Buried Piping: M.Vijay Gopal
Buried Piping: M.Vijay Gopal
Buried Piping: M.Vijay Gopal
BY
M.VIJAY GOPAL
WHAT IS THE NEED FOR BURIED PIPING?
SAFETY CONSIDERATIONS
TO PREVENT VANDALISM (DAMAGE OR DESTRUCTION)
TO PREVENT FREEZING OF WATER IN SUB-EXTREME CONDITIONS IF RUN
ABOVE GROUND.
TO CARRY HAZARDOUS CHEMICALS.
SAFE FROM UNWANTED THEFT (IN CASE OF CROSS-COUNTRY PIPING).
TO PREVENT VEHICULAR AND HUMAN INTERRUPTIONS.
TO ELIMINATE TRAFFIC BARRIERS
WHEN TO USE BURIED PIPES AND WHEN TO USE PIPES
IN TRENCHES?
BURIED PIPES -
SUCH LINES SHOULD NOT BE RUN UNDER PROCESS AND SERVICE AREAS
SHOULD BE LAID IN DUCTS OR SOLIDLY ENCASED IN CONCRETE.
SHOULD NOT BE USED UNDER ROADS AND OTHER CONCRETED AREAS.
WHERE VALVES, METERS AND SIMILAR FITTINGS ARE USED ON BURIED PIPING, THEY
SHOULD BE HOISED IN A SUITABLE BRICK OR CONCRETE CHAMBER WITH PROPER
ACCESS TO THE SURFACE.
BURIED GAS PIPING SHOULD NOT BE LAID IN PLASTIC MATERIAL OR LAID ADJACENT
TO POTABLE WATER PIPING OR PLASTIC OR ASBESTOS MATERIALS.
WHERE BURIED LINES ARE LAID NEAR TO OR ACROSS ELECTRIC POWER CABLES, THEY
SHOULD ALWAYS BE LAID AS FAR AWAY FROM THE CABLES AS POSSIBLE.
IF UNDERGROUND PIPING AND CABLES ARE USED, IT IS ESSENTIAL THAT THE PIPE
AND CABLE IS PUT INTO POSITION AT THE SAME TIME AS FOUNDATION WORK IS
BEING UNDERTAKEN.
PIPE TRENCHES –
OPEN TRENCHES MAY BE USED IN PLACES WHERE THERE IS NO RISK OF FLAMMABLE
VAPOURS COLLECTING OR OF THE MATERIAL FREEZING, EG. FOR STEAM MAINS.
THEY SHALL NOT BE USED WHERE THERE IS A DANGER OF FLOODING. IT IS OFTEN
CONVENIENT TO RUN PIPE TRENCHES ALONGSIDE ROADWAYS AT SUCH AN ELEVATION
THAT THE PIPE CAN RUN UNDER THE ROAD WITH NO CHANGE IN ELEVATION.
MIN. WIDTH OF PIPE TRENCHES SHOULD BE 600MM.
MIN. CLEARANCE OF 100MM SHOULD BE PROVIDED BETWEEN PIPE PROJECTIONS AND
WALLS AND 50MM TO THE HIGH POINT OF TRENCH BOTTOMS.
WHEN LOCATED BELOW GRADE, PIPING PROVIDED WITH PROTECTIVE HEATING AND
PIPING IN SERVICES REQUIRING INSPECTION AND SERVICING, SHALL BE IN
TRENCHES. OTHER PIPING SHALL BE DIRECTLY BURIED.
INPUTS REQUIRED FOR BURIED PIPING
PIPE DATA –
PIPE OUTSIDE DIAMETER
PIPE WALL THICKNESS
LENGTH OF PIPE RUNS- TRANSVERSE AND LONGITUDINAL
YOUNG’S MODULUS, E
PIPE DEPTH BELOW GRADE *
SOIL CHARACTERISITICS – *
SOIL DENSITY (FROM SITE TESTS)
PIPE TRENCH WIDTH AT GRADE
RANGE OF COEFFICIENT OF FRICTION BETWEEN PIPE AND BACKFILL
TYPE OF BACKFILL
DEGREE OF COMPACTION
OPERATING CONDITIONS –
MAXIMUM OPERATING PRESSURE
MAXIMUM PIPE TEMPERATURE
AMBIENT PIPE TEMPERATURE
PIPE COEFFICIENT OF THERMAL EXPANSION
GRAVEL
INDIVIDUAL GRAINS VERY FROM 0.08 TO 3 in (2 TO 75 mm) IN DIAMETER
AND ARE GENERALLY ROUNDED IN APPEARANCE.
SAND
SMALL ROCK AND MINERAL FRAGMENTS ARE SMALLER THAN 0.08 in
(2mm) IN DIAMETER.
SILT
FINE GRAINS APPEAR SOFT AND FLOURY.
CLAY
FINE-TEXTURED SOIL FORMS HARD LUMPS WHEN DRY AND IS STICKY TO
SLICK WHEN WET.
