Contained in this specification are the
classification requirements for low-alloy steel electrodes used for SMAW of
carbon and low-alloy steels. These electrodes include steel alloys in which no
single alloying element exceeds 10.5%. The classification system is similar to
that for SFA-5.1. However, there are more designators because these electrodes cover
a wider range of steels. Mechanical properties of the weld metal deposit are
also required in the as-welded or post weld heat treated condition.
Because hydrogen can pose a significant problem when
welding low-alloy steels, moisture testing of the covering is required to
classify some of the electrodes to this specification. However, the
supplementary tests for absorbed moisture (the “R” designation) and the
diffusible hydrogen (the “HZ” designation) are not required for classification
of the low-hydrogen electrodes. Optional supplemental designators are included
in the SFA-5.1 discussion.
This specification also includes a “G”
classification that includes electrodes classified as E(X) XXYY-G. The “G”
indicates a general electrode classification with requirements usually agreed
to by both the purchaser and the supplier. The AWS Classifications now include
both the U.S. Customer, Unit designation and the International system of Units
(SI) in the Tables. Electrodes may be classified as both U.S. and metric (i.e.,
E7018x and E4918-x). Electrodes classified in this specification require
mechanical properties and soundness to be determined from a groove weld test
assembly. The groove test assembly usually consists of a base metal having
similar characteristics to the tested electrode. The test plate is welded
following the welding procedure requirements
E
– 8018 – C3
E
– Electrode
80
– Tensile Strength
1
– (All)
Position
8
–
Covering and Current
C3
– Weld Metal Chemical Composition
Of SFA-5.5 for the classified electrode after post
weld heat treatment (if required), testing for classification may include
radiography, tension testing, and Charpy V-notch impact testing. Since most of
these electrodes are of low-alloy steel, the majority of weld metal deposits
are required to be tested in the post weld heat treated rather than the
as-welded condition.
Users of Section III in the ASME Code should note
that the testing required for classification is different than the testing
required by NB-2400. To certify that the weld material is in accordance with
NB-2400, the welding process and conditions that represent Section III
fabrication requirements must be used for welding the test assembly. Mechanical
testing of the weld is then performed to the NB-2400 requirements not the
Section IIC requirements. For example, five Charpy V-notch impact specimens are
required to be tested at temperatures listed in SFA-5.5 for classification. If
weld metal deposited from this electrode requires impact testing to Section
III, the test temperature and impact requirements would be determined by the
component design. In addition, only three Charpy V-notch impact specimens would
be required.
SFA-5.5 contains a variety of low-alloy steel
electrodes having different chemical compositions and mechanical properties. Electrodes
can be selected to deposit weld metal that closely match the chemical
composition and the mechanical properties of the base metal being welded. Table
3.4.2 contains a listing of the electrode F-numbers from QW-432 and the
A-numbers from QW-442 of Section IX for undiluted weld metal deposit. The
various types of electrodes are also discussed briefly in the following
paragraphs.
Carbon
Molybdenum (C–Mo) Steel Electrodes
The E70YY electrodes are similar to carbon steel
electrodes except for the addition of approximately % molybdenum for increased
strength, especially at elevated temperatures. ASME Material Specifications SA-204,
Grade A plate (UNS K11820) and SA-335, Type P1 pipe (UNS K11522) are typically
welded with these electrodes. These base metals are grouped as P-No. 3, Group 1
in QW/QB-422 of Section IX.
Chromium
Molybdenum (Cr–Mo) Steel Electrodes
The EX01Y-BX and EX01Y-BXL low-hydrogen electrodes
produce deposits ranging from %–9% chromium and %–1% molybdenum. These
electrodes are used for vessels and components, such as those of Section I (Power
Boilers) that are designed for high temperature service. SMAW with Cr-Mo
electrodes generally requires both preheat and post weld heat treatment. Base
metals that can be welded with these electrodes are grouped as P-Nos. 4, 5A,
5B, and 5C in QW/QB-422 of Section IX. The 9Cr-1Mo electrodes have now been
included in A5.5. Electrodes classified as E90XX-B9 are used to weld the
enhanced creep resistant 9Cr-1 Mo base metals. Thermal treatment of these alloys
is critical and must be closely controlled. Additionally, restrictions are
imposed on the Mn and Ni to ensure the PWHT can be maintained below the lower
transformation temperature.
Nickel
Steel (Ni) Electrodes
The EX01Y-CX and EX01Y-CXL electrodes are produced
to have nickel contents with five nominal levels of 1%, 1 %, 2 %, 3 %, and 6 %
nickel. These low-hydrogen electrodes each have good notch toughness at low temperatures.
Nickel
Molybdenum (Ni–Mo) Steel Electrodes
The E8018-NM1 electrodes contain approximately 1%
nickel and % molybdenum. Typical applications include the welding of high strength,
low-alloy, or micro alloyed structural steels.
Manganese
Molybdenum (Mn–Mo) Steel
Electrodes the E(X) X01Y-DX electrodes produce
deposits with a nominal 1 % manganese and % – % molybdenum. These electrodes
are designed to match the mechanical properties and corrosion resistance of
low-alloy steels, such as ASME SA-302, Grade B.
Other
Low-Alloy Steel Electrodes
The E(X) X01- YM (1) electrodes are low-hydrogen
electrodes designed to weld the high-yield strength steels. EX010-P1 electrodes
have cellulose coverings and are intended to weld API-5L-X52 and API-5L-X65 piping.
EX015-WX electrodes are low-hydrogen electrodes designed to weld deposits that
match the corrosion resistance and coloring of the ASTM weathering type
structural steels, such as ASTM A242 and A588.
Comments
Post a Comment