Deternination of hydrogen in weld metal using the Glycerine Method (LR)

Materials and NDE
Book J
MQPS 11-7
Procedure 11-7
Determination of Hydrogen in Weld Metal using the Glycerine Method
1 1.1 1.1.1
Introduction General When low hydrogen approval is required of a welding consumable, there are two principal methods of testing to establish the status of the consumable. These are referred to briefly as the `Mercury Method' and the `Glycerine Method'. This document provides the details of the Glycerine Method for weld metal hydrogen determination. This is no longer the preferred method, and for some welding consumable approvals it is not an acceptable method. This is because it cannot be used to achieve the low hydrogen approval grades `H10' and `H5' due to potentially significant losses of hydrogen in the analysis method itself. In practice, therefore, the Glycerine Method is acceptable only for the following cases: (a) (b) H15 for manual welding with covered electrodes. H15 for other types of welding consumable where the process and deposition characteristics allow the method to be used.
1.1.2
1.1.3
1.1.4
In view of its limitations and its limited acceptability, it is strongly recommended to abandon this method in favour of the preferred method of ISO 3690 (the Mercury Method) or one of the methods derived from that standard. Method Principles The method consists of two parts. The first is the making of weld samples under nominally standard conditions. The second is the analysis of the samples to determine their hydrogen content and to relate that content to the weight of deposited weld metal. When making the sample welds the rate of deposition (bead size) is to be controlled in order to control the cooling rate, as this affects that proportion of hydrogen initially in the weld metal which remains after cooling. The time taken to cool the sample to near room temperature by quenching in water is also to be controlled. A further proportion of hydrogen is lost by diffusion before the sample is enclosed for analysis, and this interval is also to be controlled. The analysis is performed by collecting the evolving (diffusible) hydrogen in a closed apparatus in which the volume of gas evolved is made visible and measurable by the displacement of a liquid, namely, glycerine. The results are expressed in cubic centimetres of hydrogen at standard temperature and pressure that would have existed in 100 g of metal deposited from the welding consumable. 2.1.6 To qualify for the `H15' grading using the Glycerine Method, the weld metal hydrogen content must not exceed 10 ml per 100 g of deposited metal. (It may be
2 2.1 2.1.1
2.1.2
2.1.3 2.1.4
2.1.5
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Hale Waihona Puke Rev. 1Materials and NDE
Book J
MQPS 11-7
noted that this is equivalent to 15 ml per 100 g of deposited metal determined using the ISO 3690, or equivalent, method). 2.2 2.2.1 Preparation Four test specimen blanks are to be prepared, measuring 12 mm by 25 mm in cross-section by about 125 mm in length. The parent metal from which these blanks are made may be any grade of ship structural steel with a specified minimum tensile strength not exceeding 2 490 N/mm . Before welding, the specimens are to be weighed to the nearest 0,1 g. The electrodes, prior to welding, may be submitted to the normal drying process at the minimum temperature recommended by the manufacturer. Welding and preparation of analysis On the 25 mm surface of each test specimen, a single weld bead is to be deposited, about 100 mm in length, from a 4 mm electrode, using about 150 mm of the electrode. The welding is to be carried out with a short arc, in accordance with the manufacturer's recommendations, and with a current of about 150 amperes. Within 30 seconds of the completion of the welding of each specimen the slag is to be removed and the specimen quenched in water at approximately 20°C. After a further 30 seconds, the specimens are to be cleaned, dried (using organic solvents and ambient temperature air blast) and placed in an apparatus suitable for the collection of hydrogen by displacement of glycerine. The interval between welding and insertion in the analysis apparatus should be as short as possible, and certainly no longer than 30 minutes. Analysis All four specimens are to be welded and placed in separate hydrogen collection apparatuses. Each apparatus, including the glycerine, is to be kept at a temperature of 45°C during the analysis. The specimens are to be kept immersed in glycerine for a period of 48 hours and, after removal, are to be cleaned in water and spirit, dried and weighed to the nearest 0,1 g to determine the amount of weld metal deposited. The amount of gas evolved is to be measured to the nearest 0,05 ml. The temperature of the apparatus is to be measured at the time of measuring the volume of evolved hydrogen. The volume is to be corrected for temperature and pressure to 20°C and 760 mm.Hg. The content of diffusible hydrogen is to be reported. The value for each sample is not to exceed 10 ml per 100 g of deposited weld metal.