Hydrostatic pressure test for ductile iron water pipeline 2

[sowhatso]

Dear All ,

During my reading for the procedure of the pipeline hydrostatic testing , I observed that it is required to flush the pipeline before testing , the contrcator insisted to flush the pipeline after the testing and during the disinfection process for the pipeline , Is it ok to test the pipeline without flushing ??

 

[itsleighton]

you should flush it so particulates, rocks, debris dont act as a plug in whatever potential leak the pipe may have. Chances are low that the debris will actually plug it, but it makes it impossible if it is flushed.

 

[semo]

It also needs to be flushed prior to disinfection. The debris, mud, dead critters, etc. in the pipeline will make it more difficult to obtain a passing test.

He might as well do it now.

 

[rconner]

Wow, everyone has their own “ideas”!

I suspect many project specifications address in some manner general sequence and required operations, or at least refer to consensus standards that have been around quite a while such as AWWA C600 for Installation… (and also referring to many aspects of flushing, disinfection, and hydrotesting etc. operations) of ductile iron pipelines, as well as AWWA C651, Disinfecting Water Mains. I believe these standards in particular “make for good reading” for those involved with many aspects of water work.

AWWA C651 requires in an early section 4.4.3.2 entitled “Preliminary flushing”, “Before the main is chlorinated, it shall be filled to eliminate air pockets and flushed to remove particulates. The flushing velocity in the main shall not be less than 2.5 ft/sec (0.76 m/sec) unless the purchaser determines that conditions do not permit the required flow to be discharged to waste.” There are later requirements for “Final flushing”, that of course require that not long after successful disinfection is complete the heavily chlorinated water be expeditiously removed (flushed) from the main …”until chlorine measurements show that the concentration in the water leaving the main is no higher than that generally prevailing in the distribution system or that is acceptable for domestic use.”

While I guess it may not necessarily dictating sequence of all operations nor mean there is risk in your allowance (as I suspect there may be special cases that may make this difficult?), AWWA C600 also states in section 4.3.9 Flushing, “Foreign material left in the pipelines during installation often results in valve- or hydrant-seat leakage during pressure tests. The pipelines shall be kept clean during installation. Thorough flushing is recommended prior to a pressure test. Flushing should be accomplished by partially opening and closing valves and hydrants several times under expected line pressure, with flow velocities adequate to flush foreign material out of the valves and hydrants.” Thus at least some flushing before test is actually known to benefit the contractor in getting successful pressure tests!

In any a case, it is hoped that all parties to a water project, including the installer/contractor etc., respect the end purposes of a pipeline (not the least of which is delivered water quality) and keep same in mind in all operations well upfront. In this regard, AWWA C651, “Disinfecting Water Mains” also states “In either case, it is strongly recommended that pipe crews be aware of the need to maintain clean pipes and avoid contamination.”

 

[sowhatso]

rconner , super thanks ,

I have another three questions about the same issue :

1. Is there any limit for the maximum length of pipeline to be tested , for example can we test a pipeline of 10km length as one piece ???

2. The pipeline will be tested with a pressure value of 1.5 times the maximum operating pressure ,this value of pressure will be at the lowest level point through the pipe line , is there are any limit for the minimum pressure value that we may have at the highest level point ???? , the working pressure for the line is 350 psi and the line will be tested with 500 psi , due to the big difference in level between the high and low level points we may have a low pressure value at the high level point ??? is there are any limit or minimum pressure value at the high level point ???

3. for the cement mortar-lined pipe material, the specifications call for " Test sections shall be filled with water under low pressure for a minimum of 48 hours prior to testing" my concern is that the ductile pipes we have with internal cement lining , but the internal lining is coated with bitumen , do we have to fill the line for 48 hrs if thh cement line is coated ????

Thanks in advance .....

 

[rconner]

1. AWWA C600 does not place a specific value on the maximum length of pipeline to be tested, as I suspect practices have varied much from locale to locale and even very long lengths have been tested and performed well (and of course this is a consensus standard). Nevertheless, some authorities and perhaps in some cases Contractors on their own, with perhaps very good reason(s) sometimes perform tests at rather frequent intervals of perhaps a only kilometer or two or less. While much ductile iron pipe is very simple to install, an example of a good reason for short length tests, at least early in construction of some large projects. arguably might be (say e.g. at least with a crew unfamiliar with the specific type of pipe or joints etc.) that small problems of e.g. potentially repetitive nature such as errors or carelessness in assembly by a particular crew etc. are caught and corrected before they become much bigger problems. After all, a long line [and maybe particularly one with few if any valves and a lot of elevation change] etc. represents a lot of water to evacuate and re-fill as opposed to a much shorter line.
2. There is likewise no minimum value for test pressure in C600, although I will note significant pressure can be developed in some cases/practices just filling (and fully evacuating air from) even more or less gravity lines for test. Similarly to “1”, for whatever reasons some authorities nevertheless require quite high pressure testing of even gravity water or sewer lines that arguably have no significant pressure developed in service! While ductile iron and its most common joints are of course eminently suited for handling very high pressures, one disadvantage of very high pressure testing where it may arguably not really be necessary is that with some layouts/testing it might require quite formidable thrust blocks, test bulkheads (temporary and/or permanent etc.), or quantities of restrained joint pipes that arguably may not really necessary for any real service loading. In such cases, I guess it could be argued there may be unnecessary expense borne ultimately by the Owner etc.
3. Again AWWA C600 does not require a “48 hour” (I guess sort of “soaking”?) period before tests can be run, although I bet many lines are exposed more or less full for at least some length of time while the Contractor prepares the line for test (going around to air release and other vaults to make sure air it fully out, and other final operations etc.) While I guess there could be some value to getting a line to sort of stabilize in many respects, including any absorption of water into linings etc. (e.g. under working/filling pressure for at least a little while prior to test), I’m not sure e.g. that if a full line can hold required test pressure with no loss for the test duration much more quickly there is anything necessarily wrong with that!

