Radiographic (RT) Gap Shots and Other RT Examinations for Fillet and Socket Welds In Accordance With ASME B31.3The following has been provided from an article by Jon K. Lambert. Jon describes himself as recently retired and returned to his adopted homeland from long-term tenure overseas as Project Welding Engineer on a major oil field development. He is a Member of the American Council of the International Institute of Welding (AC IIW, and of the US Technical Advisory Group (TAG) for ISO/TC 44/SC10; Unification of Requirements in the Field of Metal Welding.

Ive recently had the great pleasure and opportunity of working at one of the many New Zealand Petrochemical processing plants; this has been my first working experience in New Zealand.

During my first week, I discovered what was to me a phenomenon in the Clients inspection requirements; that is they require radiographic examination (RT) of socket welded joints after welding to assure the 1.5 mm gap is present. The Client also requires radiography in a number of other instances, as discussed further below.

It is the writer's hope and intention to shed some light on what ASME B31.3 actually requires in order of avoiding unnecessary expenses and time delays during fabrication or maintenance of process piping systems.

Radiographic Gap Shots for Socket Welds ASME B31.3 Normal and Category D fluid services do not require RT of gaps after welding, in fact the language of the code specifically states a 1.5 mm gap shall be present before welding. Gaps may or may not be present after welding, depending on heat input, alloy selection and a number of other factors.

There is no maximum gap currently addressed by ASME B31.3, however enough pipe should be inserted into the body of the fitting to provide a full strength connection while keeping the gaps small enough to avoid setting up turbulence. The best method for establishing the required gap is to perform random fit-up inspections whereby the pipe is inserted to full depth, a scribe or permanent mark applied to both the pipe and the fitting and then pulled back to the required gap setting. Arbitrarily, scribe marks could be placed at 25 mm apart when fully inserted, then pulled back to 27 28 mm for tacking. The gap pull back should be witnessed (and recorded) by competent QA/QC staff.

Radiography of Fillet Welds as a Final NDE Inspection Method Radiographic examination of fillet or socket welding as a method for final acceptance is not required by ASME B31.3.

Although there is radiographic acceptance criteria indicated in Table 341.3.2 for fillet welds, it is only intended that those criteria may be demonstrated by using the prescribed methods.

Typically, socket or fillet welds require only a percentage of visual examination; i.e., 5% for normal fluid service.

Radiography of Fillet and/or Socket Welds as a Means to Justify Waiver of Hydrostatic Testing Radiography of fillet and/or socket welding in order to justify waiver of hydrostatic testing is not required by ASME B31.3.

Where the owner considers both hydrostatic and pneumatic leak testing impracticable, the alternative leak test may be used under the conditions stated in Para. 345.1(c). Circumferential, longitudinal, and spiral groove welds must be radiographed or ultrasonically examined.

All welds, including structural attachment welds, not covered above require liquid penetrant or magnetic particle method inspection.

The code (and this writer) recognizes it is always the owner's prerogative to exceed code requirements; however the points above are made simply as the writers personal opinion that a very low cost to value-added ratio exists in the mentioned practices.

If you would like to communicate with Jon in respect to this and other code compliance issues you can contact him on jon20013@hotmail.com.