Estimation of Hazen-William Roughness Coefficient of Old Cemented Mortar lined MS Force Mains

[M. Adeel Khan]

Hello everybody!

A feasibility study for replacement of force mains (Cemented Mortar lined Mild Steel pipes) has to be performed regarding which estimation of current Hazen-William Roughness Coefficient of the pipeline needs to be performed. The pipeline has been in service for 30 years now and had a HWR Coefficient value of 120-130 when installed.
The pipe specifications are,
Diameter: 1500mm & 1800mm
Pipe Type: MS Pipe (Grade-42 API 5LX)
Internal coating: 13mm Cement Mortar lining
Can anybody help with their valuable input or cite any helpful reference regarding this problem?

 

[bimr]

Pumping Station Design has some estimates.

 

[LittleInch]

I was going t say that without knowing the actual condition you won't know if it has got bit missing / started to fail or got plant growth or has actually got smoother over the passage of time.

If your pipeline is running then why don't you back calculate it based on actual data of flow and pressure?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cvg]

typical new installation would be 130 - 150. your estimate of design value seems low. to estimate current condition, suggest you need to get a video inspection

 

[M. Adeel Khan]

@littleInch
Actually a client of ours asked us for some help in this matter, I have already suggested them about the back calculation. Just wanted to know if there has been any other mathematical method in use for this purpose keeping in view the experience of people on the forum.

Appreciate all your valuable inputs. Thankyou all!

 

[M. Adeel Khan]

@cvg
Yes it seemed lower than all the values I have seen at various places while searching on the issue. It was provided by the client and may be the pipeline is older than 30 years and the values measured were from 30 years ago.

 

[bimr]

If you are interested in further references on this subject, I refer you to Pumping Station Design which has an extensive discussion. Below are a few paragraphs from the book.

The basis of the Hazen-Williams C factor in Equation 3-8 has resulted in some confusion. The factor is a function not only of the smoothness of the pipe wall, but also of the difference between the actual ID of the pipe and the nominal pipe size.

Matters are not improved by the apparent increase of C with diameter. According to AWWA Manual M11 [10], the average value of C for pipe with smooth interior linings can be approximated as C = 140 + 0.17J, where d is inside pipe diameter in inches. After a long term of lining deterioration, slime buildup, etc., C = 130 + 0. 16 d. However, above a diameter of about 900 or 1200 mm (36 or 48 in.), there is little increase in C values according to Gros [11], who has had many years of experience in measuring C values in the field. The values of C listed in the first part of Table B-5 reflect this experience.

In addition to the discussion above, there are other limitations on the value of C. Values of C less than 100 are only applicable for velocities reasonably close to 1 m/s (3 ft/s). At other velocities, the coefficients are somewhat in error. For water pipes, Lamont [12] advises the following:
• C values of 140 to 150 are suitable for smooth (or lined) pipes larger than 300 mm (12 in.).
• For smaller smooth pipes, C varies from 130 to 140 depending on diameter.
• C values from 100 to 150 are applicable in the transitional zone (between laminar and turbulent flow), but the scale effect for different diameters is not included in the formula.
• The formula is unsuitable and, hence, not recommended for old, rough, or tuberculated pipes with C values below 100.
• Force mains for wastewater can become coated with grease and C values may vary down to 120 for severe grease deposition.

In the past (before 1940 or 1950), it was common to line steel and cast-iron pipe with hot coal-tar dip, which provided poor protection and allowed C values to drop from 130 for new pipe to 100 or less for pipe in service for 20 yrs or more [13]. The modern use of cement mortar or plastic linings makes pipe very smooth, prevents corrosion and tuberculation, and maintains its smoothness indefinitely. In field measurements [14] made all over the United States on new water pipe with diameters of 100 to 750 mm (4 to 30 in.) lined with cement mortar, the values of C varied from 134 to 151 (median = 149, average = 144). For 150 to 900 mm (6 to 36 in.) pipe in service for 12 to 39 yrs, C varied from 125 to 151 (median = 139, average = 140) — a decrease of only about 5 units.

Water treatment often creates deposits that greatly increase friction in pipes. In one pipeline, lime incrustation reduced the measured value of C to only 80 downstream from the treatment plant. Pipe can, however, be cleaned and relined with cement mortar in situ and restored nearly to its original smoothness. Under some circumstances, deposits of bacterial slime in water pipes can change the smoothest pipe (whatever the material) into very rough pipe. Fortunately, chlorination destroys the slime and restores the former smoothness.