Test methods for quantitative determination of corrosive sulfur compounds in unused and used insulating liquids - Part 3: Test method for quantitative determination of elemental sulfur

IEC TR 62697-3:2018(E) specifies a test method for the quantitative determination of elemental sulfur in used and unused insulating liquids over a 2 mg kg–1 to 400 mg kg–1 concentration range.

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Status
Published
Publication Date
13-Feb-2018
Current Stage
PPUB - Publication issued
Start Date
14-Feb-2018
Completion Date
14-Feb-2018
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IEC TR 62697-3:2018 - Test methods for quantitative determination of corrosive sulfur compounds in unused and used insulating liquids - Part 3: Test method for quantitative determination of elemental sulfur
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IEC TR 62697-3
Edition 1.0 2018-02
TECHNICAL
REPORT
colour
inside
Test methods for quantitative determination of corrosive sulfur compounds in
unused and used insulating liquids –
Part 3: Test method for quantitative determination of elemental sulfur
IEC TR 62697-3:2018-02(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 62697-3
Edition 1.0 2018-02
TECHNICAL
REPORT
colour
inside
Test methods for quantitative determination of corrosive sulfur compounds in
unused and used insulating liquids –
Part 3: Test method for quantitative determination of elemental sulfur
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.040.10 ISBN 978-2-8322-5361-8

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 62697-3:2018 © IEC 2018
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 8

4 Sampling ......................................................................................................................... 9

5 Procedure ........................................................................................................................ 9

5.1 Principle ................................................................................................................. 9

5.1.1 Determination with gas chromatography .......................................................... 9

5.1.2 Determination with differential pulse voltammetry ............................................ 9

5.2 Significance and use ............................................................................................... 9

5.3 Interferences......................................................................................................... 10

5.3.1 Co-eluting compounds ................................................................................... 10

5.3.2 Electron capture detector (ECD) .................................................................... 10

5.3.3 Flame photometric detector (FPD) ................................................................. 10

5.3.4 Mass spectrometer (MS) ................................................................................ 10

5.3.5 Interference from the matrix ........................................................................... 10

5.4 Apparatus ............................................................................................................. 10

5.4.1 Balance ......................................................................................................... 10

5.4.2 Gas chromatography system ......................................................................... 11

5.4.3 Differential pulsed voltammetry ...................................................................... 11

5.5 Reagents and materials ........................................................................................ 11

5.5.1 Purity of reagents .......................................................................................... 11

5.5.2 Gases ............................................................................................................ 11

5.5.3 Solvents ........................................................................................................ 12

5.6 Standard materials ................................................................................................ 12

5.6.1 Elemental sulfur ............................................................................................. 12

5.6.2 Diphenyl disulfide (DPDS) ............................................................................. 12

5.6.3 Blank oil ........................................................................................................ 12

5.7 Standard solutions ................................................................................................ 12

5.7.1 Stock solutions .............................................................................................. 12

5.7.2 Internal standard (IS) solution ........................................................................ 13

6 Instrument set-up .......................................................................................................... 13

6.1 Gas chromatograph .............................................................................................. 13

6.1.1 General ......................................................................................................... 13

6.1.2 Carrier gas .................................................................................................... 13

6.1.3 Injector .......................................................................................................... 13

6.1.4 Separation parameters .................................................................................. 13

6.1.5 ECD detection ............................................................................................... 14

6.1.6 FPD detection ................................................................................................ 14

6.1.7 MS detection ................................................................................................. 14

6.2 Calibration ............................................................................................................ 14

6.2.1 General ......................................................................................................... 14

6.2.2 Calibration procedure .................................................................................... 14

6.2.3 Response factor determination (ECD and FPD) ............................................. 15

6.2.4 Response factor determination (MS) .............................................................. 15

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IEC TR 62697-3:2018 © IEC 2018 – 3 –

6.3 Analysis ................................................................................................................ 15

