BLOCKBUSTER Contact Lee Brand 083 458 4836 Info@blockbusterdrain.co.za

RUST

Home    |   Drain Cleaning     |   Tips    |   General Plumbing

Link to EMERGENCY  leak repair! RUST and Water pipes - rust eventually wins! Rust is probably the main cause of leaks in underground water pipes in South Africa. I say probably because plastic pipes don't rust, but I suspect that the vast majority of domestic systems still use galvanised steel pipes. As plastic pipes replace the steel the situation will improve. Galvanised steel pipes will all ultimately be destroyed by rust - some pipes will go faster than others. Some within the building may even outlast the building but ultimately all steel reverts back to dust:-). On a more positive note there are a number of things that we can do to slow down this process - in fact we can more or less stop the process relative to our life times. By far the most effective way is by coating the pipes with a protective layer so that rust cannot occur. Rust is an electro/chemical process caused by the flow of electrons from one place to another. If we can stop the flow of electrons then we can stop the rust. This is done by a number of methods including galvanising, painting, etching and covering the material that we wish to protect. In the case of water pipes, galvanising is the most common method of protection. So why do the galvanised pipes still rust? Galvanising forms an active layer of protection that protects the metal underneath from rust, but the galvanising also corrodes - albeit very slowly and ultimately there just isn't enough zink left to protect the steel. There are often problems in the galvanised coating in that it does not cover the entire surface. Examples being at cut threads and at tool mark damage. This gives the rust a place to start and spread. The rust can in these cases "undercut" the protective layer and ultimately destroy the integrity of the pipe. The other problem with rust is that it takes up more space than pure steel. This causes the pipe to swell and scale - exposing fresh areas of steel underneath to the corrosion process. Note that rust is not a "living" thing! If you remove any of it's prerequisite components it stops. You can in fact paint a slightly rusted surface with a sealer and as long as it stays sealed the rust will not continue. The problem is that if you seal loose rust then the sealer will fall off with the rust! Factors that contribute to accelerated corrosion (rust). External - outside the pipe. Shallow pipes, buried in the soil's "active layer" - like under flowerbeds  Highly acidic "wet" soil conditions. Damaged protective (galvanised) layer. Low quality galvanising. Internal - inside the pipe.  Acidic water. Hot water and highly oxygenated water. Damaged protection - particularly at threads. Faulty seam. Low quality galvanising. Dissimilar metals in galvanic coupling. Because many home owners have had bad experiences with steel pipes there is a tendency for people to say that steel pipes are "rubbish" and should never have been used in the first place. This is NOT correct. In most cases these steel pipes may have been in service for 50-60 years or more without any problems. It was cheap to install and for the first say 40 years much stronger than copper and plastic pipe. In fact there are many industrial applications where steel pipe is still required. Because we understand corrosion better now, we can install steel pipes underground that will last over 100 years or more. So how would we do this? First we would make sure that we bought top quality pipes with top quality galvanising. We would take the extra trouble to galvanise the threads on full lengths. Cut pieces would get etch primer on the threads after being tapped. Utmost care would be taken in fitting the pipes - minimal damage to the galvanised coating by pipe wrenches. Once the pipe is laid out it would be painted with zink compatible primer - especially thick on damaged areas and joints. Hemp joints will be sealed so that water cannot be wicked in from outside.  After this a topcoat would be applied - If we had lots of spare cash we would use a resin based product. If not just a normal corrosion inhibiting paint would be used. We would check the soil conditions and this would determine the depth required to a large degree. Very active surface soil we go as deep as we can. The deeper the soil the more inactive it becomes - in most cases. Then we would bond the pipe together with copper wire and install a number of magnesium anodes at calculated intervals - this is to protect the pipe if there are any "holidays" in the protective layer. After adding up the costs of this we would figure out that we could have run 4 lines using polycop (plastic) at half the cost! :-) What can be done to existing steel pipe that is already rusted? A couple of things - but it really depends on how far gone the pipe is and it is always better to replace badly rusted sections with plastic. Unfortunately there are a couple of consequences to this. The first time a pipe springs a leak due to rust, a couple of things happen. First - the leak is very small and often unnoticed. This immediately adds more water to the area surrounding the first leak and will increase corrosion in a localised area around the first leak. The small leak enlarges due to continued corrosion and supplemented by additional water, helped along by a thing called flow corrosion. Additional oxygen is also added to the mix. Eventually the leak becomes noticeable. The leak is then repaired. There are two ways of doing this - "clamping" the leaking area to stop the flow or cutting out a section