Buried Piping: M.Vijay Gopal

 

BURIED PIPING   M.VIJAY GOPAL

 

WHAT IS THE NEED FOR BURIED PIPING? SAFETY CONSIDERATIONS  

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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    

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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 – 

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OPEN TRENCHES MAY BE USED IN PLACES WHERE THERE IS NO RISK OF FLAMMABLE VAPOURS COLLECTING COLLECTING OR OF THE MATERIAL FREEZING, FREEZING, EG. FOR STEAM MAINS. THEY SHALL NOT BE USED WHERE THERE IS A DANGER OF FLOODING. IT IS OFTEN CONVENIENT TO RUN PIPE TRENCHE TRENCHES S 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 TEMPERATUR TEMPERATURE E AMBIENT PIPE TEMPERATUR TEMPERATURE E PIPE COEFFICIENT OF THERMAL EXPANSION

* - PARAMETERS TO BE SPECIALLY CONSIDERED FOR BURIED BURIED PIPING.

 

FACTORS TO BE CONSIDERED FOR BURIED PIPING STRENGTH UNDER MAXIMUM OR MINIMUM COVER, BEDDING AND BACKFILL CONDITIONS ANTICIPATED LOADINGS LENGTH OF SECTIONS EASE OF INSTALLATION CORROSIVE ACTION BY LIQUIDS CARRIED OR SURROUNDING SOIL JOINTING JOINTIN G METHODS- BELL & SPIGOT JOINTS, JOINTS, BUTT WELDED JOINTS, JOINTS, MECHANICALLY COUPLED JOINTS ETC. EXPECTED DEFLECTION COST OF MAINTENANCE AVAILABILITY AND SUITABLITY OF PIPING MATERIALS FOR LOCAL CONDITIONS AS A WHOLE, WE HAVE TO GO FOR THE MOST ECONOMICAL MODE.

 

DESIGN OF BURIED PIPING DESIGN BASED ON PRINCIPLES OF SOIL-STRUCTURE INTERACTION, THAT IS, THE PIPE AND THE SURROUNDING SOIL ACT TOGETHER TO CONTROL THE PIPE PERFORMANCE. THE DESIGN IS BASED ON RELATIVE STIFFNESS OF BOTH SOIL & PIPE. INITIAL DESIGN STEP IS TO DETERMINE DEAD LOADS AND SURCHARGE LOADS. SEVERAL PIPE SELECTIONS MAY NEED TO BE TRIED TO ARRIVE AT THE OPTIMUM DESIGN. ALL LOADS ACTING ON THE SYSTEM. DESIGN MUST BE STRONG ENOUGH TO: 

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WORKING STRESSES FOR COMBINED BENDING AND DIRECT TENSILE STRESS