Patchett and Yarmuch layout:Layout 1 11/10/10 2:45 PM Page 262 Hydrocarbon Contamination and Diffusible Hydrogen Levels in Shielded Metal Arc Weld Deposits Oil contamination of basic H4 and H4R SMAW electrodes removes low-hydrogen characteristics on contact, and conventional baking treatments for humidity and water exposure restore electrodes to approximately the H8 designation BY B. M. PATCHETT AND M. A. R. YARMUCH ABSTRACT ence, for example 10 mL/100 g equating to 11 ppm. This difference is often within the typical variability of results in electrode Published literature suggest the avoidance of hydrocarbon contamination (oil or testing. grease) of shielded metal arc welding (SMAW) electrodes to prevent diffusible hy- The International Institute of Welding WELDING RESEARCH drogen cracking in weld zones, but there are no published data on the contamination (IIW) designation system for hydrogen mechanisms of exposure to hydrocarbons on the diffusible hydrogen level. This paper potential of welding consumables are explores hydrocarbon contamination of low-hydrogen basic SMAW electrodes. Con- “very low” for up to 5 mL/100 g; “low” for tact with oil causes instant and gradually increasing contamination and diffusible hy- 5–10 mL/100 g; “medium” for 10–15 drogen levels with time, and the contamination is greater with lower oil viscosity. mL/100 g; and “high” for more than 15 Standard reconditioning heat treatment for water contamination lowers the dif- mL/100 g of weld metal deposited. The fusible hydrogen content to about H8 levels for the electrodes and oils investigated. American Welding Society assesses elec- trodes via a logarithmic scale for diffusible hydrogen levels in a weld deposit. H16 is Introduction to weld deposits by various welding for 16 mL/100 g of weld metal (17.6 ppm), processes was hampered by imprecision in H8 is for an electrode producing less than The presence of hydrogen in ferritic the measurement of the diffusible hydro- 8 mL/100 g (8.8 ppm), the common upper steels welded by the shielded metal arc gen in the deposited weld metal. This was limit for “low hydrogen,” and H4 is for less welding (SMAW), submerged arc welding traced to the varying solubility of molecu- than 4 mL/100 g or 4.4 ppm. Commercial (SAW), flux cored arc welding (FCAW), lar hydrogen in the liquid media used to consumables that are able to reduce the and other flux-bearing processes has been collect the hydrogen expelled by a weld diffusible content further down the loga- studied for many years. The studies have sample (Ref. 3). Standardized tests based rithmic scale (2 or 1 mL/100 g) are not re- concentrated on humidity and moisture on the use of a liquid without measurable liable at present for arc welding processes effects on absorbed hydrogen levels. Hy- solubility (mercury) or vacuum extraction involving fluxes (SMAW, FCAW, and drogen-assisted cracking (HAC) in hard- produced accurate and reproducible re- SAW). AWS A5.1, Specification for Car- enable steel weld zones is controlled by sults (Refs. 4, 5). In these extraction tests, bon Steel Electrodes for Shielded Metal Arc several methods — electrode flux chem- results are conventionally reported as Welding, was revised in 2004 to reflect this istry and conditioning, procedure control “mL/100 g deposited weld metal,” which is new optional (voluntary) designation sys- (a combination of suitable preheat and a characteristic of the hydrogen collection tem. The specification also permits an op- heat input) in steels of relatively low hard- method, not of atomic hydrogen levels in tional supplemental “R” suffix designator enability, and the addition of postweld the actual weld deposit. This paper uses a for electrode coverings that satisfy ab- heat treatment (PWHT) on steels of high dual reporting system including parts per sorbed moisture limitations. Note that the hardenability (carbon equivalent) (Ref. million (ppm), a more relevant number H16, H8, and H4 designations should not 1). The strength level and microstructure for atomic hydrogen in solid solution. be confused with the H1 (extra-low hy- of low-carbon steels has emerged as an- There is only approximately a 10% differ- drogen ≤ 5.5 ppm or 5 mL/100 g), H2 (low- other criterion (in addition to hardness) hydrogen ≤ 11 ppm or 10 mL/100 g), and governing the susceptibility to HAC (Ref. H3 (hydrogen not controlled) designa- 2). In both cases, the amount of diffusible tions in AWS D1.1 Annex XI for assess- hydrogen imparted to the weld zone is of KEYWORDS ment of hydrogen cracking susceptibility importance in determining suitable proce- via the Pcm method. dural parameters. Initial assessment of the Hydrocarbon Contamination Attempts to connect weld metal dif- amount of diffusible hydrogen imparted Shielded Metal Arc Welding fusible hydrogen to moisture in the flux (SMAW) (Ref. 6) and weight gains during exposure Diffusible and Low-Hydrogen to humidity met with higher variability in B. M. PATCHETT ([email protected]) is H8 Levels professor emeritus of welding engineering at the the results. This is due to the fact that University of Alberta, Canada, and M. A. R. Low Moisture Pickup (LMP) weight gain is partially due to carbon diox- YARMUCH is program leader — welding engi- ide absorption (Ref. 7). Water exists in neering at the Alberta Research Council, Edmon- most low-hydrogen fluxes in the following ton, Alb., Canada. 