Conceptos básicos del IMAP4

The minimum wall thickness at any location along the pipeline shall be the greater of:

(a) The sum of the thickness required for pressure containment and allowances.

(b) The thickness required for resistance to penetration by the design threat, if this is used as a method of providing external interference protection in accordance with Clause 5.5.2.1. In T1 and T2 location classes, where thickness is the method chosen to provide penetration resistance, the thickness necessary to provide a minimum level of penetration resistance.

(c) The thickness required to provide the minimum critical defect length needed to prevent rupture in Location Classes T1 and T2, or elsewhere if required by the Design Basis.

(d) The thickness required to satisfy the stress and strain criteria.

(e) The thickness required to control fast running fracture.

(f) The thickness required for “special construction”.

(g) The thickness required for constructability and maintainability of the pipeline, including provision for future hot tapping, where required.

(h) The thickness required to achieve a design stress level selected for its contribution to SCC mitigation at locations where the SCC risk is increased by operation at temperatures above 45°C, and at locations subject to high operating pressure range.

(i) The thickness required to achieve adequate fatigue life where this is determined to be a consideration in the operating life of the pipeline

(j) The thickness required to prevent collapse from external pressure.

5.4.2 Wall thickness for design internal pressure

The wall thickness (t_W) for design internal pressure of pipes and pressure-containing components made from pipe shall be the thickness required for pressure containment (tDP) plus the thickness provided for allowances (G) determined by the following equations:

G t

t_W = _DP + ... 5.4.3.1 NOTE: It can be shown by stress analysis that the lowest stress in a bend is on the outside of the bend. A reduction in wall thickness on the outside of the bend up to the limits permitted in the material standards for induction bends (up to 10%) will not reduce the pressure strength of the bend.

The design factor (F_D) for pressure design of pipe shall be not more than 0.80, except for the following for which the design factor shall be not more than the values nominated in Table 5.4.2.1:

TABLE 5.4.2.1

MAXIMUM VALUE OF DESIGN FACTOR

Location Maximum value of F_D

Pipeline assemblies 0.67

Any section of a telescoped pipeline for which the MAOP is based on a test pressure factor of less than 1.25

0.60

Pipelines on bridges or other structures 0.67

5.4.3 Allowances

Allowances shall be added to the pressure design wall thickness of a pipe or a pressure-containing component made from pipe to provide for identified factors that may during construction, or over the life of the pipeline, reduce the pressure design thickness.

Allowance may be made to compensate for a reduction in thickness due to manufacturing tolerances, corrosion, erosion, threading, machining and any other necessary additions.

The allowance shall comply with the following:

5.4.3.1 Manufacturing tolerance

The manufacturing tolerance for line pipe manufactured from strip or plate to nominated standards such as API 5L shall not be applied to the required thickness calculated using equation 5.4.3.1

NOTE:This manufacturing tolerance relates to local thinning. General wall thickness is controlled by the weight tolerance of the pipe.

The seamless pipe manufacturing process can result in pipe of minimum thickness along one side of the length whilst still complying with the weight tolerance. Pipes manufactured by this process may require a specific manufacturing tolerance determined by the requirements of the nominated standard or the project specification (see Section 3).

5.4.3.2 Corrosion or erosion

Where a pipe or a pressure-containing component made from pipe is subject to any corrosion or erosion, G shall include an amount equal to the expected loss of wall thickness.

NOTE:A corrosion allowance is not required where satisfactory corrosion mitigation methods are employed.

5.4.3.3 Threading, grooving and machining

Where a pipe or a pressure-containing component made from pipe is to be threaded, grooved or machined, G shall include an amount equal to the depth that will be removed.

Where a tolerance for the depth of cut is not specified, the amount shall be increased by 0.5 mm.

Where a significant allowance is included, consideration should be given to the benefits of appropriately increasing the strength test pressure. This may require the use of stronger fittings.

5.4.4 Wall Thickness Design for External Pressure

The permitted external pressure P_EXT shall be determined from the following equation:

5 0 5.5 EXTERNAL INTERFERENCE PROTECTION

5.5.1 General

A pipeline shall be designed with the intent that identified activities of third parties will not cause injury to the public or pipeline personnel, loss of contents which would damage the environment, or disruption of service.

A pipeline shall be designed so that a combination of physical measures and procedural measures are implemented to prevent loss of integrity from external interference by identified threats.

