Derating for Vinidex HDPE pipe due to Temperature

[dsg1985]

I have some conflicting information from Vinidex (Aus HDPE pipe manufacturer) on the allowable pressures for their HDPE pipes.

Australian Standard 4130 lists a MAOP (maximum allowable operating pressure) for PE pipes. Doing the calculations from the standard for 35 degrees (celcius) and PN25 pipe (2500kPa) conveying water the MAOP = 2000kPa (*1).

The Vinidex catalogue lists 2000kPa for 35 degrees as well.

Recently I've been sent a derating table from Vinidex which tells me the allowable pressure is ~224m of head for PE25 pipe at 35 degrees.

I'm not sure which to believe. Their explanation was 'HDPE has come a long way' and confirmed it in an email. I'm looking for a second opinion, I'm just not 100% ready to believe suppliers these days.


(*1) (MAOP = 0.125*PNrating/C, where C = factor to account for temperature and other factors, C=1.25(water)*1.25(35 degrees) in this case).

 

[2ndIntegral]

dsg,

I have found that, as an engineering professional, to reluctantly or not blindly follow that which vendors quote. Not to say that we have all the time in the world to delve into things or that we don't trust vendors, but seldom are we given all the facts to understand the parameters.

I would suggest that, in your case, find which standard they're using as their basis for manufacture. I have found that few HDPE manufacturers intentionally deviate from BS EN ISO 15494.

The prescribed derating according to temperature and service life (very important!) is outlined even so far as include both a graph and equation form

 

[zdas04]

There is an equation in ASME B31.8 that has a couple of factors. The first one is an envirnomnetal design factor. For water it is 0.5, for natural gas it is 0.32, for hydrocarbon liquids it is 0.25. The other one is the Service Temperature Design Factor. This value runs from 1.20 at 4C (for ASTM 3408 pipe) to 0.50 at 62C. At 100F (38C) it is 0.78.

The pressure rating that is stamped on the pipe is always for water at 23C and whatever standard the pipe was built to. I find that at elevated temps and anything but water, the stamped number is very high for every DR number.

For SDR-13.5 using ASTM 3408 in water service at 23C it is rated at 1792 kPa. Change that to Gas and the MAWP goes to 570 kPa, raise the temp to 38C in gas (closest number I have to your 35C)and the rating goes down to 441 kPa. If I look at SDR-7 in ASTM 2100 at 38C, the MAWP is 1882 kPa in Water service, so 2000 kPa at 35C is reasonable.

So to answer your basic question, you need to know the SDR (or DR) number, and the standard (Driscopipe is what most people copy and it is ASTM 3408).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[dsg1985]

Thanks for the advice.

I cleared up the issue after some digging around the office. Hope this helps anyone who runs into the same issue. To quote the message sent to me -

"The discrepancy is related to the compilation date of the two Manuals,which reflected the recommendations of Standards and industry at the time of publication. Since the original publication of the Vinidex PE Manual, maximum allowable pressures for PE pipes at elevated temperatures have been revised to reflect the elevated temperature
behaviour of modern PE pipe materials. The PE Manual is in the process of being updated and will incorporate these new recommendations shortly."

 

[stanier]

I am confused by what you are being told. AS 4130 is dated 2009 . If you look at AS 2033-2008 you will find the figure of 224m head in Table 3.2. This was an amaendment A1 dated 31st october 2008. AS 4130 was published 4th June 2009. AS 4130 has specific derating factors for PE100 and is what should be used.

Of course there are also fatigue requirements to be taken into account if you have repetitive pump starts or other fatigue related loadings.

From my knowledge there has been no earth shattering changes in PE in the last two years.

 

[dsg1985]

Thanks stanier, I had a look at the Vinidex catalogue and some of its references are as follows:

AS 2033-1980
AS/NZS 2566.1-1998
AS/NZS 2698-1984
AS 3723-1989
AS/NZS 4129(Int)-1997
AS/NZS 4130-1997
AS/NZS 4131-1997

Looks like it's an old catalogue that needs updating, hence the low figures used in the tables, and the email I recieved. I checked their website and this is the one you can still download.

If I was to use 4130 though and select a design factor of 1.25 (water) and 1.25 (temperature <= 35 degrees) I still get 2000kPa (although over 35 degrees they say to consult the manufacturer). The 4130 I'm using is dated 2009.

 

[stanier]

The other document you could use is by the Water Association of Australia. this organisation represnts the 15 largest water authorities in Australia. They are also represented on Standards Australia committee PL006 Polyolefins Pipe materials.

WSA 01 covers PE pipelines.

https://www.wsaa.asn.au/Publications/NationalCodes/Pages/NationalCodesList.aspx

 

[zdas04]

I was digging into this stuff last night and found that they have a pending Hydrostatic Design Basis (HDB) of 3150 psig at 73F. This is nearly twice Drisco Pipes's 1600 psig so for a given fluid at a given temperature, a dimension ratio of the Vinidex (when their 10,000 hour test is accepted by the regulators) will have nearly twice the MAWP of ASTM 3408 HDPE. They use the same equations that all the other thermoplastic pipe manufacturers use so the rated pressure at the temperature and fluid you choose should not be a mystery.

David