3LHDPE or 3LPP? 1

[JohnLL]

I have a offshore pipeline which typically has to be coated with 3LPP, due to operating temperature and subsea application. Pipe will be also coated by concrete coating.
Now there is an offer to use 3LHDPE.

Question is:
- Is there any drawback for 3LHDPE compared to 3LPP?
- 3LHDPE is not mentioned in DNV-RP-F106 or DNV-OS-F101. Is there any reason for that? is it allowed to use it as per DNV code?
- what is major difference between HDPE and usual 3LPE? is it only density and applicability temperature range OR breakdown ,etc are also enhanced?

Regards,

 

[SJones]

offshore pipeline which typically has to be coated with 3LPP due to operating temperature

"Typically has" or is it really 'has been specified'? If the latter, on what basis will an offer of 3LPE be evaluated, since some criteria must have been applied to have selected 3LPP in the first place.

DNV-RP-F106 does not differentiate between grades of PE because it is a performance based specification, i.e. provided that it meets the specified performance characteristics, any grade of PE can be used. ISO/FDIS 21809-1 (I don't have the final standard)addresses LDPE along with MDPE and HDPE lumped together.

Provided that you are satisfied that the offered HDPE can give the performance required of PP, then the only real drawback will be that, in general, PE being softer will run a higher risk of damage.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[JohnLL]

Steve
thanks for reply.
to my best knowledge, in external pipeline coating application, what mainly differentiates between PE and PP is working temperature.
Since my case has to operate at 90 deg. Celsius, PE addressed in DNV-RP-F106 can not be used, but PP can.

Now we have HDPE tolerates temperature up to 120 deg. and I was wondering if there is any reason to not use it.
Your note about damage is very helpful for me. but still I don't understand how HDPE and PE are categorized in one batch in DNV, while their working temperature is quite different.
Any Idea?

 

[SJones]

ISO/FDIS 21809-1 places a notional temperature limit of 80 deg C on MDPE/HDPE and then states "use of coating classes outside of these guidelines shall be approved by the purchaser or end user".

So, does the offer of taking HDPE to 120 deg C meet with your approval? One thing to bear in mind is how many lines are operating satisfactorily at 120 deg C with this offered HDPE coating?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04