Arc Machines 307 - Manual (Page 166)

Arc Machines, Inc. Model 307 Orbital Tube Welder Training
Document No. 740096 Chapter 17. Page 5.
Rev. A
with defined qualifications who represents the owner. It is important that
welding operators examine their welds and be able to recognize when there
may be a problem with the weld parameters or with purging, electrodes, or
fit-up and be able to take corrective action.
Most owners hire third-party QA inspectors for weld inspection in high-purity
applications. The BPE requires a minimum of 20% of welds to be randomly
selected for ID inspection which would typically be done with a borescope.
A borescope, or fiberscope, is a fiber optic instrument with a monitor (TV
screen and optional video tape recorder) used for inspecting the weld on the
tube or pipe ID. Some borescopes can measure concavity or convexity of
the inner weld bead, but it is difficult to detect light oxidation with a bore-
scope. For SEMI the percent of welds inspected is subject to agreement as
part of the purchase order for services.
Use of Test Coupons
The 3-A Sanitary Standards written by the dairy industry in the 1950s rec-
ommended the use of preproduction weld samples to determine that the
manual welder had the necessary skills to make a sanitary weld and so that
the owner and installing contractor could agree on quality standards in ad-
vance of a job. For orbital welding, test coupons help to establish quality
standards in advance of an installation, and the repeatability of the process
offers assurance that if the test weld is good, previous welds done with the
same weld parameters and conditions should also be acceptable.
Test coupons should be made:
• at the beginning and end of each shift
• after a change in welding procedure
• change in material heat
• change in tubing size
• change in gas supply
• change of welding equipment
• change of power supply location
• test coupons should be made any time there is a concern about
deterioration of weld quality.
Since 100% inspection of the ID of orbital welds is not always possible or
practical, the use of test coupons is the next best thing. To be meaningful,
test coupons should be done on the actual material with the same heat
number as that being used on the job. They should be cut open to expose
the entire weld bead for viewing. If the test coupon is found to be defective,
the weld is rejected and all welds made since the previously accepted test
weld must be cut out and replaced. Note that with smaller tube sizes, the
cut will remove a significant part of the weld. For small diameter tubes,