Thursday, July 16, 2015

Repair by welding: 5 Crucial Questions Management Should Ask Beforehand

To ensure successful welding repair at the first attempt, management should have those key questions answered.

Very often, components crucial to plant operations are repaired by welding. That said, at times, those repairs fail to work, or even much worsened. To avoid repeated uh-oh welding repairs, plant supervisors should ask those in charge of repairing those key questions. Rather, those questions are raised to make certain whether the repair can be successfully done right the first time.

Question 1: 

If the component was produced by welding, it can be repaired by welding. Still, possibly, the heat treat is applied after welding to gain the required properties; or special techniques, welding electrodes or processes were applied in the original construction.

So supervisors should know which the material is prior to welding it. To do so, just examine construction drawings, consult the maintenance handbook, contact the manufacturer, or find for a SAE, AISI, ASTM, or other material specifications that define the material on the part. Collect any other information about how the part was fabricated. As the last choice, you can cut the part’s small wedge and have it examined in a laboratory.

Geared up with this information, you can contact a reliable resource like a welding engineering consultant or welding consumables manufacturer for guidance. Pass ahead of your regular welding supply salespersons unless you know they they have a technically competent consultant. At a minimum, follow what said below:

The proper welding process(es) to be used
Welding filler metals or electrodes to be used
Requirements of pre-heating and post-weld heat treatment
Such special requirements as heat input control, peening. The requirements are unique to the material and may enhance its weldability
When appropriate, a way to get rid of defects, and a requirement to confirm that they have been removed prior to welding.
Such in-process inspection points as verification that appropriate materials are being employed, the fit-up and tack welding are correct, the root pass is good, the welder cleaned and contoured properly the weld beads between passes.
Final inspections and non-destructive examination (ex. ultrasonic or X-ray) where appropriate.

Question 2:

Is the material safe? Once your staff has realized how to weld the component, ensure that it is safe to weld on the component and the environment is safe.

Parts that may have included combustible materials need thoroughly cleaning and venting. Any connections that may provide combustible gas or liquid for the component in process should be disconnected where possible. Take special preventive measures when dust can arrive at explosive concentrations. Clearly, if a welder has to come in a confined space to repair the component, whether the air in that space is suitable should be verified, and the proper confined space entry practices must be conform to.

To-be-welded parts should be clean and free of oil, rust, grease, moisture, paint and any other contaminants. 

The welding environment should have nothing related to combustible materials. Commonly, any combustibles within 35 feet in which the repair to be made should be removed or covered with fire resistant fabric for ignition prevention. 

Question 3: 

Are there any jurisdictional rules or codes that have to be complied with? 

Formal welding procedures are often a must in AWS D1.1, Structural Welding Code – Steel when welding on structures or building, and in the ASME B31 Code for Pressure Piping or the ASME Boiler and Pressure Vessel Code when welding on such pressure parts as pumps, piping, vessels or boilers. 

When formal welding procedures are not required, get guidance from the filler metal or welding electrode manufacturer, and make it a concise form  for the welder in charge of repair work to obey.
That formal welding procedures are required also means that formal qualifications of the welder is required. Probably, the welding worker with a previous history of attempted welding in your facilitty with the filler metal type and welding process to be used for repair work is sufficiently skilled.

For welders with unknown skill, or if the materials bring up a new experience, the successful welder for the repair work can show off the skill at minimum cost to you. Namely, he will fillet weld together 2 plates of a material just the same as that to be repaired, to create a ‘T’. 

The welder welds in the shown location.  The portions named as ‘discard’ are saw cut-off. The remaining portion is bent for the weld root to be put in tension. The weld is good if the plate bends on itself. If the weld fractures, the fracture surface is inspected for excessive defects.
Question 4: 

Is it necessary for preheating or post-weld heat treatment. Suggested practices from welding consumables suppliers should refer to preheating regarding the base metal to be welded. For such typical structural steels as A-500, A-36, preheating the parts above ambient isn’t often required, given that low hydrogen processes like GMAW, GTAW, or low hydrogen electrodes like E8018 or E7018 are employed.

When welding those materials and the component thickness surpasses ¾ inch, it is good practice to preheat steel to 200°F. Such other materials as 4130 and same low-alloy steels employed for gears and shafts normally need preheating, and you should follow the recommendations from the welding consumable manufacturer. Post-weld heat treatment is required for some materials to restore toughness and ductility, so capable technical assistance plays a more important role when the materials being welded become more sophisticated.

Question 5: 

Are you fixed this before? When something requires multiple repairs, it’s time to make a failure analysis. This may be as simple as having a capable engineer look at what is going on and define the root cause, or as cloudy as examining the fracture surfaces in the scanning electron microscope and carrying out other metallurgical tests and examinations.

(The said advice is given by Walter J. Sperko, President of Sperko Engineering (Greensboro, N.C).)

1 comment:

  1. The first question should be answered before even thinking about hiring a welder. It's a waste of time to try and fix something that may only need to be completely replaced. I'd probably just get a consultation with welding services beforehand.