February 12, 2004
Weld inspection, weld logging, and weld recordkeeping always have been a part of quality assurance (QA) procedures for certain industries, particularly aerospace, nuclear power, semiconductor, and pharmaceutical.
|Photo courtesy of The Murray Co. Mechanical Contractors, Rancho Dominguez, CA.|
However, in recent years the demand for logging of orbital weld records has increased dramatically, particularly in the biopharmaceutical industry, in which weld inspection and weld records are a significant part of the huge amount of documentation required to achieve validation. Validation must be complete before the U.S. Food and Drug Administration (FDA) approves a facility for the manufacture of a new drug.
About 99 percent of the welding done at high-purity biopharmaceutical facilities is autogenous orbital gas tungsten arc welding (GTAW). In orbital GTAW, weld components have a square end preparation that fits snugly in an enclosed weld head filled with inert gas. An arc is struck between a nonconsumable tungsten electrode and the weld joint, and the electrode rotates (orbits) around the joint to make the weld. The weld head and weld components remain in place.
If a facility is installed to the American Society of Mechanical Engineers (ASME) Bioprocessing Equipment Standard (BPE-2002), all of its welds must be examined visually on the outside diameters (ODs) by the installer and recorded in a weld log, and the inner diameters (IDs) of at least 20 percent of the welds must be inspected with a borescope by an inspector representing the owner.
Coupon logs are maintained for each sample weld to test whether the welding equipment is properly set up and functioning. Borescope logs are maintained for each inspected weld, weld data is etched onto the tube next to each weld, and weld information is recorded on the isometric (ISO) drawing. Furthermore, manufacturers of accessory equipment, such as skids, that will be installed at the pharmaceutical plants must maintain similar weld records that become part of the validation package.
As an example of the effort required, Donovan Engineering and Construction Co. Inc. completed about 33,000 and 20,000 orbital welds at Wyeth Pharmaceuticals and Lonza Biologics, respectively. At the Wyeth site, the contract called for 100 percent borescopic inspection, but out of the 32,851 welds, 850 were "blind" welds; in other words, they were inaccessible for borescopic inspection. The BPE standard requires that contractors have a written procedure in place to examine blind welds.
One QA/QC inspector and one borescope technician were present for each of the eight to 10 welding machines. The number of welding machines on-site peaked at 25 to 30 during the course of the installation, which took two years to complete. This site had 2,316 ISO drawings, and data for each weld had to be recorded on a particular drawing. The percentage of welds rejected for concavity, convexity, or excessive discoloration was 0.815 percent, or 268 welds. Another 347 welds, or 1 percent, had lack of penetration, but in accordance with BPE, they were permitted a reflow to achieve full penetration. All of this information was recorded in a weld log. Donovan estimated that weld inspection, documentation, testing, and commissioning comprised 15 to 20 percent of the time required to do the job.
More and more such information is collected and stored electronically. Currently, however, weld records usually still are delivered as printouts from the orbital welding power supply. Information on the printout is logged manually by third-party quality assurance (QA) inspection personnel before being converted to electronic form.
Orbital welding is not new technology, but over the past 20 years or so, orbital welding power supplies have evolved from digit-switch machines—on which weld parameters such as welding current (amps), electrode travel speed in revolutions per minute, pulse times, and level times were set on the front panel of the machine—to microprocessor-based machines that store weld parameters as programs or schedules in memory. With these newer machines, the operator doesn't have to re-enter a program each time it is changed, and the power supply can print a record that can be used for weld procedure qualification and weld logging.
The next generation of orbital welding power supplies can store the data or upload the electronic data directly to a computer for compilation of weld records for a particular job or for printing of QA records for manufactured parts. Electronic data also can be printed on part labels and etched next to a weld on the tube. At a minimum, this data would include the power supply and weld head serial numbers, name or identification number of the welding operator, and the date the weld was made.
