Calculating weld strength

Please refer to Specification: Welding of Piplines and Related Facilities, API 1104 -1999 (to be read with errata dated October 31, 2001) Element # 5.6: Testing of Weld Joints - Butt Welding. The method of preparing test coupon is described in element 5.6.2.1 and testing method in element 5.6.2.2. Tensile Strength Test Specimen shown in Fig-4 is with weld re-inforcement un-removed, which gives the tensile load with re-inforcement on of whole piece. If you want to apply tensile load concentrated on to weld deposit only and not on the whole strip (coupon) do it with reduced section tensile test and get the load reading direct from the tensile machine. Reduction of coupon's width should be perfectly centered to weld root. Please make sure that you do not depart from dimensional requirement of Specification. A. W. Siddiqui

Useful information, but I am just trying to find the estimated YS, UTS, and torsional strength of the weld joint as defined through calculation.

To evaluate the weld strength (tensile, yield, elongation & toughness) you are requested to take a samples from the coupon test pipe in according to the dimensions and locations determined by the code you fellow.

For example, according to API 1104, the 8" NPS requires preparing the following samples from the coupon test pipe:

2 samples for nick-break test,

2 samples for root or side bend test,

2 samples for tensile test, and

2 samples for face or side bend test.

The tensile test can be carried out by a test machine featured by means of automatically plotting the stress strain curve, where you can easily find yield stress, ultimate tensile stress, and fracture stress. The elongation can be measured. The area underneath the curve represents the toughness.

Stress in psi = Force in lb / Area in in²

Mr. Abdel Haleem Gala,

Please mention make and model of tensile testing machine you are refering.

The strength of a complete penetration weld joint should at least equal the strength of the base metal. Procedure qualification tests by the various codes are intended to confirm that the intended weld procedure can produce welds with the intended design strength, but designers typically use the base metal strength to calculate the strength of structural joints with full-penetration welds. Fillet and partial penetration welds have reduced strengths owing to the stress-riser notch effects in the weld geometry. The exact amount of reduction in the design strength for these types of welds will vary with the given design code, but typically the reduction factor for fillet welds is on the order of 50% or so.

HTH

Your numbers do not match ER80S-D2 tensile strength is 80 kpsi minimum not 110 area X psi X joint efficiency = strength

The 110 (as welded) is what the manufacturer has listed for typical mechanical properties, but I understand what you are saying (80min). What do you mean joint efficiency?

I agree with " One test worth thousand openion of experts".

Lincoln Arc Welding Institute has an excellent book, Design of Welded Structures, by Omar Blodgett. It used to sell for only $6.00. I expect it's gone up from that, but it will still be one of the best bargins you'll ever find in a design text. It explaines how to size welds by calculating the load per inch of weld. Do a google on Lincoln Arc Welding Institute.

You might check The "Welding Handbook", American Welding Society first. There are many texts available that treat the problem froma theoretical point of view B.E. Rossi's "Welding Engineering" is a typical source. ASME literature is available on the subject. As an example:

If you are checking Circumferential Butt Weld Stress with Combined Shear and Axial Stress; the Resultant Reduced Stress (MPa,psi) equals the square root ( Normal Stress squared) plus (3 times the Shear Stress squared).

The assignment of safety factor and consideration of Stress Concentration; Metallurgical changes due to the welding process; Surface purity; and Residual Stress must be examined. Of course, the final proof of theoretical to actual weld performance is proved in testing the weld sample.