Solvent Welding PVC Pipe cost effective for restraining? 3

[yahoo123]

Would it be more cost effective to solvent weld a bell and spigot pvc pipe or would it be more cost effective to use mechanical restraints?

Also, is it possible to remove the gasket in an AWWA PVC bell and spigot pipe and solvent weld it?

 

[bimr]

You can not solvent weld a bell and spigot PVC pipe. Solvent weld fittings are made specifically for solvent welding. The fittings are not interchangeable with gasketed fittings.

http://sunny.crk.umn.edu/courses/gfts/3077/Mod12-Basic_Guidelines_for_Connecting_PVC_Pipes.ppt

Whether it is cost effective to use mechanical restraints depends on the application. Are you talking about 2" buried pipe or 6" above ground? It makes a difference.

 

[stanier]

Solvent welding always beats thrust blocks hands down for costs. Thrust blocks are not required for a solvent welded system

Thrust blocks require extra excavation, forming, supply & pouring of concrete and disposal of surplus material.

Mechanical restraints can be sued aboveground. These are the type with teeth that cut into the PVC to withstand axial loads. They cost much more than a simple solvent cement joint.

 

[LCruiser]

The type of PVC pipe matters. C-900 uses a gasket, but many others are solvent weldable.

 

[stanier]

PVC-U and PVC-C are what is commonly used in a solvent weld applications. PVC-O and PVC-M are rubber ring jointed.

 

[yahoo123]

So mechanical joint restraints are for above grade applications only?

Also can I solvent weld a spigot end into a belled end joint for AWWA C900 or C905 pipes?

 

[stanier]

Mechanical joints can be used below ground. Invariably you will need to wrap them in a Denso tape system or some other protective layer. 316ss will pit and corrode in some soils. If in dry sand you have a good chance that it will not corrode. But with any clays around then I would wrap the joint.

If the teeth that provide the restraining of axial loads corrode then the coupling will fail. If the coupling is of the "non restraining" type then you will need to use thrust blocks. Check that any restraining type has the same pressure rating as the pipe, including for surge.

 

[rconner]

“Cost” and “effective” are arguably two separate questions. While I guess good pvc glue is not necessarily real cheap (and I otherwise wouldn’t consider myself an expert on the subject), I suspect it is far cheaper than (anything close to) well-designed mechanical restraints.
The strength/performance of solvent-cement connections, at least with pvcu etc. pipes, is however reportedly highly variable and dependent on a lot of conditions (e.g. see the history and research on page 93 of the reference at

http://books.google.com/books?id=yS...=X&oi=book_result&resnum=3&ct=result#PPA93,M1

) , and I suspect the significance and prevalence of these variables likely increases with increasing size of piping involved. Careful reading of these papers reveals that much more is involved than just the type and amount of glue smeared on the members and the specific technique (of a slight twist etc.) of the installer.
I suspect it is for practical ramifications e.g. of the statement in the aforementioned reference, “The results indicate an extreme sensitivity to minor variations in preparation…” and other reasons that many users (and for that matter also AWWA standards for many years, at least until recently) require rubber-gasketed joining ends only for municipal pvc water pipes, as in practice perhaps these joints have offered at least a little more utility, dependability, or robustness. Notice also pages 201, 209, and 210 of the reference at

http://books.google.com/books?id=RG...=book_result&resnum=4&ct=result#PRA1-PA210,M1

some other limitations of solvent-cementing (and see particularly the safety and environmental issues regarding solvents mentioned on page 210, that I could see the competitive manufacturers arguing might not necessarily be issues of mechanical restraints).
As a perhaps interesting vignette, I was coincidentally told by a Contractor two days ago (and before I saw this thread) of an interesting case where a specific ductile iron line was changed to pvc as a “cost saving” measure, but when the required mechanical restraints were located and purchased the restraint cost was actually higher than the basic pvc pipe cost involved, and he said that actually made the total material cost higher than the originally specified restrained joint ductile iron that had a higher strength/pressure rating (not to mention the extra labor required to install the more bulky mechanical restraints for the pvc!!)

Some of this could have relevance also to your question about plastic flanges and solvent-cementing etc. same, as I guess flanges could arguably be subject to even higher localized field stressing as a result of vigorous and/or imperfect bolting with normally quite strong steel bolts, and/or also field misalignments or imperfect support conditions etc. Plastic flanges have neither the basic strength, nor the fracture toughness (or as large critical crack length, flaw or damage size etc.) of ductile metals.

