Components critical to plant operations often get repaired by welding, but occasionally those repairs don't work, or, even more exasperating, a part must be repaired repeatedly. There are key questions plant operations and maintenance supervisors should ask of those who will make the repair to determine whether they’ve researched what they’re about to do well enough to get it right the first time.
Question 1: Can it be welded successfully?
If the component was fabricated by welding, it’s a good indicator that it can be repaired by welding. However, it might be that special techniques, welding processes or electrodes were used in the original construction, or that the part was heat treated after welding to achieve the required properties. Supervisors should know what the material is before welding it. This can be done by examining construction drawings, consulting a maintenance handbook, contacting the manufacturer or looking for an ASTM, AISI, SAE or other material specification and grade markings that identifies the material on the part itself. Gather any other information that can be obtained about how the part was made. As a last resort, you might have to cut a small wedge from the part and have it analyzed in a laboratory.
Armed with this information, you can contact a reputable resource such as a welding consumables manufacturer (Lincoln, Hobart, ESAB, etc.) or a welding engineering consultant for guidance. Go beyond your regular welding supply salesmen unless you know they have a technically competent consulting staff. At a minimum, establish the following during this step:
- The appropriate welding process or processes to be used
- Welding electrodes or filler metals to be used
- Preheating and postweld heat treating requirements
- Any special requirements, such as cleaning, heat input control or peening, that are unique to the material that might improve its weldability
- When appropriate, a way to remove defects and a requirement to verify that they have been removed before starting to weld.
- In-process inspection points such as verification that the correct materials are being used, the tack welding and fit-up are correct, the root pass is good, and the welder properly cleaned and contoured the weld beads between passes
- Final inspections and nondestructive examination (e.g., X-ray or ultrasonic) where appropriate.
Question 2: Is it safe?
The second question is whether welding the material is safe. Once your staff has figured out how to weld the component, make sure the component is safe to weld on and that the environment is safe. Parts that might have contained combustible materials need to be thoroughly cleaned and vented; any connections that might supply combustible gas or liquid to the component during welding should be disconnected where possible, or a combustible gas meter used to monitor the vent exhaust gas. Take special precautions when dust can reach explosive concentrations. Obviously, if a welder has to enter a confined space to make a repair, the suitability of the air in that space should be verified and appropriate confined-space entry practices must be followed.
The welding environment should be free of combustible materials. Generally, any combustibles within 35 feet of where the welding is to be performed should be removed or covered with fire-resistant fabric to prevent ignition. This includes floors both above and below the work area where sparks might fly through gratings or manways or under partitions. Fire watches are always a good idea when welding in the plant environment.
Figure 1. An N-95 type welding fume particulate mask is effective against zinc oxide when torch-cutting or welding galvanized steel, but a fume mask is not a substitute for proper ventilation of the welding area.
Parts to be welded should be clean and free of paint, grease, oil, rust, moisture and other contaminants. Lead-containing paint was banned in 1977, so any paint that was applied before then should be sampled to see if it contains lead and, when it is removed in preparation for welding, appropriate precautions taken to avoid contaminating the workforce. Galvanized surfaces should be power-wire-brushed to remove heavy galvanizing; however, workers can protect themselves from the zinc oxide that is developed by torch-cutting or welding galvanized steel and other particulate by wearing an N95-type particulate filter mask such as that shown in Figure 1.
Consult ANSI Z49.1 Safety in Cutting, Welding and Allied Processes for further guidance on welding safety. It’s available for free download from the American Welding Society.
Remove external loads from components before welding by disassembly, depressurization or other means. Building steel presents a special situation since loads typically can’t be removed, so consult with a competent structural engineer before welding on it. Guidance on welding on existing building steel can be found in AWS D1.7, Guide for Strengthening and Repairing Existing Structures.