POWER PLANT : MECHANICAL WORKS ( Piping - Valves )

POWER PLANT

 MECHANICAL WORKS OF FUEL GAS PIPELINE 

Piping :

a]  Piping Design Criteria :

i.  The design parameters of piping shall be as follows, unless otherwise specified:
Nominal dia to be decided by the contractor as per requirement).                                                                                                   
         Design pressure    1060 PSIG (73 bar)
       Design temperature:   Max.           50ºC     Min.     0ºC
Max. flow rate to be decided by the contractor as per requirement

ii.          The gas pipeline shall be laid buried with a minimum 1m cover over the pipeline. An additional 0.5m berm shall be provided over the pipeline.

   1st.    Design of Transportation Piping System
2nd       Construction requirements for cross country pipelines
        Pipeline markers shall be provided at every kilometer, road crossing (within 10m on both sides of the road) and near appurtenances, deflections, junctions, etc. 

         The anchors, support etc. of the pipeline shall be provided according to the requirements
        The pipeline shall conform to the trench bottom such that it is supported on all points.

The trench bottom shall be free of rock or other material that could damage the coating
         The pipeline shall be embedded in an annulus of clean sand not less than 300mm thick in a manner, which shall not damage the coating. Rest of the backfill material shall not contain rocks larger than 50mm.

         The piping joints shall be designed to meet the requirements.
The piping shall have welded connections except for the connection to the scraper launcher/receiver and where specifically agreed otherwise by the COMPANY.

The installation of pipeline in the metering station shall conform to the requirements 

The piping system in the metering station shall generally be flexible enough and anchored to absorb the expected expansion stresses imposed by thermal load or the combination of loads transmitted from the piping outside the station.

The underground piping shall be externally protected through fusion-bonded epoxy coating whereas the above-ground piping shall be painted in accordance with the requirements outlined.

b] Material

i. The material of the piping and its accessories shall conform to the requirements standards.

 The pipeline shall be seamless or SAW pipe, API 5L grade X60, or ASTM A106 grade B.

 The piping shall have the required wall thickness based on size and class of line.

ii.  Fabrication of pipes shall be in compliance with added requirements of ASME B31.3 using a design factor of 0.40. For pipe size 50 mm (2-inch) and larger, joints shall be butt-welded.

 The minimum wall thickness for 50 mm (2-inch) and smaller piping shall be Schedule 80.

c]   Piping Classes

             The piping classes (Class 900), 6CS9P (Class 600) and  (class 300) as applicable.

d] Piping Layout Criteria

i.  The layout of the piping shall meet the requirements minimum clearance between the centerline of the nearest underground pipeline in the corridor and the new pipeline shall be 15m

  
ii.  The piping layout and arrangement shall be such that it allows adequate access for operation and maintenance for all equipment, valves, etc.

e]  Elbows, Bends & Tees

i. The pipe fittings elbows, bends, tees, etc. shall be fabricated. 

The fittings up to 50mm dia shall be from A105 material conforming to ANSI.B16.11. The fittings 80mm dia and above shall be from A234-WPB as per ANSI/B16.9.

ii.  In the pipeline, only long radius elbows shall be used unless otherwise approved specifically. For lines 16” NPS and larger, the radius of the bend shall not be less than 3D.

iii.  Fabricated fittings and mitered welds shall not be used.

iv.   Flattening of bends shall be within the allowable limits as specified 

f]  Supports

i. The supports and anchors of the piping.

 The buried pipeline shall be provided with full thrust anchors at each end of the pipeline.

 The piping in the metering station shall be supported on concrete sleepers and/or on structural steel.
        For the above-ground pipeline, saddle-type supports with pads shall be provided.
         The pipeline shall be adequately supported to prevent excessive stresses, vibration, sag, etc.
        The supports design shall be based on all the concurrently acting loads transmitted on to such supports.

ii.  The attachments welded or bonded to the pipeline shall have the same or compatible material as that of the pipeline.

iii. The free movement of unrestrained piping shall be controlled within acceptable limits by adequately designed and located guides, anchoring points, etc. 

