a question concerning “When can Face Bend and Root Bend weld coupons be substituted for side bend?”
The standard ASME IX standard guided bend fixture uses a 1 1/2-inch diameter mandrel is intended to bend carbon steel specimens that are 3/8-inch-thick and results in elongating the specimen 20% along the convex surface.
This size test jig works well for carbon steels when the welded coupon is thicker than 3/8-inch-thick, and ASME code allows the side bend in lieu of the standard face and root bend…
There are reasons why…
If you think for a moment about the clearance between the plunger and the die of the typical guided bend testing machine. If you tried to perform a face bend on a 1-inch-thick specimen, it simply would not work, i.e., there isn't sufficient clearance between the plunger and the die.
The side bend test allows the supplier’s weld laboratory to cut 3/8-inch-wide specimens from the welded coupon to eliminate the need for time consuming, expensive machining.
If the supplier’s weld laboratory prefers, they can machine each bend specimen to the required 3/8-inch thickness so the specimen can be bent as a face of root bend. It that route is taken, the laboratory must machine the face bend specimen to a thickness of 3/8 inch by removing material from the root surface. If the root bend is performed, the face surface must be machined to reduce the thickness to 3/8 inch.
It is easier and more efficient to simply cut side bend specimens and eliminate all the machining discussed in the paragraph above.
Be aware that the bend diameters used to evaluate the welded coupon is dependent on the base metal properties, the filler metal properties, and the thickness of the welded coupon. For example, a welded coupon consisting of 6061-T6 base metal welded with 4043 filler metal must be machined to 1/8-inch-thick and bent with a mandrel that is about 16 times the thickness of the coupon.
The reason is that the welded specimen of the 6061-T6 has very poor properties of elongation. The very large bend diameter is needed to prevent breaking the specimen. As a matter of fact, because the HAZ is overaged, it is recommended that a wrap-around bending machine be used instead of a standard plunger and die bending fixture.
In a similar manner, high strength steels require a larger bend diameter because the high strength steel has lower elongation properties than the lower strength steel. The code dictates the proper bend diameter to be used.
There is a potential for a supplier’s weld laboratory to use the incorrect bend diameter if no one pays close attention to the code requirements and the material properties of the welded coupon.
For that reason, I always include the bend diameter used when the test results are reported. It allows us, suppliers and owners to "audit" the bend test to ensure the proper test was performed.