Welding effect on internal pipe cement lining 1

[win]

Hi all,

I have a question on the effect of welding heat on the internal cement lining of mild steel water pipes. Is it possible for the heat during welding of collars, flanges etc. to damage these cement linings?

Currently involved in a project where we have a 15 inch ND MSCL pipe for a curved bridge crossing. As this size is too small for workers to enter and inspect/patch up any cement lining damages, we are thinking of using specially factory fabricated flanged bends to maneuver this curved alignment. However, this will mean that the fittings can only be fabricated after the bridge is constructed and remeasured.

Another option will be to use plain ended pipes/bends which is welded together with collars but this leads us back to the question as to if the welding heat will damage the cement lining.

Also, is it a practice to use mild steel for pipes smaller than 500mm or 600mm? As far as i understand, the cement lining in these small pipes can not be inspected, repaired or patched up at the joints due to limited working space in the pipes.
Any help is much appreciated

 

[weldstan]

Yes damage can occur. What is the thickness of the pipe? If thick enough fillet weld attachments can be used to weld the slip on flanges to the pipe. Have you considered Vanstone flanges? You can visually inspect for damage using video cameras. We have used this method over 25 years ago. It is much easier to do now.

 

[win]

Hi Mr Weldstan,

Thanks for the reply! The thickness of our 15 inch MSCL is roughly 4.5mm thick. Would this be enough? For your info this mild steel cement lined is used as a water distribution pipeline with roughly 5 bar operating pressures.

Do you mind to elaborate further on the weld attachments and Vanstone flange? Did a quick google search and the Vanstone flanges seems to look like those stub end slip on flanges that we use on HDPE pipes. Some pictures might help.

Im also curious to know how did you fix the damaged cement linings (if any) for these small pipes.

 

[rconner]

AWWA Manual M11 says that for field welds of lined and coated steel pipe a short length of pipe must be left "bare" (i.e. the linings and coatings must be held back). Furthermore, M11 indicates for specifically pipes smaller than 24 in. (600mm) the linings should be filled/"repaired from the outside, using handholes."
Other than a few arguably applicable entries in AWWA C602 for field-applied cement mortar linings (regarding comparable composition and workmanship e.g. "Hand-placed mortar shall have a uniform surface with smooth transitions to adjacent machine-placed linings..." and "Access openings necessary for the lining work shall be prepared and closed by the constructor, unless otherwise specified by the purchaser" etc), I don't believe AWWA C200 for steel pipe, C205 for Shop-applied cement mortar linings nor that standard really address in any more detail these specific "hand hole" procedures for filling/repairing linings at field-welded steel water pipe joints less than 24" in size. Maybe these references will help get further information.

 

[robyengIT]

AWWA Manual M9 (Concrete Pressure Pipe as per AWWA C 301 - Lined and/or embedded type) suggests what detailed in attached excerpt

 

[robyengIT]

a further suggestion

 

[win]

Hi Mr RConner,
Thanks for the reply. Will look into the given references for more info. Am i correct to assume these handhole openings will have to be something like a small tee which is to be closed up with a blind flange as opposed to cutting an opening on the pipe itself and welding it back on which leads back to the problem of patching up the affected lining.

Hi Mr RobyengIt,
The attached awwa m9 suggests 'buttering the back face of the bell'. Does this mean to apply extra mortar in the bell, push in the spigot, and complete the weld? This would mean that the cement lining on the inside will still be wet while welding? If so then this could be the solution to our problems!

 

[rconner]

I have not seen the hand hole process applied myself, as modern bridge crossings of smaller diameter piping are instead often made with rubber-gasketed, restrained joint piping systems that do not require this process; however, the OP implied the joints of this installation would instead be field-welded (hence the non-elaborated MOP reference).
As to buttering of joint bells with mortar immediately before they are assembled, I have heard of that being done with some stab (rubber-gasketed?) joints of steel piping, followed by bullets or bladders etc to smooth excess across the joint; however, I don't think it feasible to weld on less than 3/16 inch thick, fresh mortared steel pipe joints, as it will likely blow the mortar or other coating off inside the joint(hence maybe one reason many designers choose restrained joint systems that do not require field welding of joints after assembly).

 

[weldstan]

Welding on your very thin pipe will doubtless cause damage to the cement lining. You need to remove the cement lining from the area to weld a slip on flange and restore the lining after welding. Since the pipe ends were not designed and fabricated to enable the use of Van stone flanges, I don't see how you can use them now. It appears that someone did not do his homework before the pipe was cement lined.

 

[win]

Interesting points indeed! Actually we are in the process of finalizing the design for this bridge crossing. Most likely we will be using factory custom flanged bends to maneuver the curve of the bridge. Thanks for the help!