6.3.1 Sample pre-treatment .................................................................................... 15

6.3.2 Sample injection ............................................................................................ 16

6.3.3 Chromatographic run ..................................................................................... 16

6.3.4 Peak integration ............................................................................................ 16

6.4 Calculations .......................................................................................................... 16

6.4.1 ECD and FPD ................................................................................................ 16

6.4.2 Mass spectrometer (MS) ................................................................................ 16

6.4.3 Differential pulse voltammetry measurements ................................................ 17

6.5 Results ................................................................................................................. 17

7 Precision data ............................................................................................................... 18

7.1 Detection limit ....................................................................................................... 18

7.2 Repeatability ......................................................................................................... 18

7.3 Reproducibility ...................................................................................................... 18

8 Report ........................................................................................................................... 18

Annex A (informative) Figures with typical chromatograms and results ................................ 19

Annex B (informative) RRT results Statistical evaluation of elemental sulfur data GC-

ECD/FPD ....................................................................................................................... 21

Bibliography .......................................................................................................................... 23

Figure 1 – Typical peak form and concentration calculation .................................................. 17

Figure A.1 – GC-ECD chromatogram of 5 mg kg elemental sulfur and (IS) in white

mineral oil ............................................................................................................................. 19

Figure A.2 – GC-ECD chromatogram of 100 mg kg elemental sulfur and (IS) in white

mineral oil ............................................................................................................................. 20

Table 1 – Column oven temperature programming parameters ............................................. 14

Table 2 – Mass spectrometer parameters ............................................................................. 14

Table 3 – Repeatability limit .................................................................................................. 18

Table 4 – Reproducibility limit ............................................................................................... 18

Table B.1 – Reproducibility with same chemical analysis approach ....................................... 21

Table B.2 – Reproducibility with different chemical analysis approach .................................. 21

Table B.3 – Repeatability ...................................................................................................... 22

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– 4 – IEC TR 62697-3:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TEST METHODS FOR QUANTITATIVE DETERMINATION
OF CORROSIVE SULFUR COMPOUNDS IN UNUSED
AND USED INSULATING LIQUIDS –
Part 3: Test method for quantitative determination
of elemental sulfur
FOREWORD

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The main task of IEC technical committees is to prepare International Standards. However, a

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data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 62697-3, which is a Technical Report, has been prepared by IEC technical committee

10: Fluids for electrotechnical applications.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
10/1014/DTR 10/1028/RVDTR
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IEC TR 62697-3:2018 © IEC 2018 – 5 –

Full information on the voting for the approval of this Technical Report can be found in the

report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 62697 series, published under the general title Test methods for

quantitative determination of corrosive sulfur compounds in unused and used insulating

liquids, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

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colour printer.
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– 6 – IEC TR 62697-3:2018 © IEC 2018
INTRODUCTION

During the IEC technical committee 10 plenary meeting in 2007, it was decided to set up a

working group with the aim of developing a standard on “quantitative determination of

corrosive sulfur compounds in insulating fluids”.
TC 10 decided to divide the overall task into three parts:

• Part 1: Test method for quantitative determination of dibenzyl disulfide (DBDS);

• Part 2: Test method for quantitative determination of total corrosive sulfur (TCS);

• Part 3: Test method for quantitative determination of elemental sulfur.

Part 1 was published in 2012, however the work for the preparation of Part 2 and Part 3 took

longer than anticipated. During the TC 10 plenary meeting in 2015, in order to finalize the

important work achieved, a proposal was made to complete the work and publish Part 2 and

Part 3 as Technical Reports.

Sulfur can be present in insulating liquids in various forms, including elemental sulfur,

inorganic sulfur compounds and organic sulfur compounds. The number of diverse sulphur

species comprised of different isomers and homologous can run into hundreds. The total

sulfur (TS) concentration in insulating liquids depends on the origin of the liquid, refining

processes and the degree of refining and formulation including addition of additives to the

base oils. Base oils include mineral based paraffinic and naphthenic oils, synthetic iso-

paraffins obtained through gas to liquid conversion process (GTL-Fischer-Tropsch), esters,

poly alpha olefins, poly alkylene glycols, etc. Additives can be comprised of electrostatic

discharge depressants, metal deactivators, metal passivators, phenolic and sulfur containing

antioxidants such as the polysulfides, disulfides, dibenzyl disulfide (DBDS).