Some users might want to be able to trace material heats of tubing and fittings, purge gas certification numbers, or electrode type. In these cases, the power supply can record project management data—such as weld identification number, type of piping system being installed, and the building in which the weld was made—and supply it to QA in electronic format without the need to re-enter the data manually.
The ability to search for weld records by date, system, welding operator, or another field can be useful to end users who might need to locate a particular weld record quickly during an audit by the FDA or other certifying authority.
The aerospace industry has frequently required the use of chart recorders to verify the performance of orbital welding equipment. Some new orbital welding power supplies eliminate the need for an external chart recorder by capturing weld data for welding current, pulsation, arc voltage and travel speed; displaying it in real time on the power supply screen during the weld; and showing an information chart on the screen shortly after the weld is complete. The power supply can compare the actual data gathered during the weld and report whether the weld parameters were performed within preset acceptance limits.
It is important to understand an orbital welding power supply's limitations in performance monitoring. When a welding power supply indicates that all parameters have been performed as programmed, it means that the power supply executed the instructions that were programmed. The arc continued to move around the joint, and the amperage did not deviate significantly from the programmed value.
If the power supply fails for some reason to execute all of the program variables, it signals the welding operator or quality control (QC) person that something might be wrong. For example, the power supply might fail to deliver the programmed amperage if it's plugged into a circuit shared by other equipment operating at the same time, or a gas fault could be triggered because of insufficient gas flow for the weld head being used.
However, even if the power supply performs within acceptable limits, the weld could still be defective. Any number of factors can result in an unacceptable weld without being detected by the power supply. For example, the operator could enter the wrong weld program or load the wrong material or material heat or size into the weld head.
Heat-to-heat variation in stainless steel is such that a heat change may require the operator to program a change in welding current to achieve the right amount of penetration. Because amperage is roughly proportional to wall thickness, loading material with the incorrect wall thickness into the weld head could produce a weld joint with excessive or insufficient penetration. Loading the wrong diameter for the weld program can cause the electrode in the weld heat to travel too far or not far enough.
Failure also can occur if, for example, a welding operator with poor eyesight or working in a dimly lit area fails to align the electrode to the weld joint. This can create a perfectly penetrated weld that misses the joint, with all of the penetration occurring on one side of the weld joint.
Improper ID purging is another situation the power supply might not detect. Excessive or insufficient flow rate, as well as poor-quality purge gas with excessive amounts of moisture or oxygen, can cause unacceptable discoloration of the weld and heat-affected zone (HAZ). A power supply can detect gas flow to the weld head, but an oxygen analyzer connected to the tube outlet is necessary to determine when it is safe to start the arc. While a power supply can indicate obvious fault conditions such as insufficient gas supply to the weld head or stubbing out of the electrode in the weld pool, it cannot guarantee that a good weld has been made.
Performance monitoring by a power supply can be useful in applications such as orbital welding of semiconductor process gas lines that are not normally inspected on the ID. This industry relies on frequent test coupon welding. Coupon welds are done in lieu of inspection because most of the tubing is small-diameter (0.25 to 0.50 inch OD), and inspecting the ID without damaging the electropolished surface is difficult.
Performance monitoring is less important for industries such as the biopharmaceutical industry, for which borescopic inspection is required on at least 20 percent of the welds selected randomly from each separate system. Performance monitoring cannot replace weld inspection or guarantee a good weld. No welding machine can unequivocally detect and record the quality of a particular weld.
Some orbital welding power supplies can, however, provide a detailed record of each weld so that if a problem arises, tracing the problem's root cause is simplified. The power supply's capability to download weld information directly to a laptop computer can eliminate the need to re-enter the weld data manually and simplifies the weld documentation process.
Barbara K. Henon, Ph.D., is manager of technical publications with Arc Machines Inc., 10500 Orbital Way, Pacoima, CA 91331, 818-896-9556, fax 818-890-3726, email@example.com, www.arcmachines.com. The author acknowledges helpful discussions with Gene DePierro of Pro-Tech Process Inc. and Michael Hession of Donovan Engineering and Construction Co. Inc. in the preparation of this article.
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