Connecting a titanium grade 7 pipe spool to a super duplex pipe.
Connecting a titanium grade 7 pipe spool to a super duplex pipe.
(OP)
We have been suffering with pitting corrosion on two removable piping spools (super duplex stainless steel). Corrosion is located on the welds at the elbows.
- the medium is seawater.
- the spool is located at the outlet of the plate heat exchanger.
- it is a 12" schedule 10 pipe(s).
- low operating pressure (9 bar); Design pressure = 15 bar.
- Operating temperature = 65 deg C. During de-waxing = 90 deg C.
at first we though it was probably a bad weld, so we fabricated a new spool and replaced the removable spool. It took only 2 months operation for corrosion to emerge again.
I am looking at buying replacement piping spools in Titanium Gr7 or Gr12.
the problem with that:
down stream of the pipe in question i have connected a carbon steel valve followed by super duplex pipe.
Note: last time found corrosion on the faces of the valve (wrong gaskets).
Does anyone have experience on what do I need to do to successfully make this work without bringing more problems on board due to dissimilar materials? any proven techniques out there?
- the medium is seawater.
- the spool is located at the outlet of the plate heat exchanger.
- it is a 12" schedule 10 pipe(s).
- low operating pressure (9 bar); Design pressure = 15 bar.
- Operating temperature = 65 deg C. During de-waxing = 90 deg C.
at first we though it was probably a bad weld, so we fabricated a new spool and replaced the removable spool. It took only 2 months operation for corrosion to emerge again.
I am looking at buying replacement piping spools in Titanium Gr7 or Gr12.
the problem with that:
down stream of the pipe in question i have connected a carbon steel valve followed by super duplex pipe.
Note: last time found corrosion on the faces of the valve (wrong gaskets).
Does anyone have experience on what do I need to do to successfully make this work without bringing more problems on board due to dissimilar materials? any proven techniques out there?





RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.
RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.
Welding procedure specification as per: ASME IX; ASME B31.3.
Welding position = All
Position qualified = All
Preheat temperature = Drying if necessary.
Inter-pass temperature = 150 deg C.
Preheat Method = hot air blowers.
Measurement = Tempilstick or thermometer.
Preparation method = Machining or plasma cutting and/or grinding
Cleaning method = Brushing + degreasing.
Oxigen content = 500 ppm.
RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.
We have also used these filler metals successfully when similar duplex alloy weld metals suffered pitting attack (perforation) in service.
RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.
I take it that you are using an overalloyed SD filler already.
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Plymouth Tube