Derating for Vinidex HDPE pipe due to Temperature
Derating for Vinidex HDPE pipe due to Temperature
(OP)
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).
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).





RE: Derating for Vinidex HDPE pipe due to Temperature
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
RE: Derating for Vinidex HDPE pipe due to Temperature
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
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
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RE: Derating for Vinidex HDPE pipe due to Temperature
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."
RE: Derating for Vinidex HDPE pipe due to Temperature
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.
RE: Derating for Vinidex HDPE pipe due to Temperature
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.
RE: Derating for Vinidex HDPE pipe due to Temperature
WSA 01 covers PE pipelines. https://w
RE: Derating for Vinidex HDPE pipe due to Temperature
David