Protection for GRE Flange Joint 3

[Lunbawang Piper]

Hi Fellow Pipers,

Anyone had experience with glass fibre reinforced (GRE) flange joint that buried underground? What is the additional protection that should be applied on the flange joint other than the normal coating. Is wrapping required, which I normally practice for underground carbon steel pipe? My concern is on the possible corrosion of the carbon steel bolts and nuts, and deterioration of EPDM gasket once having direct contact to soil.

The best thing is to remove the flange, but it is critical for sectionalizing for planning purposes.

Thank you in advance guys.

 

[TugboatEng]

There are fastener options that tolerate direct burial. Aluminum bronze is an example. Maybe, test the soil for sulfides. The EPDM gasket will tolerate direct burial without issue.

 

[Lunbawang Piper]

TugboatEng, thank you for the feedback. Will look into aluminium bronze. Do you happen to know if stainless steel fastener is also able to tolerate direct burial?

 

[HTURKAK]

Common practice is , the use of galvanized bolt+nut+ washer .. SS is prone to soil corrosion..

My opinion based on experience ..










Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[TugboatEng]

Stainless steel is subject to crevice corrosion and will not tolerate burial, even with protective coverings.

 

[Lunbawang Piper]

Thank you HTURKAK and TugboatEng for the helpful feedback!

 

[LittleInch]

Look up PTFE coated bolts and see if they work for you.
Interesting comparison here

http://www.impactimpex.com/ptfecoatedstudsboltsnuts.html

Also grease the ends where you attach the nut(s)

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

 

[bimr]

"After removal of the corrosion products, the bolts were examined, weighed, and photographed. The average weight loss was used to calculate the weight loss per year for each type of material used. Although the silicon bronze and the stainless steel bolts lost the least amount of weight during the study, they caused severe corrosion of the nearby glands. As a result of these tests, most pipe manufacturers began to recommend the use of low alloy steel bolts over high strength gray-iron with 0.5% Cu. Since that time, the low alloy steel bolt has been used extensively with success in the large majority of cases. However, just as the case of the high strength gray-iron bolt, it has not been 100% successful.

It is much more reasonable, then, to reduce the corrosion current to its lowest value possible and provide protection to the bolts, either by wrapping in polyethylene, providing cathodic protection to the whole system, or simply coating each individual bolt with a protective coating."

Link

 

[MJCronin]

My vote is with Littleinch .... Quality PTFE bolt coatings are best ... for UG service

XYLAN coatings are the pioneers in this area

https://toefco.com/coating-capabili...Hfrhzn1LCqs45cTgCoDMIuyeAeC-fjwsaAuHgEALw_wcB

MJCronin
Sr. Process Engineer

 

[TugboatEng]

Remember that these bolts are fully isolated as they will be installed in plastic piping. There will be zero protection in the event of a coating defect or failure. That is why I would suggest using corrosion resistant fasteners

Also, as steel fasteners corrode they swell. This can break the plastic flanges.

 

[Lunbawang Piper]

In recent years, at the plant that I worked for, we use PTFE fluorocarbon coated as the standard coating for fasteners. Even for aboveground application, I observed that all the fasteners started to corrode after 1 year, although not excessively. Therefore, I am not confident it will not corrode for buried application.

 

[swazimatt]

Stainless steel is subject to crevice corrosion and will not tolerate burial, even with protective coverings.

That is interesting. The local council insist we use SS pipes for wastewater pumpstation rising main from the submersible pump to the flow meter, this is normally about 10m of buried pipe

 

[TugboatEng]

Our classification society also insists on SS pipes for seawater. The engineers likely know better but the field inspectors don't and it's the field inspectors that enforce the rules... When you suggest otherwise they threaten you with change orders.

Sewage does have sulfides which can be problematic for copper alloy pipes. The fasteners should not be exposed to the sewage so copper alloys should be acceptable.

Stainless steel can work provided the soil is very dry or cathodic protection is used. Remember, the OP asked about plastic pipe which excludes cathodic protection.

 

[saplanti]

Good practice is not to use flange connection underground. You should be able to use threaded connection instead.

In case if you must use one only connection underground, the best is to organise a dedicated room for this connection with suitable materials.