Volume-II of IV - GAIL

MECON LIMITED
REGD. OFF : RANCHI (BIHAR)
Document6
PROCESS & PIPING
DESIGN SECTION
NEW DELHI
TITLE MAINLINE CONSTRUCTION
(ONSHORE)
6.12 Provisions for negative buoyancy to the pipe
7.0 BENDING
STANDARD SPECIFICATION
SPECIFICATION NO. PAGE 27 OF 53
MEC/S/05/62/01 REVISION A
CONTRACTOR shall check if up-floating danger is present in open trench and
then shall take appropriate measures to prevent up-floating such as applying soil
dams and dewatering of trench or temporary filling of water into the line (in
exceptional cases).
In the case of water on the ditch bottom when the pipeline is being laid, the ditch
shall be drained to the extent and for the time required to make a visual
inspection of the ditch bottom. After this inspection, the presence of water will be
allowed provided its level does not cause sliding of the ditch sides and pipe
floating before backfilling when no concrete weighting is provided.
The water pumped out of the ditch shall be discharged into a natural water
course.
Wherever up-floating of the pipeline after backfilling is to be reckoned with, antibuoyancy
measures shall be provided by CONTRACTOR for areas indicated in
the drawings or as may be encountered during construction, using one or a
combination of the following methods :
weighting by applying a continuous concrete coating around the pipe;
weighting by installing saddle weights;
installing metal anchors screwed into the suboil in pairs;
deeper burial of pipeline;
provision of select backfill material.
The above provisions shall be in accordance with the relevant specifications
and/ or job standards/ drawings.
CONTRACTOR shall preferably provide for changes of vertical and horizontal
alignment by making elastic bends. CONTRACTOR may provide cold field
bends, at its option for change of direction and change of slope. COMPANY at
its option, may authorise fabricated bends for installation at points where in
COMPANY's judgement the use of such bends is unavoidable.