No Specs-Capacitator Discharge Pin Welds

By foolio1957 Date 11-09-2005 00:07

Need info / advice. I am a PM for an insulation company. For years, we have used cup head pins installed with AGM capacitor discharge guns to hold insulation on bottom of ducts. The pins are 12 / 14 gage galvanized with sharp points, welded to 16 to 24 gage galvainzed ducts. These pins produce a small spot weld that holds great with a static load perpendicular to the duct surface. Now the inspector wants to "test" each pin, but these welds are small and break easily when bent.

The problem is, on this project, the specs are silent on the subject. There is no language at all in the specifications on pin pull tests, or welding requirements for this type of pin. Our insulation industry has used these pins for years because they hold as they are designed to, and do not result in blow holes in the thin galvanized ductwork.

I find tons of information on welded pins and studs, ASTM standards, etc., but I have found nothing on this type of small-weld, capacitor discharge pins. I have contacted a few of the manufacturers of these capacitor discharge welders, but no one has any information on testing / specifications for these pins. Anyone out there have any information / suggestions?

This inspector is ADAMANT in wanting to "wiggle" these pins back and forth, and we are at a stalemate. I have written an RFI to address the situation, but need some hard evidence to back up my position.

By MBSims

Date 11-09-2005 05:00

Perhaps the inspector has some previous experience with bending shear studs for AWS D1.1 aplications and believes insulation pins are similar. Shear studs are used to transmit structural loads and warrant the use of a bend test, however insulation pins only need to support the weight of the insulation. This weight is rather insignificant, as evidenced by the slip-on clips that are used to retain it on the pin. I would suggest you propose to demonstrate the adequacy of the pin welds by welding several (perhaps 5) to a scrap piece of plate of the same thickness and material type as the duct for a "demonstration" of the equipment condition and process at the beginning of the job and periodically when changes or repairs are made to the equipment, or pin diameter changes. You might also perform this check at the beginning of the work week or some other mutually agreeable interval, although it is not really necessary considering the non-critical nature of the welds.

By jon20013 (*****)

Date 11-09-2005 12:57

I'm not really sure this is of any help to you but in my business (commercial nuclear), we are extremely strict about process qualifications and testing yet for CD welding, we exempt personnel qualifications and testing of the attachments.

In my humble opinion your inspector is trying to test something which needn't be tested. NORMALLY, these welds are acceptable under almost anyones standards if they simply exhibit a "flash" all the way around the attachment. Ask your inspector to cite a requirement for the "tests" he/she wishes to perform.

GOOD LUCK!

By CHGuilford (****)

Date 11-09-2005 14:20

I agree; if there are no specs that apply to the pins, what business does the inspector have in wiggling the pins back and forth? It should be "hands off" until such time that a test or examination and acceptance criteria are defined.

Chet Guilford