99 Diseases of Pressure Equipment: Practical/Communication Issues That Can Lead to Welding Flaws

What do we mean by practical/communication welding issues? When we talk about welding QA/QC we typically focus on the technical requirements and what QA/QC is needed to assure that the technical requirements are met. Examples include the preheat, interpass, and PWHT temperatures and how to assure that the correct temperatures and hold times are used. Sometimes the more subtle practical issues cause defective welds, and not necessarily lack of specifications or welding QA/QC. You’ve heard the phrase that "you don’t get what you expect, you get what you inspect". This issue is along the same line of thinking, but deals more with clear communication of welding requirements. Have you played the game where you look at a photo of a simple object, you verbally describe it to someone who can’t see it, and they, in turn, try to draw a picture of what you see. It doesn’t always come out exactly as you intended, does it? The same can be true with welding QA/QC.

The following anecdote is an example of a practical welding QA/QC issue that we experienced. A shop was making several large, heavywall Cr-Mo welds. Some of the welds were taking more than one shift to complete. The requirement was to maintain and hold the preheat temperature into the PWHT cycle. The normal QA/QC requirements were occurring. The shop foreman and the welders were checking the preheat temperature and when they finished the weld the preheat temperature was maintained until the component entered the furnace for PWHT. But if the weld was not complete at the end of the evening shift, everyone walked away and allowed the weld to cool for the night. It was of course preheated again the next day when the next welder completed the weld. And no one in the shop understood why they were having hardness control problems.

As inspectors and engineers we generally do well at specifying all the requirements for making a sound weld, but we don’t always do well at making sure these requirements are communicated and, more importantly, clearly understood by the people doing the work. We don’t always thoroughly think through which things could be misinterpreted and develop the needed QA/QC to avoid those communication pitfalls. This is especially important in today’s environment where there’s a shortage of skilled craftsmen and laborers. It is very important that the person doing the work understands the requirements, the importance of the requirements, and what to do if there are problems. This is even more important for field and/ or repair welds where the situation may have changed significantly from the engineer’s drawing. In these situations, much can be accomplished by having the inspector or engineer knowledgeable with the potential problems have a face-to-face discussion with the welder and discuss how the problems may manifest themselves. This same discussion holds true for all parts of manufacturing and fabrication, not just welding.

Other experiences we’ve had with practical and communication issues associated with welding QA/QC:

• Cooling in still air: After welding or after PWHT the requirement may be to remove the insulation or remove the component from the furnace and allow it to cool in still air. Removing the insulation and allowing it to rain or snow on the weld is not the same thing as cooling in still air. Also, cooling a 2 inch thick fabrication in still air, is
  not the same cooling rate as cooling a 6 inch thick reactor in "still air". The people doing the work really need to understand the required "cooling rate".
• Thermocouple attachment: the thermocouple must stay in contact with the component throughout the heat treatment process. Bands or wires expand
  and the thermocouple lifts. Tack welds are bumped and thermocouples detached while components are loaded into the furnace. For thick components, the time at temperature for the furnace is not the time at temperature for the component. If your thick,
  large component is in the furnace with thin components, it may not reach the desired PWHT temperature. If your thin component is in the furnace with thick components it may reach a much higher than the expected temperature or be at temperature longer than desired.
• Porosity or cracking problems: When repairing vessels that have been in hydrogen service, does the welder know to stop welding and discuss changes needed when he is confronted with porosity or cracking problems? During maintenance turnarounds, complete shifts of welding can be lost because of the pressures to finish the job and the welder is pushing to make the best weld possible in the time allotted only to have the radiograph show cracking and porosity. Yes a conscientious welder may stop and get help, but some contract welders have not when pressed to complete the job.
• FCAW: Welders are often qualified in the shop with no outside environmental factors, e.g. wind. Does the welder know the importance of shelter in the field and the need to maintain shielding? The loss of shielding may cause problems with the weld that are not always apparent to the welder, e.g., toughness or hardness control.

Do the people doing the work know and clearly understand the requirements and the reasons for them? Do they know what problems can occur? Do you know when these problems might occur so that you would know when is the best time to conduct an audit of the welding QA/QC?