I need to determine the acceptability of external transverse loads exerted on pipeline as a result of construction and farming machinery crossing the pipeline at locations other than designated roads.

The calculation can be carried out for 900mm, 1200mm and 1500mm depth of covers as per API-1102. But there are some instances that depth of cover is 750mm. Figures 15 and 17 of API1102 (Highway Geometry Factor for Cyclic Circumferential/Longitudinal Stresses) do not cover 750mm DoC and as per Clause 4.5 of API1102, extrapolations beyond the design curve limits are not recommended. So calculation for 750mm DoC should be done using another method. i.e. Spangler method or etc.As far as I know there are various doubts on the validity of the Spangler method for high pressure steel pipelines.

Does anyone have a suggestion and/or guideline that can be used.

Thanks in advance

Doesn't your engineering judgement give you a clue here? Use your head!
First rule of Engineering is common sense. If you can't muster up any of that, this will be a tough business for you.

Normal soil cover WITHOUT ANY SPECIAL CONSIDERATIONS FOR HEAVY MACHINERY IS 3 feet, 0.91 meters.
On what basis are you proposing to put heavy machinery on 750 mm cover? You said it is for nondesignated locations, so I assume you will not case the pipe, or put a reinforced concrete spanning slab on top everywhere you expect to have a nondesignated crossing locations.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

BigInch,

3feet is the minimum cover if you design to B31.8.
Australian Standards allow 750mm depth of cover. If infrequent crossing of heavy machinery, farming machinery, etc. does not cause any problem for the pipeline there is no reason to have 900mm DoC.

OH! I guess this isn't Kansas then, is it Toto.

So, if you are already under 1102 recommended cover, you must be pleanty close to the limit then, right. If you guys start using "heavy" farm equipment some day, that sounds like trouble. The reason API 1102 doesn't cover those shallow clearances is that 3 ft is the absolute minimum and 4 feet is the customary US depth for normal weight farm equipment passages, due to usual maximum depths of root plow penetration, and for unpaved track crossings. Yes, we bury the pipe at 4 feet cover in farmland. I and 1102 are telling you 750 mm isn't safe for what I/we would consider as "heavy farm equipment", no matter what is, or isn't, allowed under Oz standards.

Do Oz standards allow heavy farm equipment passing on 750 mm cover, or is that really just the minimum clearance allowed, to which you must add extra depth when it is expected that "heavy" farm machinery will cross? Read your Oz code with a more critical eye and see if your opinion is still the same.

I'm afraid that with 750 mm cover, in a farm area where heavy equipment is active, I would want to fence off the RoW completely.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

Ok,How can I demonstrate that 750mm is not safe? by doing some calculation?

Check it using Spangler. I feel that the problem with Spangler and gas pipelines is that it is too conservative for high strength steel pipe with internal pressure. As I recall, it was based on rather thin wall, corregated steel drainage pipe with no internal pressure. Technically, internal pressure helps the collapse resistance of pressure pipe, even though a break in a high pressure gas line would potentially be much more disasterous. I think Spangler's conservatism in regard to pressure containing pipes somewhat compensates for the risk of a disaster of considerabley greater magnitude. You might also just want to ignore the internal pressure contribution, as you can't ensure there will be pressure at all times.

What magnitude of load is considered "heavy" farm equipment in AU?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

And in pipeline work, design pressure is only right at the compressor discharge.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

"Ok,How can I demonstrate that 750mm is not safe? by doing some calculation?"

Bury a 20-ft joint of pipe with exactly 750mm of cover on one end, rising to 600mm of cover on the other.
Then run a Chisle plow across the pipe, set to dig deep. You should dig up and/or scar the shallow end, might scar the 'deep' end. Think about tolerances in the "Real World". If you specify 750mm, anticipate getting 600-900mm of cover in places. If you specify 900mm, you should never end up with less than 750mm of cover. Digging ditches is not like machining parts -- the tolerance zone is pretty wide.

Minimum cover is the specified quantity and includes all the negative tolerance allowed, 0. All the positive tolerance you want can be provided.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

Marston and Spanglers work was based on rigid concrete drainage pipe, not flexible and not under pressure. It does not consider internal pressure or pipe deflection. modifications in the analysis for flexible / pressure pipe must be made in order to use the method.

Sounds odd to rely on internal pressure in the calculations. Occasionally pressure is shut off - shouldn't you design for that situation?

I attached a calculation to AS 25666.1 and the minimum cover that may be useful.
Ibrahim Demir

• http://files.engineering.com/getfile.aspx?folder=b550e9f9-3ded-49a2-8c63-0e

I think the threads does not handle multiple files.

• http://files.engineering.com/getfile.aspx?folder=3dda0b86-1de0-4453-84d0-f3

Thanks Saplanti, but AS 2566.1 is for flexible pipes and it does not specify how to calculate cyclic circumferential stress and cyclic longitudinal stress due to vehicular loads. Also there is no requirement to do a Girth Weld Fatigue Check and Longitudinal Weld Fatigue Checks in AS 2566.1. Also combined loading stress equation is different from Von Mises theory.

This standard cannot be used for steel pipes.

You are correct about the fatigue applications to AS2566.1. I have attached the required information for you. However, you can use AS2566.1 for steel pipes as well. This code takes the impact effect of the live load into consideration. However you still need to consult API 1102 for the fatigue case if needed.
Regards,

Ibrahim Demir

• http://files.engineering.com/getfile.aspx?folder=2726bc43-7119-4753-a591-6a

Buried Pipelines by Moser
Structural Mechanics of Buried pipelines by Watkins

Two very good books on the subject.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

I have been on the AS 2566 committee for 20 years.

I believe it is appropriate for steel pipelines as they are flexible in diameters that you refer. In fact ductile iron pipe is also referenced in the standard. The criteria assessed are strain, stress , buckling, deflection and combined loading. The standard is quite conservative particularly in the use of native soil modulus. The concept follows that of Spangler Iowa, ATV etc.

Rigorous assessment using this standard will render you a design. The native soil will carry most of the load when the steel pipe deflects. Hence you need to assess the properties of the native soil, design an embedment to suit and make sure it is installed correctly.

If you are concerned about fatigue with a large number of cycles then you will need to establish the number. Does it apply to the whole pipeline or just for tracks and road crossings? If so then perhaps a pavement is required for crossings.

Even at 750mm deep the trapezoidal spread of wheeled loads will reduce the pressure at the pipe considerably.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/