Steel pipe design Standards - surge 1

[BRIS]

our specification requires steel pipe for water supply to be designed to AWWA M11.

I understand that this allows a maximum stress of 50% yield for working pressure and 50% increase (up to 75%) yield for surge pressure.

The designer is designing to ASME B31.4 with a design factor of 0.5 and states thatthe maximum over pressure allowed for transient events is 10%.

However, he appears to be mixing AWWA and ASME standards. (I work with British Standards and don't have access to ASME)

1) Are AWWA M11 and ASME B31.4 compatible? 2) is a factor of 0.5 and a surge allowance of 10% not over conservative?

If design is to ASME should he not use a factor of 0.72 for working pressure and allow 10% over pressure for surge?

Pipeline is a buried cross country water transmission pipeline.

 

[BigInch]

No. There is no relationship between the two specs, other than for what the physics and a certain amount of chance allows. I don't have the AWWA code, but I think it allows a higher transient, if a detailed surge analysis is done on the system. PLEASE check the wording on that.

B31.4 PIPELINE TRANSPORTATION SYSTEMS FOR LIQUID HYDROCARBONS AND OTHER HAZARDOUS LIQUIDS, so why use that on a water line?

B31.4 design factor is 0.72 and it allows 10% overpressure for surge. It requires a surge analysis, as does AWWA.

http://virtualpipeline.spaces.msn.com

 

[JStephen]

M11 is a manual, not a standard. There are separate AWWA standards for pipe, for lining and coating, for flanges, for fittings, etc.

I would avoid trying to mix the AWWA and industrial standards. Some of the approaches to them are quite a bit different.

 

[BigInch]

"A man with two watches never knows the time."

Besides, it can create a hell of a legal problem. Its difficult to design for both and even if you try and choose the most conservative approach in every case, somebody can always accuse you of overdesign in relation to the minimum criteria.

http://virtualpipeline.spaces.msn.com

 

[johnp]

Hi BRIS,

It depends on what you mean by surge. The stress equations are based on Hooke's Law - the idea of bundles of spaghetti. When a strand gets too stressed it breaks in tension, and the camel collapses under the load of the extra straw. That's why you have to calculate your load of straw to within 10%.

Real life is not like that. If it did we would have a lot more trouble in the piping industry.

Steel is plastic. It yields. That's why in thermal expansion we speak of a stress range, and the stresses are in a different category to static stress. It's the same with earthquakes, water hammer and shock waves.

Shock waves can show pressure changes in nanoseconds. Thank god the steel doesn't follow Hooke's Law to that degree.

Regards - Sgt John Rozentals
Univesity Regiment (retired)
CEO Latvian Tourist Society

http://www.latviantourists.com.au

Johnp.Rz

http://www.mets.net.au

 

[BigInch]

(B31.4 surge is a temporary internal pressure with a value exceeding that of maximum allowed operating pressure.)

http://virtualpipeline.spaces.msn.com

 

[BRIS]

Thanks for the replies which confirm my concerns that we should not be mixing AWWA M11 design manual and AWWA 200 series specs with ASME B31.4.

Designing to AWWA allows a safety factor of 2 on working pressure and 1.33 on transient surge pressure (50% of yield for working pressure and 75% of yield for transient) . I note when taking all other tolerances into account the FoS can reduce to- 1.0 under transient loads. (i.e stress = yield stress).

ASME allowes a factor of 0.72 (72% of yield stress) plus 10% additional for transients. If pipe is manufactured to AWWA tolerances and designed to ASME it appears to me that we may exceed yield stress under transient loads.

I am reviewing design criteria and standards that are already mixing the two and need a case for rejection of what has been done.

 

[stanier]

It is never good practice to mix design codes, standards and manuals.

The fact that ASME B31.4 is for hydrocarbons and AWWA M11 is for water tells you that the risk issue of "consequence" is in the mix somewhere.

Without a surge analysis you dont know where you are. The use of factors to allow for surge without a proper analysis leaves you exposed. AWWA M11 and other industry standards were prepared before waterhammer software and the expertise to analyse surge events became common place. Now that tools are readily available engineers would be unprofessional not to use them.

Courts take a dim view of engineers who do not use the most up to date techniques to analyse and test a matter.

In the event of column separation and rejoining the surge event could be much larger than the factors you refer to.

Remember what Lord Kelvin said: "If you cannot calculate it or measure it your knowledge of a subject is meagre and unsatisfactory"

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[BRIS]

Stainer - thanks for your response- surge analysis is my field - steel pipes to American standards is not. We have accurately modelled transient pressures. Design of the steel pipe is the responsibility of the contractor's designer. The Specification calls for design to AWWWA M11 and series 200 specs. The designer is mixing with ASME B31.4. From the helpful responses above, and some research on the Net, I see that the two are incompatible i.e design to AWWA or ASME but not bits of each. The Designer has used a yield stress factor of 0.5 in the hoop stress calculations to comply with AWWWA but a factor of 0.9 in the effective stress calculations in compliance with ASME. he is limiting surge to 10% (ASME) although allowing only 50% of yield stress in the hoop stress. I am sure there are many other incompatibilities between the two such as allowance for milling tolerance. (AWWA appears to be on gross wall thickness: net thickness could be 12.5% less while ASME is based on net thickness requiring and addition to calculated T for mill tolerance - I may be wrong)

I am inclined to reject the designer's calculations outright and require that he complies with AWWA.

 

[stanier]

Hi BRIS,

Apologies I should have remembered from previous postings. Perhaps we need a waterhammer forum?

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[BRIS]

Hi Stanier

I have not been around on the forum for a while!

Regards