Plant Piping Design

Manual Drafting Method

Piping Design Model Method

CADD Method

CADD Model Combined with Physical Scale Model

Piping Design Methods

Involves determination of detailed piping with the use of drawings

Process scheme transposed from flow diagrams onto Equipment Location Plan

Designer then produces detailed drawings in form of Piping Plans and Piping Sections called Piping Arrangement DrawingsDrawn to a scale of 3/8” = 1’0” (imperial) or

1:30 (metric)Isometrics are then developed from the

Arrangement Drawings

Manual Drafting Method

Plastic Scale ModelsLay out piping and valves directly on modelArrangement and isometric drawings

developed from modelscale of 3/8” = 1’0” (imperial) or 1:30 (metric)

AdvantagesAccurate and reliablePoints out costly interferences & construction

problemsProduces better plant layoutImproves communication between design

disciplines

Piping Design Model Method

Better indication of progress to managementReduces construction costs by eliminating

“ignorance contingencies” used by biddersAssists in the writing of better operation

manualsReduces amount of time spent training plant

operators

Speed up drawing function and enhance design function

Allows production of “intelligent” flow diagramReports line & instrumentation list and prelim

M.T.O.Reports inconsistencies in pipe sizing and

specs

Major strength: data storage and retrieval capability which allows massive amounts of design information to be available for checking and reporting

Plant Design Using CADD

Designer produces plant design using following steps:Set up section of plant as computer model in

isometricInsert foundations and structuresConstruct vessels and equipmentRoute piping between nozzlesAdd fittings, vales and instrumentsReport interferencesReport inconsistencies re: size, specs or spaceProduce double line plan or section viewsAutomatically produce isos incl. M.T.O.Link all sections of plant together

Combined to produce faster, more efficient and effective design with cleaner constructionEarly design – plastic modelPlastic model data fed into CADD database which:

Allows for interference checks to be madeAllows Structural load verification to indicate supports and

hangars and interface with stress analysis programsProvides easy access to drawings of each areaAids with MTOs and spec compatibility checking

CADD designs related back to physical modelCADD develops Isos, arrangement drawings, MTOs and

inventory lists for use during constructionPhysical model available during approvals, construction,

operator training and as basis for revision

CADD Model Combined with Physical Scale Model

Positive Pressure Head must be present at piping outlet Produced by pump, gravity, displacement or static head, suction

Friction loss Keep piping runs short as possible with few fittings

Viscosity (internal friction of fluid) Design piping and valving for minimum liquid hold-up during shut-down

Vents and drains Properly placed to allow filling and draining of vessels during testing and purging

Turbulence is required Avoid dead spots in piping and use bends of 5 pipe diameter

Control valves Commonly one pipe size smaller than line size

Points of sudden pressure drop causing “flashing” Provide sufficient N.P.S.H.

Vapour lock Slope the line or vent high point

Condensable vapours like steam piped to avoid liquid pocketing Special pipe materials

may be needed when transporting hazardous liquids

Flow Related Piping Design Factors

Economics Minimize length of lines and number of fittings Carefully consider design changes due to increasing

operation costs in facilitiesMaintenance

Adequate space must be provided for assembly, disassembly, adjustment and lubrication of equipment

Utility stations should be readily available Special lifting or rigging devices may be required Breakout flanges may be required to aid equipment removal

Vibration Air chambers may be required for quick valve opening &

closing Reciprocating equipment requires surge tanks or pulsation

bottles plus sufficient piping support

Non-Flow Related Piping Design Factors