Certain sulfur compounds present in the insulating liquids exhibit antioxidant and metal

deactivating properties without being corrosive, whereas other sulfur compounds have been

known to react with metal surfaces. Specifically, sulfur compounds such as mercaptans are

very corrosive to metallic components of electrical devices. Presence of these corrosive sulfur

species has been linked to failures of electrical equipment used in generation, transmission

and distribution of electrical energy for several decades. Therefore, IEC 60296 states that

corrosive sulfur compounds shall not be present in unused and used insulating liquids.

The serious detrimental impact of corrosive sulfur has also been linked to the presence of a

specific highly corrosive sulfur compound, DBDS. This compound has been found in certain

mineral insulating oils [1], [15], [16], [17] ; presence of this compound has been shown to

result in copper sulfide formation on the surfaces of copper conductors under normal

operating conditions of transformers [2]. It has been reported that elemental sulfur and other

corrosive sulfur compounds such as mercaptans may be introduced during reclamation of

mineral oil with adsorbents reactivated through a combustion process. A proposal for

inclusion of a test method for quantification elemental sulfur in IEC 62697 was made by

CIGRE WG A2.40. The proposal was approved by IEC TC 10 in 2013. Several methods for

quantification of elemental sulfur in petroleum products and other matrices have been

reported, however, methods do not directly deal with quantification of elemental sulfur in

insulating oils.

However, current standard test methods for the detection of corrosive sulfur ([11] and [13])

and potentially corrosive sulfur in used and unused insulating oil [8] are empirical and

qualitative. These methods rely on visual and subjective perception of colour profiles. The

methods do not yield quantitative results in regard to the concentration of DBDS or other

corrosive sulfur compounds present in insulating liquids.
___________
Numbers in square brackets refer to the Bibliography.
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IEC TR 62697-3:2018 © IEC 2018 – 7 –

Furthermore, methods for corrosive sulfur and potentially corrosive sulfur in insulating liquids

([8] and [11]) are applicable only for mineral insulating oils that do not contain a metal

passivator additive, as these methods can otherwise yield negative results even when

corrosive sulfur compounds are present in the insulating liquids – thus providing a false

negative test result. On the other hand, the test method when used with aged insulating oils

(e.g. those with relative high acidity), may give ambiguous results and lead to a false positive

test result. Further analysis of insulating liquids is stipulated, for example IEC 62535 specifies

that if there are any doubts in the interpretation of the results of the inspection of paper, the

composition of precipitate should be analysed by other methods (e.g. by SEM-EDX).

For this reason, a working group within IEC TC 10 was set up to prepare test methods for the

unambiguous quantitative determination of corrosive sulfur compounds in unused and used

insulating liquids.
WARNING – Health and safety

This part of IEC 62697 does not purport to address all the safety problems associated with its

use. It is the responsibility of the user of this document to establish appropriate health and

safety practices and determine the applicability of regulatory limitations prior to use.

The insulating liquids which are the subject of this document should be handled with due

regard to personal hygiene. Direct contact with eyes may cause slight irritation. In the case of

eye contact, irrigation with copious quantities of clean running water should be carried out and

medical advice sought.

Some of the tests specified in this document involve the use of processes that could lead to a

hazardous situation. Attention is drawn to the relevant standard for guidance.
WARNING – Environment

This document involves mineral insulating oils, natural ester insulating liquids, chemicals and

used sample containers. The disposal of these items should be carried out in accordance with

current national legislation with regard to the impact on the environment. Every precaution

should be taken to prevent the release of chemicals used during the test into the environment.

