17TR2-2003 The Ageing of PA-11 in Flexible Pipes.pdf

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The Ageing of PA-11 in Flexible Pipes

API TECHNICAL REPORT 17TR2 FIRST EDITION, JUNE 2003

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The Ageing of PA-11 in Flexible Pipes

Upstream Segment API TECHNICAL REPORT 17TR2 FIRST EDITION, JUNE 2003


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SPECIAL NOTES API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. API is not undertaking to meet the duties of employers, manufacturers, or suppliers to warn and properly train and equip their employees, and others exposed, concerning health and safety risks and precautions, nor undertaking their obligations under local, state, or federal laws. Information concerning safety and health risks and proper precautions with respect to particular materials and conditions should be obtained from the employer, the manufacturer or supplier of that material, or the material safety data sheet. Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent. Generally, API standards are reviewed and revised, reafÞrmed, or withdrawn at least every Þve years. Sometimes a one-time extension of up to two years will be added to this review cycle. This publication will no longer be in effect Þve years after its publication date as an operative API standard or, where an extension has been granted, upon republication. Status of the publication can be ascertained from the API Upstream Segment [telephone (202) 6828000]. A catalog of API publications and materials is published annually and updated quarterly by API, 1220 L Street, N.W., Washington, D.C. 20005. This document was produced under API standardization procedures that ensure appropriate notiÞcation and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this standard or comments and questions concerning the procedures under which this standard was developed should be directed in writing to the standardization manager, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the general manager. API standards are published to facilitate the broad availability of proven, sound engineering and operating practices. These standards are not intended to obviate the need for applying sound engineering judgment regarding when and where these standards should be utilized. The formulation and publication of API standardsSign is not inthis anytitle way to upintended to vote on inhibit anyone from using any other practices. Useful Not useful Any manufacturer marking equipment or materials in  conformance  with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such prod-

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FOREWORD API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conßict. Suggested revisions are invited and should be submitted to the standardization manager, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

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CONTENTS Page

1

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .

2

THE AGEING OF PA-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2.2 The Effect of Water in Saturated & Unsaturated Conditions . . . . . . . . . . . . . . . . 1 2.3 The Effect of the pH of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2.4 The Effect of Different Crudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 2.5 The Effect of Hydrate Treatment Chemicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.6 The Effect of Treatment Chemicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 2.7 Other Effects on Chemical Ageing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 2.8 Determination of Ageing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

3

SERVICE LIFE PREDICTION MODELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 3.2 Input Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 3.3 Initial Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 3.4 Ageing Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

4

FIELD MONITORINGYou're OF PA-11. . . . . . .a. .Preview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Reading 4.1 Methods of Field Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 4.2 Implementation ofUnlock Monitoring Strategy . . .trial. .............. .............7 full access with a. .free

5

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.

APPENDIX A APPENDIX B APPENDIX C APPENDIX D

APPENDIX E APPENDIX F


DETAILED CHEMISTRY OF POLYAMIDE 11 AGEING. . . . . . . . . . 9 GUIDANCE ON LABORATORY EXPOSURE TESTING . . . . . . . . . 15 COMPARISON OF MOLECULAR WEIGHT DETERMINATION TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 RECOMMENDED PRACTICE FOR VISCOSITY  MEASUREMENT OF AGED AND FRESH Sign up to vote on this title POLYAMIDE 11 IN M-CRESOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19  Useful. . . SUMMARY OF ROUND ROBIN RESULTS . . . Not . . . .useful . . . . . . . . . . 25 VALIDATION OF INITIAL ACCEPTANCE CRITERION THROUGH DOCUMENTED FIELD EXPERIENCE. . . . . . . . . . . . . . 27

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CONTENTS Page

G-1 Comparison of KIC Values Obtained on Compact Test Specimen and Charpy Bars Aged in H 2SO4 pH 4 at 120¼C and Water at 140¼C . . . . . . . . . . . . . 29 G-2 Tensile fatigue: Samples Cut From Pipe and Sheath Aged in Benzoic Acid at 120¡C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

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The Ageing of PA-11 in Flexible Pipes 1 Introduction

appropriate acceptance criteria for the PA-11 w antioxidant are currently subject to further inves In the construction of a ßexible pipe, an inner polymeric quantiÞcation to assure at least equivalent ag pressure sheath is the only layer which seals the conveyed mance. Therefore it is assumed that the same serv ßuid within the pipe structure. Therefore, its integrity is crudiction method can be used for all PA-11 pipe. cial to safe and reliable operation. Polyamide 11 (PA-11) is The rate of the PA-11 ageing reaction is highl the most commonly used pressure sheath material (1), other on a number of operational factors including the options being polyvinylidene ßuoride and polyethylene. tent of the ßuid, temperature, acidity (due to car This document provides comprehensive guidance on matehydrogen sulphide, organic acids, inorganic acid rials and pipe issues regarding the use and operation of PA-11 position, and presence of oilÞeld treatment chemi in ßexible pipe applications, typically in production and gas methanol. Considerations regarding the chemic handling applications up to 100¡C. PA-11 are detailed in Appendix A, and summa The document concentrates on the use of PA-11 in the intersections which follow. Outline guidelines for con nal sheath of ßexible pipes, although similar considerations oratory ageing experiments are given in Appendix may also apply to other uses of PA-11 within ßexibles, e.g., It should be noted that other aspects of p anti-wear layers, intermediate sheathes and outer sheathes. unrelated to chemical ageing, may inßuence th The collective goal of this document is to prevent failure of polymeric material in a ßexible pipe, e.g., mech the internal pressure sheath, as a result of ageing and associerties, fracture toughness, creep, blistering p ated loss of mechanical properties, by determining and discoefÞcient of friction, thermal expansion, dyna seminating the necessary scientiÞc and practical information. ties, etc. These other aspects of performance are (2,3) API SpeciÞcation 17J and Recommended Practice 17B You're Reading ascope Preview of this document. contain only limited information with respect to these pheUnlock a freeTHE trial. EFFECT OF WATER IN SATUR nomena, and this report supplements and updates the full dataaccess in with2.2 (3) the Third Edition of API RP 17B . UNSATURATED CONDITIONS PA-11 is also used in umbilicals. However, the exposure Download With Free Trial Experimental results derived through JIP proj temperatures are frequently lower than production temperahouse research along with fundamental chemist tures. In cases of higher temperature exposure, the informaations conÞrm that the process affecting the agei tion contained in this document applies. in a water environment is reduction in the mole due to hydrolysis. This process is independent o 2 The Ageing of PA-11 thickness in typical pipe designs. There is now ment on from  different s 2.1 BACKGROUND Signthis up aspect to voteof onageing this title chemical mechanisms are discussed in Appendix useful The main ageing concern regarding PA-11 in ßexible pipe  Useful  Not If there is free water in a production stream, the applications, in the absence of oxygen in the bore ßuids, is age as if immersed in 100% water. It has also bee the effect of water at elevated temperature. The hydrolysis a free water phase is not necessary for such agei

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API TECHNICAL REPORT 17TR2

reßect in-situ operating conditions it must be carried out under pressure in order to account for the effect of the acid gases. Consideration of using either the partial pressure (and/or fugacity) of acid gases or pH of the water phase in determining the effect of acid gases on PA-11 ageing is currently under further investigation. Within this document, pH calculated using full water analysis is employed. There may also be a contribution to the pH of the water phase from acids in the oil phase, although there may also be other effects of such acids, as described in the following section.

2.4 THE EFFECT OF DIFFERENT CRUDES

becomes available, extrapolation of high temperature to lower operating temperature can then be used conservative indication of the effect of the batched on a PA-11 pressure sheath. The detailed effects of methanol are subject t investigation.

Glycols are also widely used offshore, e.g., M hydrate inhibition and TEG for gas drying. Glyco diffuse into PA-11 as quickly as methanol, and do n major swelling. Conservatively, the ageing effect is ble to water at pH = 7. Operators should be awa potential effects of acids created during glycol regen

Different crude compositions may affect PA-11 differently. 2.6 THE EFFECT OF TREATMENT CHEMI The most important ageing effect is derived from the socalled TAN (Total Acid Number) of the crude, rather than pH, Many different types of production chemical which applies only to the water phase. TAN is a gross meadeployed in the oilÞeld, some of which can have sure of the amount of organic acids, typically naphthenic carPA-11. The method of deployment is important. boxylic acids, within the crude (4). been prepared by considering data derived mainly f The effects of TAN are generally secondary relative to the ing of umbilicals. It should be taken as giving pre effects of water and pH. The principal effect of these high guidance only. If there is any doubt about compatib molecular weight acids, which are not soluble in water, is to production chemicals, then speciÞc evaluation shou give an extra ÒskinÓ effect, effectively a highly aged surface ried out. layer, on top of the pH effect. SpeciÞc ageing testing may be You're Reading a Preview required for very highly acidic crudes (TAN > 3.5). 2.7 OTHER EFFECTS ON CHEMICAL AG In order to quantify the effect of a speciÞc crudeUnlock on PA-11 full access with a free trial. it may be necessary to gain a more detailed knowledge of the 2.7.1 Wax and Scale acid species. Different ageing effects have been observed at Download With Free Trial similar TAN numbers. The effect of wax and scale is as yet undeÞned, there is some evidence to suggest that they may incre 2.5 THE EFFECT OF HYDRATE TREATMENT sure sheath life, e.g., as thermal barrier. This is, how CHEMICALS Þcult to consider in either initial pipe design or opera Hydrate treatment chemicals may affect the ageing of PA-11. Pure, liquid methanol diffuses easily and quickly through PA-11 and very effectively extracts plasticiser and swells the material. As a hydrate prevention and remediation measure, methanol is typically introduced either by continuous injection or in

2.7.2

The Effect of Treatment Fluids Trapp  Behind Carcass Sign up the to vote on this title

useful inNot It has  beenUseful shown that some circumstances, ßui trapped behind the internal steel carcass giving a environment. While this is not thought to be a proble

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THE AGEING OF PA-11 IN FLEXIBLE PIPES

Table 1 Chemical Nature

Continuous Injection

Scale inhibitor

Acrylate polymers or phosphates/phosphonates in aqueous solution, with ether and alcohol additions. Generally acidic.

