1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU L.27 (I 0196) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Method for estimating the concentration of hydrogen in optical fibre cables ITU-T Recommendation
2、 L.27 (Previously CCIlT Recommendation) STD-ITU-T RECMN L-27-ENGL 177b 48b257L Ob35214 T5rl ITU-T L-SERIES RECOMMENDATIONS CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT For firther details, please refer to ITU-TList of Recommendations. FOREWORD The ITU-T (Te
3、lecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. T
4、he World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedur
5、e laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation L.27 was prepared by ITU-T Study Group 6 (1993-1996) and was approved by the WTSC (Geneva, 9-18 October 1996). NOTES 1. In this Recommendation, the expression “Administration” is used for conciseness to indicate
6、both a telecommunication administration and a recognized operating agency. 2. The status of annexes and appendices attached to the Series L Recommendations should be interpreted as follows: - - an annex to a Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation
7、 does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photoc
8、opying and microfilm, without permission in writing from the ITU. Recommendation L.27 (10/96) i CONTENTS Introduction . Annex A - Measurement of hydrogen released by each cable component by gas chromatography A.l Principle A.2 Equipment . A.3 Measurement procedures Annex B - Measurement of the conce
9、ntration of hydrogen in a cable sample A.4 Analysis B.l Unfilled cable B.2 Filled cable Annex C - Measurement of the long-term effectiveness of hydrogen-absorbing materials C.l Principle C.2 Apparatus C.3 Measurement procedures C.4 Analysis Appendix I - UK experience of hydrogen concentrations in mo
10、isture barrier optical fibre duct cables 1.1 Field experience 1.2 Analysis 1.3 References . Appendix II - Japanese experience of the loss increase due to hydrogen generation in water-blocking tape optical fibre cable II . 1 11.2 11.3 11.4 Structure and materials of the water-blocking tape cable Hydr
11、ogen generated from cable components Evaluation of loss increase due to hydrogen generation . Increase in loss in water-penetrated cable . Appendix III - Spanish experience of hydrogen generation in moisture barrier optical fibre cables 111.1 Cable structure 111.2 Field experience 111.3 Origin of th
12、e problem 111.4 Problem solution . Page 1 2 2 2 2 3 5 5 5 6 6 6 6 6 7 7 7 8 9 9 9 9 10 12 12 12 12 12 Il Recommendation L.27 (10/96) Recommendation L.27 METHOD FOR ESTIMATING THE CONCENTRATION OF HYDROGEN IN OPTICAL FIBRE CABLES (Geneva, 1996) Introduction Considerable experience has been gained usi
13、ng optical fibre cables in terrestrial and subsea applications showing that optical fibres provide a stable transmission medium. There are some situations where the concentration of hydrogen within a cable can rise to a sufficiently large value to cause the optical loss of the fibre to increase (see
14、 Appendix III). Therefore, there is a need to determine the build-up of hydrogen in a cable by considering the ways that hydrogen can be generated within it. If the escape of hydrogen through the polyolefin sheath or the overlap of a moisture barrier balances the hydrogen generated in the cable, the
15、 resulting concentrations within the cable do not cause a noticeable change in optical loss (see Appendices I and II). Considering a that hydrogen within a cable can result from: - - - - the hydrogen released from the cable components; the electrolytic action between components of different metal in
16、 the presence of moisture; the corrosive reaction of metallic components in the presence of moisture; the hydrogen within the air pumped into pressurised cable networks; b) external concentration of hydrogen is greater than that within the cable core; that hydrogen can escape by permeation through t
17、he cable sheath except for hermetically sealed sheaths of where the c) that the optical loss change, which is most noticeable at the wavelength of 1.24 pm andor 1.38 pm, arises from: - a temporary change due to molecular hydrogen within the fibre core which is proportional to the concentration (part
18、ial pressure) of hydrogen; a permanent chemical change which depends on the dopant and its concentration, due to hydroxyl formed by the chemical combination of diffused hydrogen molecules and structural defects in the silica glass of the fibre, - it is recommended 1) which could cause a noticeable i
19、ncrease in optical loss: that for cable types which may allow the Concentration of hydrogen within the cable core to build up to a value i) the concentration of hydrogen anticipated within the cable core should be estimated from a knowledge of the hydrogen released from the components of the cable.
