Commentary on CSA Z662-11, Oil and gas pipeline systems
|Publication Date:||1 June 2011|
The scope statement indicates which aspects and parts of pipeline systems and which service fluids are covered by the Standard.
Carbon dioxide was added as a new service fluid in 1996. The definition of "gas" was changed in 1983 to accommodate the coverage of gaseous service fluids other than fuel gas and sour gas; however, until 1996, none had been added.
The carbon dioxide pipelines that are covered are those onshore pipelines that are for use in enhanced oil recovery operations, involving the transportation of high-purity carbon dioxide from a suitable source to the injection site at an oil well. These pipelines were added to the Standard because it was considered that there had been sufficient experience with such an application to warrant their inclusion. Pure carbon dioxide is non-toxic and non-flammable; however, it has some specific characteristics that necessitated the addition of requirements specific to carbon dioxide pipeline systems. It should be noted that the definition of a carbon dioxide pipeline system permits the service fluid in such a pipeline to be other than pure carbon dioxide, so additional special requirements are in some cases appropriate.\It should be noted that carbon dioxide might additionally be present in conventional pipelines as a component of a multiphase fluid or as a component of a fluid in a gas pipeline system. For such fluids, the conventional requirements applicable to the multiphase liquid or gas pipeline system continue to be appropriate.
The parts of pipeline systems that are included in the scope are listed here, and the pictorial representations in Figures 1.1, 1.2, 11.1 to 11.5, and 12.1 are intended to augment the information provided in Clauses 1.2 and 1.3. The figures are schematic and are intended to convey broad functions rather than specific details.
The parts of pipeline systems that are not included in the scope are listed here, along with a list of some related items that are beyond the defined limits of pipeline systems. Items that are within the defined limits of pipeline systems but are currently outside the scope of the Standard could be included in the scope in some future edition of the Standard, should the CSA Technical Committee on Petroleum and Natural Gas Industry Pipeline Systems and Materials and the Strategic Steering Committee on Petroleum and Natural Gas Industry Systems deem that such additions to the scope are appropriate.
The requirements in the Standard are considered adequate under conditions normally encountered, and requirements for abnormal or unusual conditions are not necessarily specifically addressed. Although in some instances in the Standard the requirements are necessarily quite prescriptive, the Standard is not a design handbook and the exercise of competent engineering judgment is necessary when using the Standard. The exercise of competent engineering judgment is intended to recognize circumstances in which the essential requirements and minimum standards contained in the Standard may be insufficient. The note provides a specific instance of such circumstances, pertaining to the use of high-strength materials.
The design and construction requirements have been primarily developed with new pipelines and facilities in mind. Some practices that are reasonable and practicable during design and construction are in some cases not practical for an existing pipeline (e.g., the requirement to use piping that has proven notch toughness properties). The requirements in the Standard have been modified and generally made more stringent through the years, primarily to provide improved safety, but also to reflect technological improvements that have been made in the manufacturing processes used for pipe and components. Design requirements can be readily changed; however, the mechanical properties of in-service piping cannot. Where upgrading involves the replacement of existing piping with new piping, what was not practical for the old piping is practicable for the new piping.
Note: The terms "practicable", "practical", and "impractical" are not defined in the Standard because the ordinary dictionary meanings are intended, whereby "practicable" means capable of being effected or accomplished; "practical" means adapted to actual conditions; and "impractical" is the negative form of "practical". The term "not practicable" is used in the Standard rather than the dictionary term "impracticable" to indicate the negative form of "practicable". The similarity of the terms can lead to confusion for the reader unless the specific meanings are understood.
Clause 1.6 defines the basis for the numerical rounding practices used throughout the Standard. It is important to understand its effect when applied in conjunction with the number of digits indicated in the specific requirements of the standard.
A requirement in the Standard cannot be superseded by a less restrictive requirement in a referenced publication.
Practices are not included in the Standard until sufficient experience has been accumulated for them to become generally accepted as being good practices. Even new practices that are superior to established practices are not included in the Standard until the Technical Committee deems such new practices to be acceptable. It is not the intent of the Standard to prevent the development of new practices, and generally such practices would need to be approved for use by the regulatory authority having jurisdiction.