stringer or weave for pipe strain
stringer or weave for pipe strain
(OP)
I have an engineer who wants the welder to grind out part of the cap and part of the fill pass (from 3 o'clock to 7 o'clock) and the refill that area in an attempt to cause the pipe to move because it is too far out of alignment with a pump. What would cause more pipe movement; refilling with one weave with a bigger electrode or refilling with stringers with a smaller electrode but more passes.





RE: stringer or weave for pipe strain
RE: stringer or weave for pipe strain
RE: stringer or weave for pipe strain
Better though to cut and use a new spool piece, field fit and welded with the flange bolted to the pump.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: stringer or weave for pipe strain
Consider a T-joint welded with a single sided fillet weld. A three-pass fillet weld will exhibit more angular distortion than a single pass fillet weld because the three pass weld has heated and cooled the base metal three times. The large single pass fillet weld only requires the joint to be heated and cooled once.
Another factor is the thermal gradient from one area (the weld and HAZ) and the unaffected base metal. The greater the gradient, the greater the distortion. The stinger beads will result in higher thermal gradients because there is less heat (Q=VxAx60/TS) in comparison to the large single pass fillet. Each pass of the weld deposited with stringers has higher thermal gradients because the heat dissipates into the adjacent base metal quickly. Each pass introduces additional angular distortion. The large single pass fillet weld heats the joint more completely reducing the thermal gradient through the thickness of the base metal and adjacent to the weld. It cools slower, has less thermal gradient, and introduces less distortion.
The temperature gradient required to reach the approximate yield point of the base metal is relatively low. For carbon steel it is on the order of 220F to 230F degrees above the surrounding metal. That temperature gradient is all that is needed to introduce residual stresses on par with the yield strength of the base metal resulting in plastic deformation, i.e., angular distortion.
The trick to flame straightening or cambering is to maximize the delta T from the area heated to the adjacent area. There is no need to heat the base metal above the lower temperature or transformation. A delta T of 230F is sufficient to begin to see some "controlled" distortion. I usually place a barrier between the area being heated and the adjacent area. I pack the area beside the heated area with wet rags to maximize the delta T to maximize the "distortion" without any danger of introducing metallurgical problems because the metal (carbon steel) was heated above the lower temperature of transformation (about 1330F). The idea is the heat one area while not heating the adjacent areas so the unheated areas offer restraint. The heated region expends and deformed by plastic deformation as a result of the heated area developing compressive forces in excess of the yield point of the base metal. Upon cooling the compressive forces become tensile forces if the unheated areas offered sufficient restraint. That is why the entire member is not heated to a uniform temperature. Both delta T and restrain have to work together to cause distortion that can be to your favor as in the case of cambering a beam or against you in the case of a single sided multiple pass fillet weld.
Best regards - Al
RE: stringer or weave for pipe strain
RE: stringer or weave for pipe strain
RE: stringer or weave for pipe strain
Best regards - Al
RE: stringer or weave for pipe strain
Dan T