 

[stanier]

Yahoo123,

Rconner makes some goood points about the variance in quality of PVC-C solvent welded joints. that is why it is important to use practices and trained tradesmen to do the work. it is no different to a workman not lubricating a ductile iron rubber ring joint or fitting a defective O ring. Any piping system can be compromised.

That said there ar emany existing lines containing dangerous chemicals where PVC-C is the norm. So solvent cemented PVC-C is fine for potable water. Anyone saying different is just a marketing person for another product.

Ductile iron has its place in water pipelines . Where there is a high pressure requirement it is used. in Europe pipelines for water and wastewater are 90% thermoplastic these days.

As for costs do the numbers on any system in a thorough manner.

Ductile iron takes about 6 times the energy to manufacture and thus the environmentalists may give you a hard time. on the other hand PVC-C has some problems with VC emissions. PVC-C does not rate well with building codes in respect of this matter.

 

[bimr]

You have not said what PVC piping size that you are using. Solvent welded PVC is generally limited to piping less than 8" in diameter.

If rigid joints are being used, they will need to be protected against ground movement. The manufacturer's instructions must be rigorously followed.

Flanged joints require special protection to the bolts to avoid corrosion. Depressions in bedding material should be fashioned to accommodate flanges. It is essential to ensure that the pipe is evenly supported along its barrel.

Flexible joins are most commonly used and provide limited articulation, longitudinal travel, and ease of jointing.

What you should be referencing is an in-house piping standard.

Guidance supplementing piping standards is necessary because the various codes provide no explicit rules for functional design, material compatibility with fluid and environment (erosion/corrosion protection, radiation effects, etc.), layout, serviceability, steam tracing, grounding, valve and component selections, design of pipe supports, material traceability, gasket selection, as-built tolerances, insulation, cleaning for special process, etc.

For certain services some options available through piping codes must be excluded made more stringent or supplemented by the designer.

Larger CPI and HPI corporations have in-house piping standards that guide the design of piping systems.

If you do not have access to any corporate standards, I would build on the standards that were developed by other firms. It would be wise to read through a few of these standards for design inputs.

Have are a couple of references:

http://engstandards.lanl.gov/engrman/6mech/pdfs/D20-AppA-ASME_B31.3-r1a.pdf

US Army Engineering and Design - Liquid Process Piping

http://www.usace.army.mil/publications/eng-manuals/em1110-1-4008/toc.htm

 

[bimr]

Dig trenches 18” deep and wide enough to allow side to side movement of pipe associated with expansion and contraction. At 70°F, a 100’ long PVC pipe that is solvent welded will shrink 1” when it is put underground and is bearing 40° water.

 

[stanier]

Also get hold of the Unibell Handbook.

The website of Iplex Pipelines, Eurapipe and Vinidex provide design guides.

http://www.iplex.com.au

http://www.vinidex.com.au

http://www.tycowater.com/plastic_pipeline_systems

 

[LCruiser]

"Cost Effective" is the very definition of engineering.

 

[yahoo123]

Thanks guys for all the informative answers. I was asking this as a general question because I found it curious why people normally specify mechanical restraints in-lieu of solvent welding.

 

[rconner]

