Temperature and Weld-Joint Efficiency

Hi,

You may join this FORUM at AWS, American Welding Society, you may raise your question there and got an answer, let me know if this helps

Very good site, below is the link

http://www.aws.org/cgi-bin/mwf/forum_show.pl

In Very simple English:

Welding is Solidification of a melted pool of metal say from 1450 DegC .Once Solidified ,the Weld behaves (same/nearby/better) like the parents welded.

NowOperating Temp. --if the parents can bear it-the weld can too.

And Design Temp.-- if somebody designed the Welded Body to operate say~ 750C, yesthe Welded joint can too.

Operating Temperature is the actual temperature at which, the equipment fabricated is expected to work, say Boiler (for steam generation), Furnace (to crack crude petroleum to produce end products like petrol, diesel) etc.

Design Temperature is the temp. at which the equipment fabricated should function safely. Since the equipment including boilers, pipes / tubes connected to it also undergo cyclic temperature, pressure etc. Then its withstanding temp. should be higher than the operating temperature and designed ( type of base metal, filler metals, thickness, Welding procedure etc.) accordingly.

Weld Joint Efficiency is the actual strength, metallurgical, structural integrity of the weld metal, Heat Affected Zone ( HAZ) and depends upon combination of many factors. The weld metal & HAZ like the base metal should withstand the cyclic temp. during the operation. The grain growth due to initial heat input during the welding, weld defects ( if any) during the process in the said areas should be controlled to give overall efficiency of the joint.

That is why designer selects appropriate type of parent metal, Welding Process, Heat input during welding, Pre and post heat treatments depending upon thickness and type of metals used ( CS, AS, SS etc.) for the equipment .

All these are done taking into consideration the Design – Operating Temperature and service conditions.

Sridhar – Advance Institute of welding Technology, Chennai- India.

According to ASME BPVC, Sec. VIII, Div. 1, [Para. UG-21], the Design Pressure shall be at least the most severe condition of coincident pressure and temperature expected in normal operation. Design pressure = Max. Allowable Working Pressure.

Operation Temp. is the temp. where the system is normally operated, while Design Temp. is the temp. at which we proceed a desig for the system. Design temp. is the most severe temp. expected in normal operation.

According to AWS A3.0 Standards Welding Terms and Definitions, the Joint Efficiency is the ratio of strength of a joint to the strength of the base metal, expressed in percent.