COLLAPSE OF IN SERVICE DEEPWATER PIPELINES JOINT INDUSTRY ... fileCOLLAPSE OF IN SERVICE DEEPWATER...

3rd COPEDI Forum / 2013 – April 15, 2013 – CSDP JIP Proposal

COLLAPSE OF IN SERVICE DEEPWATER PIPELINES

JOINT INDUSTRY PROJECT PROPOSAL

(CSDP JIP PROPOSAL)

Adilson C. Benjamin (PETROBRAS R&D Center)


PRESENTATION TOPICS

BACKGROUND

CORROSION IN CARBON STEEL PIPELINES

DEEPWATER SCENARIO

CHARACTERISTICS OF THE PROBLEM

CSDP JIP PROPOSAL

INTRODUCTION

OBJECTIVE

SCOPE OF WORK

REFERENCES


PRESENTATION TOPICS

BACKGROUND



(1)

As the oil and gas fields discoveries are moving into deeper waters

far from the coast, the use of large diameter export pipelines is

increasing in the offshore industry.

Due to economic reasons lengthy export pipelines have to be made

of carbon steel.



(2)

Despite being the most cost effective option of pipeline material,

carbon steel has a major drawback: the susceptibility to corrosion.

Therefore sooner or later a carbon steel pipeline will be corroded.

Even when the transported fluid is dry gas, after some time in

operation it is not uncommon that corrosion begins to occur

because corrosive water does enter the pipeline occasionally as a

result of upsets in the gas processing facility.



(3)

In submarine pipelines it is generally accepted that the major threat

is internal corrosion rather than external corrosion which is

generally quite well addressed using good cathodic protection and

coatings.

The mitigation of internal corrosion requires attention throughout

the life cycle of the pipeline.

Besides the corrosion allowance that is established in the design

phase several techniques are employed during the operation phase

in order to mitigate internal corrosion.



(4)

Recognizing that it is almost impossible to preclude the occurrence

of internal corrosion in submarine pipelines, operators perform

periodically inline inspections using smart pigs to detect corrosion

defects.

After the detection of the corrosion defect the submarine pipeline

must have its structural integrity checked in at least two loading

conditions:

dominant internal pressure (pi > pe) and

dominant external pressure (pi < pe).



(5)

Due to the high cost of repairing deepwater pipelines the service

life of the corroded pipeline segments must be maximized.

In order to achieve this maximization it is necessary that the

assessment of the corrosion defects detected in the inline

inspection is performed using an accurate and experimentally

validated method.



(6)

The literature on corroded pipelines subjected to dominant internal

pressure is extensive and several experimentally validated

assessment methods are currently available.

The literature on corroded pipelines subjected to dominant external

pressure is limited and experimentally validated assessment

methods are not available.



PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO


(1)

Ever since the first pipeline was installed offshore, pipeline

developments have been moving into ever deeper waters.

While in the early days of the offshore industry 100 m water depth

was considered as deep, now pipelines are being installed in 2500 m

water depth or more.

Herein, water depths equal to or greater than 1000 m (3281 feet) are

considered deep.

DEEPWATER SCENARIO


(2)

As a pipeline is installed in deeper water, the external pressure that

the pipe have to be able to withstand increases.

Consequently the pipe becomes thicker.

Submarine pipelines usually have De / t ratios smaller than 30 while

deepwater pipelines usually have De / t ratios smaller than 20.

DEEPWATER SCENARIO

During installation the pipeline is empty and its portion that is

resting on the seabed is subjected to an external overpressure

(external pressure alone).


(3)

Corrosion is a time dependent phenomenon that usually requires

several years to produce a corrosion defect sufficiently large to

cause a significant reduction in the collapse pressure of the

pipeline.

Consequently during installation it is considered that the pipeline is

free of any metal loss due to corrosion.

In service, if the transported fluid is gas, an external overpressure

occurs when there is a shutdown of operation (scheduled or not).

