Welding of A312 TP 321H to PII pipe

[baig1111970]

I would like to know the requirement of inconal Cladding on 1¼Cr. ½Mo. (PII) pipe & its PWHT prior to its welding to Stainless steel piping (SS321H)

Ayaz

 

[sayee1]

Here is an excerpt related to your query. The problem noted below occurred with an overlay being used on the face of the bevel ... and the base metals were high carbon low alloy steel (8630).


BACKGROUND

1st case: Failures on flanges overlaid with CRA weld metal have been reported. XX reported a hub weld failure on a flowline riser base. The weld failed during hydrotest and several hubs had to be replaced. The hub base material was AISI 8630 overlaid with Alloy 725.

2nd case: The failure in this case was a hub weld on a gas-transfer riser that was detected after two months in service. Similar to the earlier flowline riser base hub weld failure, the hub material was AISI 8630. However, the
weld overlay was Alloy 625. Preliminary failure analysis indicate that areas of non-fusion were present along the weld overlay fusion line. It is not known what role these area of non-fusion played in the failure.

In both cases mentioned above, the weld overlay was not qualified as a strength weld, but only tested per ASME Section IX requirements for weld overlay for corrosion resistance. When welding CRAs onto any high carbon
low alloy steels such as 4130, 4140, 8630, etc., the potential for embrittlement at the CRA/base metal fusion line is likely. When used only for non-load bearing service, where no tensile stresses are present,
embrittlement of the weld fusion has not been a problem. However, weld failures have occurred when the CRA overlay is applied on a weld bevel face where it is subjected to residual and applied tensile loads.

A primary contributing factor in the above failures is the application of post-weld-heat-treatment( PWHT). After the weld bevel is overlaid with the CRA material, PWHT is required to control hardness in the low alloy steel base material weld HAZ. However, the PWHT promotes diffusion of carbon from the low alloy steel into the CRA fusion line,
where brittle carbide phases and intermetallics form. These deleterious phases render the CRA/low alloy fusion line prone to fracture.

WAY FORWARD

Materials/Welding Engineers should be consulted in cases where CRA weld overlays are used on weld bevels and other areas that subject the CRA to tensile stresses..

The following points need to be considered when applying CRA weld overlay to any pressure containing component :

Assess how the CRA weld overlay will be loaded during service. Any CRA weld overlay that will be subjected to tensile stress should be brought to the attention of Materials/Welding Engineering. Practical solutions for addressing these cases are available.
At a minimum , the weld procedure should be qualified per ASME Section IX for butt welds. Hardness and Charpy impact testing should also be employed. Specific Charpy and hardness test requirements will be advisable.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[baig1111970]

Thanks for reply. I understand that for any these kind of welds we need to have PQR & WPS. However, have anybody practical experience of welding PII pipe with A312-TP321H without cladding. please also mention service for which this piping system is in use. In my case service is natural gas & steam (Steam reformer inlet manifold piping of NH3 plant)Pressure = 38 kg/cm2 & temp=550 C.