in Orbital Welding
Process Piping: Case
Study and Simulation
Jorge Domingo and Margarita Morquillas
used in the construction of distribution
systems for utilities are some of the most critical activities on projects with
high sanitary requirements in the life sciences and similar industries.
Project implementation experience, both domestically and internationally,
indicates that activities requiring high levels of quality monitoring are related to the installation of critical fluids distribution systems, most specifically
those constructed from stainless steel alloy tubes jointed by gas tungsten
arc welding (GTAW), also known as tungsten inert gas (TIG), using orbital
Difficulties are more likely to occur when working on-site, where the welding
conditions are not as favorable as those in specialized workshops, which provide better opportunities for control. Another challenge is the need in many
cases to use resources that are unfamiliar, due to the project requirements of
the, the client, or locally applicable regulations. It is also worth noting that local welding companies contracted to perform work often don’t have enough
experience in large welding projects. This increases the risk of noncompliance
and may require additional resources for performance monitoring.
This article evaluates the causes of defects in welds. The approach taken
was to simulate conditions that can affect the quality of welds by changing
the parameters used to diagnose defects. Weld quality was verified
visually, since this is the most common method in pharmaceutical facilities,
as recommended in American Society of Mechanical Engineers Bioprocess
Equipment (ASME BPE) group regulations.
This article also presents a case study performed after extensive experience
in installation of international projects, during which various types of
nonconformities were identified in a variety of welds (Figure 1).
Over the years, the pharmaceutical industry has become increasingly
aware that the welding process used to join components of process piping
systems that will be in contact with the product must be controlled and
consistent to reduce the likelihood of defects in individual welds.
The pharmaceutical industry currently uses orbital GTAW/TIG welding
almost exclusively. This produces welds of high quality with very low
rejection percentages; these joints possess high strength, high purity meta,
and good surface finish.
Orbital welding is the controlled rotation of components within a fixed
support, while an adjustable, nonconsumable tungsten electrode attached
to a guide moves (or “orbits”) the joint. The electrode, the arc, the area
surrounding the weld, and tube interior are protected by a shield of inert
gas—usually argon—with a purity of 99.995/99.999% (Figure 2).
Although orbital welding is an automated process, weld quality depends
on a number of parameters, in addition to the operator’s training and skill.
Changes in any of these parameters can result in weld defects, which can
lead to nonconformities. As a result, each weld must be verified individually.
Nondestructive Weld Verification
Nondestructive weld verification inspects the surface and subsurface of the
weld and surrounding base material to verify weld quality. Commonly used
nondestructive verification methods include:
¡ Penetrant liquid
¡ Magnetic particle
Within the world of critical facilities, however, visual verification by video
endoscopy has wider acceptance. The main advantage of this method over
those listed above is that provides visual verification of the weld surface
Figure 1: Weld rejection due to scratches (a and b)