Grade P11 Weld failure between ellipsoidal head and tubesheet 2

[qualitypro]

We encountered a weld failure between an ellipsoidal head and the tubesheet material in the field even before the equipment had been started up. The head in the new HX equipment was over 3 inch thick and had gone through all necessary preheat, NDE, PWHT, hydros etc in an overseas shop with no anomalies. What could be the potential causes for this failure? Appreciate if anybody can share any past experiences with HX weld failures.

 

[GD2]

Op,
My believe is that the weldjoint may have failed due to brittle fracture due to wrong hydrotest temperature. And it was done twice at the Operator's facility.
If I assume both Head and the Tubesheet materials were Normalized, it falls on Curve C of UCS-66. Taking the governing thickness as 3 inch, the MDMT (without impact testing)from the curve gives 42 F .

UG-99(h) requires minimum hydrotest temperature of (42 F + 62F)=104F. The site hydrotest were done at 60F(most likely at the ambient temperature).

Try to obtain a Hydrotest Report from the Manufacturer, if possible and compare the test temperatures.

Even if I eliminate weld crack due to other reasons, the crack in the dish suggests a strong evidence of brittle failure.

GDD
Canada

 

[r6155]

@ GD2
UG-99 is ASME VIII Div 1, this PV is ASME VIII Div 2
See my post 10 Jan 24 00:55

Regards

 

[r6155]

ASSUME THE WELD IS OK

1) it is impossible to access to see the tubes in the floating head.
This is a big and incredible mistake..

2) the pressure test was incorrect and invalid: impossible to check the tubes for leaks

3) it makes no sense to continue with this design.

4) I can't believe how the AI doesn't detect this mistake.

Regards

 

[GD2]

Sorry, based on Div 2, the test temperature will be following:
Assumptions: Fig 3.8 Curve B, subject to PWHT and non-welded part
MDMT exemption: 62F
Test temp =(62 +60)=122F (50C).
OP- please check MDMT marked on the Nameplate. It could be different. You need to use the nameplate MDMT and add 60F for test temperature.

The floating head welded design to the tubesheet is weird. It's usually not seen. Imagine you need to replace couple of tubes, the head has to be cut everytime maintenance work is involved in the tubes. It's essentially a maintenance headache. I am not sure why Designer didn't opt for one of the floating head design from TEMA?

GDD
Canada

 

[r6155]

Weld cracks (solidification crack) may occur 24 hours or more after welding.

Regards