Where the combination of physical measures and procedural measures specified in Table 5.5.4.2 cannot be fulfilled, failure analysis shall be conducted in accordance with Clause 2.3.4.

The purpose of physical measures is to prevent loss of integrity resulting from an identified third party interference event by either physically preventing contact with the pipe, or by providing adequate resistance to penetration in the pipe itself.

The purpose of procedural measures is to ensure that no third party activity, with potential to damage a pipeline, occurs without the knowledge of the pipeline operator, and that the people undertaking such activity are aware both of the presence of the pipeline and the possible consequences of damaging it.

A complete package of external interference protection measures also includes safe operating procedures for working near a pipeline and an emergency response plan. These are covered in AS2885.3.

5.5.2 Depth of Cover

Table 5.5.2.1 provides minimum depth of cover for each location classification. The minimum cover requirements may be reduced where other physical protection measures provide effective physical protection to the pipeline.

Additional protection shall be provided where the minimum depth of cover cannot be attained because of an underground structure or other obstruction, or maintained because of the action of nature (e.g. soil erosion, scour).

The depth of cover over a pipeline shall be taken as the distance from the top of the pipeline or casing to the lower side of the finished trench.

Specific requirements are established for road and rail in Clause 5.8.7.

TABLE 5.5.2.1

MINIMUM DEPTH OF COVER

Minimum Depth of Cover

Contents Location Class

Normal Excavation Rock Excavation (See Notes 1 to 5)

U, HD, I, HI S, W 1200 900

HVPL (See Note 6)

R1, R2 900 600

S, W 1200 900

U, HD, I, HI 900 600

Other than HVPL

R1, R2 750 450

5.5.3 Depth of Cover —Rock Trench

Figure 5.5.2.1 shall be used in applying the reduced cover provisions of Table 5.5.2.1 in areas classified as continuous rock.

At locations where cover is reduced in rock, normal cover shall continue for a minimum distance of 1200 mm into the rock. The minimum length of continuous rock over which a reduction of the depth of cover for rock may be applied shall be 50 metres.

Natural ground elevation Soil

50,000 Min.

1200 Min.

1200 Min.

Rock cover (Table 4.2.5.3) Rock cover

(Table 4.2.5.3)

Rock cover (Table 4.2.5.3)

Normal cover (Table 4.2.5.3)

Normal cover (Table 4.2.5.3)

FIGURE 5.5.2.1 DEPTH OF COVER IN ROCK NOTES:

1 This Standard defines “rock” as material with a uniaxial compressive strength greater than 50 MPa. For field assessment, hand held specimens of the weakest material in this classification can be broken by a single blow with a geological hammer. This material requires excavation by special “rock” excavation equipment, or by blasting. Material satisfying this criteria is defined as Class A – Strong Rock in AS 1170 (currently 5212-PDR – the earthquake code).

2 To provide effective physical protection, the rock forming the trench walls must be generally vertical, unbroken, and containing few fractures.

3 Good practice requires that the trench design is based on the depth required to provide the minimum cover at the lowest rock elevation. Pipe should be laid with the top of pipe at this elevation until changed by another governing feature, rather than varying the elevation as the rock surface elevation changes.

4 Design measures should ensure that selected material specified to protect the pipeline coating and to ensure continuity of an electrolyte for continuous cathodic protection will not erode with time when protected by a porous crushed rock backfill.

5 Marker tape shall be installed above the pipe over the full extent of rock excavation.

6 HVPL requirements shall apply to dense phase fluids.

5.5.4 Design for protection—General Requirements

The pipeline design shall identify and document the external interference events for which design for pipeline protection is required. Activities which could occur during the design life of the pipeline shall be considered.

NOTE: Appendix B provides guidance on the definition of design cases for protection.

External interference protection is to be achieved by selecting a combination of physical and procedural measures from the methods given in Table 5.5.4.1.

Compliance with the minimum requirements for pressure design wall thickness, depth of cover and marking shall not be considered to constitute design for protection.

TABLE 5.5.4.1

Resistance to penetration Wall thickness Barrier to penetration

Each of the methods given in Table 5.5.4.1 are considered separate independent protection measures and each can be used in conjunction with any other method in Table 5.5.4.1 to achieve compliance with the requirements of this Clause.

The minimum number of physical and procedural measures adopted shall comply with Table 5.5.4.2.

