Pipeline isometrics 1

[BRIS]

As a civil Engineer with 30 years background in water engineering I am a little defensive of mechanical and piping engineers moving in on the patch of water conveyance and distribution system design.

I am presently reviewing a 1.2 m diameter raw water conveyance pipeline which has been dominated by piping engineers. Where I could probably have detailed all of the appurtenant structures on 20 drawings the project is swamped by 100's of piping drawings, P&ID's, isometric drawings etc. We even have P&IDs and isometrics for each air valve and wash out assembly, and there are a lot of them. The pipe materials are ductile iron and GRP with standard fittings !.

Is this becoming the norm?. Has a new job creation industry for piping engineers started while I had my back turned ?

 

[stanier]

Hi BRIS,

I understand your frustration as a piping engineer. Unfortunately there is room for critique of the way civil engineers have undertaken their designs.

The use of P&IDs is seen as a positive as these documents are not only used in design but in procurement, commissioning and operation. These are fundamental document. WEhen developed using attributes in Autocad or similar the schedules are developed automatically. Thus if the P&ID is revised your schedules are automatically revised. This makes procurement and installation more efficient.

P&IDs identify each pipe by line number. These line numbers are transferred automatically to general arrangement drawings and isometric drawings. I have argued long and hard with civil engineers who use generic descriptions to identify services on their drawings. This is admittedly in a plant situation. When asked what line was what when services had similar names they have been unable to do so.

The use of isometrics drawings should be restricted to pump & valve stations. Isometrics for scour and air valves are overkill.

Detail spool drawings can be automatically generated and are needed for MSCL, MSEL & SWSS piping systems. Automatic generation is not design hours consuming and improves accuracy.

As someone who has to look at legacy pipeline designs I always find it very difficult to find fundamental information. It appears in the 20 or so drawings that you refer to a lot is left to the field and the information required is not there.

Somewhere between the two extremes is the answer.

I think from previous correspondence that you are Australian based. If so you will be familiar with the National Safety in Construction Act. The consequences of this is that the engineer is always to blame. Hence more certainty is required in Design.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

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

 

[rcooper]

I think some of it comes from where you come from. My experience of civil engineering consultants is they tend to leave a lot of detailed design to the contractors to complete. This is appropriate as the contractors tend to have experience of the details, but not necessarily experience of the overall scheme.

Mechanical/piping engineers, often coming from contractor backgrounds, are used to producing documentation for procurement and fabrication. The drawings and documents produced can be handed straight to a supplier for purchase and to a fabricator to fabricate.

The purchase/fabrication information would have to be produced anyway. When the civil engineer does the 20 drawings, the information in the remaining 80 is produced anyway, but is hidden to the civil engineer as it is not relevant to him.

 

[BRIS]

Stanier/Rcooper thanks for your response –sorry for my delay in acknowledgement. I am in fact UK based, but since 1977 have spent most my time overseas. UK practice was that pipeline in the ground was civil engineering and pipework within facilities was either civil or mechanical engineering. I started my career in a water board and often saw projects through from design, procurement, construction to commissioning using direct labour. The engineering department employed only civil engineers. I acknowledge Rcooper's comments however I know from experience that my civil engineering pipework drawings produced for appurtenant structures on a trunk water main and pump station installation will provide all the information that is needed. General arrangement drawings that show all pertinent civil and pipework details can be understood by the operation and maintenance staff.

It is a question of appropriate engineering. Producing 4 different drawings and a line list for an air valve assembly is not appropriate. It is done because that is what the computer software produces.

I am now reviewing designs where not only is it that the drawing production is not appropriate but the engineering produced by piping engineers is also not appropriate. I have raised one example on the piping and fluid mechanics forum:

The example is 800mm diameter buried pipework serving a series of buried tanks and a pump station. If civil Engineers had designed the pipework they would produce a design using standard ISO dimensioned fittings, push in spigot and socket joints with restraint by thrust flanges in chambers and thrust blocks. The main design effort would be in the thrust block design. I would have produced P&IDs after producing the GAs.

For the design I am reviewing the buried pipework has been designed by an engineering consultant specialising in piping design.

They have used GRP pipe with all joints restrained (they have specified adhesively bonded spigot and socket joints). There are no thrust blocks, all pipes through chambers are in sleeves to allow lateral movement. The whole of the buried pipe system is anchored from nozzles cast into the concrete tanks. Thewhole of the pipe system is rigid with no allowance for differential settlement. All dismatiling joints are specified as restrained to transmit longitudinal thrusts. The design process was, as described by Stanier, to produce P&IDs and then allow the computer software to generate piping diagrams, complex finite element stress analyses, isometrics and line lists. Civil engineering GA’s are then produced at the end of the process.

If I compare the two solutions:

1) The civil engineering approach produces a third less drawings, fittings and pipes are all standard catalogue items.

2) The civil Engineering solution using push in spigot and socket joints can be constructed in half the time and cost 30% less

3) The civil engineering solution is robust- with flexible joints it can cater for any amount of differential settlement, expansion etc.

4) The Civil engineering solution can be easily maintained- The pipe can cut at any point and it doesn’t fall apart.

5) The civil engineering solution is designed by Luddites; it doesn’t use the latest stress analysis and piping software but it is cheap and fit for purpose. !

The response I am getting from the piping designer is that we are only civil engineers and they are experts in piping design.

I am being facetious, I agree with Stainer and Rcooper. Engineering needs to be appropriate and piping engineers need to recognize that sometimes the ways of the civil engineer may be the right way!