No effect

PA-11 pressure sheath n contact with neat chemical, phonates can be aggressive.

Pour point depressants/ wax inhibitors

Ethylene Vinyl Acetate copolymers in solvents

No effect

No effect. PA-11 pressur normally in contact with nea

DemulsiÞer

Alkoxylated phenol formaldehyde, in solvents

No effect

PA-11 pressure sheath n contact with neat chemical.

Aromatic solvents

Benzene, toluene, xylene

No effect

Swelling above 40 ¡C. Minimise exposure.

Drag reducing agents

Very high molecular weight polyalphaoleÞns and polyacrylamides.

No effect

No effect. PA-11 pressur normally in contact with nea

Ca carbonate scale dissolver

Strong inorganic acids, Na EDTA and alternatives

Not used in dilute form

Strong inorganic acids shou used in PA-11 pipe.

Ba sulphate scale dissolver

Strong alkalis


Strong alkalis above pH = 1 not be used in PA-11 pipe.

Production Chemical

Effect of Neat Chemical

You're Reading a Preview Wax & asphaltene dissolvers

Aromatic solvents, e.g., No effect full based accesssolwith a free trial. xylene,Unlock or terpene vents, e.g., based on leminene

Aromatic solvents can ca above 40¡C. Minimise exposure.

Hydrate inhibitor

Neat alcohol, normallyWith metha-Free See section 2.5 Download Trial nol or glycol, but may be ethanol

See section 2.5.

NaOH

Hydrate inhibition


Strong alkalis above pH = 1 not be used in PA-11 pipe.

Corrosion inhibitor

Ethoxylated and quaternary amines in aqueous glycols or alcohols. pH in range 4 Ð 8

No effect

Note: Storage of umbilicals containing glycol or methanol at high ambient temperature has resulted in plasticiser extraction, which was

PA-11 pressure sheath n contact with neat chemical, Sign up to vote on this title aggressive and should be

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with the most highly aged material within the pre thickness rather than on the internal surface.

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Acceptable limit

Failure

t h g i e W r a l u c e l o M

k a e r B t a n o i t a g n o l E

s s e n h g u o T e r u t c a r F

Time

You're Reading a Preview

Figure 1—Illustration of the Transition in Mechanical Properties and MW with Time Unlock full access with a free trial.

need to use numerous, large samples, the fact that the tests are 3 Service Life Prediction Models destructive, and the fact that test samples are very susceptible Download Trial 3.1Free GENERAL to mechanical damage during machining. However, the big- With gest problem with this method is that it does not detect the The service life prediction models consist of tool extent of ageing until the material has entered the stage where dicting the ageing of PA-11 with time over Þeld e it begins to experience the sharp change in properties at the and initial acceptance criteria, based on corrected ductile-brittle transition. Other mechanical property measureviscosity, as described in 2.8. ments, such as fracture toughness, have been much less studService life prediction tools can be used to predic ied in ßexible pipe applications, but may offer advantage over Sign up to vote on this title in molecular weight and correlated properties over Þ elongation at break. Typically at the preliminary design stage, where  Useful  Not useful In contrast, molecular weight, and its associated experimenoperational parameters are not completely deÞned, tally measured properties, are able to detect changes throughapproach, a MinerÕs type rule is assumed for acc out the ageing period from new material up to and through the

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detailed review of the manufacturing history of a speciÞc ßexible pipe supplier. For evaluation of manufactured or aged pipes, the initial molecular weight or inherent viscosity should be that measured on the manufacturing run of the actual pipe in question, according to procedures in Appendix D. Operational data must be provided, in as much detail as possible. For example, at the design stage, a typical data set might include: temperature; water cut with time; CO 2 levels; pressure; predicted downtime; crude acidity; hot oil regime; etc. It is also necessary to include estimated cumulative exposure to production chemicals, e.g., methanol, acid etc. Temperature gradients across the pressure sheath thickness should not be considered. Given the sensitivity of the service life models to temperature, inclusion of the temperature proÞle of the development over Þeld life in any analysis can improve the reliability and accuracy of the predictions derived. As a project moves into the operational phase, the extent and accuracy of this data should increase and PA-11 service life veriÞcation can form part of the overall ßexible pipe integrity assurance process.

1.2 dl/g. This initial acceptance criterion typicall time based safety factor of 1.6 or more over failu at pH = 4, 1.75 at pH = 5, and 2 at pH = 6. It is recognised that this initial acceptance cri based on a large statistical base. However, from t ure results indicate it is conservative, and it is con laboratory experience. It should be noted that there is potentially a g reducing the initial acceptance criterion to 1.1 dl static applications. There are several reasons for t a. Stress levelsÑIn static applications, a pressu typically only subjected to thermal stresses whic than 3 MPa, e.g., in the case of cool down from 7 In a dynamic application, stresses as a result of ve typically range from 6 to 26 MPa, ignoring therm b. Number of cyclesÑA static pipe is typically 1000 to 5000 temperature and pressure cycles o time, whereas a dynamic pipe will see a much la of stress cycles, typically 10 8. c. Low strain rateÑIn static applications, strai typically very low. There is a growing body of suggest that under such circumstances the duc transition occurs at temperatures below those en 3.3 INITIAL ACCEPTANCE CRITERIA You're Reading a Preview typical Þeld conditions. The initial acceptance criterion for PA-11 pressure Unlocksheathes full access withd.a free trial. Field experienceÑAs shown in Appendix F, is based on the corrected inherent viscosity of the most highly ures of static lines have involved PA-11 m degraded material on the inside bore of the sheath reaching a corrected inherent viscosity lower than 0.95 dl/g. Download With Free Trial certain deÞned level. This case for setting a reduced initial acceptan It is acknowledged that in practise there may be a gradient for static pipe is currently undergoing further reÞ of corrected inherent viscosity across the wall thickness of the pressure sheath. Therefore, depending upon the failure mode, consideration of only the most highly degraded material is a conservative approach. Once the initial acceptance criterion is reach ed, the pressure sheath has aged signiÞcantly, as illustrated i n Figure 1. In order to continue using the pipe, an analysis of potential failure modes should be performed. This will aim to evaluate the margin of safety and address risk and criticality, in a remnant

3.4 AGEING CURVES

The prediction curves in Figure 2 are derived Sign up to vote on this title tial acceptance criterion of CIV = 1.2 dl/g. Useful relations Not useful The for these curves a mathematical in Table 2. The API RP 17B relations have been taken

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100.00

r e s c a n e a Y t p / e / g c l c d a l 2 . a 1 i t i = 10.00 n i I h V c C a f e r o o n t o i e r e t m i i T r c

pH = 5

pH = 7

API RP17B "Unsaturated

pH = 4

API RP17B "Saturated"

1.00 50

55

60

65

70


75

80

85

Temperature in deg C

Unlock full access with a free trial.

Figure 2—Time to Reach the Initial Acceptance Criterion of 1.2 dl/g


Table 2

Service condition

Mathematical relation for time to reach up to on this title initial acceptanceSign criterion of vote 1.2 dl/g

pH 7:

ln (Time in years) = 14033/T(K) - 38.383

pH 5:

ln (Time in years) = 14033/T(K) - 38.974

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4 Field Monitoring of PA-11 Section 13.2.1 of API RP 17B(3), and other international guidelines(9), call for the implementation of a risk based inspection & monitoring strategy for all ßexible pipes. Some outline guidance speciÞc to polymers is currently given in 13.4.3 and 13.4.4, and this is expanded in the sections which follow here.

4.1 METHODS OF FIELD MONITORING

` , , ` ` , , ` , , ` , ` , , ` -

For PA-11 pressure sheaths, monitoring options are either Òpassive,Ó i.e., coupons of PA-11 immersed in ßowing stream for removal at regular intervals (API RP 17B section 13.4.3), or Òactive,Ó i.e., dielectric sensing (API RP 17B section 13.4.4).

It is possible to install monitoring equipment and topsides. In production systems, subsea allows direct access to the most severe operating although coupon retrieval for example is more dif effort is required to enable topside monitoring t report the state of pipes throughout the system. T service history of all ßexible pipes is required condition can be determined through approp models. There is a need to place sample holders will be exposed to the most representative con downstream of chemical injection points. Any between the pipe exposure and the coupon expo be considered(11, 12). There is also a need for accurate, reliable ope for extrapolating topsides monitoring results to o the system: temperature; pressure; pH of the prod % water cut; and cumulative use of productio (acids, amines, alcohols, and hot oil). Periodic review of all this data to assess the pre technical integrity should form part of the ove pipe Integrity Management System (13).

Under the passive options, it is possible to construct ßanged spools to accommodate a number of samples held ßush with the pipe ID. This has the advantage of single sided exposure of the material, but access is difÞcult. The alternative option is to employ a standard access Þtting, with either ßush coupons or a ladder rack type coupon holder. This has the advantage of simpler access using standard equipment, commonly accommodating six to ten samples on a single 5 References probe, all exposed from all sides. A ßush coupon exposes a You're Reading a Preview 1. ÒState of the Art Flexible Riser Integrit very limited amount of material, but has the advantage of sinInternational for UK Offshore Operators Unlock trial. gle sided exposure of a thickness equivalent to that usedfull inaccess the with a free UKOOA reference: VES07A, 2002. ßexible pipe. In all cases, coupons should be manufactured

from material taken from the same manufacturing run, with Specification for Unbonded Flexible Pipe, 2. Trial Download With Free baseline properties characterised. Small sample analysis techcation 17J, Second Edition, November 1999. niques are availableÑtypically, CIV measurement requires 3. Recommended Practice for Flexible Pipe, approximately 1g of material. Larger samples for mechanical mended Practise 17B, Third Edition, March 2 testing have also been used by some operators. The only current ÒactiveÓ on-line option is the FDEMS (Frequency Dependent Electro-Magnetic Sensing) sensor. FDEMS measurements can be correlated to changes in mechanical properties, such as elongation at break. It has been shown that while mechanical properties change slowly with time until relatively close to failure and have large scatter, electrical measurements

4. ASTM D664-01 Standard Test Method fo ber of Petroleum Products by Potentiometric T 


5. Specification for Subsea Production Contro  Useful  Not useful API SpeciÞcation 17E, Second Edition, Septem 6. F. Dawans, J. Jarrin, T. Lefevre &

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11. M. H. Ottoy, H. Finstad, M. W. Mathisen, B. Moursund, & T. Nakken ÒField Experiences on RilsanTMÑ Ageing Compared to Data From Ageing ModelÓ in Proceedings of the 20th International Conference on Offshore Mechanics and Artic Engineering, Vol 3, pp. 391-398, American Society of Mechanical Engineers, 2001. 12. J. Chang & W.J. Newman ÒAnalysis of ßexible pipe polyamide 11 linerÓ in Proceedings of the 20th International Conference on Offshore Mechanics and Artic

Engineering, paper OMAE 2001/MAT-3580, A Society of Mechanical Engineers, 2001.

13. J.W. Picksley, K. Kavanagh, S. Garnha Turner, ÒManaging the Integrity of Flexible P Systems: Industry Guidelines and their Appli BPÕs West of Shetland AssetsÓ 2002 Offshore ogy Conference held in Houston, Texas, 6Ð9 M Paper OTC 14064.

` , , ` ` , , ` , , ` , ` , , ` -




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APPENDIX A—DETAILED CHEMISTRY OF POLYAMIDE 11 AGEING A.1

Introduction

where

The ageing of thermoplastics and the consequent loss of [-NHCO-] = concentration of amide units, materialsÕ properties are always complicated phenomena [-NH2] = concentration of amine end gr because of the superposition of several effects. Errors in the precise deÞnition of the real life ageing conditions can easily (-CO2HH] = concentration of acid end groups lead to false conclusions. [H2O] = concentration of water, In the case of PA-11 three main ageing processes have been identiÞed for the case of ageing in oilÞeld ßexible k = rate constant for solid state polyco p pipes(1, 2, 3, 4, 5, 6) : ¥ Structural changes due to annealing upon heating; k h = rate constant for hydrolysis. ¥ Swelling by oil components and water uptake as well as Four assumptions are made in order to calculat plasticiser loss; hydrolysis: ¥ Loss of molecular weight due to a chemical reaction with water, i.e., hydrolysis. Where: In oilÞeld ßexible pipes there is an absence of oxygen, and 1. Concentration of acid and amine end therefore, hydrolysis is clearly established as the main mechequal, i.e., anism for molecular weight loss. Moreover, as molecular weight goes down, the performance of PA-11 is eventually [-NH2] = [-CO2], at the beginning of the re affected, in particular elongation at break or impact resistance 2. Amide concentration is constant, i.e., (see also Appendix 6). There is wide experience within polyYou're Reading a Preview mer science of the concept that material toughness is lost with [-NHCO-] = constant. This hypothesis assume decreasing molecular weight (7, 8, 9). polymerisation level (conversion o ` , , ` ` , , ` , , ` , ` , , ` -


A.2 Hydrolysis in Neutral Medium, Water Download With Free Trial at pH 7 The hydrolysis reaction is reversible and can be described in simpliÞed form as follows:

to polymer) is high at all times. O beginning of the conversion of the reaction is relevant. Example: number-average molecular wei 11 around 30000 and a weight lar weight ( M w ) of 60000, ther

O CO2 H +

NH 2

C

N

+ H2 O

150 amide units per chain. To redu  it is nec molecular weight by half, Sign up to vote on this title hydrolyse one amide unit per chain



 is 1/150 parts or 0.67%. conversion

Useful

Not useful

H

3. Concentration of water is constant, i.e.,

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The rate equation for the reactions involved is:

A simpliÞed equation has been proposed as a tool, to describe the molecular weight decrease l hydrolysis (1, 23):

d [ -NH 2 ] d [ -C O 2 H ] Ð --------------------= Ð ------------------------dt dt

h t = h e + ( h Ð h e ) exp [ Ð K . t ] = k q [ ÐCO 2 H ] [ Ð NH 2 ] Ð k h [ Ð NHCO - ] [ H 2 O ]

where

The two opposing reactions, hydrolysis and recombination, lead to an equilibrium molecular weight being reached. A full derivation of this equation using the above approximations leads to the following equation describing the evolution of polymer molecular weight change as it decays from its initial value of M w to an equilibrium value M w as a i e function of time (3, 10): Mwi + Mw e 1+

M w

t

= M w

Jt

e

Mwi + Mw e - 1+

ht = corrected initial inherent viscosity, ht = corrected inherent viscosity at equili K = constant.

It is possible to trace this equation back to the exa ical expression if two additional assumptions are tak 1. The molecular weight depends linearly on inherent viscosity, such that: M nt = Aht , with A as constant.

Mwi - Mw e e

ht = corrected inherent viscosity at time

Jt

e

Mwi - Mw e

Starting from well-deÞned Mark-Houwink equati a [h] = K MH M w could be stated that such relationship could be You're Reading ait Preview

where

quite similarly to corrected inherent viscosity i

J = 2(k hk p[ÐNCHOÐ][H2O]) 0.5,

Unlock full access with a free trial. approximation: a'

and MW e µ ( k h ¤ k p [ Ð NH C Ð O ] [ H2 O ] ) Ð0.25 .

h = K ¢ M w .


Here, the notion of concentration must be used with care. Concentration is only well deÞned in homogeneous media, but solid PA-11 is not strictly homogeneous as there are amorphous and crystalline regions. The amount of crystallinity depends on thermal history but is typically 20% to 30%. As the amorphous regions largely prevail the notion of a quasi-homogeneous material is justiÞed. Furthermore, it has been shown that PA-11 hydrolysis is random along the chain supporting the assumption that heterogeneity due to the semi-

A linear interpolation is valid in a well-limited m weight range, leading to:

h = AM w + B, with A and B as constants.

However, in this case, constant B cannot be cons negligible, and it becomes difÞcult to validate the as  describedSign above. up to vote on this title h +h

e Useful expression 2. The holds: ---------------= 1 following  Not useful

h e + hi

This is only valid when the range of viscosities an close to the initial viscosity.