DEEPWATER SCENARIO

If the transported fluid is oil, an external overpressure occurs when

after a shutdown of operation the line is evacuated (emptied).


(4)

For large diameter, heavy walled linepipe, the UOE pipe

manufacturing process is the general method applied by pipe mills.

The name UOE stems from the initials of three mechanical steps

which are carried out during the process:

U for U-ing cold forming from the plate,

O for O-ing cold forming from the Ushape,

and E for cold expansion to meet the geometric tolerances

DEEPWATER SCENARIO


(5)

Out-of-roundness (ovality) of the pipe cross section is one of the

imperfections introduced during the UOE pipe manufacturing

process.

Typical deep water pipelines can have an initial out-of-roundness of

at most 1%.

Another side effect of the UOE process is the reduction of the tube

compressive yield stress in the hoop direction.

DEEPWATER SCENARIO

As a result of the cold deformation caused by forming operation,

the transverse compressive yield strength measured on the pipe

may be lower than that measured on the plate.


(6)

However extensive research has shown that the de-rating of the

compressive yield strength can be compensated for by a heat

treatment at a moderately elevated temperature (about 200°C to

220°C).

This heat treatment is analogous to what the linepipe experiences

during the application of the anticorrosive coating (polyethylene or

polypropylene).

DEEPWATER SCENARIO


(7)

It is anticipated that over the next 20 years, deepwater field

developments will increase substantially in number and water

depth.

Potential areas of developments around the world include:

Gulf of Mexico;

Offshore Brazil;

West Africa;

UK Atlantic Frontier and

Norwegian sector.

DEEPWATER SCENARIO


(8)

The figure below presents a map in which oil and gas fields located

off the Brazilian coast are shown.

DEEPWATER SCENARIO


PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO



(1)

From a structural point of view an empty pipeline resting on the

seabed is a long circular tube subjected to an external hydrostatic

pressure.

Depending on its external diameter to thickness ratio (De / t) the

pipeline is classified as a thick tube (De / t less than 20) or as a thin

tube (De / t equal to or greater than 20).



(2)

Submarine pipelines usually have external diameter to thickness

ratios (De / t) that range from 10 to 30.

In this range of De / t ratio the failure behavior of a non corroded

pipeline subjected to an external pressure is characterized by the

interaction between plasticity and geometric instability.

That is, yielding of the pipeline cross section begins before the

collapse by geometric instability is attained.



(3)

The failure behavior of a non corroded pipeline subjected to an

external pressure is sensitive to initial imperfections introduced by

the manufacturing process, as for example:

Out-of-roundness (ovality) of the pipe cross section and

reduction of the tube compressive yield strength.



(4)

The failure behavior of a corroded pipeline subjected to an external

pressure is sensitive not only to initial imperfections but also to the

dimensions of the corrosion defect, that is,

the defect depth (d),

the defect length (L) and

the defect width (w).



(5)

The corrosion defect can be seen as a geometric imperfection

whose dimensions grow with time.

The detrimental effect of the corrosion defect on the pipeline

strength varies in function of its position in relation to the ovality of

the pipe cross section.

Depending on its relative position the corrosion defect intensify or

lessen the pipe ovalization.



(6)

Due to the complexity of the problem, the Nonlinear Finite Element

Method is the best method to calculate the collapse pressure of a

corroded pipeline subjected to an external hydrostatic pressure.

However a method composed of closed form equations,

experimentally validated, is more adequate to perform the collapse

check of the great quantity of defects detected in the periodical

inline inspections.



PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO


CSDP JIP PROPOSAL

INTRODUCTION


(1)

The literature about the problem of hydrostatic collapse of

corroded pipelines is limited.

Until now little research on corroded pipelines subjected to

external pressure has been carried out.

So far only nine full scale tests of tubular specimens containing

single corrosion defects have been performed.

INTRODUCTION

And research on pipelines containing closely spaced corrosion

defects subjected to external pressure has not been undertaken.


