Testing for the Hydrogen Content of Welding Consumables

In this article we will be discussing how we perform the hydrogen test. However, first we need to examine why we need to do hydrogen testing and on what type of electrodes.

In most arc welding operations, filler metal is added to the weld pool to complete the welded joint. The processes, Shielded Metal Arc Welding (SMAW), Flux Cored Arc Welding (FCAW) and Metal Cored Arc Welding (MCAW) all use a type of flux or metal compound, on or in the electrode to help with shielding the atmosphere from contaminants that may allow hydrogen to be present in the weld and heat affected zone (HAZ). There are other alloys or ingredients in the coatings that assist in controlling things like metal transfer and other benefits but we will not discuss these in this article. The focus here will be on the control of hydrogen in the weld zone and how we test electrodes for this.

When hydrogen is present in the weld zone, specifically in ferritic steels, hydrogen induced cold cracking (HICC) can occur in both the weld or heat affected zone (HAZ). This hydrogen is trapped and can initiate cracking after solidification or can be delayed over time.

Therefore, a low hydrogen electrode or process must be used to reduce the amounts of diffusible hydrogen that is present in the weld. For example, using the SMAW process on a standard 350 Mpa structural steel we would use a E4918 (E7018) electrode that has a basic flux coating that is low in hydrogen. The manufacturers of these electrodes must follow strict guidelines when producing these low hydrogen electrodes and test them to determine the amount of diffusible hydrogen the electrode will deposit as required by the Standard CSA W48 “Filler Metals and Allied Materials for Metal Arc Welding”. Additionally, the FCAW and MCAW electrodes are also subject to hydrogen testing if the makers want to designate them CH, or controlled hydrogen.

What is the amount of diffusible hydrogen allowed in the welds and how do we test electrodes to determine the allowable amounts? CSA W48 provides provisions for testing and assigns a hydrogen designator which electrode manufacturers need to meet. In these standards the maximum amount of diffusible hydrogen allowed is 16 mL/100 gr of deposited metal, if the electrode is to be considered low hydrogen. The electrode will then be given a hydrogen designator of H16. Today electrode manufacturers exceed this maximum amount and now produce electrodes with the designations of H8, H4 and H2 in addition to the H16. 

So how do we test these electrodes to make sure they meet the hydrogen designators. When electrode manufacturers produce an electrode deemed low hydrogen in Canada, they are required to test for the total amount of diffusible hydrogen under the provisions in CSA W48 Standard along with AWS A4.3 or ISO 3690 Standards for determining of the diffusible hydrogen content of martensitic, bainitic, and ferritic steel weld metal produced by arc welding.

The modern, and rapid, method for testing the samples for diffusible hydrogen is gas chromatography. The standard dictates the requirement to prepare four small test samples by placing each sample, one at a time, in a special copper clamping fixture that is used to clamp and hold the test samples in alignment and to serve as a heat sink. Figure 1 shows a typical welding fixture made to hold the test samples during welding. The copper clamping fixture is designed to give clamping pressure from both sides and permit a rapid release mechanism for removal of the test sample for quenching with a minimum of delay.

In the test, a weld bead is deposited on each of the small test samples. Once the arc is extinguished the clamping mechanism is released and the samples are removed and immediately quenched in a container of ice water, vigorously agitated for 20 to 30 seconds and then immediately transferred to a low temperature liquid bath (-60°C or colder) for storage. Both AWS A4.3 and ISO 3690 Standards, specify the size of the test samples to be used in the hydrogen test.

Figure1, Typical copper fixture to hold the test assembly for welding

Prior to placing the samples in the gas chromatograph unit, Figure 2, each of the four samples are removed from the liquid bath and then cleaned. Special care must be taken when cleaning and timed to ensure that no diffusion of hydrogen from the weld zone takes place. Once cleaned the sample is immediately placed into a tube, in the gas chromatograph, and in an inert atmosphere (usually Argon gas) at a specific temperature for a time specified in the ISO 3690 Standard. After the determined time has elapsed, a sample of the atmosphere is taken from the gas chromatograph tube and deposited into the gas chromatograph analyzer for the reading of diffusible hydrogen.

Figure 2, Typical gas chromatograph unit

The amount of hydrogen released is measured, and the hydrogen content of the weld metal is calculated. 

The amount of diffusible hydrogen is recorded for each test piece and averaged to determine the total amount of diffusible hydrogen for the electrode in mL/100gr of deposited metal and the electrode given its hydrogen designator (Example an amount of 8 mL/100gr of deposited metal will be given a designator of H8) 

CSA W59-2018 (R2023) Standard mandates the use of the hydrogen designator in the classification of the electrodes and the designator shall be printed on the SMAW electrode, or on the box and tags in the case of FCAW and MCAW filler metals.