stanier, with all due respect I feel compelled to respond to what I believe are at best some misrepresentations made in your last post. At least beyond the realm of small household plumbing and into the realm of common larger sizes of municipal water and wastewater pipes (that I suspect from past writings the poster is likely dealing with), I believe it is highly deceptive to say or imply that from a practical perspective solvent-cement joining of pvc pipe is “no different” than rubber-gasketed joining (an online check of available specifications would quickly reveal that rubber-gasketed is what have been/is now being specified by most users, even though both types have been available for decades – while I am not promoting either, I do not believe this widespread specification predilection is an accident). I am even aware that in a report to the International Standing Committee on Water Distribution many years ago, Mr. R. Y. Bromell Assistant Director of Operations for Severn-Trent Water Authority made the statement, ”Solvent joints were used extensively when small diameter plastic pipes were first introduced but have proved unsuccessful.”
To say or imply that somehow plastic pipe competitors have governed or will govern the historical evolution or user choice of joints at least for plastic municipal water pipe is equally injudicious. As a matter of fact, the AWWA pvc water pipe standards sub-committee itself removed solvent-cement pipe joining from the AWWA C900 standard in the1989 version, with the first note in the Foreword, “Provisions for solvent-welded joints throughout the standard were deleted.” [Later C90X pvc standards however did sort of resurrect “solvent-welding”, though only for gluing together larger fabricated pvc fitting sections together n factory conditions/with factory control, I believe due to cheaper manufacturing cost than integral molding.] As far as I know no pvc “competitors” sat on the subcommittee that instituted these changes.
Pipe market shares are perhaps also interesting subjects, as are in aggregate all aspects of sustainability/life cycle (including the perhaps much narrower and maybe even some vague verbiage you mentioned of “energy to manufacture”, you have chosen to introduce in this thread). I do not consider myself an expert in all detailed aspects of these fields; nevertheless, I quite frankly believe your claim of near complete plastic market share, your claim of applicability of ductile iron pipes to only high pressure applications, and your claim that “Ductile iron takes about 6 times the energy to manufacture…” are all likewise probably highly inaccurate when considered in any sort of fair comparison, and maybe even to the point of irresponsibility [see e.g. the “Western Europe – Non-Automotive” market of ductile iron pipe of 1,591,000 tons reported at

http://goliath.ecnext.com/coms2/gi_0199-3917144/Global-boom-shipments-to-reach.html

!, and the Australian pipe material energy study with far different figures than wherever yours came from etc. mentioned in the last post of the thread at

http://eng-tips.com/viewthread.cfm?qid=221731

].
While manufacturing anything, particularly in a highly regulated environment like the USA, is a challenge in many respects, I believe all of us should nevertheless have appropriate concern and respect for all aspects of the environment and conservation of natural resources. However, I’m not exactly sure why you would think that ductile iron would be a preferred target of “environmentalists” when compared to polyvinyl chloride [For instance, see related information in the 221731 post mentioned above, and also while it of course doesn’t necessarily mean anything I just did a google search with the keywords “ductile iron toxicity” and got 12,700 “hits”, while a search with “pvc toxicity” got 389,000 hits!]

 

[stanier]

rconnor What was stated has been cherry picked to suit an argument.

1) Solvent cement jointing can be as good or bad as any system jointing. If there is not quality control there will be failures. This occurs in rubber ring joints, fusion welding, solvent welding and the welding of metallic products. Any joining process requires a joint procedure, joint qualification and trained personnel.

Some thermoplastic materials have been successfully solvent cemented at diameters of 800mm. It is by no means restricted to small diameter pipe. Perhaps the USA has such constraints but in Europe, S. Africa, SE Asia and Australia the technology exists to joint large diameter pipes in such a manner.

2) The dominance in the water and wastewater market in Europe is data provided by a representative of the WRc from the UK as was the advice that ductile iron is used for mainly high pressure application.

3) Ductile iron and other materials are all considered on their merits when it comes to the environmentalists. From an energy perspective it takes more energy to make ductile iron than a thermoplastic pipe. The environmental negatives of PVC-U relate to the emissions not the energy considerations. Of course of you use the word "toxicity" in your search you will get more hits on PVC. That is point made in the above posting?

 

[cvg]

as usual when posting on this forum, it can be important to know what country the poster or project is located in as the specific answer should be tailored to that region of the world.

Because large diameter pvc pipe is successfully solvent cemented in some countries does not make it an effective method in the US when neither the US contractors, engineers, suppliers or specifying agencies are not familiar, experienced or comfortable with doing it that way.

Again, with ductile iron pipe, I have not seen a preference for DIP over PVC based on the pressure rating. Most of the higher pressure lines I have seen used welded steel or concrete steel cylinder pipe - not ductile iron.

 

[stanier]

In Australia DICL is available in Class 35 (ie 3500kPa rating). As the source of the material is scrap iron and steel the cost is competitive to other products. It is generally about 10% cheaper than steel pipe cement lined.

There is only one manufacturer. That manufacturer also is the primary producer of steel pipe and also has a plastic pipe division.

DICL took over from the asbestos cement when that became unpopular.

Small population, large country with long pipelines is atypical when it comes to statistical analysis of a market.

 

[rconner]

fyi

http://www.dailyamerican.com/articles/2009/03/30/news/local/news257.txt