Arc Machines 307 - Manual (Page 165)

Arc Machines, Inc. Model 307 Orbital Tube Welder Training
Document No. 740096 Chapter 17. Page 4.
Rev. A
Discoloration
While the semiconductor industry demands color-free welds, the pharma-
ceutical and food and dairy industries are generally willing to accept some
light blue or straw color of the ID. The ASME BPE standard provides for
ID discoloration to be held to a minimum, with the ID weld bead free from
color, but with the level of discoloration to be permitted in the HAZ to be
determined in advance by the owner and contractor. The allowance of some
discoloration is in recognition that zero discoloration is quite difficult to
achieve unless additional gas purification is available and that oxygen, man-
ganese, moisture, etc. that contribute to discoloration may originate from
the weld components themselves, and are thus difficult to control. AWS
D18.1 and AWS D18.2 contain a colored photo which allows owners and
contractors to agree to a level of discoloration appropriate for their applica-
tion.
Slag islands
Certain heats of material are especially prone to slagging or oxide islands
that form on either ID or OD of the weld. AWS D18.1 prohibits oxide islands
greater than 1/16” (1.6 mm) and limits the number of islands to 4 in the
size range from 1/64” up to but not including 1/16” in any weld. The small
silicon dioxide spot at the end of downslope on 316L tubing is generally con-
sidered to be acceptable. Testing materials for weldability prior to accept-
ance should help to eliminate difficult heats.
Company Weld Specifications
Qualification to ASME Sect. IX of the Boiler and Pressure Vessel Code re-
quires that there be an In-House Quality Assurance Manual in-place. Indi-
vidual companies frequently write their own specifications in full compliance
with specifications for their industry, but with additional details.
Inspection Techniques and Requirements
Both SEMI specifications and ASME BPE-2002 (in accord with B31.3)
recommend 100% visual inspection of the weld OD. B31.3 makes the
distinction between Inspection and Examination. Weld examination is done
by the operator or the installing contractor while the Inspector is someone
Photo from AWS D18.1/D18.2 standard which shows a series of orbital welds
on the ID of a 316L SS tube. Welds were purged with argon containing
oxygen as a contaminant at levels from 10 ppm (1) to 25,000 ppm (10).