of pipe. The former method is temporary at best - the corrosion under the clamp continues at an accelerated rate. The latter option also has consequences. The pipe is often manhandled during the cutting and re-threading phases and this puts strain on the weakened pipe which results in more leaks on either end of the replaced section. It is also near impossible to cut decent threads on a 50 year old rusted pipe! So we use a thing called a "Johnson Coupling" because there is no other way - other than to replace the entire length with plastic! After the leak is stopped another factor comes into play - increased pressure in the line. The leak had dropped the pressure in the line so that other weak areas of the pipe could cope. The moment the pressure goes back to it's normal level they also let go. It is not unusual to repair a pipe once and then repair subsequent leaks for many months thereafter. The other thing is that you upset the electrical continuity of the pipe. You now have two pipe lines in the ground instead of one. Now this may work in your favour and decrease the corrosion potential but it can just as easily work the other way and cause the already weakened section to corrode faster. The bottom line is that when you get to this stage the entire line must be replaced with plastic!  In some extreme cases where full replacement is near impossible we treat (convert) the rust - if only to see how much steel is left. If it looks ok we treat the steel with an inhibitor coating and attach anodes to facilitate local cathodic protection. The benefits of this are suspect though - it postpones the failure. Having said that,  this method can be effective if you indeed have localised corrosion  - Assuming that the rest of the pipe is okay and that the first leak was due to a localised external cause - like a leaking drain for example. Okay, that pretty much covers pipe underground. So what about pipes in concrete and plaster. Fortunately external corrosion is usually no problem and these pipes can outlast the building as long as some conditions are met. Galvanised steel in cement/concrete/plaster is generally a great combination. Think of all the uncoated re-bar in concrete structures all over the place. concrete is alkaline rather than acidic and provides a great protective coating for the galvanised pipe - AS LONG AS IT IS DRY! Here the threat is primarily from inside the pipe. Should it spring the slightest leak on a seam or joint, it soaks the surrounding plaster and brickwork like a sponge. Not only does the original internal leak grow but you find that accelerated local corrosion starts on the outside of the pipe. This can have pretty severe consequences because these leaks in structures are harder to fix - you may need to bash down half the bathroom to replace the bad pipe! This kind of leak becomes a catastrophe when the leaking pipe has been cast into the floor slab or other major structural component! Never put water pipes in slabs! Run them from the outside wall directly into the dwelling. Use service channels and make sure that any pipe can be replaced if need be. Chase them into bedroom walls if you must - but avoid structural concrete - if a joint fails then that's it. It cannot be replaced without knocking down half the building! Why is it more difficult to repair galvanised pipes compared to copper? The difficulty lies in the method of joining the pipes - the threads. Steel pipe should be removed back to the first good thread attachment point. This means that a single leak may cause 3 to 6m of pipe to come out!. In the case of copper pipe you can  remove the leaking section and solder in a new piece very easily. This means that the new piece of copper pipe may only be 8cm long or less. With the result that you destroy only about 10cm of tiles - as opposed to 3-6m! BBDC has developed some innovative ways of repairing galvanised pipes in walls that only removes the broken section and joins in a new pipe by means of what we call a balanced coupling rather than threads. This system relies on the strength of the pipes in the wall  rather than threads and can be used to repair localised corrosion. The length of the repair is typically about 25cm. This can be used on 1/2 inch and 3/4 inch pipes, but they must be in good condition on either side of the failed area. This is very useful if you are faced with the prospect of chopping out your new kitchen units to get to a corroded steel pipe! Finally - I said that the pipes we see most often are ones that have rusted from the outside in. This is not to say that pipes that have rusted from the inside out are rare. This happens fairly often too. In fact you generally find a combination where the two areas (internal/external) of rust meet and then the pipe leaks. Internal failure is (in our experience) most often on the pipe seam and threads. The pipe seam is not perfectly welded during manufacture and this defect eventually causes a leak. Sometimes we come across multiple leaks on the seam within the same length of pipe. Obviously the way to fix this is to replace the length from end to end. Threaded joints are also a common source of failure. Again you see a combination of internal and external corrosion. Remember that the threads are seldom properly protected and there is often a layer of hemp there that complicates things. If you disagree with anything I have said about rust please let me know. I do not claim to be a rust expert. What you read here is based on common experience - mine and others. Terms and Conditions of Use       Contact me if you have any specific rust related questions - info@blockbusterdrain.co.za