TABLE 5.5.4.2

MINIMUM NUMBER OF PROTECTION MEASURES

Classification of

1 The number of physical measures in locations Class T1 and T2 may be reduced to 1 where the designed physical measure is determined to provide absolute protection from the design event in the location. Note is not mandatory – is clarify this

2 Physical measures for protection against high powered boring equipment shall not be considered absolute.

3 In CIC locations, formal procedures should be developed with other users of the CIC to control the activities of each user

5.5.5 Physical protection measures

Physical protection measures shall be selected from the following:

(a) Separation

Protection of the pipeline may be achieved by separation of the pipeline from the activities of third parties. Methods of separation include the following:

(i) Separation by burial

Burial is a protective method which separates the pipeline from most activities of third parties. Burial may be counted for compliance with Table 5.5.4.2 when the depth of burial is considered to preclude damage to the pipeline by the defined third party events relevant to the location.

Burial is not required where—

(A) The pipeline is on land under the direct control of the pipeline licensee;

or

(B) When approved, in Location Class R1 for pipelines carrying liquids where an approved investigation determines that the risks of external interference do not require burial. Pipelines carrying compressed gases, HVPLs or multiphase or dense phase fluids are excluded from this exemption.

For the purposes of this Clause, the depth of cover shall be taken as the distance from the top of the pipeline or casing to the finished construction measured at the lower side of the trench.

Specific requirements are established for road and rail in Clause 5.8.7.

Table 5.5.2.1 provides minimum depth of cover for each location classification where burial is used as a protective measure. The minimum cover requirements may be reduced where other physical protection measures provide effective physical protection to the pipeline.

(ii) Separation by exclusion

Exclusion is a physical protection measure intended to exclude external interference from access to the pipeline. Fencing is an example of exclusion.

Exclusion is considered to meet the requirements of Table 5.5.4.2 where access to pipeline facilities is controlled by the pipeline licensee.

(iii) Separation by barriers

Barriers are a physical protection measure against certain types of external interference events, particularly those involving vehicles and mobile plant.

Crash barriers on bridges carrying pipelines are an example of separation by barriers.

(b) Resistance to penetration

Resistance to penetration is a physical measure for protection if the resistance to penetration is sufficient to make penetration improbable.

NOTE: For fibreglass pipe resistance to penetration is not considered to be an effective control for most pipe that would be considered cost effective as an alternative to steel.

Resistance to penetration may be achieved by the following:

(i) Wall thickness

The required wall thickness to resist penetration by the defined interference activities may be determined experimentally or from experience.

Wall thickness may be counted for compliance with Table 5.5.4.2 where the nominal thickness is greater than the thickness required to prevent penetration, for the design events relevant to the location.

NOTE: Wall thickness for resistance to penetration is not determined directly by stress calculations. An increase in penetration resistance may be achieved by changing the grade of the pipe used, provided the resultant stresses in the pipe comply with Clause 5.4 (Wall thickness).

(ii) Penetration barriers

Physical barriers may be used to resist penetration. Where a barrier prevents the design external interference threat (see Clause 5.5.4) from access to the pipeline the barrier may be counted for compliance with Table 5.5.4.2.

Barriers may be one of the following:

(A) Concrete slabs Slabs used to provide protection shall have a minimum width of the nominal diameter plus 600 mm. Slabs shall be placed a minimum of 300 mm above the pipeline.

(B) Concrete encasement Concrete encasement used to provide protection shall provide a minimum thickness of 150 mm on the top and sides of the pipeline.

(C) Concrete coating Concrete coating used to provide protection shall be reinforced and shall have a minimum thickness determined in the protection design.

(D) Other barriers Other physical barriers may be used.

Barriers shall have the mechanical properties necessary to provide the required protection for the design events, and have the electrical, chemical and physical properties necessary to maintain the efficacy of cathodic protection to be applied to the pipeline.

Where the performance of barriers cannot be established by calculation, the performance may be established by testing.

5.5.6 Procedural measures

Procedural measures shall be selected from the following:

(a) Pipeline Awareness Pipeline awareness measures are active or passive measures implemented to inform external parties of the presence of and potential danger from external interference to the pipeline. Pipeline awareness measures include:

(i) Marking Clause 4.4 defines the minimum requirements for marking. Where marking is to be counted as a procedural measure for compliance with Table 5.5.4.2 at any location, one of the following shall also apply:

(ii) Signs Signs shall be installed so they are visible to any party undertaking a design external interference event.