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in offshore oil and gas production conditions is important to estimate the lifetime of the PA-11. First detailed studies on acid degradation of PA-11 are given in References 31 and 32. The overall reaction is as follows: CO O

-

NH 3

pKa = 4,8

+

pKa = 10.6 COOH

+

O N

NH 2

C

+

A.5 The Effect of Organic Acids P in Oil

In the case of carboxylic acids present in crud ation must be given to the acidity (increase in pro tration) due to the acid additionÑas discussed a also to the carboxylic acid participating as an groupÓ in the equilibrium polycondensation / hyd tion, according to the following scheme:

H2 O

H

COO

-

+

NH3

By calculation, in water at pH 7, 99.97 % of amine end groups exist as ionic species (protonated form) and 99.37% of COOH O acid end groups exist as ionic species (deprotonated form). If + N C NH 2 then, for example, an acid of pH 4 is added, the deprotonated H R COOH carboxylate species, -COO-, is reduced to 13.68%, and the ammonium species, -NH3+, is increased to 99.99997%. This is important because the amine function, -NH2, is decisive for the pKa carboxylic acid polycondensation reactionÑit is the nucleophilic species capable of forming the chemical bond with the carboxylate group. R COO Therefore, the presence of acidity (with pH going from 7 to 4, for example) induces a very large decrease of the concentraYou're Reading a Preview tion of chemically active species in polycondensation, -NH 2, In the case of carboxylic acids, interaction of by three orders of magnitude (3 x10-2 to 3x10-5Unlock ). full access with a free trial. with PA-11 necessitates the diffusion of large m This decrease can also be considered as amine functions the polymer layer. This diffusion can be conside being eliminated from participation to the polycondensation depending Download Trialon nature and size of considered acid, equilibrium, as they become protonated. In chemical terms,With Free fusion of water or CO2(33). Therefore, a gradient this is amine scavenging linked to the presence of acids. reaction across the sample thickness can be obs samples retrieved from the Þeld have shown this Ò ` , , ` ` , , ` , , ` , ` , , ` -

A.4 Acidity Created by Carbon Dioxide

The presence of carbon dioxide and water creates carbonic acid: CO 2

+

H2 CO 3

H2O

H2CO 3 HCO 3

-

+

+

H

pKa = 6.37

The action of carboxylic acids participating a groupsÓ in polycondensation/hydrolysis reactio  reduced diffusion rate of large acid molecules in Sign up to vote on this title been illustrated by a case study where PA-11 w (34).Not Useful useful  acid phthalic buffer In this case, incorporatio ylic acid into PA-11 as chain end group was prove ical methods (FTIR, NMR, MALDI-T

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50 45 40

n 35 o i t b r 30 o s b a l 25 o n a 20 h t e M 15 % 10 5 0 0

20

40

60

80

100

120

140

160

Temperature ( C)

The presence of methoxy end groups, in the same amount importance to perform experimental tests in cond as amine end groups, correlated with the absence of acid end close as possible to the Þeld. Appendix B contains You're Reading groups in the PA-11 after reaction with methanol, has been asatoPreview how to exclude oxygen from laboratory tests, 13 1 (35) fully conÞrmed by C, H NMR, and FTIR analyses . mental precaution during any laboratory study devoted Unlockunder full access with a free trial. conditions. The concentration of methanol absorbed by PA-11 ageing in oilÞeld saturation conditions is much higher than the amount of water If no special care is taken during laboratory age absorbed at saturation. This explains why the extentDownload of molec- With oxidative degradation can easily occur, and results Free Trial ular weight decrease can be more than for water. Moreover, tests are of little use for oilÞeld applications. Th the amount of methanol absorbed in the PA-11 under saturahigher temperatures in laboratory tests to accelera tion conditions is much more temperature dependent than for reactions, in order to reduce experiment times, also water. Methanol absorption of BESNO P40 grades is illusutes to emphasise the potential inßuence of thermo-o trated in the above graph (36). processes. This Òquasi-solventÓ behaviour at high temperature (such  Experience that the Sign shows up to vote on presence this title of oxygen dur as 120¡C) induces modiÞcations of the polyamide morpholageing leads to speciÞc consequences: ogy which have a much more pronounced inßuence on mate Useful  Not useful 1. Rapid PA-11 coloration, yellow, then brow rial properties than molecular weight loss. Extrapolation of absence of oxygen, samples remain white. high temperature ageing results to actual service conditions 2. Typically, lower molecular weight values. is, therefore, not ideal.

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A.8

Literature References

1. F. Dawans, J. Jarrin, T. Lefevre, & M. Pelisson ÒImproved Thermoplastic Materials for Offshore Flexible Pipes,Ó Offshore Technology Conference Paper 5231, 1986. 2. P. Dang, Y. Germain, B. Jacques, J. Mason, & M. Werth, ÒLifetime Prediction of PA-11 and PVDF Thermoplastics in OilÞeld ServiceÑA Synthetic ApproachÓ American Chemical Society Rubber Division meeting in Dallas, 3/04/2000. 3. A.O. Meyer, N. Jones, Y. Lin, & D. Kranbuehl, ÒCharacterization and Modeling the Hydrolysis of Polyamide 11 in pH 7 Water Environment,Ó Macromolecules 2002, 35, 2784-2798. 4. M. Werth, G. Hochstetter, P. Dang, & N. Chedozeau, ÒPolyamide11ÑA High Tenacity Thermoplastic, its Material Properties and the Inßuence of Ageing in Offshore ConditionsÓ OMAE Conference June 24 Ð 28, 2002, Oslo, Norway.

14. D. Ravens & J. E. Sisley in Chemical R Polymers, ed. G.M. Kline Wiley Interscience p. 561.

15. Flory, P.J., Principles of Polymer Chemi University Press, Ithaka 1953: p. 75: ÒIntrinsic R Large Molecules is Independent of Molecule Random Hydrolysis Process Occurring in and p. 318: ÒTheory for Molecular Mass Distr 16. M.I. Kohan, Nylon Plastics Handbook, lisher, Munich 1995: p. 70.

17. Kunststoff Handbuch, Band VI Polya Vieweg, A. MŸller, Carl Hanser Verlag, MŸnc 483.

18. M.I. Kohan, Nylon Plastics Handboo lisher, Munich 1995: p. 18, 34: ÒReversib Reaction, Equilibrium;Ó p. 40: ÒDescription o ics;Ó and p. 43: ÒLimitation Effect Du stoechiometric Conditions.Ó

19. H.R. Kricheldorf, Handbook of Polymer 5. J. Jarrin, A. Driancourt, R.Brunet, & B. Pierre ÒDura A, Marcel Dekker, New York, 1992, p. 812 bility of Polyamide 11 For Offshore Flexible Pipe You're Reading a Preview polycondensation. Applications,Ó at MERL OilÞeld Engineering with Polymers, London, October 1998. Unlock full access with a free 20. trial. F. Pilati, Solid State Polymerisation in Co Polymer Science Vol. 15. Pergamon Press, Oxf 6. H.J. Fell & M.H. Ottoy, ÒAccelerated Ageing of PolyaDownload mide 11: Evidence of Physical Ageing Playing a Role inWith Free 21.Trial AtoÞna internal report, ÒPA-11 pH 7 Hyd the End-of-life CriteriaÓ Proceedings of OilÞeld Engi22. ENSAM JIP, Hydrolysis report, OMAEÕ neering with polymers 2001, MERL Conference 28-29/11/2002-03-18. 23. Coßexip CIV method. 7. F.W. Billmeyer, Textbook of Polymer Science, 3rd Edition, Wiley Interscience, New York, 1984, p 339. 8. Kunststoff Handbuch, Band VI Polyamide, ed R. Vieweg, A. MŸller, Carl Hanser Verlag, MŸnchen 1966, page 445.

24. B. Dolezel Chem. Prumysl 31, 218 ( (1956): Effect of acid diffusion into  solid p Sign up to vote on this title measured with color indicators dispersed in Not useful mide. Role of  diffusion control correlated  Useful molecule size and solubility in polyamide. 25. A. MŸller, R. PßŸger Kunststoffe 50,

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30. Frey, H.J., Knox, J.R. in Analytical Chemistry of Polymers Wiley, New York, 1959, ÒInßuence of Polyamide Nature and Crystallinity on Hydrolysis.Ó 31. G. Serpe, N. Chaupart & J. Verdu, ÒAgeing of Polyamide 11 in Acid Solutions,Ó Polymer, Vol 38 n¡8, 19111917, 1997. 32. G. Serpe, N. Chaupart & J. Verdu, ÒMolecular Weight Distribution and Mass Changes During Polyamide Hydrolysis,Ó Polymer, Vol 39 n¡6-7, 1375-1380, 1998. 33. Literature on acid diffusion in polyamides refer to [24] and [28].

35. AtoÞna internal report, ÒPA-11 Methanolys ysis of End Groups.Ó

36. AtoÞna internal report, ÒPA-11 Methanol Ab

37. T.R. Andersen, J.I. Skar, & C. Hansteen ÒP ity of Methane, Carbin Dioxide and Water in P PVDF for Flexible Pipes,Ó Eurocorr Congress 99

38. B. Flaconneche, M.H. Klopffer & C. Tara ÒHigh Pressure Permeation of Gases in Semic Polymers: Measurement Method and Experimen Proceedings of OilÞeld Engineering with Polym MERL Conference 28-29/11/2002-03-18.

34. AtoÞna internal report, ÒPhthalic Imide End-groups after PA-11 Ageing in Phthalic Acid Buffers.Ó




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APPENDIX B—GUIDANCE ON LABORATORY EXPOSURE TESTING B.1

General

This Appendix contains general guidance on the proper way to carry out ageing experiments to simulate oilÞeld environments, capturing the learning of the last few years.

