If the number __ appears in the last digit of an AWS electrode classification number, the electrode is designated as a low-hydrogen electrode.
A. 1, 2, or 3
B. 2, 3, or 5
C. 5, 6, or 8
D. 6, 7, or 8
The correct answer and explanation is :
Correct Answer: D. 6, 7, or 8
Explanation (Approx. 300 Words):
In the American Welding Society (AWS) classification system for covered electrodes used in Shielded Metal Arc Welding (SMAW), each electrode has a designation that provides information about its characteristics. A common classification format is:
E7018
Breaking it down:
- E stands for “electrode.”
- 70 indicates the tensile strength of the weld metal (in this case, 70,000 psi).
- 1 represents the welding position (1 = all positions, 2 = flat and horizontal only).
- 8 is the key digit of interest here — it indicates the type of flux coating and current characteristics.
The last digit in this classification number is especially important because it tells you about the electrode’s coating type and its usability characteristics, including its moisture resistance and hydrogen content in the weld.
Electrodes with the numbers:
- 6, 7, or 8 in the final position are low-hydrogen electrodes.
These are engineered to produce welds with minimal hydrogen content, reducing the risk of hydrogen-induced cracking, especially in high-strength steels or thick sections.
For example:
- E7016: Low-hydrogen potassium, AC or DCEP
- E7018: Low-hydrogen iron powder, AC or DCEP
- E7048: Low-hydrogen, iron powder, vertical-down welds
Low-hydrogen electrodes are commonly used in structural welding, pipeline work, pressure vessels, and other applications requiring high strength and crack resistance. They often require storage in heated ovens to prevent moisture pickup, which can increase hydrogen content and lead to weld defects.
In contrast, electrodes with other terminal digits (like 2, 3, or 5) generally have higher hydrogen content and are not suitable for critical welds where hydrogen embrittlement could be a concern.
Summary:
AWS electrode classification numbers ending in 6, 7, or 8 denote low-hydrogen electrodes, making Option D the correct answer.