Volume 3, Number 4 October 2004
A. RT location marker tapes, or numbers lines, are commonly made using duct tape and lead numbers. Here are the steps required to make number belts or marker tapes:
Calculate or measure the circumference of the pipe. Keep in mind that nominal and actual pipe diameters are different for pipes under 14 in. in diameter. For example, an 8 in. diameter pipe (nominal) is actually 8.625 in., and a 12 in. (nominal) pipe is actually 12.75 in. So you must use the actual diameter when you calculate the circumference. For 14 in. pipe and larger, nominal and actual diameters are the same.
Decide if you want markers at the ends of each exposed film or at regular intervals. Markers at the ends of film are most common because fewer lead numbers are needed.
Next, decide what film size (4.5 in. x 10 in. or 4.5 in. x 17 in.) you’ll use for the pipe size, as this determines where marker numbers will be located. For film 10 in. long, numbers are usually placed every 8 in. on the tape, which allows an inch of film overlap at each end. For film 17 in. long, they're at 15 in.
Tear off a strip of duct tape about 6 in. longer than the calculated circumference and approximately 3 times as wide as your lead letters are tall. Lay the duct tape out, adhesive side up, on a flat surface next to an extended tape measure. At one end, place a lead number zero (0) at the end of the tape and adjacent to the end of the tape measure. The lead number should be along one edge of the duct tape strip because you will be folding the tape lengthwise over the numbers when you are done. Continue to add numbers at required intervals until you reach the end of the tape. Some people use 0, 1, 2, 3, ..., others use the actual number of inches from zero; this is often determined by the specification or NDT procedure.
Carefully fold the tape over the lead numbers until you have a fully wrapped numbers line the same length as the circumference of the pipe. Finally, starting at the zero end, roll up the completed numbers line and mark it with the pipe diameter it is intended for.
To use a numbers line, select the proper line for the pipe to be shot and unroll it. Use a short piece of duct tape to anchor the zero end to the pipe and wrap the rest around until the other end overlaps zero. Tape that end down. You're ready to go.
If you're shooting really hot pipe, the heat can cause the numbers line to stretch. If it stretches to the point where the numbers are no longer under the cassette, you can always cut out a piece between each pair of numbers and retape the pieces together to extend the life of the line.
E-mail, fax or phone questions for the Inbox to the Editor:
hhumphries@asnt.org
(800) 222-2768 X 206
(614) 274-6899 fax
[ The NDT Technician ]
Copyright © 2008 by the American Society for Nondestructive Testing, Inc. ASNT is not responsible for the authenticity or accuracy of information herein. Published opinions and statements do not necessarily reflect the opinion of ASNT. Products or services that are advertised or mentioned do not carry the endorsement or recommendation of ASNT.
IRRSP, NDT Handbook, The NDT Technician and www.asnt.org are trademarks of the American Society for Nondestructive Testing, Inc. ACCP, ASNT, Level III Study Guide, Materials Evaluation, Nondestructive Testing Handbook, Research in Nondestructive Evaluation and RNDE are registered trademarks of the American Society for Nondestructive Testing, Inc.
ASNT exists to create a safer world by promoting the profession and technologies of nondestructive testing.
