stop, regulate or prevent flow, selected by function, pressure rating, material and the fluid it handles.

A single-line or double-line pictorial drawing on three axes at 30 degrees that shows pipe routing, fittings, valves, coordinates and welds for a defined line.

An identifier on drawings and tags that encodes size, service, sequence and piping class, allowing a specific pipe run to be traced through drawings and records.

A schematic showing process equipment, piping, valves, instruments and control loops with symbols and tag numbers, used to understand system function rather than physical layout.

A list on a drawing or specification giving every component required for the work, with size, material, standard and quantity, used for requisitioning and checking.

A document that fixes the permitted materials, components, ratings and joining methods for a given service, so designers and fitters select consistent parts.

Any structure that carries pipe weight, controls movement or restrains vibration, including shoes, hangers, guides, anchors and spring supports.

A support containing a spring that carries pipe weight while allowing controlled vertical movement, used where thermal expansion would otherwise overload a rigid support.

A rigid restraint that fixes a point on a pipe against translation and rotation, dividing the line into expansion sections and directing movement to expansion loops or joints.

A deliberate offset or U-shape formed in a pipe run that absorbs thermal growth by flexing, reducing loads on anchors and connected equipment.

The increase in pipe length as temperature rises, calculated from length, temperature change and the material's coefficient of expansion, and accommodated by loops or joints.

A pressure test in which the system is filled with water and pressurized above design pressure to prove strength and tightness before service.

A pressure test using air or inert gas, permitted only where water testing is impractical and carried out under stricter controls because stored energy makes failure violent.

A controlled application of internal pressure to verify that a piping system or component is leak-tight and can safely contain its design pressure.

Inspection methods such as radiography, ultrasonic, magnetic particle, dye penetrant and visual testing that reveal defects without damaging the component.

Evaluation of a completed weld against acceptance criteria using visual examination and NDE, with results recorded and any repairs re-examined.

Evidence that an individual welder has passed tests for a given process, position and material, permitting that person to weld within the qualified range.

A written document that gives the qualified variables for a weld, including process, filler, current range, preheat and pass sequence, so production welds match tested conditions.

The process of aligning two flanges with the correct gasket, lubricated fasteners and controlled bolt tightening in a cross pattern to achieve a leak-tight seal.

A compressible sealing element placed between flange faces that deforms under bolt load to fill surface imperfections and prevent leakage of the contained fluid.

Preparing pipe ends to the required length and edge geometry by cutting and machining or grinding a bevel, so the joint can achieve full penetration.

Aligning and temporarily holding pipe and components to the correct gap, root opening, angle and dimension before welding, using clamps and tack welds.

A change of direction made by cutting pipe ends at an angle and welding them together, used where a standard fitting is unavailable or space is restricted.

A deck drain or discharge penetration through the shell or bulwark, subject to SOLAS and MARPOL requirements on non-return devices and pollution prevention.

A physical barrier inserted between flanges, or a spectacle plate, that positively isolates a section of piping from process fluid during maintenance or testing.

A prefabricated section of pipe with fittings and flanges assembled as a unit, fabricated off-line and then lifted into place for final connection.

A wrench that applies and indicates a set tightening torque, used on flange bolts and critical fasteners so joint loading matches the specification.

A device such as a laser, spirit level, plumb bob or flange alignment gauge used to check straightness, level, square and rotation before joints are made permanent.