Thursday, December 17, 2009

A study on Activity of Titas Gas Transmission & Distribution Company ltd. (TGTDCL), Bangladesh( Part-4)

2.5.5 Operation [10].
Inspections of operational works are:
 Co-ordination of pigging programs
 Cathodic protection readings
 Foreign crossing inspections
 Daily reading as required
 Co-ordinate R. O. W. surveillance

2.5.6 Maintenance and repair [10].
 Pump and compressor preventive maintenance and repair
 Pipeline repairs
 Valve maintenance and repair

2.5.7 Inspect the pipeline integrity programs 

Pipeline integrity programs are very important part of both pipeline operation and maintenance procedures. There are several functions that are required to form a complete pipeline integrity program, such as:
 Schedule pressure testing programs
 Annual river crossing profiles
 Pipeline coating assessment programs
 Depth of cover surveys
 Internal inspection surveys [10].

2.5.8 Inspection the Preparation for Welding

Safety regulations require the welding operation be protected from weather condition that would impair the quality of the welding. Before beginning the welding, welding surface must be clean and free of any material that may be detrimental to the welding. Also, pipe sections must be properly aligned for depositing the root bead. Specifications require that carbon steel with carbon content in excess of 0.32% must be preheated for welding. In some cases; steel with lower carbon contents must also be preheated. When steels with different preheated temperatures are being welded, the higher preheat temperatures must be used to weld the seams. Preheat temperature must be monitored to ensure the proper temperature and maintain that temperature during welding.             

Qualified trained welders must be employed for welding operation. TGTDCL has it’s own welder grades specified as Titas grade-A, B, C.  For high pressure pipeline a welding procedure specification (WPS) is established and suggest to follows these procedure strictly. Welding conducted as per the welding procedure and must be tested to ensure the WPS requirements fulfilment. Welded joints are inspected visually, mechanically and by using non-destructive test (NDT) methods. Mechanical test includes tensile test, nick break test, macro tech test, etc. Test results are to be documented and record the procedure of welding operation [1-2].

2.6 Inspection and Testing

Pipeline welds must be inspected visually to ensure the performance in accordance with the welding procedure and the welds are acceptable under the appropriate specifications. In the United States, to comply with provisions of 49 Code of federal regulation (CFR), non-destructive testing is also required on welds made on a pipeline that will be operated at a pressure that results in a hoop stress of 20% or more of the specified minimum yield strength (SMYS). There are two exceptions to this non-destructive testing requirement. Non-destructive testing is not required even though hoop stress will exceed 20% of SMYS if
·         the pipeline has a nominal diameter of less than 6 in.
·         the hoop stress will be less than 40% of the SMYS and the number of welds is so small as to make such testing impractical.
Non-destructive testing must be performed according to written procedures by specially trained personnel.

Radiography (X-ray) is the most widely used method for testing pipeline welds in non-destructive method. In radiography, a picture is made on a sensitized film by exposing the film to X-ray. Defects in the weld, such as cracks, porosity, or slag inclusions, appear as spots or lines on the developed film.

Seismic Energy Dissipation Devices

Seismic Energy Dissipation Devices