 

[BRIS]

PS I show the depths of my ignorance what are ; 'MSCL, MSEL & SWSS piping systems'

Brian

 

[stanier]

MSEl Mild steel epoxy lined
MSCL Mild steel cement lined
SWSS Spiral Wound Stainless Steel

BRIS,

In respect of your lengthy reply I make the following comments:-

1) catalogue items being listd is fine as long as procurement buy that brand. All catalogues have a clause warning the details are subject to change. GRP is like a curry, it can have anything in it. You cannot rely upon the properties of the GRP from one manufacturer to another.

2) Modern practice is to laminate GRP rahter than using rubber ring joints. But this does lead to problems with differenia settlement. GRP has a very low strain tolerance and delamination may occur under high strain levels.

3) this is essential for GRP and is a mistake not to include.

4) Not sure what your point is

5) Sure civil engineers are considered bottom dwellers but they have managed to produce relevant designs over the years. GRP pipe desig requires specialist techniques but to use packages such as Caesar to design buried pipe is not appropriate. Design to AS 2566 is more relevant with GRP design to ISO14692.

GRP is an enigma. It can be a good product or it can be dreadful. If there is a disconnect between Design and Procurement you can end up with a disaster. RPocuremet are only interested in the lowest price and the design in GRP is complex and requires an alliancewith the designer/manufacurer of the GRP

The reinforcing can be chopped glass, chopped glass with longitudinal strandsor roved laminates (and this has different angles). You can end up with a pipe with no longitudinal stress capability.

Thrust blocks are required with GRP, even if laminated because of the weak longitudinal properties and loww strain tolerance. Strin capability can onl be determined by testing and that takes 9 months minimum.

The design before you sounds like a disaster.

4)

 

[Ussuri]

I am a civil engineer who used to work in the water industry and my experience is the same as BRIS's. IMHO the majority of civil pipelines are DI, uPVC or MDPE. The pressures are low (usually <10 bar) so there is no need to use CAESAR II to calculate pipe stresses as standard pipes are rated to 16 bar. To me it is overkill. I have never used GRP so I cannot comment as to whether a full stress analysis is required.

I now work in oil and gas where we runa at pressures up to 300 bar. This is where CAESAR comes into its own. Thsat said we do not use CAESAR for the pipeline. It is used for piping within manifolds including valves, pipe supports, chokes, flow meters etc, and for short rigid tie in spools. For a 20km pipeline I dont think it works, possibly trenched or not.

Pipers are usually concerned about stresses generated due to pressure, temperature, restraint, expansion etc. These are the sorts of thing CAESAR will tell you as standard in the outputs. It will not do a structural capacity check of the under 'x' metres of soil with an applied road surcharge. So I wonder if they are focussing on the wrong things.

It is true that 'experts' in design are not always aware of the fact that the design is not constructable or maintainable. And quite often they dont find out because the contractor will fix the 'mistake' on site by having a discussion with the clerk of works or resident engineer.

 

[dcasto]

and to top it off, when you get to the field, they drawings don't work every so often, Who put that gas line in or why is the city widening that road next year.

So its time for as builts...

 

[BRIS]

I started this thread on the Civil/Environment forum to question the role of civil engineers in water pipeline design and methodology of design. I also posted a thread on the Mechanical Piping forum questioning the use of adhesive bonded GRP joints (a jointing system that I have no experience of).

The situation I have is a clash of engineering cultures. The contract is for the design and construction of a 600km long water conveyance system with several pump stations. The Contractor (who is in fact owned by the Client) has appointed a consulting engineer whose background is petro/Chemical. The Client has also appointed a review consultant. Their background is water and civil engineering. I am trying to sort out the conflict.

What is obvious is that the lead discipline in the design consultant is the Piping Engineering Discipline. The design methodology is to first prepare PFDs and very basic GA's. Then produce P&IDs, piping arrangements, isometrics, line lists and materials take offs all automatically generated. The civil engineers then design chambers and structures to go around the various valve stations etc. Vendor data is obtained and plinths and supports are detailed. For example take a simple valve chamber. In order to understand the design it is necessary to interrogate at least 6 documents. The P&ID gives tag numbers, the piping drawing gives very little, the isometric gives dimensions and materials, the civil drawing gives the arrangement of the space but no piping details, the line list tells me what things are, and plinths and supports are on a separate drawing.

Conversely the lead discipline in the review consultant is the civil/water engineering discipline. They don't have any piping engineers. Their design methodology would be to detail each valve chamber civil and pipework as a single entity. They would produce a civil drawing with the pipework in ghost and a pipework (mechanical) drawing with the civil work in ghost, schedules of pipework are shown on the drawing. Basically the civil and pipework drawings are the same drawings but with different information. Thrusts are carried by thrust flanges cast into the chamber walls and flexible spigot socket joints are provided each side of the chamber.

Neither consultant has broad enough experience to recognize the problem and to understand why they are in conflict. The review consultant is asking for detailed GA drawings and refusing to accept isometric drawings for review whereas the design consultant cannot understand how it is possible to review the design without an isometric. Even for an air valve chamber the isometric is the only drawing that shows the piping materials and joint types. Furthermore the design consultant has no experience of GRP pipe. In order to use his computerized design process he is treating it the same way as steel pipe. Hence the extensive use of adhesive bonded joints. He is expecting the GRP pipe supplier to manufacture a pipe that meets his design. My savior here is that any reputable GRP manufacturer will bin the design and start again.

This may all sound unbelievable!! I would not contemplate that consultants may get appointed on other than technical experince in some areas of the world.

PS Taking Dcasto’s point a major concern I have is how all of these drawings will resolve into a clear set of operation and maintenance manuals based on as built drawings.

PPS Sorry for this long and rambling post: as a civil engineer my inclination is to side with the review consultant. I very much appreciate the responses from the piping engineering perspective.

Brian
Somewhere in Africa