ORGANIC
PEAT.
BURIED PIPELINE THAW SETTLEMENT
BENDING MOMENT AT BURIED PIPE BEND
IMPACT OF SIDEFILL SOIL ON A FLEXIBLE PIPE
WORKING OF FLEXIBLE PIPES
PIPE AND SOIL WORKING AS A SYSTEM
TERMS ASSOCIATED WITH BURIED PIPING
GROUND LEVEL – GROUND LEVEL IS THE HEIGHT OF THE SOIL SURFACE W.R.T
THE GLOBAL ORIGIN. IT IS NOT THE MEASURE OF THE DEPTH OF PIPE’S
CENTERLINE.
BURIED PIPING LOADS
THERMAL EXPANSION LOADS –
INSTALLATIONS WITH CONTINUOUS RUNS(WITHOUT COUPLINGS)- HIGH
AXIAL FORCES AND BENDING MOMENTS.
INSTALLATIONS WITH FLEXIBLE COUPLINGS- BENDING MOMENTS AND
STRESSES SUBSTANTIALLY REDUCED.
INSTALLATIONS WITH PENETRATION ANCHORS- IF FLEXIBLE COUPLINGS
ARE USED , PIPING REACTIONS AT THE PENETRATION RESULTING FROM
UNBALANCED FORCES DUE TO INTERNAL PRESSURE TO BE CONSIDERED.
INSTALLATIONS WITH FLEXIBLE PENETRATIONS.
PRESSURE LOADS –
DEAD LOADS CAUSED BY EMBANKMENT OR TRENCH BACKFILL PLUS
SUPERIMPOSED STATIONARY SURFACE LOADS, UNIFORM OR
CONCENTRATED.
LIVE OR MOVING LOADS INCLUDING IMPACT.
WHEN ONE OR BOTH ENDS OF A PIPE RUN TERMINATE AT A PENETRATION
OR AN ANCHOR, OR AT CONNECTED EQUIPMENT, THE PRESSURE FORCES
CAN BE QUITE HIGH AND MUST BE CONSIDERED IN EQUIPMENT OR
ANCHOR DESIGN.
FOR DISCHARGE EQUIPMENTS LIKE PUMPS, THE REACTION FORCES DUE
TO THE UPSTREAM PRESSURE AND MASS FLOW MOMENTUM IN THE
DISCHARGE LEG MAY BE HIGH AND MUST BE CONSIDERED IN THE DESIGN
OF THE LAST ELBOW OR BEND BEFORE THE DISCHARGE.
BURIED PIPING LOADS (contd.)
INTERNAL PRESSURE –
THE INTERNAL PRESSURE DESIGN OF A BURIED PIPE AND THE CORRESPONDING AG PIPE
DERIVE FROM THE SAME EQUATION. (PIPE WALL THICKNESS FORMULA)
VERTICAL EARTH LOADS -
IMPORTANT CONSIDERATION WHEN DESIGNING PIPING CASINGS USED FOR RAIL AND
ROAD CROSSINGS.
PRIMARILY A CONSIDERATION FOR NON-OPERATING CONDITIONS OF BURIED STEEL
PIPE WHEN THE PIPELINE IS UNDER NO INTERNAL PRESSURE.
SURFACE LIVE LOADS –
IN ADDITION TO SUPPORTING DEAD LOADS IMPOSED BY EARTH COVER, BURIED PIPES
CAN ALSO BE EXPOSED TO SUPERIMPOSED CONCENTRATED OR DISTRIBUTED LIVE
LOADS.
SURFACE IMPACT LOADS –
LOADS RESULTING FROM LARGE WEIGHTS FALLING FROM SIGNIFICANT HEIGHTS.
BUOYANCY –
NET UPWARD FORCE ON BURIED PIPE WHEN THE BUOYANCY FORCE CREATED BY THE
PIPE BELOW THE WATER TABLE ( THE LEVEL OF STANDING WATER IN THE SOIL) EXCEEDS
THE COMBINED DOWNWARD WEIGHT OF THE PIPE AND SOIL COLUMN ABOVE THE PIPE.
RELATIVE PIPE-SOIL DISPLACEMENT –
UNDER THE EFFECTS OF GROUND MOVEMENTS OR LARGE PIPELINE LOADS LIKE THOSE
FROM A LARGE THERMAL DIFFERENTIAL, BURIED PIPES MAY BE SUBJECT TO LARGE
BENDING AND TENSILE LOADS. SOURCES OF GROUND MOVEMENT CAN INCLUDE
DIFFERENTIAL SOIL SETTLEMENT, FAULT DISPLACEMENT OR LATERAL SPREAD
DISPLACEMENT IN EARTHQUAKES, LANDSLIDE DISPLACEMENT, FROST HEAVE OR THAW
SETTLEMENT, ETC.
BURIED PIPING LOADS (contd.)