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– 8 – IEC TR 62697-3:2018 © IEC 2018
TEST METHODS FOR QUANTITATIVE DETERMINATION
OF CORROSIVE SULFUR COMPOUNDS IN UNUSED
AND USED INSULATING LIQUIDS –
Part 3: Test method for quantitative determination
of elemental sulfur
1 Scope

This part of IEC 62697 specifies a test method for the quantitative determination of elemental

–1 –1

sulfur in used and unused insulating liquids over a 2 mg kg to 400 mg kg concentration

range.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

IEC 62697-1, Test methods for quantitative determination of corrosive sulfur compounds in

unused and used insulating liquids – Part 1: Test method for quantitative determination of

dibenzyldisulfide (DBDS)

IEC TR 62697-2, Test methods for quantitative determination of corrosive sulfur compounds

in unused and used insulating liquids – Part 2: Test method for quantitative determination of

total corrosive sulfur (TCS)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 62697-1 and

IEC TR 62697-2 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
elemental sulfur
unbound form of the element with atomic number 16

Note 1 to entry: Under normal conditions, sulfur atoms occur in different forms (allotropes) of which the

orthorhombic, cyclic octatomic form with chemical formula S is the most abundant. This form is a bright yellow

crystalline solid at room temperature.
3.2
allotropy

property of some chemical elements to exist in two or more different forms, in the same

physical state
---------------------- Page: 10 ----------------------
IEC TR 62697-3:2018 © IEC 2018 – 9 –
3.3
sulfur allotropes
sulfur which exists in a number of different allotropic forms

Note 1 to entry: These include the most abundant S and sulfur rings comprised of 6, 7, 9, 15, 18 and 20 atoms. In

addition to the allotropes, each allotrope often exists in polymorphs, delineated by Greek prefixes (α, β, etc.).

3.4
polymorphs

two or more minerals that have the same chemical composition for example S , but differ in

their atomical arrangement and crystal structure
4 Sampling

Samples should be taken, following the procedure given in IEC 60475. A representative

portion should be taken after thorough mixing. The specific sampling technique can affect the

accuracy of this test method. Precautions should be taken to prevent cross-contamination

during sampling.
5 Procedure
5.1 Principle
5.1.1 Determination with gas chromatography

The oil sample is diluted approximately 1:20 with a suitable solvent, fortified with a known

amount of an internal standard (IS) such as DPDS, and injected into the split/splitless injector

of a gas chromatograph equipped with a suitable detector including an electron capture

detector (ECD), a sulfur chemiluminescence detector (SCD), a flame photometric detector

(FPD), an atomic emission detector (AED) or a mass spectrometer (MS).

Separation of oil constituents, elemental sulfur (if present) and IS is achieved with a suitable

column such as a 15 m to 30 m × 0,25 mm (internal diameter) fused silica column with 5 %

polyphenylsiloxane and 95 % methyl polysiloxane or other suitable stationary phase and

helium or other suitable carrier gas. Separation is facilitated through temperature

programming over a suitable temperature range. Elemental sulfur is monitored with the

detector and quantified with the internal standard.

NOTE During the Round Robin Tests on the ECD, an FPD and an MS were used. Other suitable detectors such

as sulfur chemiluminisence and atomic emission detector were not used.
5.1.2 Determination with differential pulse voltammetry

The test procedure is based on two standard additions. 10 ml of the base electrolyte is

positioned in the test cell with the electrodes. 0,5 ml of the oil to be tested is added. The

current density is recorded.
5.2 Significance and use

This test method describes the determination of elemental sulfur in insulating liquids for

analysis.

The most common form of elemental sulfur is the octacyclic form with formula S If present,

elemental sulfur can react with copper and other metal conductors in transformers, reactors

and other similar devices to form copper and other metal sulfides. Therefore, this compound

is classified as potentially corrosive sulfur (see IEC 62535).

Elemental sulfur is present in petroleum and may be present in insulating mineral oils

...

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