Dissimilar material between Nozzle and Shell (ASME VIII Div I) 2

[GusMontiel]

Hello all!

I designing a Pressure Vessel where the body is SA-516 70 but three nozzles would be A335-P92, A335-P1, and A335-P11 (the same material as the end-pipe connection considering the steam temp). There is an internal spray system that keeps the internal surface of the shell at 400 °C.

So my doubt is regarding the weld between these dissimilar materials:

Some experiences in plants with similar situations?
The thermal stress in the weld can lead to failure in it, what would be the recommendation for the weld and filler?

Thanks in advance!

 

[GD2]

OP,
Do you need to weld the low alloy steel pipes directly to the vessel? Why don’t you flange it to the CS vessel nozzles?
It could easier from design perspective for both the vessel and the pipings in terms of thermal loads and displacement.
If it must be welded directly to the vessel, develop a WPS for welding CS to low alloy steel. It’s common.

GDD
Canada

 

[fleischfresser]

If a company were to make such a suggestion to me, I would immediately blacklist them as an unqualified supplier, as they do not have sufficient knowledge of the manufacturing processes for pressure vessels. This is typical for engineering companies that have lost all connection to the pressure vessel production.

I assume in the following that ASME VIII/1 was chosen as the design code. The SA-335 P92 is only permitted by the Code Case 2179-11
Required minimum PWHT temperatures:
SA-516 Gr. 70 assigned to P. No. 1: 595 °C (Table UCS-56-1)
SA-335-P1 assigned to P. No. P3: 595°C (Table UCS-56-2)
SA-335-P11 assigned to P. No. P4: 650 °C (Table UCS-56-3)
SA-335-P92 assigned to P. No. P15E: 730°C to 800 °C (Code Case 2179-11)

If the shell thickness of the pressure vessel made of SA-516 Gr.70 is larger than 38 mm, the seams must be annealed. This is preferably done in a furnace. The SA-335 P1 nozzle can also be included in this furnace annealing without any problems, as the same PWHT requirements apply to both materials

The situation is different with SA-335 P11. If this nozzle is included in the furnace annealing described above, this must be carried out at a minimum of 650 °C and the two other materials SA-516 Gr.70 and SA-335 P1 are then annealed to an unnecessarily high temperature. This can affect the mechanical values of these materials and must be taken into consideration, as according to UCS-85 the mechanical values for the base materials must be determined after simulated annealing. In this case, SA-516 Gr.70 and SA-335 P1 should be ordered with a tempering temperature at least 20°C higher than the annealing temperature.

The situation is totally different with SA-335 P92. The PWHT holding temperature must be between 730°C and 800°C according to the Code Case. This annealing temperature is therefore higher or reach the approximate Lower Critical Temperature of SA-516 Gr.70 (725 °C) and SA-335 P1 (730°C).
In order to be able to produce a joint between a carbon steel and SA-335-P92, transition pieces are required. This means that an SA-335 P11 nozzle is welded in the SA-516 Gr. 70 shell and and annealed as described above. Then a transition piece made of SA-335 P22 is welded to the SA-335 P11 and annealed locally (approx. 700 °C). The SA-335 P92 is now welded to the SA-335 P22 transition piece and annealed locally (approx. 740 °C).

SA-335 P92 is a Creep strength enhanced ferritic (CSEF) steels and is not easy to weld. You therefore need an experienced welding engineer to advise you.


Regards - Juergen

 

[GD2]

OP,
Flieschfresser had given you a detailed scenario on welding and PHWT difficulties when you weld the low alloy steel pipes to the vessel.
The design of the vessel will depend on how you want to configure the vessel and how much easy you want to make your life.
Here is the discussion:
1. Vessel configuration - vessel with CS vs alloy steel nozzles. With CS nozzles, you simply flange off the alloy steel piping with the spec break at the flange. With alloy steel nozzles, Flieschfresser has given you the scenario.
2. SA 516 Gr 70 Vessel at normal operating temp 400 C. This temp. falls in creep regime. Temp limit to define the creep range for this material is 371C. Sec II Part D (assuming it's a Sec VIII Div 1 vessel) will still give you an allowable stress value at 400C but you need to be alert when the vessel will normally operate at 400C for two reasons - one, the creep values in Part D are to be used when the vessel is designed for normal operation under creep (elastic region) with excursion that might occasionally see the creep temp. Second, the Part D allowable stress values are only good upto 100,000 hrs. rupture life, which is approx. 14 yrs. If the vessel is designed say for 30 yrs.the rupture allowable stress will be much lower. Designers will be able to calculate the rupture allowable stress at 200,000 or 300,000 hrs but you will be looking at a thicker vessel.

Hope it makes sense

GDD
Canada