Thursday, December 17, 2009

A study on Activity of Titas Gas Transmission & Distribution Company ltd. (TGTDCL), Bangladesh( Part-3)

2.5 Standard Inspection Methods:

2.5.1 Material procurement inspection
2.5.2 Visual inspection
2.5.3 Design inspection
2.5.4 Construction inspection
2.5.5 Operation
2.5.6 Maintenance and repair
2.5.7 Inspect the pipeline integrity programs
2.5.8 Inspection the Preparation for welding

2.5.1 Material procurement inspection
During pipeline construction materials are inspected visually and mechanically for their physical, dimensional defects and design accuracy. Materials are pre-qualified / inspected as per international standard during procurement [1].
The most common standards are:
 American Petroleum Institute ( API )
 American National Standard Institute ( ANSI )
 American Society of Mechanical Engineers ( ASME )

2.5.2 Visual inspection
Visual inspections are important in welding jobs for construction of pipelines. Cracks, incomplete penetration, burn-through, undercut, unequal leg length, and other imperfections in the test welds shall be assessed in accordance with the applicable requirements. Undercuts adjacent to the final test weld bead on the outside of the pipe shall not exceed 1mm in depth. The test welds shall have a neat appearance. Imperfections detected by visual inspections must be into consideration and take corrective measures.

2.5.3 Design inspection
The requirements for design inspection of pipeline construction project are:
 Fluid flow capacity
 Design pressure for each segment of pipeline system

°                       External pressures and loadings
°                       Ambient influence
°                       Temperature
°                       Location of Class
2.5.4    Construction inspection
Inspection of pipeline construction based on:
°                       Pre-construction activities
°                       Construction activities
°                       Post-construction activities

Pre-construction activities
Inspections of pre-construction activities of pipeline are as follows:
°                     Route selection
°                     Legal surveying and land acquisition
°                     Pipe hauling
°                     Equipments and vehicles

Construction activities:
Inspection of construction activities is very important for pipeline operation and integrity. When any pipe manufacturing defects are detected during installation inspection, the defective portion of pipe shall be repaired by the applicable pipe manufacturing standard or specification or cut out as a cylinder or where necessary replaced with another pipe that meets the design requirements. Inspection shall be performed by the experienced personnel. Inspection for piping defects shall be indentified immediately prior to the application of any field coating and during lowering in and backfilling operations. Pipe and component shall be inspected for defects. Such inspection shall include but not necessarily be limited to inspection for flattening, ovality, straightness, pits slivers, cracks, gouges, dents, defective weld seams, and defective field welds. Bends shall be inspected for conformance with the free from buckling, cracks, and other evidence of mechanical damage. Where the pipe is field coated, inspection shall be carried out to determine that the cleaning/coating machine is not creating defects in the pipe. Coating shall be inspected immediately before, during and after pipe installation. Faults in the coating shall be repaired and re-inspected. Plant-applied coatings shall be inspected immediately after field-bending to confirm that the integrity of the coating has been maintained. Where applicable, each pipe shall be visually inspected prior to welding for defects in its lining. Inspection of field and shop welds is in accordance with the applicable requirements of clause 7 [9]. Inspection of pipe portion repaired, replaced, and altered shall be made before it is backfilled. Where necessary and as appropriate, non-destructive inspection of piping shall be performed using one or more of the following methods:
(a)        Radiographic inspection of welds in accordance with the applicable requirements of clause 7.
(b)        Ultrasonic inspection of welds in accordance with the applicable requirements of clause 7.
(c)        Ultrasonic inspection of pipe
(d)       Electrical inspection of protective coating
(e)        Inspection using internal inspection devices and
Other methods are below:
°                     Stringing pipe
°                     Welding
°                     Coating
°                     Ditching
°                     Crossing
°                     Lower-in
°                     Backfilling
°                     Compression and pump station
°                     Pressure testing
°                     Clean-up and restoration    [10].

Post-construction activities
After the pressure test has been completed, it is then necessary to displace the test median from the pipeline and purge the system with sweet natural gas or an inert gas such as nitrogen to make the system ready for operation.

Seismic Energy Dissipation Devices

Seismic Energy Dissipation Devices