Thermal stress relief in nozzle welds
Thermal stress relief in nozzle welds
(OP)
Greetings, we have certain doubts about the stress relief in the welds of nozzle in the shell of an AST, in API 650 2013 in 5.7.4, states in 5.7.4.2 and 5.7.4.3 that the connection "shall be prefabricated into the shell plate or thickened insert plate, and the prefabricated assembly shall be thermally stress-relieved within a temperature range of 600 °C to 650 °C (1100 °F to 1200 °F) for 1 hour per 25 mm (1 in.) of thickness prior to installation."
My doubts are first the PWHT apply to the internal weld of the nozzle and external reinforcement and internal welds, or second we have to do the internal weld first, next the PWHT, and then complete all the external welds without the PHWT.
There is a great risk about having deformations in the shell during de PWHT, that's why we may have to do a bigger hole in the shell for the neck of the nozzle.
Or we just make the Nozzle with the Reinforcment or the thickened insert, PWHT, and then put it in the shell, and then make the internal weld, without the PWHT.
My doubts are first the PWHT apply to the internal weld of the nozzle and external reinforcement and internal welds, or second we have to do the internal weld first, next the PWHT, and then complete all the external welds without the PHWT.
There is a great risk about having deformations in the shell during de PWHT, that's why we may have to do a bigger hole in the shell for the neck of the nozzle.
Or we just make the Nozzle with the Reinforcment or the thickened insert, PWHT, and then put it in the shell, and then make the internal weld, without the PWHT.





RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
This statement is almost correct but I'm not sure what you mean by "internal weld".
Are you working on a flush type fitting (5.4.7.1) or a nozzle meeting (5.4.7.2) ?
For flush fittings 5.4.7.1 you PWHT an assembly that includes a part of the bottom.
For nozzles meeting 5.4.7.2 the assembly you are PWHT does not include a part of the bottom.
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
Just checking - why are you PWHT this nozzle?
Is it over 12" NPS and the shell plate over 1" ?
Is the shell plate material grade over IV or higher ?
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
Since API don't mention how to do the heating, clearly states that shall do it prior to the installation of the nozzles. My doubt is how we can pre heat the preassemble , doing all the welds, without complete the installation of the nozzle in the shell, if we shall going to use an insert plate, it would be easy to do, using a furnace, but we are using reinforcements.
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
stress-relieving requirements need not include the flange-to-neck welds or other nozzle-neck and manhole-neck
attachments, provided the following conditions are fulfilled." applied also for those specified in the 5.7.4.3, apparently not, if I don't mistake.
This mean that we need to have to stress relief all the assembly, flanges, neck, reinforcement pad and put into an insert shell plate, and then weld this "pre-assembly" into the Shell?
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds
There is a matter about the local heating, in the inquiries forbid any local heat at least it is made in all the tank, and then the definition of pre-assembly and complete assembly it's not quite clear, how I state it before, IMHO, we should weld the neck of the nozzle first, in the reinforcement pad or thickened insert, then weld over the shell opening, finally we complete the weld of the reinforcement pad in the shell, and do the PWHT.
The problem comes when you can't do the pre assembly in the shop, and we must install the nozzle in field.
RE: Thermal stress relief in nozzle welds
RE: Thermal stress relief in nozzle welds