×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Connecting a titanium grade 7 pipe spool to a super duplex pipe.

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?
 

RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.

Sounds very difficult- What was the welding procedure?

RE: Connecting a titanium grade 7 pipe spool to a super duplex pipe.

(OP)
Hi,

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.

A number of Engineers & manufacturers require up alloying; e.g., ERNiCrMo-3, -4 or -10 for these welds. Pickling and passivating can also be used to further mitigate corrosion in the weld metal.  

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.

Have you looked into having the SD elbow annealed after all welding?
I take it that you are using an overalloyed SD filler already.
 

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources