WELDING RESEARCH MARCH 2016 / WELDING JOURNAL 87-s process. Cr(II) readily oxidizes to Cr(III) oxide in the air and ozone that are present outside the gaseous shield (Ref. 8). Cr(III) oxide and Cr(VI) compounds occur in the welding plume as a result of oxidation of chromium atoms vaporized during the welding process (Ref. 9). Cr(VI) compounds are less stable to heat than Cr(III) compounds. Formation of Cr compounds occurs outside the shield under the influence of oxygen and ozone (Ref. 8). Ozone is by far the more reactive agent. However, ozone reacts at the same time with nitric oxide to produce nitrogen dioxide. Health-related concerns of chromium compounds vary according to toxicological properties. Metallic chromium Cr(0) and Cr(III) oxide cause respiratory irritation (Ref. 8). Watersoluble Cr(VI) compounds cause respiratory tract irritation and lung cancer, dermatitis, and possible kidney damage. Water-insoluble Cr(VI) compounds cause respiratory tract irritation and lung cancer and skin irritation. Many jurisdictions use the Threshold Limit Values (TLVs) published by the TLV Committee of the American Conference of Governmental Industrial Hygienists as regulatory limits (Ref. 10). The TLVs are intended for use as guidelines and not as regulatory limits. Threshold Limit Values are not fine lines between safe and unsafe conditions. They incorporate safety factors to ensure that exposure of nearly all workers can occur without adverse effect at the level of the TLV day after day during a normal work Fig. 1 — A2 welding machine prior to installation of fume collector hood. Table 1 — Elemental Composition of Aluminum Alloys Used in Marine Applications Alloy Element (%) Si Fe Cu Mn Mg Cr Zn Ti Al 5052 0.25 0.4 0.10 0.10 2.2–2.8 0.15–0.35 0.10 remainder 5083 0.40 0.40 0.10 0.40–1.0 4.0–4.9 0.05–0.25 0.25 0.15 remainder 5086 0.40 0.50 0.10 0.20–0.7 3.5–4.5 0.05–0.25 0.25 0.15 remainder 6061 0.40–0.8 0.7 0.15–0.40 0.15 0.8–1.2 0.04–0.35 0.25 0.15 remainder 6063 0.20–0.6 0.35 0.10 0.10 0.45–0.9 0.10 0.10 0.10 remainder 6066 0.9–1.8 0.5 0.7–1.2 0.6–1.1 0.8–1.4 0.40 0.25 0.20 remainder Adapted from Refs. 3–7. Fig. 2 — A2 welding machine and associated fume containment and collection devices and sampling pumps.
Welding Journal | March 2016
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