Rubber lining is an application method that protects the interior or exterior surfaces of pipes, tanks, and other similar vessels from corrosion. Metals that house liquids are prone to corrosion which is why rubber lining is done to enhance resistance against this natural process. To achieve a durable finished product, rubber lining requires precision and expertise. Factors such as working conditions, the state of the metals, and the equipment to be lined can affect the outcome of a rubber lining. Therefore, it is crucial to follow rubber lining principles for proper corrosion resistance.
General Rubber Lining Guidelines
- Prerequisites for metals to be lined.
First off, it’s important to evaluate the state of the metal to be lined. The metals should be thoroughly inspected for any pits and crevices that can cause blisters in the rubber lining. Any uneven surfaces on the metal should be addressed before application to prevent air from expanding during the curing process.
The primer can be applied in advance as well as the tack cement before the lining sheets are applied so that, 1) the cement is tacky and 2) allows for the last sheet of rubber to be applied at the end of work. This way, the tack cement won’t dry so much that the rubber won’t stick once it’s ready.
Temperatures of the metals should be around 60ºF (15ºC). Any lower than that and the rubber applicators will have a tough time applying the rubber lining and the adhesives might not dry on time. Warming the rubber liners to about 120ºF (49ºC on a warming table is recommended to make them easier to apply.
- Application of primer and cement.
Any primer and intermediate application should be conducted before the linings are applied and the tack cement and sheet application should be applied on the same day. Make sure that the cement is still tacky yet solvent free. Areas that have been cemented but not lined should be re-cemented the following day for maximum adhesion.
III. Guidelines for lining.
- The rubber sheets should be unrolled from a warming table and then cut to the required shape and size. Utmost care should be practiced to allow the tie gum side of the lining to face out during cementing. Edges should be cut at a minimum 45° skive to help with forming the seam. To achieve the best results, the plastic side of the lining should be cemented to the substrate. If preshrinking is required, carefully unroll the lining and allow it to shrink before cutting down to desired size. Once the cement has been applied and left to dry, a fabric liner should be placed on the rubber sheet and then aligned on the cemented metal. Partially tack down as the liner is being pulled out. Roll down the lining with steady overlapping strokes at a maximum width of 2 1/2”.
When rolling the lining, begin in the center of the panel and work your way towards the edges to remove all of the air from behind the lining. To make things easier, the crew can mark portions of the panel that have been rolled to identify complete contact between the rubber and the metal. If any blisters appear, these should be punctured and allowed to vent before a 4” patch is overlaid.
- Seams come in two styles: a skive butt joint (that comes with or without cap strips), and an overlap (open or closed skive). An open skive is used when the rubber is a one construction lining. A closed skive is often reserved for multiple construction linings to provide protection to the underlying plies such as a tie gum lining construction. A 2” overlap with a closed skive is one of the most common seam constructions where the top of the panels are skived with a 45° down skive on the exposed edge and a 45° up skive on the bottom portion.
You can cut a piece of lining on the second layer of stock at a 2” square and use it for corners where a triple lining thickness appears. Utmost care should be practiced in high flow areas to ensure that the seams are following the direction of the flow. This is very important so that the seams are prevented from lifting.
- If skive butt joints are required, the sheets of lining should be skived at 45° and paired together. For the cap strip, the width should be around 4” with the seam in the middle. Utmost care should be practiced to prevent stretching of the lining as well as the corners where the lining can be joined, folded, and seamed. For sharp inside corners, a V strip fillet can be used to provide sufficient radius.
The sheets should be applied to ensure that there is minimal waste of stock. The panels can be laid down either horizontally or vertically on the sides and crosswise on the bottom. Vertical panels are easier to apply in cylindrical tanks. For a professional look, always stagger the seams to avoid four layers of rubber that could otherwise ruin its uniformity and neatness.
- When lining tanks outdoors, the tanks should be warmed to around 60ºF (15ºC) first. Heating equipment is essential when lining tanks in cold weather and insulation is highly recommended. Tanks should be treated as a confined space and workers are advised to follow the safety procedures when operating in a confined space.
Application of rubber lining on pipes
1. Specification of the metal pipe.
The pipe should be constructed in accordance with the requirements stated in ARPM IP-4-2. Other requirements that are specified should be discussed in further detail by all parties prior to pipe fabrication.
2. Preparation of the metal.
Metal surfaces that will be lined should be blasted to a white metal blast for preparation. The metal surface should be free of any oxidation, dirt, oil, debris, and other foreign materials.
Primer should be applied immediately after blasting. Apply additional coats of primer and cement as per instruction. A roller, swab, or spray should be used when applying primer and cement on the inside of a pipe. Allow enough drying time in between cement coats.
- Procedure for lining standard flanged pipe.
- Use longitudinal skived seams to form a tube with lining stock. Wrap the lining stock around a mandrel using a liner inside the tube. The outside circumference of the spliced tube should be less than the pipe’s inside circumference. The tube length should also be less than the pipe length.