(iii) Buried marker tape Buried marker tape shall be installed so that the design interference event cannot damage the pipeline without first exposing the tape.

The design interference event is of such a nature that it is likely that at least one person involved in the event will see the marker tape immediately it is exposed.

Minimum requirements for buried marker tape are as follows:

(A) Tape shall be located a minimum of 300 mm above the pipeline.

(B) Tape shall be permanently coloured with a high visibility colour.

(C) Tape shall identify the nature of the buried pipeline.

(D) Tape shall have sufficient strength, ductility and slack to prevent it breaking before it becomes visible.

(E) Tape shall have a lifespan not less than the design life.

(iv) Landowner, occupier and public liaison Landowner, occupier and public liaison is an important measure in maintaining the awareness of landowners, authorities and the public of the presence of the pipeline and the limitations on

activities in the vicinity of the pipeline. Liaison is considered to contribute to compliance with Table 5.5.4.2 when:

(A) Systematic landowner and public liaison is carried out in accordance with AS2885.3, and

(B) The liaison program includes liaison with the developer, planning authority, or contractor responsible for the design interference event and, in the case of an event on private property, the owner and occupier of the land.

(C) The operator can demonstrate that the target audience has comprehended the information provided.

In developing public liaison programs, landowners and occupiers should be considered separately from public authorities such as shires, utilities, land use planners and contractors because of the different ways that each group can affect a pipeline.

(v) Participation in one-call service A one-call service which allows third parties to obtain accurate information on the location and nature of buried services before undertaking activities in the vicinity of a pipeline is an important measure for preventing unauthorized activities. One-call services are not considered to be as effective in R1 and R2 Locations. Participation in a one-call service is considered to contribute to compliance with the requirements of Table 5.5.4.2 when:.

(A) The location of the design interference event is within the area covered by the one-call service, and

(B) The pipeline operator has systems in place to ensure an accurate and timely response to one-call inquiries, and

(C) The pipeline operator has suitably qualified staff available to provide assistance and advice in cases where work is to be performed near the pipeline.

Where a one-call service is mandated by legislation or regulation, participation in a one-call service is considered to be of greater value and may substitute for one physical measure of protection.

(b) External Intrusion Detection External intrusion detection is a procedural measure which can reduce the occurrence of potentially damaging events. It includes the following:

(i) Patrolling Patrolling is an important measure in protecting the pipeline from external activities and also protecting it from damage caused by natural events such as erosion. Patrolling of the pipeline route is considered to contribute to compliance with Table 5.5.4.2 when:

(A) Systematic patrolling is carried out in accordance with AS2885.3, and (B) The frequency of patrolling, and the methods of surveillance used, are

such that there is a high probability of detecting the design interference event before the pipeline can be damaged

(ii) Planning notification zones Planning notification zones are considered to contribute to compliance with the requirements of Table 5.5.4.2 when:

(A) The design interference event is part of a project that is required by law to be notified to the pipeline operator at the planning stage.

(B) The pipeline operator has systems in place to ensure that the progress of the project is monitored regularly following notification.

(c) Remote Intrusion Monitoring Remote intrusion monitoring is considered to contribute to compliance with Table 5.5.4.2 when:

(A) The monitoring system is able to reliably detect the design interference event, and raise an alarm, before the pipeline is damaged, and

(B) The alarm indicates the location of the activity with sufficient accuracy that a person standing at the indicated location can readily see the threatening activity, and

(C) The pipeline operator has systems in place to ensure a patrol is mobilised after an alarm is raised, and can reach the indicated location before damage to the pipeline occurs, and

(D) The incidence of false alarms is low. 5.5.7 Other protection measures

Other measures which are effective in protecting the pipeline or in preventing events which could cause damage to the pipeline, may be approved by the pipeline licensee and counted towards compliance with Table 5.5.4.2.

Note: Additional information on the effectiveness of awareness measures can be found in Appendix D.

5.6 PRE-QUALIFIED PIPELINE SAFETY DESIGN

The pipeline design as set out below shall be deemed to be pre-qualified for AS2885 design to the extent as set out below and under the restrictions set out below.

The pipeline design as set out below shall be deemed to be pre-qualified for AS2885 design to the extent as set out below and under the restrictions set out below.

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