B.2

Oxidation

Oxidation is primarily of concern in laboratory ageing tests rather than in the Þeld. If no special care is observed during laboratory ageing tests, two different degradation mechanisms will be present, and oxidative degradation will occur in addition to the hydrolysis. The use of higher temperature in laboratory testing than in real service conditions (in order to reduce experiment times) can also contribute to emphasise the inßuence of oxidation processes.

B.4 Single-sided Versus Multip Sample Exposure

Single-sided versus multiple-sided sample expo tutes another difference between real service an test conditions. Single-sided sample exposure rep ageing conditions, but is rarely reproduced in labo This is rarely a real issue in laboratory experimen primarily designed to determine or conÞrm agein

B.5 Sample Preparation for Me Testing

Tensile testing is often performed to char mechanical properties of aged PA-11. In such c preparation has an important inßuence on the resu

Different sample preparation methods can be ageing of a tensile specimen punched out extruded sheet; ageing of an extruded sheet befo out the tensile sample; ageing of an injection m To ensure the absence of oxygen in ageing experiments, ple; or ageing of tensile specimens machined fr high purity nitrogen or argon (> 99.999%) should be bubbled You're Reading a Preview pressure sheath. The sample preparation induce through the solution until the residual oxygen in the outlet gas surface is < 10 ppm. Unlock full access withina free trial.roughness and crystallinity, and ther results of mechanical tests carried out after age Even with proper ßuid replacement and oxygen removal larly elongation at break, without any effect on t procedures, performed at each sampling time, some very low Download With Free Trial weight. residual amounts of oxygen are nevertheless present after It is preferable to use extruded pressure sheath nitrogen bubbling. This results in conservative ageing data. order to adequately represent the mechanical b Any gas used as the ageing environment should likewise aged pipes in offshore conditions. have oxygen content < 10 ppm. As a result, a proper oxygen removal procedure is required for any laboratory study devoted to PA-11 ageing in Þeld conditions.

B.3

Open or Closed System

Another difÞculty concerning the relation between laboratory and Þeld conditions is linked to the ßowing service encountered in the Þeld compared to the static conditions mostly employed in laboratory tests.

B.6 Simulating Acidic Condition  Laboratory Sign up to vote on this title useful  Useful  Notthat It must be recognised different methods pH will affect ageing kinetics.

The effect of CO2 should be directly simulated

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the upper temperature limit for performing useful ageing tests on PA-11 samples. The presence of methanol greatly magniÞes the consequences of high temperature during laboratory experiments. Methanol solubility in PA-11 greatly depends on temperature, especially above 90¡C, and methanol becomes a solvent of polyamide at 140¡C. Therefore, experiments performed in pure methanol at high temperature (such as 120¡C for example) are in fact carried out in Òquasi-solventÓ conditions. It

has been observed that polymer structure (crystall and morphology) is hugely modiÞed by such Òquasi interactions. Methanol ageing data obtained at tem above 90¡C cannot be extrapolated to lower tempera High temperature (>120¡C) ageing of PA-11 with glycols can lead to the formation of acidic degradat ucts in the ßuid. This makes interpretation of such h perature tests difÞcult.




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APPENDIX C—COMPARISON OF MOLECULAR WEIGHT DETERMINATION TECH C.1

General

There are many different possible methods to measure polymer molecular weight, each with advantages and drawbacks. In the general case of polyamides, very limited solubility is an important factor making molecular weight determination a difÞcult task compared to many other polymers. However, an abundant literature exists and molecular weight determination of polyamides can be considered as standard today, though not necessarily ÒeasyÓ (1Ð12). The following methods are of interest:

amount of non-polymeric species present in the s ing to so-called Òcorrected inherent viscosityÓ assumption is made that these impurities do not affect the viscosity behaviour of PA-11 solutions. It is important to note viscosity gives relative m change in Molecular Weight based on the solvent ture usage. It does not provide an absolute measu lar weight. The solution viscosity can be converted weight, and vice versa, using the Mark-Houwi described in Appendix D. It is a robust method wh standardised and is reproducible in different labora d. Size exclusion chromatography (SEC) or gel chromatography (GPC) is based on the hydrod ume of dissolved polymer chains in solution and particles show when they pass through a porous has been shown that larger particles do not penet smaller pores and thus traverse more quickly th porous substrate than smaller particles which longer path-lengths.

a. End group analysis, i.e., titration of amine or acid end groups, is a very useful method for the molecular weight characterisation of polyamides. It counts the total number of chains in a very direct manner and is thus sensitive to the Ònumber-average molecular weight.Ó However, as the number of end groups is inversely proportional to the molecular weight, the method becomes limited for higher molecular weights. Experience shows that precision drops drastically at number-average molecular weights above 10000. Another Direct access to absolute molecular weight is drawback is the possibility of end group modiÞcation You'reduring Reading atoPreview the SEC method, but depends on the output d ageing. This method is not recommended for analysis of ßexand / or the calibration of the molecular weight us Unlock full access with a free trial. ible pipe components. standards. By connecting a multi-angle laser lig

b. Colligative methods, such as cryoscopy or vapour pressure (MALLS) detector to a GPC/SEC system, the ab osmometry, are based on thermodynamic principles (melting mass Trial and size distributions of a sample can be Download With Free point depression or vapour pressure depression). They are directly, without resorting to calibration technique sensitive to the number of molecules dissolved and hence assumptions about a sampleÕs conformation. allow the measurement of the Ònumber-average molecular MALLS instruments allow the molar mass and s weight.Ó The methods have not gained acceptance for polyation to be calculated. mides, mainly due to lengthy procedures and a lack of Different parameters such as the treatment of b standardised equipment. The often aggressive (corrosive, the choice of integration boundaries have  extensi Sign up to vote on this title toxic) character of polyamide solvents necessitates specialthe values obtained. Moreover, due to the aggre ised equipment. In principle, these methods are powerful and Not useful common polyamide solvents, care has to be take  Useful give absolute molecular weight data, but there is very little progressive deterioration of the porous statio data and experience available today. Minor changes in solvent quality can also have st

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g/mol; and 1.05 dl/g to M w 22500 to 27500 g/mol. Reports of molecular weight measurements should always state whether values are measured or calculated. If calculated, a full list of constants used should be included.

C.2

3. A.O. Meyer, N. Jones, Y. Lin, D. Kranbuehl terization and Modeling the Hydrolysis of Poly in pH7 Water Environment,Ó Macromolecules 2784-2798.

4. A.O. Meyer, Y. Lin, N. Jones, D. Kranbuehl Ò ment of a Room Temperature Laser Light Scatte System to make Absolute Measurements of the C Mw and Distribution in PA-11 During Degradat Chem. Soc. Poly. Mats. Sci. & Eng. 82, 58-59 (2

Conclusions

Of the methods available to quantify the molecular weight characteristics of PA-11, solution viscosity is a good standard method. It is widely used, simple to perform, easily automated and has a good chance to being reproducible in differ5. G. Marot, J. Lesec, Journal of Liquid Chrom ent laboratories. It provides a relative average of the 11 (16), 3305 (1988). molecular weight and does not provide a full description of the molecular weight distribution. Knowledge of the full 6. Y. Lin, Ph.D. Thesis ÒA Study of the ageing molecular weight distribution is not crucial in an hydrolysis mide-11 Based on Molecular Weight Measur experiment as it generally remains unchanged. College of William and Mary, 2000. SEC-MALLS is an additional method for molecular 7. C. Chuquiln Teran, E.M. Macchi, R.GV. Fig weight determination, which has potential to be useful in ßexnal of Applied Polymer Science, 34 (1987). ible pipe applications. Industry consensus regarding the application of this technique for routine assessment of PA-11 8. P.J. Wyatt, D.N. Villalpando, J. Liq. Chrom. life has not yet been reached. Fundamental work to establish Technol., 20 (1997). this as a standard method is on-going, as is determination of 9. D. W. Shortt, D. Roessner, P. J. Wyatt, Ameri the mathematical relationship between the various measures ratory, Nov. (1996). of PA-11 molecular weight. You're Reading a Preview 10. P. J. Wyatt, Analytic Chimica Acta, 272 (199

C.3

References


11. A. Moroni, T. Havard. Polym. Mater. Sci 1. Z. Tuzar, P. Kratochvil, M. Bohdanecky ÒDilute Solu(1997). in With Free Trial tion Properties of Aliphatic PolyamidesÓ in Advances Download 12. C.A. Veith, R.E. Cohen. Polymer. 30 (5) (19 Polymer Science 30, Springer Verlag, Berlin, 1979. 2. A.O. Meyer, Ph.D. Thesis ÒCharacterizing and Monitoring Changes in the State of a Polymer During Cure and Use-Ageing,Ó College of William and Mary 2001.


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APPENDIX D—RECOMMENDED PRACTICE FOR VISCOSITY MEASUREMEN OF AGED AND FRESH POLYAMIDE 11 IN M-CRESOL D.1 General D.1.1

SCOPE

Number and Limiting Viscosi Polymers in Dilute Solution. Glass capillary kinematic 3105 Specifications and operating in 6427-1982(E) Plastics—Determination of ma able by organic solvents (c methods). 3 DIN Viscometry: Determination o 51562-2 viscosity using Ubbelohde mi ter (1988).

This procedure describes a method for measurement of the dilute solution viscosity of plasticised Polyamide11 (PA-11, RilsanTM) in meta-cresol. The calculated corrected inherent viscosity gives information about the degree of degradation of the polyamide and thus can be used to determine the remaining service life of the material. It should be noted that the viscosity of polymer solutions can be affected by the presence of additives and absorbed species in the sample, including but not limited to colorants, ATOFINA Procedure MOD-LEM/ANACHIM Þllers, plasticisers or low-molecular weight species. It is (12/11/96) Determination de la Viscosite des P important with PA-11 to check what the absorbed or added Solution. species may be, and establish good methods to quantify them. Coßexip Ref.04DEET104 Viscosity test of po solution. Also, it must be known that the polymers used to establish Kranbuehl Lab. JIP Procedure for the Charac the correlations and those to which they are applied does not the ageing of Polymers in an Oil-Gas-Offshore E consist of or contain branched species. Severely aged PA-11 (Dec. 4, 1997). IV Intrinsic Viscosity Sample M may contain branches. You're Reading a Preview and Viscometer Cleaning. One should notice that the use of gravity type capillary visUS Patent 5,614,683: Method and apparatus cometers is limited to polymer solutions that do not deviate Unlock full access with a free trial. ing nylon 11 made from polyamide plastic mad much from Newtonian behaviour. noundecanoic acid. The procedure does not describe the safety concerns (if Measuring Download With Free Trial temperature in this procedure is any) connected with its use. due to practical and historical reasons. ASTM uses 30¡C while Kranbuehl lab. and ISO 1628 D.1.2 NORMATIVE STANDARDS AND recommends 25¡C. PROCEDURES API RP 63

D.1.3 REFERENCES Recommended Practices for Evaluation of Polymers used in Enhanced Oil Recovery Operations, Section 3, ÒPolymer Solution Rheology and Flow Through Porous Media.Ó

 Textbook FredSign W. up Billmeyer, Jr.;this to vote on title of Polymer S Wiley & sons. 1984.  Useful  Not useful R. Lapasin and S. Pricl, ÒRheology of Indust charides,Ó Blackie Academic & Professional, 199 J. Brandrup, E.H. Immergut, Polymer Han

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Table D-1 Common name

Also known as

Symbol and DeÞning Equation

Relative viscosity

Viscosity ratio

h r = h ¤ h 0 @ t ¤ t 0

SpeciÞc viscosity

Ñ

h sp = h r Ð 1 = ( h Ð h 0 ) ¤ h 0 @ ( t Ð t 0 ) ¤ t 0

Reduced viscosity

Viscosity number

h red = hsp ¤ c

Inherent viscosity

Logarithmic viscosity number

h inh = ( ln hr ) ¤ c

Intrinsic viscosity

Limiting viscosity number

[ h ] = ( h sp ¤ c ) c=0 = [ ( ln hr ) ¤ c ]c=0

h = viscosity (mPas) h0 = viscosity of the solvent (mPas) t = efßux time of polymer solution (seconds) t 0 = efßux time of the solvent (seconds) c = polymer concentration (g/cm3)

equation, see below). This is the case for linear, ßexible polywhere mers, but not for most branched polymers. The Mark-Houwink relations are tabulated in for instance Polymer k ' Ð k '' = 0.5, k '' = Kraemers constant. Handbook (Brandrup and Immergut). A number of quantities are related to viscosity; these include the relative viscosity, Inherent viscosity equals the intrinsic viscosity on ReadingNote: a Preview speciÞc viscosity, reduced viscosity and inherentYou're viscosity concentrations, but since Kraemers constant is usually low viscosity at a low concentration (0.5 g/dl for polyamide 1 (see below for deÞnitions). Unlock full access with a free trial.measure of intrinsic viscosity and therefo an approximate All these quantities are related to the polymer concentrapolymer chain length. tion in solution. Therefore, the intrinsic viscosity (which is All the above considerations hold for neutral p independent of concentration) is a more fundamental quantity With Free Download Trial Polyamide 11 has charged chain ends and protonat for determination of molecular weight. The intrinsic viscosity groups in solution. If such a solution is diluted the is the limit of the reduced (or inherent) viscosity as the conionic association between the polymer and its cou centration of polymers in solution goes to zero. That is, we becomes smaller. This causes an increase of the operate in the dilute regime, and often at a low Þxed shear effective net charge, which again causes an expansi rate. For more information see for instance ASTM D 2857-95 polymer and therefore also an increasein visco or Lapasin and Pricl (1995). up to vote on thisdilution title can be elim expansionSign of the polymer with Nomenclature of Solution Viscosity [from Billmeyer the ionic strength during dilution. In Usefulis kept Not useful (1984)] is given in Table D.1. constant of polyamide we measure at a polymer concentrati In the equation deÞning the relative viscosity, the efßux times is high enough to eliminate this so-called electro obtained from measuring with a capillary viscometer is used.

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where the parameters K , and a, depend on the particular polymersolvent pair and on the temperature, and M the polymer molecular weight. Note: The Mark-Houwink equation gives a relationship between intrinsic viscosity and the absolute molecular weight of a monodisperse polymer. Since most polymers are polydisperse, applying equation 3 gives a molecular weight ( M ) that is a so-called viscosity average molecular weight. The value of M lies between the number and weight average molecular weight. Generally, M is much closer to the weight average molecular weight than the number average molecular weight, and with a = 1 in Mark-HouwinkÕs equation, they are equal.

D.3 PA-11 Material Storage and Handling

¥ Glass sinter Þlters (pore size between 40m Dried glassware should not be used the nex stored under very dry conditions.

D.4.2 POLYAMIDE

Solid, powder, PEBAX or granulated Rilsan analysed with this method.

D.4.3 REAGENTS

Use only reagents of recognised analytical gra distilled water or water of equivalent purity. m-cr stored in a brown glass bottle.

m-cresol; meeting the speciÞcations of ISO 30

m-cresol content: 99 % (m/m) min. RilsanTM contains additives (10 Ð 12 wt %), and absorbs water and other solvents. Care must be taken when retrievo-cresol content: 0.3 % (m/m) max. ing, handling, transporting and storing samples from laborawater content: 0.13 (m/m) max. tory ageing or Þeld service, or long time storage of fresh reference samples. m-cresol of the required purity can also be ob To ensure that Rilsan TM samples does not change before distillation of chemically pure m-cres characterisation, it is recommended to store under dry, dark Alcohol or acetone for cleaning. and cool (below 20¡C) conditions. Irradiation may also You're Reading a Preview change the material. Chromic acid solution for cleaning, according For viscosity measurements: Sealed plastic bags, in refrigUnlock full access with a free trial. erator or at room temperature. D.5 Preparation of Test Samples For measurement of extractables: Wrap the samples in Alfoil, and keep them in sealed plastic bags, preferably in aWith Free D.5.1Trial REMOVING THE HIGH MW TAIL A Download refrigerator until measurement. EXTRUSION

D.4 Apparatus, Reagents and Materials This procedure refers to ISO 307:1994, with 20¡C in the bath instead of 25¡C.

D.4.1 APPARATUS ¥ ¥

Vacuum drying cabinet. Constant temperature bath at 20¡C ± 0.1¡C , oil bath or

Freshly extruded pressure sheath has a hig weight component in the MW distribution, whic of a regular polycondensation molecular weight with a polydispersity of 2. This high molecular  ponentSign is immediately hydrolysed up to vote on this title and does not c the working life of the polymer.  Useful  Not useful In order to deÞne the starting molecular weigh able to eliminate this component. This is done the sample to deoxygenated water (pH = 7) for

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samples may cause plasticizer to diffuse during drying). An additional 1-2 samples from the middle of the cross section and one sample from the outer surface. Dehydrate as described above. After this time, put samples to cool during 15 minutes in a drier/desiccator. The concentration is 5 ± 0.02 * 10 -3 g/cm3. Weighing must be done rapidly to minimise moisture pick-up (less than 2 min). Then, with a density for m-cresol of 1.034, we have: C = m ¤ v = ( m * d ) ¤ M = ( 1.034*m ) ¤ M

the upper graduation mark, and stop it exactly as th cus passes the lower mark.

The test result is valid as soon as three successiv agree within 0.5 %.

D.6.2 MEASUREMENT OF FLOW TIME OF SOLUTION Put the bath at a temperature of 20¡C ± 0.1¡C.

Pour a volume of 30 cm 3 of the solution in a grad tube, and then repour it through a glass sinter Þlter i cosimetric tube to a level between the two marks of

Wait about 30 minutes with the tube in the bath in reach the correct temperature in the solution.

m = weight of the polyamide (grams)

Bring the liquid above the upper graduation mar tion or pumping.

M = weight of m-cresol (grams)

Prepare about 30 cm3 of m-cresol in a graduated test tube. Pour 30 g of m-cresol into an Erlenmeyer ßask (250 cm 3). Weigh 0.145 g of polyamide to obtain a concentration of 5 ± 0.02 * 10-3 g/cm3.