 

[sowhatso]

Dear rconner ,

I need your help and advice to resolve this issue,

I had a discussion with the contractor engineers regarding the factor that we need to use for the hydrostatic pressure test. Our specifications call for “if no test pressure is specified, test to 1.5 times the operating pressure ( 1.5 X Operating Pressure) ”. The problem that I have is that the maximum working pressure for the system is 25 bar (362 psi) and the rated pressure for the ductile iron pipe that we have is 350psi, the contractor contacted the manufacturer but still they did not answer, and it seems that the manufacturer prefers to go for low factor and maybe they will ask for 350psi testing pressure only.

Some of the contractor Engineers proposed the below table for the pressure factor depending on the working pressure range :

Working Pressure Range, atm Factor*
0 – 12 1.5
13 – 20 1.25
More than 20 1.1
*: Test Pressure = Working pressure x Factor

I need to know if we have to stick and to insist on the 1.5 factor for our DI pipeline or it is ok to go for lower factor like 1.1 , 1.2, or 1.25 ?????? Is there any AWWA standard that specifies the factor must be 1.5 ????

Your quick response is highly appreciated.

 

[sowhatso]

rconner ,



Inaddition to the question above , and while I am reading the AWWA C600-05 , Sec 5.2.1.1.1 , I observed that they call for " The test pressure shall not be less than 1.25 times the stated working pressure of the pipeline measured at the hoghest elevation along the test section and not less than 1.5 times the stated working pressure at the lowest elevation of the test section" .

Is it important to follow the above !!!! , because I am still waiting the manufacturer's answer , but I think they will not ask for 1.5 factor , they may go for lower factor !!!!

 

[rconner]

In reading your latest inquiry I may be a little confused as to exactly where you are or what you are after in the design, installation, or testing etc. processes. I would however think it is normally best practice to quite early (say in contract documents) spell out upfront very clearly, in at least as unambiguous terms as possible, and for the benefit of all parties including bidders exactly how pipelines and appurtenances etc. are to be designed, installed, and yes, tested. While I think AWWA C600 is a quite long-standing and pretty well-“vetted” standard, I believe field testing philosophies around the world in fact vary all over the map. The vast majority of differing practices are probably successful with DIP.
In this regard, I believe various ISO and EN standards, that prescribe much higher standard pressure ratings for DIP [e.g. that have talked about working pressures up to 40 bars (~580 psi) or more] than AWWA design, also publish a little different default field test pressure philosophy. I believe they say that instead of a sort of direct multiplier like AWWA, the test pressure should be the maximum allowable operating pressure of the system + 5 bars (~73 psi)]. While this perhaps gives results not much different than AWWA for much common lower pressure work, it is obvious that with very high working pressures a constant 5 bar default addition results (in back-calculated effect) like a much smaller direct multiplier on the operating pressure as compared to AWWA. I guess it could be argued this is reasonable if e.g. any greater e.g. transient pressures e.g. due to surge to be imposed on th system are a function of common flow velocity (not pressure level), and/or if there are now better surge prediction tools and surge preventive/dependable hardware available for pipelines now than when older standards guidelines were established/older pipelines built..
I would suspect that the most common ductile iron pipelines (as far as the hundreds of thousands of miles of at least ductile iron pipes out there in distribution systems) operate in the normal (steady) working pressure range of 60-100 psi, and it may not be a coincidence that there have been so many municipal projects (and most perhaps also with not huge elevation differences) out there that for many years have specified that their pipes be field tested e.g. to 150 psi (that happens to be 1.5x100 psi). I suspect at least early drafters/versions of this standard may have kept this in mind. Over the years and for whatever reasons (boosting of pressures to extend service areas, more needed water delivery, more and longer transmission mains over rougher terrain to more remote sources etc., or realizations that greater pressures might occur?) I think I have seen more and higher specified test pressure projects.
Now, I must also note that the clause you quoted in AWWA C600-05 is immediately followed by another rather common sense (sort of a chain is only as strong as its weakest link) clause,

“5.2.1.1.2 The test pressure shall not exceed the thrust restraint design
pressures or 1.5 times the pressure rating of the pipe or joint, whichever is less (as
specified by the manufacturer).”

I believe these are good reasons (among others) to provide as much information as possible in consistent terms in the contract documents to allow such determinations to be made, so that all parties are on the same page. A transmission pipeline with widely varying elevations, of course that results in a non-level hydraulic grade line, obviously has “operating pressure” that varies and is not a constant with the contents in motion or even bullheaded off (like a closed valve, or test bulkhead at the bottom for static/hydrostatic test).
All that being said (and while DIP may have some more security with regard toover-pressurizations than other pipes), I believe a well run field test of any pipeline to at least at pressure levels not likely to be exceeded in service probably benefits and perhaps provides some level of protection to all parties, including the pipe supplier. Have a good weekend!