Is a dielectric union required on 316SS tubing used for chemical injection.?

[TXRVD]

I have an installation where a pneumatic chemical pump is approx. 100 FT from a wellhead. The chemical injection pump discharge 316SS tubing is buried around 4 FT deep, comes above ground and connects to a 316SS ball valve, check valve and injection quill that is on a carbon steel flowline. The flowline has a dielectric kit on the flange before the flowline goes underground towards the facility. (there is cathodic protection on the buried flowline). The upstream side is the wellhead - around 10,000ft deep.

 

[TugboatEng]

I would first address the issues related to direct burial of stainless steel piping before I worry about galvanic corrosion. Stainless steel won't be able to passivate itself without air exposure.

As for the connection to the pipe, small connections of noble metals to much larger systems usually pose little galvanic corrosion potential.

 

[EdStainless]

Tug, let him direct bury SS. I need the consulting work.
If the water table is 100' deep and this location NEVER gets rain then you have nothing to worry about.
But if this soil is ever damp then you have issues.
The two that are most common are chlorides and/or bacteria in the soil. Many bacteria excrete acids and then when they die they often acids are also formed.
Buried SS requires protection.

With so much area of CS and so little SS the only galvanic impact might be right adjacent to the fitting, but there won't be any real imapct.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[SJones]

Indeed, the stainless needs to be coated. In addition, the need for bonding across to the buried flowline should be examined:

a) - to get it into the CP system for supplementary protection

b) - to lower the risk of stray current destroying the chemical line

If a) is adopted, then isolation from all the other buried metal in the well will be required


Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[TXRVD]

thank you TugboatEng, EdStainless, SJones for your quick response, knowledge and advice. I needed some backup since some thought that the DU was to protect the buried tubing. I am going to check that the isolation kit is properly installed where the flowline goes into the ground. We'll use sand in the trench as well.

 

[SJones]

Still need to coat the stainless!

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[TugboatEng]

For a short run like this there are tapes available for coating.

 

[SJones]

Don't know what a DU is, but the isolation is to stop the mass of steel down the hole drawing CP current resulting in the need for a power station to protect the flow line.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

Always remember this about stainless steel:
'Steel' came from the engineering dept
'Stainless' came from the marketing dept

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[LittleInch]

Best bet is to buy some ready coated stainless steel tubing. You can even get nice colours!

https://www.obcorp.com/product/tubing-bundle/coated-tubing/pvc-j-line

If the chemical injection point is on the well side of the Isolation joint of the flowline ( I assume this is just in the same trench as your chemical line?) then you should be Ok, but if not you need to add an insulation joint.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.