When the liquid reaches a level slightly higher upper graduation mark, the tube is put under atm pressure, which allows the liquid to ßow down. the efßux time, start the timer exactly as the menisc the upper graduation mark, and stop it exactly as th cus passes the lower mark.

Add the polyamide into the Erlenmeyer ßask and heat it for 60 minutes at 100¡C with stirring. Check visually that the test result is valid as soon as three successiv You're Reading aThe Preview dissolution is OK. agree within 0.5 %. After dissolving the polymer do not wait more than 24 hours before measuring.

Unlock full access with a free trial. With each sample, carry out at least two determin

the inherent viscosity, each time using a fresh solut two successive Download With Free Trial values meet the repeatability req D.6 Procedure (better than 3%). The principle of the measurement is to determine the time After Þnishing the measurements on the polymer of ßow of a polyamide solution and of pure solvent (manother measurement on pure m-cresol should be cresol) manually (or automatically) in a calibrated tube. The the resulting efßux time compared with the efß obtained from the Þrst measurements. procedure used for a robotic system may be slightly different.

D.6.1

DETERMINATION OF THE FLOW TIME FOR M-CRESOL

All the glassware (Erlenmeyer, viscosity tube and gradu-

Sign up to vote on this title D.6.3 CLEANING PROCEDURE  Useful  Not useful



No cleaning necessary between measurements p on the same solution.

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D.7.1 BY VACUUM AND ELEVATED TEMPERATURE (ATOFINA PROCEDURE) Extraction/evaporation during more than 90 minutes at 230¡C in an oven at < 0.1 mbar vacuum, measured at the pump. Record the total weight loss of the material. Make sure this procedure is done on predried samples, identical to the samples weighed into solution. At least two parallels should be run on each sample (should be within 10%).

D.8 Viscosity Calculations D.8.1 INHERENT VISCOSITY (LOGARITHMIC VISCOSITY NUMBER) Calculate the inherent viscosity ratio for each solution concentration as follows: Inherent viscosity (cm 3/g ) = ln (t / t 0) x 1/c = ln (t / t 0) x M / (1.034 = log (t / t 0) x 2.30/c

-2 x m) x 10

¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥

Complete identiÞcation of the sample Exposure conditions if aged Date of retrieval and measurement Weight change since retrieval Changes in color or appearance Solvent Precipitation in solution Bath temperature Concentration of the test solution Weight before and after dehydration Extractables, weight before and after va extraction Measured inherent viscosity in dl/g Measured efßux times Corrected inherent viscosity in dl/g (with s deviation) Description of equipment Sampling method Reference to this procedure

D.10 Precision, Sources of Unce

where

The AtoÞna procedure gives the inherent vis ßow time for m-cresol (seconds),You're Reading a Preview with ± 0.02 dl/g. t = ßow time of the solution (seconds), 307-1994 reports a repeatability of 3% a Unlock full access with a ISO free trial. ducibility of 10 % for m-cresol solutions (res M = weight of m-cresol solution (g), Round Robin in 1982). Download With Free m = weight of the polyamide (g), AnTrial assessment of other possible sources of dev results is necessary; some of the possible facto c = concentration g/cm 3. below (from ISO R1628-1970): ¥ Surface tension D.8.2 CORRECTED INHERENT VISCOSITY ¥ Capillary end effect Corrected inherent viscosity is achieved by recalculating ¥ Drainage effect  with the correct polymer in-weight: ¥ Viscous effect Sign up heat to vote on this title ¥ Deviation of the viscometer from the ve (corrected viscosity) = (uncorrected viscosity) *  Useful  Not useful ¥ Hydrostatic head variations (100 / (100 - Extractable)) ¥ Losses by evaporation Extractable content is expressed in % by weight. ¥ Errors in concentration and efßux tim t 0 =

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APPENDIX E—SUMMARY OF ROUND ROBIN RESULTS E.1

Background

During 1999 work was initiated within the Rilsan TM User Group (RUG) to establish whether determination of corrected inherent viscosity (CIV) could be used as a standardised method in different laboratories to study PA-11 ageing. The aim of this work was to demonstrate that viscosity measurements could be reproduced in different laboratories, each with different degree of experiences with such measurements. The work was organised as a Round Robin exercise, with nine different participating laboratories. The measurements were intended to be done in accordance with a ÒRecommended Practice For Viscosity Measurement of Aged and Fre sh Polyamide 11 (PA-11, RilsanTM) in m-cresol.Ó The Þnal version of the recommended practice now given in Appendix D is based, among other things, on the input from the Round Robin.

Table E-1—Round Robin Test Resu Sample Pellets Extruded pipe Aged pipe (inner) Aged pipe (middle) Aged pipe (outer)

E.4

Mean [dl/g] 1.48 1.98

Standard deviation 0.04 0.07

1.20

0.05

1.26

0.03

1.45

0.07

Conclusions

Results show that CIV can be reproduced quite ferent laboratories. For all test samples, the maxi tion from the mean value is 8%. The small variati the different laboratories strongly points to the ro E.2 Samples Provided for the Round Robin this method, and the ability to use measurements standard method to follow Rilsan TM ageing. Three different samples of PA-11 were provided for all labIt should be noted that three laboratories als oratories. These consisted of: pellets; a new extruded pipe; molecular and an aged pipe. On the aged pipe, laboratories were asked You're Reading a Previewweights of the PA-11 samples using sion Chromatography coupled to a Multi Angle to analyse samples from the outer and inner surfaces, and from the middle part of the sheath. Unlock full access withScattering a free trial.detector (SEC-MALLS). For the high lar weights, variations of approximately 20% wer measured weight average molecular weights, wh E.3 Results of the Round Robin Download With Free lowestTrial molecular weights, the variation was a A summary of the determined average CIV-values are This rather large variation compared to the mea given in Table E.1, based on measurements from nine differvalues, combined with the fact that expensive eq ent laboratories. experienced personnel are needed to run the SE further conÞrm the use of viscosity measuremen dardised method to follow PA-11 ageing.


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APPENDIX F—VALIDATION OF INITIAL ACCEPTANCE CRITERION THROUGH DOCUMENTED FIELD EXPERIENCE F.1 General

F.5 Investigation 4

The Appendix summarises available data concerning the investigation of PA-11 pressure sheaths of lines retrieved from Þeld applications, and draws conclusions regarding an appropriate initial acceptance criterion. It is important to note that all failures of PA-11 pressure sheathes described in this Appendix have led to limited leakage of the pipe, and never to catastrophic failure.

A retrieved static ßowline did not fail and had from 1.30 dl/g to 1.80 dl/g (using sample thick mm). The temperature in inner skin was 83¡C su constant, in the middle of the sheath 74¡C and i 64¡C. The pH of water was 5.3. The total duratio was 4 years but the total duration at 83¡C was un

F.6 Investigation 5

F.2 Investigation 1 Three static lines were analysed, with only one showed brittle cracks on marks 0 and 400 m. The service temperature was estimated at 105¡C. The duration in service was 2 years. The ßuid was crude oil and water. The corrected inherent viscosity (CIV) of the inner surface of the pressure sheath was 0.81 dl/g.

F.3 Investigation 2

A jumper was retrieved after 9.5 years in serv ure has been found although the sheath had reach ageing level. CIV ranged from 1.10 dl/g to 1.82 sample thickness of 0.22 mm). The pH was 5.3. T ture was in average around 80¡C with peaks at total service with ÒwetÓ ßow was 7 years i.e., 7 total life. The pipe was operational for 6.8 years o 72% of the service life.


F.7 Investigation 6 A riser leaked due to a failure of the pressure sheath under the end Þtting. The fracture was all around the Unlock circumference full access with a A free trial. riser showed a leak of the pressure sheath un of the sheath. CIV measurements ranged from 1.05 dl/g to ener, with CIV ranging from 0.94 dl/g to 1.54 1.11 dl/g). The viscosity gradient in end Þtting was low as a sample thickness of 0.66 mm). Some propaga Trial result of the low temperature gradient caused byDownload the presenceWith Free occurred as well as star shape cracks. The ßuid w of a bend stiffener. with water. The service temperature was 83¡C b Three other cracks occurred during retrieval, within the 30 ments indicate that the ßexible supported a meters of pipe closest to the end Þtting. One crack was in the higher than 100¡C (most probably 105¡C). The T section of pipe open to air, the other two in the pipe which index) was 1.5 mg KOH/g. had been submerged in water. CIV ranged from 1.04 dl/g on  the inside surface to 1.28 dl/g on the outside (using sample up to vote on this F.8 Sign Investigation 7 title thickness of 0.2mm). The temperature in inner skin was estiNotpermanently useful A gas Useful injection riser, exposed mated at 82¡C and in outer skin at 68¡C. The pipe was in sermethanol (10 litres/hour) at 60¡C for 5 year vice for 9 years. retrieved and investigated due to concerns wit

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There was no failure. The inner sheath material has been examined and elongation at break was app. 250 %. CIV of inside surface was 1.18 dl/g, while the outside surface was 1.42 dl/g.