20、If desired, the measurement method of gas chromatography described in Annex A can be used to determine the amount of hydrogen released from the cable components; the concentration of hydrogen in filled cables should be managed by one or more of the following: - - i) minimized by careful selection of
21、 the components of the cable; reduced to zero by the use, within the cable, of a hydrogen-absorbing material which should have an active life comparable to the life of the cable; have reduced influence on optical performance by the use of hermetically coated fibres or by the use of a hermetic sheath
22、 around the cable core in the event of the external concentration of hydrogen being greater than that within the cable core; - Recommendation L.27 (10/96) 1 iii) the concentration of hydrogen in unfilled cables should be purged from the cable at regular intervals; iv) lengths of unfilled prototype c
23、able or specially prepared short samples (up to 10 m) of filled prototype cable may be tested to confirm the estimated concentrations of hydrogen by the measurement method described in Annex B; 2) measurement method described in Annex C. that the long-term effectiveness of hydrogen-absorbing materia
24、l, when used, should be confirmed by the For cables of all dielectric construction, there is sufficient experience of stable transmission properties to make unnecessary the testing for significant concentrations of hydrogen which could cause an increase in optical loss. Annex A Measurement of hydrog
25、en released by each cable component by gas chromatography A.l Principle Gas chromatography may be used to estimate the hydrogen concentration. The concentration of hydrogen in a vessel is estimated by comparing the N2, O2 and H2 peaks, measured by gas chromatography, with that of a known hydrogen co
26、ncentration. Hydrogen release can usually be accelerated by raising the ambient temperature. Such acceleration conditions as temperature and time depend on the volume of the sample. The temperature is usually from 50 OC to 160 OC and the time within 48 h. The elevated temperature should be selected
27、to be below the level which would melt or deform the cable materials. The time should be long enough for the thermal activity to saturate. After thermal activation, the temperature is reduced to its initial level and the hydrogen concentration is measured by gas chromatography. A flow chart, for est
28、imating the amount of hydrogen released in the cable material sample, is shown in Figure A.l. A.2 Equipment The basic equipment is shown in Figure A.2. A gas chromatograph is used for the quantitative analysis of hydrogen. It usually measures the hydrogen content by separating hydrogen from the othe
29、r gasses by virtue of this elements unique retention time in the column and then determining its concentration with a thermal conductivity detector. The usual conditions of such a gas chromatograph are as follows: 1) Column Length: Filter: Temperature: 1 to 4 metres Molecular sieve 5A 40 “C to 50 “C
30、 2) Carrier gas (Argon gas) Flow rate: 30 to 40 ml/min 3) Detector (Thermal conductive detector) Temperature range for detection: 25 “C to 50 “C A.3 Measurement procedures A.3.1 Sample preparation Optical fibre cables usually contain components as follows: - coated silica fibres; - polymerised mater
31、ials, such as: 0 0 tubes or slotted rods in which the coated silica glass fibres may be inserted; wrapping tapes including water-blocking tapes; 2 Recommendation L.27 (10/96) - - jelly compounds or water-blocking powder which may be used as water-blocking materials; metallic, glass fibre or aramid c
32、omponents which may be used as strength members, The specimen is prepared as a test sample. It should be placed in an extraction-concentration vessel of known volume, which is filled with air or an inert gas such as argon at atmospheric pressure. The vessel is usually made of glass in preference to
33、metal, since metal surfaces provide a site for hydrogen molecules absorption-desorption phenomena which make reliable testing difficult at low concentrations. The vessel must be hydrogen-proof and not itself a source of hydrogen. In some cases, the sample may be put into a glass ampoule which has a
34、smaller volume than the vessel and the mouth of the ampoule sealed to prevent hydrogen leakage during thermal activation. In such cases the inner volume of the vessel or sealed ampoule should be about ten times or more greater than the volume of the sample for the oxidization reaction. A.3.2 Calibra
