Q & A's
General l Pipe Preparation l Pipe Joining
Q. What pipeline gas pressures in service have Zap-Lok® joints been used on?
A. Zap-Lok® lines are not de-rated, the design is based on the pipe wall and grade. In the US the regulations generally allow maximum allowable operating pressure (MAOP) of 72% of specified minimum yield, and testing at 90%. Therefore gas lines running as high as 4,000 psi (276 bar) on smaller OD lines have been joined using Zap-Lok®.
Q. Can seamed line pipe manufactured using the Electric Resistance Welding (ERW) High Frequency Induction (HFI) methods be joined using Zap-Lok®?
A. Yes ERW and HFI manufactured line pipe as well as seamless line pipe is ideal to be joined using Zap-Lok® and has been used both onshore and offshore.
Q. Can pipelines with Zap-Lok® joints be inspected with intelligent pigs?
A. Yes Zap-Lok® joints are fully piggable and tests have shown that tool travel through the joint was the same as ,or smoother than, an equivalent welded joint.
Q. Are there any test results about the Zap-Lok® joint available?
A. Yes many stress and pressure tests have been performed and more details can be found in the 2007 Technical Information Manual which can be viewed on this site under "Pipe Joint Technology". The test results are impressive. As an example a test was done on 3 inch 13 chrome line pipe joined by Zap-Lok®. Under tensile test the load required to pull the joint apart was 191,800 lbs (87,182 kgs). Under hydrostatic test the pressure applied was over 17,000 psi (1172 bar) and at that point the arc welded end cap of the test pipe blew off and the test was terminated. The Zap-Lok® joint remained fully intact.
Q. Why is a Zap-Lok® line pipe joint safer and more environmentally friendly compared to a welded line pipe joint?
A. Welding is a hazardous and complicated process that involves very high temperatures, use of 'shielding' and 'welding' gases and emission of toxic fumes, sparks and arc rays. By comparison the Zap-Lok® pipe preparation and joint process all work by hydraulics. This is a benign process which involves no hot temperatures, toxic or dangerous substances and no harmful emissions of fumes, sparks or arc rays. Consequently health, safety, environmental risk and costs are substantially reduced with Zap-Lok®. Use of Zap-Lok® equipment has an excellent safety record.
Q. Is the line pipe steel to be joined by Zap-Lok® the same as steel for line pipe to be joined by welding?
A. Yes the pipe preparation is done after the steel line pipe is milled and the client can make the choice whether the pipe is to be joined by welding or by the Zap-Lok® process. It is not necessary for line pipe to be milled to a special specification ready for preparation and joining by Zap-Lok®.
Q. What is involved in line pipe preparation?
A. The line pipe is pinned" and "belled" (see the video in the media section) by machines manufactured by Zap-Lok® Pipeline Systems Inc in Houston USA and these machines are delivered by Swiftpipe to the site where the preparation work is to be done.
Q. Where is the pipe preparation work done?
A. This work is normally done at the coating plant, where line pipe is stored after milling or can be done at the steel mill itself. If required the work can also be done at the site that the pipe is to be laid.
Q. How long does it take to prepare the line pipe?
A. Typically 20-25 pipe lengths (both ends) can be prepared per hour (300-400 end joints per shift) but this can vary depending on whether automatic pipe handling equipment is used and whether magnetic inspection tools are used for quality control purposes.
Q. Is there restriction in line pipe size?
A. Equipment to prepare line pipe outside diameter (OD) up to 12.75 inches is available and is being developed for use up to 16 inch OD.
Q. Are there restrictions in steel rating that can be prepared and joined using the Zap-Lok®?
A. Generally we can work up to API 5L X-60 rating so any steel rating above this would need referral to us.
Q. Can 13 chrome steel line pipe be prepared and joined by Zap-Lok®?
A. Yes this facility is now available.
Q. Are there issues with 'ovality' in pipe milling specification which applies to Zap-Lok®?
A. Almost all ovality problems can be fixed using the Zap-Lok® mandrel during pipe preparation.
Q. Can the line pipe be prepared if there is any surface rust present?
A. Yes we can complete the preparation work if there is rust present but it cannot be done if the line pipe is pitted.
Q. Is there a restriction on line pipe wall thickness for the Zap-Lok® Joint?
A. Line pipe joined by Zap-Lok® can be thinner than line pipe joined by most other methods. Wall thickness of 0.06ins (0.152cms) has been successfully joined using Zap-Lok®. Maximum thickness is limited to the capacity of the presses used for "belling". For API 51 Grade X-60, 12.75 inch (32.4cms) OD line pipe with a pipe wall of thickness of 0.688 ins (1.75cms) has been joined using Zap-Lok®. Page 17 of the 2007 Technical Information Manual has more details about line pipe size and wall thickness.
Q. How reliable is a Zap-Lok® joint and what is the track record?
A. The joints are very reliable and leak tight. The track record of the joint in service and installation history is excellent with over 25,000 kilometres of pipelines laid with over 2 million Zap-Lok® joints successfully installed..
Q. Can Zap-Lok® be used for joining line pipe to be used in bores ie. without surface trenching?
A. Yes "pull through" lengths the same as using welded line pipe are achievable.
Q. Why is Zapoxy used?
A. Zapoxy is a specially formulated compound prepared on site and is used to lubricate the pressing on site of the pinned end into the belled end of the line pipe. This avoids "galling" of the line pipe and seals any surface scratches in the steel when pressing occurs. The actual joint is a "steel to steel" interference joint inside the belled end of the line pipe. Zapoxy does not act as a glue and is not integral to the joint strength but hardens after curing to form a secondary seal to the actual joint itself.
Q. Are there different types of Zapoxy?
A. Yes the actual formulation mixed on site depends on whether the joining is being done onshore or offshore where the pipe will be laid in water. Also the ambient temperature of the site is relevant for the mixture composition to regulate the curing time in warmer or colder climates.
Q. How long does it take for a Zap-Lok® joint to reach full strength?
A. This takes 3-5 minutes due to the Zapoxy needing to cure (note about 80% strength is achieved after 1 minute) whereby Zapoxy stops being a lubricant and hardens to become a sealant. The curing time can be speeded up if required and this is sometimes done for offshore use as the pipe is moving over the Stinger under tension.
Q. For offshore use what is the deepest water depth Zap-Lok® joints have been used?
A. The deepest pipe lay to date is 220 feet (67m) although this depth was due to the working limit of the tensioner used on the lay barge. Preliminary work has been done which indicates that the Zap-Lok® joint could be used in much deeper water possibly up to 3280ft or 1000m water depth. An initiative is now underway to introduce the Zap-Lok® joint to the market with the objective of significantly increasing the speed of laying pipe in deep water.
Q. Can the Zap-Lok® joint be tested on the lay vessel offshore before the joint submerges during pipe lay?
A. Yes the 'Gatorhawk' external hydrostatic test can be conducted on each joint when on the lay vessel.