MOVEMENT AT PIPE BENDS –
MOVEMENT OF A BURIED PIPELINE CAN OCCUR AT THE APEX OF SIDEBENDS,
SAGBENDS AND OVERBENDS. THIS MOVEMENT CAN BE CAUSED BY EITHER A
NET OUTWARD FORCE GENERATED BY INTERNAL PRESSURE OR EXPANSION
CAUSED BY TEMP. INCREASES. THE RESULTING FORCES ARE RESISTED BY
THE PIPE BENDING AND AXIAL STIFFNESS AND BY THE SOIL BEARING AND
SHEAR RESISTANCE.
EFFECTS OF NEARBY BLASTING –
DUE TO MINING AND NEARBY CONSTRUCTION ACTIVITIES.
FLUID TRANSIENTS –
RAPID CHANGES IN FLOW RATES OF LIQUID OR TWO-PHASE PIPING
SYSTEMS CAN CAUSE PRESSURE TRANSIENTS, WHICH IN TURN GENERATE
PRESSURE PULSES AND TRANSIENT FORCES IN THE PIPING SYSTEM.
IN-SERVICE RELOCATION –
IT IS PRACTISED ROUTINELY IN THE INDUSTRY TO PERFORM CERTAIN
OPERATIONS WITHOUT TAKING THE LINE OUT OF SERVICE. SOME REASONS
ARE:
ACCOMODATING A NEW HIGHWAY OR RAIL CROSSING.
PERFORM OVER-THE-DITCH COATING RENOVATION.
INSPECTING OR REPAIRING PIPE SUBMERGED IN SHALLOW WATER.
AVOIDING ENCROACHMENT.
BURIED PIPING LOADS (contd.)
EARTHQUAKE -
TRANSITORY STRAINS CAUSED BY DIFFERENTIAL GROUND DISPLACEMENT
ARISING FROM GROUND SHAKING AND PERMANENT GROUND
DISPLACEMENT FROM SURFACE FAULTING, LATERAL SPREAD
DISPLACEMENT, TRIGGERED LANDSLIDE DISPLACEMENT AND SETTLEMENT
FROM COMPACTION OR LIQUIFACTION.
DEAD LOADS
PRISM METHOD –
PE= w H
where
PE = VERTICAL SOIL PRESSURE, lb/ft2
w = UNIT WEIGHT OF SOIL, lb/ft3
H = SOIL HEIGHT ABOVE PIPE CROWN, ft
MARSTON METHOD –
PM= CD W BD
where
PM = VERTICAL SOIL PRESSURE, lb/ft2
BD = TRENCH WIDTH AT PIPE CROWN, ft
CD = LOAD COEFFICIENT
CD= 1- e –2Ku’H/BD
2Ku’
K = RANKINE EARTH PRESSURE
COEFFICIENT
K= tan 2 ( 45 – X/2 )
where
F = ARCHING COEFFICIENT
where
PP = PRESSURE TRANSMITTED TO THE PIPE (WITHOUT IMPACT)
PS = CONC. LOAD AT THE SURFACE, ABOVE PIPE
C = DEPTH OF SOIL ABOVE PIPE
d = OFFSET DISTANCE FROM PIPE TO LINE OF APPLICATION OF SURFACE LOAD
EFFECTS OF SURFACE LIVE LOADS
OVALITY
THROUGH-WALL BENDING
CRUSHING OF SIDE WALLS
RING BUCKLING
FATIGUE
EFFECTS OF SURFACE LIVE
LOADS (CONTD.)
LIVE LOADS TRANSFERRED TO PIPES
LOAD AND REACTION IN BURIED PIPES
GENERAL MATERIALS FOR BURIED PIPING
CROSS-COUNTRY PIPING.
FOR CARRYING HAZARDOUS CHEMICALS.
WASTEWATER OR SEWAGE WATER SYSTEMS.
WATER SYSTEMS.
GEOTHERMAL TRANSMISSION AND DISTRIBUTION LINES.
FIRE-PROTECTION SYSTEMS.
BURIED PIPING (IMAGE)
DURING SOIL EXCAVATION
PIPE PLACEMENT INSIDE A TRENCH
BACKFILLING PROCESS
FINAL STAGE OF SOIL EXCAVATION
GRAVEL COVER OVER BACKFILLED TRENCH
BURIED PIPE LAYED IN A TRENCH
GROUP OF BURIED PIPE LAYED IN A TRENCH
SLIP PLATES INSTALLED TO SEAT STEEL PIPES
EXCAVATED LAND
BURIED PIPE
PIPE THROUGH A ROAD CROSSING (WITH A SUPPORT
NEARBY)
PIPE THROUGH A ROAD CROSSING (WITH A SLEEPER
NEARBY)
PIPE THROUGH A ROAD CROSSING (WITH A SLEEPER
NEARBY)
PIPE AFTER COAL-TAR WRAPPING
SOFTWARES USED
AUTOPIPE
CAESAR-II
PIPENET
CAEPIPE
Thank you