The restraints shall be designed to withstand any shock load that may occur in any normal or abnormal operation scenario.

g]  Vents and Drains

i.   An adequate number of low point drains and high point vents shall be provided to achieve proper drainage of any liquid and safe venting of gas during operation

ii.   The drain and vents shall be of a minimum of 25mm diameter.

iii.  On the drains of piping, vessels, and filter separators in the metering station, the provision shall be made to drain out the liquid automatically.

iv.   All drains shall be connected to the slop tank and shall be pumped to the oily water system.

v.   All vents shall be connected to a common header, to be led to burn pit/flare for disposal. Burn pit or flare system.

h]  Cleaning of Pipes

i.  Pre-fabricated pipe spools shall be visually inspected for cleanliness, foreign material removed from inside, and shall have end protectors installed.

ii.  After assembly and installation, the piping shall be cleaned from inside to remove all loose material either by flushing or by blowing with air as a minimum as per the Owner/Engineer’s satisfaction.

iii. The external cleaning shall be carried out as per the requirement outlined 

   Valves

a] The valves to be provided shall fulfill the requirement  indicate the minimum number of valves to be provided. However, the Contractor shall provide the other valve(s) as necessary for the safe and reliable operation of the system and its proper maintenance

b] All the valves shall be hydro-tested in the shop.

i.  All valves with actuators shall be provided with manual override.

ii.  All powered actuators, electric or pneumatic shall permit operating personnel to instantaneously stop the valve stroke and reverse from closing to opening and vice-versa at any point of the stroke.

c] Isolation Valves (Manual/Motorized)

            Isolation valves shall conform to all the applicable indicate the minimum number of isolation/relief valves to be provided.

i.  These valves shall be of a design, which provides tight shut-off.

ii.  Isolation valves at the upstream and downstream of the flow meters shall be motorized ball valves with remote and local control, and shall be of full-bore type.

iii.  Scraper launcher/receiver isolation valves shall be full-bore ball valves of the same nominal size as the pipeline.

d]  Sectionalizing Valves

i.   Sectionalizing valves (emergency Isolation Valve, EIV type),

ii.  A bypass/valve (EIV type), of adequate size, shall be provided across the sectionalizing valves.

iii.  The sectionalizing/balancing valves shall be the gas-operated type with all necessary instrumentation and bypass control to facilitate remote monitoring and control.

iv. The valves shall be full-bore ball valves. The sectionalizing valve shall be buried type with above-ground actuators.

e] Control Valves

i.  Control valves shall be pilot-operated over-pressure regulator type with anti-cavitation trim for gas service.

ii.  The control valves shall be provided with upstream/downstream isolation valves to facilitate maintenance of valves without shutting down the system.

iii. The control valves shall use pneumatic actuators, utilizing the fuel gas as actuating medium.

iv. The instrumentation of the control valves shall be as per specifications are given in Section.

 f]   Emergency Shutdown (ESD) Valve

i.  A gas-operated quick-acting ESD valve shall be installed for the protection of Gas Equipment against the emergency as per Saudi Aramco standard.

ii.   The Emergency Shutdown (ESD) valve shall be provided on the main gas supply pipe for a total shutdown.

g]  Safety/Relief Valves

i.   Safety/relief valves shall be provided to protect the system against overpressure due to operational conditions or thermal expansion of the trapped medium.

ii.  The safety/relief valves shall fulfill

iii.  The safety/relief valves shall not allow the system pressure to rise more than 10% above the max. allowable working pressure.

iv. A lockable block valve shall be provided on the inlet line to pressure relief device

v.  The discharge of safety/relief valves shall be located at least 3 m above ground.

    Gas Separators/Filters

i.  Skid mounted gas separator/filter unit shall be supplied to remove asphalt sand, wax material, and other gas bore contaminants (black powder) having a particle size of 3 microns and larger as well as liquid hydrocarbons and water,.

  The gas separator/filter unit shall consist of four (4) separators (three in service and one standby) complete with interconnecting piping, valves, and instruments.

 The skid arrangement shall be designed to allow separators to normally run in parallel or independently when one or more separator/filter(s) is out of service for maintenance.

ii)  It is pertinent to note that the Owner is facing the problem of excessive black powder collected at the filtration units of some existing plants, so the bidders shall give special emphasis on the design of filter separators to cater to this problem.

iii.  In this regard, the bidders shall submit a detailed report with their proposals  about the remedial measures to be built in the design of the filter separators, in order to take care of the excessive black powder problem.