Two liner samples were taken from each ßowline, the end-Þtting area and one from several meters from Þtting. The liner ID CIV values are 1.38 and 1.25 in Þtting area and 1.34 and 1.33 outside the end-Þtting

F.10 Investigation 9

F.12

A ßexible production riser was in service for 2.5 years. During operation the operating temperature increased from 65¡C to more than 95¡C. At the same time water cut increased from less than 0.1% to more than 70%.The total duration with water was more than 2 years. CO2 partial pressure was 0.8 bar, with an average estimated total pressure at 45 bar. There was no failure. The inner sheath material has been examined and elongation at break was 62 %. CIV of the inside surface was 1.20 dl/g, while the outside surface was 1.45 dl/g (as measured by the Round Robin exercise reported in Appendix E).

A gas injection ßexible riser was retrieved after 3 service. It was initially used 7 days for oil produc water saturated oil, pH 6 at 97¡C. After 7 days, determined to be 1.87dl/g. After that the ßexible used for gas injection until it was taken out of opera 3 years. Temperature proÞle is available for a period the temperature varying in the range 73 to 79¡C. M was used in both batch and continuous injection. M ene Glycol was injected during the last year in opera

F.11 Investigation 10

Investigation 11

There was no failure. CIV values in the range 1.2 dl/g were determined. The upper part of the riser, ex the highest temperature, was most degraded.

F.13

Conclusions

Two 3-in. ID ßexible ßowlines were retrieved after six Review of industry experience shows that when years service as subsea ßowlines to transport production ßuid You're Reading a Preview highly degraded surface of a PA-11 pressure she from the same wellhead. The pipes did not fail during service or retrieval. The ßuid temperature was estimated to be 83¡C. below CIV = 1.00 to 1.05 dl/g it is likely to fail (see Unlock full access with a free trial.

.

Download With Free Trial #7. No failure in dynamic service

1.48

#4. No failure in static service 1.3 ` , , ` ` , , ` , , ` , ` , , ` -

#10. No failure in static service 1.25 #11. No failure in dynamic service 1.24


#8. No failure in dynamic service 1.18

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#9.No failure in dynamic service 1.14

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APPENDIX G—VALIDATION OF INITIAL ACCEPTANCE CRITERION THROUG LABORATORY CONSIDERATION OF FATIGUE AND FRACTURE MECHANIC G.1

General

Pressure sheath failures have tended to initiate with a crack parallel to the interior extrusion ribs, which grows into either a brittle crack with bifurcations (Òstar crackÓ) or a fatigue crack with banding. In addition, several failures have initiated at defects in the end-Þtting caused by machining during end Þtting assembly. It is important to note that the topside endÞttings, under bend stiffener and/or Þre insulation, can be a hot spot of the pipe, such that thermal degradation due to hydrolysis may be particularly severe. In order for a crack to occur in the pressure sheath, a stress must be imposed on the Òdefect.Ó

G.2

Sources of Stress

There are several possible sources of stress in the pressure sheath:

The fact that most initial cracks originate in th lel to the extrusion ribs without any apparent Òdef strates that defects are mostly well controlled material is tolerant of the extruded surface geome

G.4

Fracture Toughness

In its as-new condition, PA-11 generally fractu tile fashion. Brittle failure has only been observed which has been considerably aged. Test data dem correlation between K IC and molecular weight by inherent viscosity (see Table G.1).

Table G-1—Comparison of KIC Values Ob Compact Test Specimen and Charpy Bars H2SO4 pH 4 at 120°C and Water at

4.5

a. Thermal stressÑThermal stress in PA-11 is very small. 4 The expansion coefÞcient is 11 x 10-5 K-1 between -20 and You're Reading a Preview 3.5 50¡C and 23 x 10-5 K-1 between 50 and 130¡C. ) 3 5 b. Bending stressÑThis is the source of greatest stress on a . Unlock full access with 0 a free trial. 2.5 pressure sheath. Strain during spooling is limited to 7.7% by m / a 2 API Spec 17J. The geometry of the extrusion ribs on the inner P CT tensile H M Download Trial surface can lead to signiÞcantly higher localised triaxialWith Free ( 1.5 C I CT tensile wa deformation at the base of the ribs, which is thought to have K 1 been responsible for many observed failures. Charpy Bars w 0.5 c. Hoop stress due to a change in pressure within the pipeÑ 0 0 0.5 1 1.5 Ideally, hoop stress should be taken by the armour wires. Some hoop stress may be exerted on the pressure sheath due CIV (dl/g)  to rapid pressure changes and the small degree of freedom of Sign up to vote on this title the sheath between the carcass and the armour wires.  Useful  Not useful d. Pressure sheath creepÑThe pressure sheath is subject to Analysis of fracture faces has shown thr creep into gaps between wires, setting up stress Þelds. behaviour: e. Clamping stress within the end-fitting ÑThe stress exerted

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Table G-2—Tensile fatigue: Samples Cut from Pipe and Sheath Aged in Benzoic Acid at 120°C

450000 400000 e r 350000 u t p u r 300000 o t s 250000 e l c y c f 200000 o r e b 150000 m u N 100000

pipe 864N sheath 864N

no break

50000 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 CIV (dl/g

G.5

Fatigue

In the region 1.0 £ CIV £ 1.2, a ductile / brittle tra a function of temperature and strain rate is curren Fatigue experiments have been performed on aged sections construction, to guide operations with highly aged p of pressure sheath, including internal ÒribsÓ and smooth bore You're Reading aThis Preview is a conservative approach. A more detailed pipes (see Table G.2). (Starting strain = 4 % corresponding to mechanics approach, taking account of real stress a 12.5 MPa. Stress controlled fatigue cycles 1 Hz Unlock (maximum full access with a free trial. in the pipe could be developed with time. This is not frequency without self heating) between 10 and 100 % of undertaking on account of highly non-linear and tim imposed maximum stress. dent mechanical Download With Free Trial behaviour of PA-11, and the difÞcu The bars indicate viscosity gradients over the sheath thickculating actual stress and strain. ness. A rapid drop in fatigue resistance is observed at a CIV = 1.0. Below this value the material is essentially brittle. G.7 Literature on Fracture Mecha It can be observed that no signiÞcant differences exist between the fatigue resistance of smooth samples (open sym1. ISO task group working on the compa bols) and samples with an extrusion rib (closed symbols). method: ISO/TC61/SC2 n¡ 572.  This demonstrates the high defect tolerance of PA-11 which Sign up to vote on this title March 199 2. J.G. Williams testing Protocol, is not totally aged. Useful Not useful Eng. Dept. Imperial College, London.

G.6 Conclusion of Fracture Toughness and Fatigue Testing

3. ASTM E 399-81 Standard Test Method f Strain Fracture Toughness of Metallic Materials.

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APPENDIX H—RISER WORKED EXAMPLE A 500 m.-long, 6" ßexible production riser, handles 5000 bpd of three-phase production. The ßexible pipe structure has an insulation factor of 9 W/m/K, as a result of which the ßuid temperature decreases slightly along the pipe. The production temperature proÞle is estimated to be: Years 1 to 6: 58¡C (at the riser base) with a pH value of 5 Years 7 to 10: 65¡C (at the riser base) with a pH value of 6

In addition, we can calculate the remaining tim reach the initial acceptance criterion for a given of temperature and pH.

(Remaining time to reach CIV = 1.2 dl/g ) = (1-S) * (Time to reach CIV = 1.2 service T and pH).

Thus, for example, if after year 10, the tempera and pH is 6, (Remaining time to reach CIV = 1.2 dl/g ) = (1- 0.44) * 9 years = 5.1 years.

To determine the contribution of each of these periods to the ageing of the PA-11 sheath, MinerÕs Rule is used. By this method, the contribution of many diffe Under the conditions for the Þrst 6 years, the time for the can be assessed, e.g., production periods with di PA-11 sheath to reach the initial acceptance criterion of tions temperatures and pH, and also methanol ba CIV=1.2dl/g according to the curves in section 3.4 is 30 and the remaining time for the PA-11 pressure sh years. Thus, in the Þrst 6 years of service, the proportion of CIV = 1.2 dl/g calculated. this time which is expended is (6 / 30) = 0.20. If in this case coupons are installed topsides, th For years 7 to 10, the time for the PA-11 sheath to reach the effect of the riser needs to be taken into account. initial acceptance criterion of CIV=1.2dl/g is 17 years. This in In case of coupons installed at the platfo TM these 4 years, the proportion of this time expended is (4 / 17) = extremity) You're Reading a Previewto follow the Rilsan ageing. In this 0.24. temperature is 50¡C at the platform for the Þrst To assess the cumulative ageing, the two periods are the subsequent four, calculated taking Unlock full access with56¡C a freefor trial. summed, giving S = 0.2 + 0.24 = 0.44. the insulation factor of the pipe, its length and s The PA-11 sheath is close to half way to the initial accepßuid composition and the ßowrate. Comparison o Download With Free Trial corrected inherent viscosity of the tance criterion. If S ³ 1, the initial acceptance criterion is and measured reached. typically in good agreement.


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17TR2-2003 The Ageing of PA-11 in Flexible Pipes.pdf

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