(2)

The problem of corroded pipelines subjected to external pressure

is much more complex than two correlated problems:

corroded pipelines subjected to internal pressure and

non-corroded pipelines subjected to external pressure.

However the literature about these two problems is extensive

and the number of full scale tests already performed is large.

INTRODUCTION


(3)

The assessment of corroded pipelines subjected to external

pressure is in an incipient stage of development.

More research projects are needed.

And much more full scale collapse tests must still be performed.

INTRODUCTION


(4)

Due to the high cost of repairing deepwater pipelines it is

anticipated that soon the oil companies will be highly interested in

the development of cutting edge methods for the assessment of

corrosion defects in pipelines subjected to dominant external

pressure.

Being aware that, in their early stage of development, several of the

key technologies in the petroleum industry were developed through

group sponsored projects, PETROBRAS decided to propose a joint

industry project (JIP) to address the problem of corroded pipelines

subjected to external pressure.

INTRODUCTION


(5)

This JIP, named Collapse of in Service Deepwater Pipelines Joint

Industry Project (CSDP JIP), will be conducted by Catholic

University of Rio de Janeiro (PUC-Rio).

Besides paying the JIP share fee PETROBRAS will have an active

participation in the project.

INTRODUCTION


PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO


CSDP JIP PROPOSAL

INTRODUCTION

OBJECTIVE


The objective of the CSDP JIP is to develop an extensive

experimental program in which full scale tubular specimens

containing internal single corrosion defects will be submitted to

external hydrostatic pressure up to collapse.

These defects will be generated using spark erosion.

Sound experimental foundations for the development and/or

validation of methods for the assessment of the hydrostatic

collapse of corroded deepwater pipelines will be established in the

experimental program that will be undertaken.

OBJECTIVE

A broad range of parameters, such as the defect depth (d), the

defect length (L) and the defect width (w) will be covered.


PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO


CSDP JIP PROPOSAL

INTRODUCTION

OBJECTIVE

SCOPE OF WORK


(1)

Twelve participants will be necessary to perform the full scope of

work of the CSDP JIP.

However a minimum of three participants will be sufficient to start

the project.

The CSDP JIP is composed of four modules.

SCOPE OF WORK

Fifteen tests will be performed in each of these modules.


(2)

If the project starts with less than 12 participants the project

activities will have to be reduced to fit the available financial

resources (see table below).

SCOPE OF WORK

60 tests12

55 tests11

50 tests10

45 tests9

40 tests8

35 tests7

30 tests6

25 tests5

20 tests4

15 tests3

Number of full scale tests performedNumber of Participants


PRESENTATION TOPICS

BACKGROUND


DEEPWATER SCENARIO


CSDP JIP PROPOSAL

INTRODUCTION

OBJECTIVE

SCOPE OF WORK

REFERENCES


The main references of this presentation are listed below.

1. Benjamin, A. C. and Cunha, D. J. S., “Assessment of the Hydrostatic Collapse of Corroded Submarine Pipelines: Current Status and Research Needs”, Proceedings of the Rio Oil & Gas Expo and Conference 2012, Paper IBP2124_12, 2012.

2. Cosham, A., “Assessment Methods for Corrosion in Pipelines”, A report to the Pipeline Defect Assessment Manual (PDAM) Joint Industry Project, Report NR99012/4238.1.72, Revision 3, September 2002.

3. Benjamin, A. C. and Cunha, D. J. S., “Assessment of Hydrostatic Collapse of Submarine Pipelines: An up-to-date Literature Review”, Proceedings of the Rio Oil & Gas Expo and Conference 2012, Paper IBP2132_12, 2012.

REFERENCES


Thank you for your attention!

COLLAPSE OF IN SERVICE DEEPWATER PIPELINES JOINT INDUSTRY ... fileCOLLAPSE OF IN SERVICE DEEPWATER...

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