MMA welding

Procedures for steels having CEs up to 0.70 for use with scales C, D and E. Heat input values in the welding diagrams and tables based on 100% arc efficiency, instead of 80% (i.e. the value appropriate to MMA welding, as discussed in Chapter 3 under Heat input and in BS 5135). 

When selecting austenitic stainless steel or nickel alloy fillers, it is necessary to ensure that dilution from the base steel can be satisfactorily accommodated. The normal choice of austenitic consumables for MMA welding is from the types 23Cr 12Ni, 29Cr 9Ni or 20Cr 9Ni 3Mo, e.g. from BS 2926 1984 Grades 23.12, 29.9, or... 

At this point in the fabrication process for the later RPVs, the welds were given a hot UT inspection to assure compliance with a pre-service examination. The shell course was then placed in a furnace and given a post-weld heat treatment (PWHT). The welds were then ground smooth on the external and internal surfaces. The ASME Code-required radiographic (RT) and MT inspections were then performed. Any required repairs of unacceptable indications were made at this point using manual metal arc (MMA) welding and a repeat of the preheat-post-weld heat treatment. 

AT40J and the increase in yield stress at ambient temperature (AcTy) for SAWs were greater than for plate, forging or MMA welds similarly... 

Figure 13.18 Arc welding (a) circuit (b) MMA Welding (c) TAGS welding (d) MAGS welding...

However, still today, when more sophisticated materials and more productive and less expensive techniques are at the users disposal, MMA welding remains a favoured process to weld pipes. Its easy use, capacity to reach positions of difficult accessibility, the simplicity of the necessary generators (or the fact of being able to use motor generators network power is not always available on installation sites), the fact that protective gases (difficult to find in certain countries, in particular third world countries), necessary in welding with solid or cored wires, are not required, all these and others are the reasons for this choice. 

An admixture of iron and other metal powders (alloying and/ or deoxidising) used either as an ingredient of MMA electrode coverings, or as an addition made during submerged-arc welding (see iron powder). 

The length of a weld bead deposited from the usable portion of a single MMA electrode, i.e. from the length of the electrode less 40 mm. 

The reciprocal of the run length (q.v.), i.e. the length of MMA electrode required to deposit unit length of weld bead and which is proportional to the heat input, divided by the square of the electrode core wire diameter. 

Gooch T G Repair welding (of hard to weld ferritic steels] with austenitic stainless steel MMA electrodes . Metal Constr 12 (llj 1980 622-677. 

Manual metal arc (MMA) or stick welding using a coated electrode manipulated manually... 

Most nickel alloys can be fusion welded using gas-shielded processes such as TIG or MIG. Of the flux processes, MMA is frequently used, but the submerged arc welding (SAW) process is restricted to solid solution alloys (Nickel 200, Inconel alloy 600 series, and Monel alloy 400 series) and is less widely used. Solid solution alloys are normally welded in the annealed condition, and precipitation hardened alloys, in the solution treated condition. Preheating is not necessary imless there is a risk of porosity from moisture condensation. It is recommended that material containing residual stresses be solution treated before welding to relieve the stresses. ... 

---