- Twisted multifilament cotton strings should be applied lengthwise to promote proper air ventilation between the lining and the pipe. Avoid using strings made from synthetic yarns. Stringing should be performed after cementing and the individual strings should have equal spacing around the circumference. In general, four strings are used on pipes that have a diameter of 6”, but larger pipes may require more.
- Wrap the tube in a liner and attach a tow rope. Pull the tube into the pipe in a slow and steady motion.
- Remove the liner and expand the tube against the pipe using air pressure. Mechanical tension and flange arrangement can be used on the pipe ends to maintain an internal pressure of 10psi in the expanded tube for 5 minutes.
- The extension and flare excess stock over the flange face should be removed and trimmed flush with the flange face.
- A covering should be applied on the full face of the flange. Skive the ID of the flange less than the ID of the lining and firmly stitch to tube stock. Soft rubber gaskets are required on the flanges when using hard rubber lining.
- For pipe sizes larger than 6”, the flange stock should be lapped onto the pipe’s inside lining instead of the skive. This lapping method creates a more structurally sound joint and is the preferred technique for lining larger pipes.
- For victaulic pipes, line the inside of the pipe according to procedures used in lining standard flanged pipe. The tube lining should extend over the end of the pipe and bent right back into the recess of the outside of the pipe when using 1/8” through 1/4” linings. A round of friction tape should be applied over the OD of the outside rubber.
It is imperative to ensure that all metal surfaces that are due to be rubber lined are abrasive blast cleaned in accordance with AS 1627.4 class 21/2. The abrasive blasting shall achieve a surface profile in the range of 40-75 μm and shall be confirmed using the comparator method as specified in AS 1627.4 if requested. Once complete, it is vital to ensure the surfaces are blown down with clean, oil-free and dry compressed air. Alternatively vacuum cleaned in order to remove dust particles, residual abrasives and debris. All of Oreflow’s treatments conform in accordance with Australian standards
General repair guidelines
Rubber linings will eventually require repairs. These repairs can vary from small blisters to large cracks in key areas of the panels of rubber. There are step-by-step procedures for different repairs in this guideline, but there may be instances where slight adjustments should be made. In general, these standards have to be met no matter which type of repair is conducted.
- Damaged rubbers and metals should be prepared by grinding or buffing. The rubber surface next to the repair area should be buffed to clean rubber back to a 4” minimum.
- The work area must be clean prior to cementing. Grindings, dust, acid fumes, and other foreign materials should be removed from any adjacent area where it might get carried or blown in.
- Mating surfaces should have a minimum 30° skive and should be of appropriate size for filling in or overlapping.
- Cements should be applied in the correct sequence on the buffed metal or rubber and allow sufficient drying between each coat.
- Mating surfaces of the repair stocks should be swabbed with cement and allowed to dry.
- Repair compounds should be rolled carefully and stitched down. Any trapped air should be removed.
1. Repairing surface flaws of the rubber lining
When a defect is present in the rubber lining and it doesn’t need to be cut out, a patch is sufficient for repairing surface damages. A 2” patch should be enough to cover most defects.
- Remove damaged or loose rubber, cutting back on areas with good adhesion.
- Buff the rubber to be lined.
- Apply a clean solvent on the buffed rubber.
- Apply cement on the buffed rubber surfaces. Several layers of coating may be required.
- Apply cement to a rubber stock patch. The patch should have skived edges when cut and should be large enough to fit the buffed and cemented lining.
- Carefully roll down the patch and eliminate any trapped air.
- Cure the patch in the same way the original lining was cured.
2. Using cover patch and fill in for repairing rubber lining.
- Remove defective rubber. If there is a pinhole leak, omit this step.
- Buff the exposed metal to a good shine. If there is damage to the metal, the rubber must be removed back to good adhesion.
- Repair the metal. When performing metal cutting and welding, keep in mind the temperature of the metal between the weld and the original rubber lining so as to not cause overheating of the rubber or the bond. Upon completion, remove the weld spatter and smoothen the weld ground.
- Buff the edges of the exposed rubber to a 30° bevel.
- Buff the surface of the original rubber lining to 4” from the cut edge. The rubber surface should be free of any foreign material such as dust, moisture, debris, and acid fumes. Moisture can ruin cement adhesion.
- Apply two coats of tack when cementing the buffed rubber.
- Cut a piece of the original uncured lining stock so it fits the edges that have been buffed to a 30° bevel.
- Inlay the cut lining stock on top of the metal. Skive it onto the beveled edges of the rubber.
- Apply a cover patch of uncured lining stock on top of the inlay.
- Roll the stock carefully and work from the center towards the edges to allow air escape.
- Cure the patch in the same way the original lining was cured.
Rubber linings are essential for adding corrosion resistance to pipes, tanks, and other similar vessels. It also protects metals from ignition, explosion, and substance contamination. The process of successfully applying rubber lining requires skill and accuracy to provide maximum corrosion resistance. With these guidelines, you’ll be able to apply rubber lining with minimal errors and conduct repairs should a defect arise.