35、tion The calibrated master line of the gas chromatograph should be determined before measurement. An outline of this procedure is shown in the upper left hand side of the flow chart in Figure A.l. A primary standard of 10 O00 ppm of hydrogen in argon is prepared as a master gas that is diluted to th
36、e desired concentrations of 10, 20, 50 and 100 ppm. Hydrogen at these concentrations is by a gas chromatograph and the calibrated master line, Le. the relationship between the gas Concentration and the area under the peaks is determined by the least-squares method. Examples of the peaks and the cali
37、brated master line obtained in the calibration are shown in Figure A.3. A.3.3 Measurement After the sample is prepared, hydrogen released from the test sample is activated thermally according to the procedure shown in the upper right hand side of Figure A.l. At this stage the sample temperature is r
38、aised to a predetermined level between 50 OC and 160 OC. The upper temperature limit should be below the level at which the test sample would melt or deform. The time should be long enough to enable the time required for achieving thermal balance to be disregarded and short enough to ensure a reprod
39、ucible test. Air is preferable as a reaction atmosphere because optical fibres in service are usually surrounded by air and oxidization affects the hydrogen release from organic materials such as jelly compounds and coating resins. Following this, the sample is returned to room temperature. 0.5 ml o
40、f gas from within the vessel or ampoule is injected into the gas chromatograph and the hydrogen concentration is obtained from the master line. When an ampoule has been used, it must be broken in the vessel before taking the measurement. The quantity of hydrogen released from the test sample can be
41、derived by: “1 (mug or mVcm, for the weight or the length of test sample) where: A is the hydrogen concentration obtained from the calibrated master line corresponding to the area under the peaks in the gas chromatograph of the extracted gas is the volume injected into the gas chromatograph is the i
42、nternal volume of the vessel VI V2 NOTE - Hydrogen in the region of lW5 ml and above can usually be detected by this method. A.4 Analysis The maximum quantity of hydrogen generated from a test sample at an elevated temperature can be estimated by the measurement described above. The law in the varia
43、tion of hydrogen release due to temperature variation is considered to follow an Arrhenius representation: where: 7 is the absolute temperature. Recommendation L.27 (10196) 3 STD-ITU-T RECMN L-27-ENGL L99b YBb259L 0b35220 258 The maximum quantity of hydrogen generated from the test sample at the in-
44、service temperature can be calculated by knowing the relationship between the quantity of hydrogen released and the temperature. Preparation of sample with known I Gas chromatography analysis Preparation of calibrated master line hydrogen conntrationipeak area Sample preparation Measurement (length,
45、 weight) Sample placed in vessel Vessel purged with argon gas Thermal activation Vessel cooled to room temperature I l I Sampled with gas-tight syringe I vessel atmosphere I I I Correction of volume inside the vessel for sample volume Absolute amount of hydrogen TC603940-96/601 Figure A.lL.27 - Flow
46、 chart for the measurement of gas chromatography Gas chromatograph Valve Il Gas extraction -+ InIl, nr Glass amDoule -. Glass ampoule Specimen u Figure A.21L.27 - Equipment configuration for the measurement of hydrogen derived from cable components Recommendation L.27 (10/96) 3- m e! a) Standard chr
47、omatogram b) Calibrated master line T0603690-941dO3 Figure A.3/L.27 - Examples of a chromatograph and calibrated master line used in the measurement of gas chromatography Annex B Measurement of the concentration of hydrogen in a cable sample B.l Unfilled cable B.l.l Laboratory method A length of cab
48、le is stored in a climatic chamber with its ends sealed. The gas chromatography measuring technique, described in Annex A, is normally used to examine a sample of gas extracted fiom the cable. For non-hermetically sealed cable sheaths, the measurement can be carried out on a sample of sheath to dete
49、rmine the rate of the escape of hydrogen by permeation. B.l.l.l Sample preparation In order to seal the cable ends into special cable connectors, a primer is used to bond the cable sheath to the adhesive which is applied to each of the metallic cable connectors. To check the gas tightness of the test apparatus, it is first connected to a length of polymer coated seamless metallic tube with a set of cable connectors bonded to each end. B. 1.1.2 Measurement After the cable has stabilized to the temperature in the environmental chamber, a sample of gas is drawn out of the cabl
