Spiral wound strengthening for composite pipeline

[corrosionman]

Our 10 inch pipeline is from thin wall pvc, externally wrapped with grp. Due to increased pressure rating the line often bursts and we consider adding extra wrapping for greater strength. Since the circumferencial stress is twice the axial it is suggested that we use a unidirectional carbon fibre tape of 2 inches width plus resin. When we start the job the speed of job completion is critical therefore we wondered if the "bandages" need not overlap but could be spaced apart by maybe 2 inches. Any comments will be appreciated.

 

[gvanbeek]

Are you sure that it is just increased pressure that is causing the failure. Glass reinforcement can be subject to stress corrosion cracking in the right environment (e.g. Hydrochloric). Is there any commonality to the failures (e.g. at the joints, near supports, etc.)


Why does increasing the spacing decrease the time required? Why not just use a standard glass / polyester overwrap, with the thickness increased to compensate for the reduced mechanicals.

What is the construction of the grp overwrap is it a typical 54° helic, or is it a nearly circumferential (hoop) wound element?

 

[Mark62]

If you leave gaps between your reinforcing tapes, you will find that the tube will simply burst between the tapes. You have to look at the ability of the tube material to be able to support the pressure across this gap.
If you are to reinforce the tube I would recommend that the tube is fully covered.

 

[corrosionman]

Hi Thanks for interest. Actually the line is a 15 year old distribution network grp pipeline, of total length several kilometers which regularly has bursts. access is very difficult due to proximity pipes so the less wrapping for strength the better it is. One Spec we were given said overwrap with 8 layers grp but we hoped that one very thick spiral might be easier. Maybe it would still help if it was widely spaced. Meanwhile we wonder if the problem is the water hammer phenomena. The line is rated at 10 bar but we tensile tested sections near a burst and find that at least 45 bar is needed to cause a failure. Very originally all the system valves were manual shut off gate type but now we believe some have been changed to lever arm butterfly type which enable instantaneous closure.
Meanwhile we arranged to over coat a few teast coupons and it seems to indicate that one single layer of unidirectional glass tape will double the burst pressure. I,ll update you when we know more. Thanks again. D W