American Welding Society Forum
I apologize now for my unfamiliar vocabulary, but I have a question on the difference between the two rods. I was on a job last week welding 24-30" cooling tower pipe grade B and we were using 7010 A-1 all the way out from root to cap. This week I have been put on a 42" grade B seamed pipe also used for water transfer from a main water source to another that is opened ended opposite of the pumps. I am required to weld 7010-A1 bead and 7018 cap. Other then customer prefeence(WPS). What is the difference between the two rods? All I can find is 7010 A1 has 1/2% moly. Why not weld all the way out with 7010-A1? They wanted me to tig using 70s-6 first, but I didn't want to burn up tig rigs. Any help will be appreciated, even if somebody can tell me where to look. Thank you
The main difference is in the fact that 7010 is basically a cellulose-sodium, non low hydrogen electrode as is 6010 whereas 7018 is an iron powder, low hydrogen electrode. The alloying will be different as well as other finished surface characteristics and physical/mechanical properties.
The decision for various electrodes will be based upon several factors: tensile/yield strength, notch toughness, alloy content, and many others. The project engineers SHOULD know what they are looking for and smaller diameters are often not as critical as when they start getting larger, thicker, and have more pressure.
Many times on piping, the roots and at least the hot pass if not some fill, are done either with 6010, 7010, or GTAW with the last of the fill or at least the cap being done with 7018.
Only the project engineer really knows why they called it out as they did.
He Is In Control, Have a Great Day, Brent
As Brent said, the difference is really in the type of flux, they are both a 70K tensile rod for all positions.
In my experience (and I have welded with both types of rod extensively) the 7010 was used when welding downhill to the API 1104 code (fill and cap only, root was done with 6010), the 7018 was used for welding uphill to the ASME B31 codes (again, fill and cap only, root was done with 6010 or GTAW).
I've never seen 7010 specified for use in an ASME B31 (uphill only) type application, only for filler and caps on pipeline projects where welding is performed downhill.
Thank you both for the replies. I have received the same answers, its per code is the only reasoning behind it and with that the person in control of the WPS, I familiar with both 1104 and B31. Being both 70xx rods was curious why we couldn't weld it all the way out with the 7010 vs 7018. If the 7010 is more corision resistance, why not fill and cap. The outside elements of nature are just as corosive as inside water being pulled from the creek. Small pump station to supply fresh water to a close plant. I just got my hands on a 1104 book. Going to do some reading while the next line is brought to us. Thank you.
The 0.5% Molybdenum is used in applications where there is an issue with high temperature creep. At elevated temperatures steel acts like taffy, that is, it stretches when subjected to a tensile load while at elevated temperature. As it stretches, the cross section is reduced to the point that it can no longer sustain the load and fails. As mentioned, creep occurs at high temperature. There is plastic flow when the steel is subject to tension and the temperatures above let's say 450 degrees. The Molybdenum "pins" the atoms so they don't slip pass each other, thus is more creep resistant.
Molybdenum also strengthens the alloy. If you review the "as welded properties" you will see the 7010-A1 is considerably stronger than the E7018. Like many alloying constituents, Molybdenum increases the hardness and strength on iron. Small additions of Molybdenum is about as effective at strengthening iron as Chromium and Vanadium.
As far as why someone would select the 7010-A1 versus plain 7010, I would guess in many applications it is because it is "what we always do." Someone said it is stronger, so it must be better!
For situations where the service temperature is below 350 degrees F, it probably doesn't make a lot of sense to use 7010-A1 for the simple fact that as hardness and strength go up, there is a reduction in ductility. For most application I would opt for improved ductility if the properties (tensile strength) of the base metal can be met using 7010.
Best regards - Al
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