Pipeline risks, Environmental Impact Assessments (EIA) and Pipeline Construction and Various Steps Involved

The most common pipeline threats which may lead to the loss of technical integrity are given below:

Internal corrosion and Hydrogen Induced Cracking (HIC)
Internal erosion
External corrosion and bi-carbonate stress corrosion cracking
Mechanical impact, external interference.
Fatigue. E.g. sudden surges of pressure in the fluid
Hydrodynamic forces
Geo-technical forces
Growth of material defects
Over-pressurization
Thermal expansion forces

Environmental Impact Assessments (EIA)

The factors which are critical to public safety and the protection of the environment should be analyzed over the entire life of the pipeline, including abandonment. The risk should be reduced to as low as reasonably practicable, with the definite objective of preventing leaks. The level of risk may change with time, and it is likely to increase to some extent as the pipeline ages.

An environmental impact assessment is carried out for all pipelines or groups of pipelines. EIA is a process for identifying the possible impact of a project on the environment, for determining the significance of those impacts, and for designing strategies and means to eliminate or minimize adverse impacts.

Pipeline Routing

Pipeline Construction

Pipeline construction is performed in accordance with the relevant sections of the ANSI/ASME Codes, and has to comply with any additional criteria resulting from the design. The construction procedure ensures that the pipeline is installed safely, on time and with minimum impact on the environment.

Steps in onshore pipeline construction are:

Survey and route selection

Securing right of way (ROW)

Site preparation

Coating and delivery of pipe pieces at site

Welding and stringing

Inspection and Testing

Laying of Stringed Pipe

Hydro-testing

Mechanical Completion

Site Restoration

Survey and Route Selection

The selection of the route is done by taking full account of the associated risks, particularly safety and environmental risks, the accessibility for maintenance and inspection, topography, soil data, river crossings, road crossings as lots of surveys and analysis of possible routes based on maps, aerial surveys, satellite imagery, GPS (Global Positioning System) and other techniques.

Securing Right of Way

For the most part, cross country pipelines are not visible because they are located under the street or are buried in rights-of-way (ROW) secured by an easement. Easement implies right held by one person to make use of the land of another person for a limited purpose, right of way, license or permit.

Before a pipeline is constructed, ROW is obtained to secure the land rights necessary to construct, operate and maintain the pipeline. The ROW agreement restricts the landowner’s rights within the ROW corridor to uses that are compatible with the operation and maintenance of the pipeline.

The ROW width is normally 30 meters for construction and 15 meters for operation.

Site Preparation

The route is cleared of trees and plant life, the topsoil removed and all material stockpiled for re-instatement (clear and grade). Pipe is delivered by truck and laid along the route.

Coating of Pipeline

Exterior of pipes is generally coated at the shop or site. But at the time of stringing coating may be partly damaged. The coating is repaired and welded joints are freshly coated for corrosion protection.

Stringing

The pipelines themselves are fabricated from 12 metre pipe lengths. They are then welded into 250 metre lengths, known as strings. The pipe is then lowered into the trench. Backfill material is added beneath and around the pipe to secure it in place.

When the pipe is converted to a depth of at least one meter, restoration of the area begins.

If necessary, the pipe is bent to follow the natural contour of the land. Welds are stringently tested to ensure with integrity. This is done while laying the pipeline in a string.

PIPING GUIDE

Wednesday, July 25, 2012