262-s DECEMBER 2010, VOL. 89 Patchett and Yarmuch layout:Layout 1 11/10/10 2:46 PM Page 263 AB AB Fig. 1 — Flux structure of standard basic low-hydrogen electrodes. A — Fig. 2 — Flux structure of low moisture pickup basic low-hydrogen elec- Cross section; B — surface. trodes. A — Cross section; B — surface. 5 two forms: water of crystallization in where HD = IIW diffusible hydrogen in type, 4 mm ( ⁄32 in.) in diameter. Both stan- binders or agglomeration stabilizers and mL/100 g; a1 = as-baked coating moisture dard and moisture-resistant (low moisture adsorbed water via hygroscopic compo- %; a2 = adsorbed moisture %; and b = at- pickup (LMP)) types were assessed. All nents in the flux. The former is “perma- mospheric humidity in mm Hg. electrodes were conditioned at 375°C nent,” in the sense that total removal This equation strictly applies only to (707°F) for 1 h before use. Cooled and destabilizes the mechanical integrity of the electrodes tested (manufactured in weighed electrodes were then immersed the flux, while the latter is transitory and Japan) and must be used with circumspec- in a graduated cylinder to 25 mm (1 in.) can be removed without destabilizing the tion if differing flux chemistries from from the top of the flux coating in two sin- flux. This dual behavior limits the temper- other manufacturing sites are used. gle viscosity grade mineral lubricating oils ature of baking to approximately These numerous investigations into of differing viscosity, a 10-W low-viscosity 400°–425°C. Published information on the the effects of humidity, adsorbed water, grade and a 30-W medium-viscosity grade. subject of water content concerns the re- and water of crystallization are not Multigrade oils were avoided to isolate lationship between water uptake and ex- matched by investigations into the effects any effect of viscosity. After various times posure conditions, including steps to fol- of hydrocarbon contamination, although of immersion, excess oil was stripped from 1 low to minimize or reduce the net amount the deleterious effects of oil and grease the flux covering with a 1.5-mm- ( ⁄16-in.-) of deposit diffusible hydrogen. Since the contamination on diffusible hydrogen thick flexible rubber grommet squeegee water from exposure appears to be ad- content are generally assumed. This paper containing a hole slightly smaller in diam- sorbed (surface) rather than absorbed is intended to provide an initial assess- eter than the electrode coating. The slight (bulk) by the flux, part of the water is dis- ment of the effects of hydrocarbon con- pressure ensured a consistent removal of persed into the atmosphere by resistance tamination on diffusible hydrogen only. surface oil. Immediate weighing deter- WELDING RESEARCH heating of the SMAW electrode during Complex hydrocarbons may contain other mined the weight gain caused by oil im- welding, and adsorbed water adds less dif- elements of interest, such as sulfur, but mersion. Since the “dry” electrode weight fusible hydrogen than does bound water further investigation is necessary to study varied, weight gain was defined as a per- (Ref. 8). The substantial efforts of several other possible contaminants. centage gain for each electrode, rather investigators, over many years, has shown than an absolute weight gain. Welding be- that the diffusible hydrogen content of Experimental Program havior/diffusible hydrogen measurements SMAW deposits is related strongly to followed within 5 min. Procedural condi- water content of the flux up to approxi- The electrodes used in the experimen- tions were 24 V, 190 A on electrode posi- mately 0.3% water, but the relationship tal program were of the E4918 (E7018) tive polarity and a welding speed of 200 becomes more scattered at higher water contents (Refs. 9, 10). Diffusible hydrogen Table 1 — Chemical Composition of Electrode Fluxes is also affected by atmospheric humidity at the point of welding, which is more no- Element Percentage Percentage Percentage Change— ticeable in low-hydrogen electrode depo- Standard Electrode Low Moisture Standard to Low sition than it is in electrodes producing Pickup Electrode Moisture Pickup higher hydrogen levels (Ref. 9). An equa- tion (Ref. 9) is available that relates dif- Silicon 17.8 14.4 –23 fusible hydrogen to atmospheric humidity Potassium 15.5 10.9 –42 and flux water content, which is consid- Calcium 57.0 54.0 –6 ered accurate up to about 0.3% adsorbed Titanium 0.0 12.7 + X and crystalline water: Manganese 3.5 3.8 +9 Iron 5.9 3.7 –55 1⁄ HD = [260a1 + 30a2 + 0.9b – 10] 2 Total >99 >99 WELDING JOURNAL 263-s Patchett and Yarmuch layout:Layout 1 11/10/10 2:46 PM Page 264 Fig.