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FAQ

Here you will find answers to the questions that crop up very commonly in connection with steel pipe production at Mannesmann Line Pipe.


1. What is high-frequency induction (HFI) welding?
HFI welding

Longitudinal welding at Mannesmann Line Pipe is done using the high-frequency induction (HFI) process, an electric resistance welding technique. In this process, the strip that has been formed in rolling stands to the shape of an open pipe passes through a ring inductor which induces high-frequency current in the open pipe. The induced current completes its path around the pipe circumference and along the strip edges, which are thus rapidly heated to welding temperature. Pressure rollers force the strip edges together, resulting in a homogeneous longitudinal weld without any filler metal being needed. For further information click here.


2. What steels are used for line pipe production?
Bare steel pipe

We select the steel grade best suited for a particular application from our range of materials. Grades vary in terms of their mechanical properties, for instance strength and toughness, and their chemical composition. These properties are defined in specific standards for the various, applications. The materials available in the manufacturing program of Mannesmann Line Pipe can be found on the application subpages of the manufacturing program.


3. What are the new standard designations for line pipe steels?

The new designations are linked to the applicable Technical Delivery Conditions.
Gas line pipe for operating pressures up to 16 bar (replacement of DIN EN 10208-1 by ISO 3183:2012) is made in material grades L 245 N to L 360 N.
Pipe for high-pressure pipelines for pressures exceeding 16 bar (replacement of DIN EN 10208 by ISO 3183:2012 Annex M) is made from material grades L 245 NE to L 485 ME.
For water line pipe (replacement of DIN 1626 by DIN EN 10217-1 "Welded steel tubes for pressure purposes" or DIN EN 10224 "Non-alloy steel tubes and fittings for the conveyance of water and other aqueous liquids."), material grades P 195, P 235 and P 265 to DIN EN 10217-1, or L 235, L 275 and L 355 to DIN EN 10224 are used. The pipe can be made to either of the two Technical Delivery Conditions. The applicable standards for our manufacturing program, sorted by application areas, can be found on the subpages of our manufacturing program.


4. What does the term weld efficiency factor mean?
HFI welding

Weld efficiency is a gauge of the quality of the longitudinal weld in welded steel pipes. The weld efficiency factor 1.0 means that the mechanical and technological properties are the same in the weld as in the base material (weld = base material).


5. What are the permissible operating pressures for steel line pipe?
Hydrostatic pipe testing

Depending on the region, steel line pipe is designed to various standards, such as ASME Codes, EN 13480, etc. The wall thickness for the intended internal pressure is calculated as a function of the steel grade used.

As a rule, the production standards for both gas and water line pipe specify nominal wall thicknesses that can take pressures well beyond the usual maximum operating pressures. Depending on the intended application, the design pressures for steel pipe may vary considerably. For example, the maximum operating pressure for gas pipes in the low-pressure range is 16 bar. Beyond this limit, high-pressure pipes are used whose nominal wall thicknesses normally have to be specifically calculated.


6. What is the service life of steel line pipe?
Pipe stack

Steel is an extremely durable material. However, depending on the application, it can be exposed to environmental influences that may affect its durability. Corrosion, especially, plays a key role here. It can be caused by contact with aqueous media either on the inside or on the outside of the pipe. Other harmful substances include saline or sour media and soils.

For external protection, pipes are usually provided with a plastic coating and, where appropriate, an additional cement mortar top coat to protect the underlying plastic coating.Drinking water and sewer pipes are additionally lined with cement mortar. In the case of buried pipelines, pipe bedding is another factor that determines the durability of pipe.

If properly protected, laid and used, pipes will last for several decades.


7. What does a plastic coating consist of?
Steel pipe with plastic coating

Today, the three-layer plastic coating is standard practice for steel line pipe. For the first two layers, powder is electrostatically applied to the preheated pipe surface, and the actual plastic coating is then extruded onto the second layer as a seamless tube. The first layer consists of epoxy resin and serves as a primer on the steel surface. The second layer is a polyethylene-copolymer and serves as a bonding agent between the epoxy resin primer and the third layer, which is the actual corrosion protection coating. The MAPEC® plastic coatings used by Mannesmann Line Pipe are unconditionally suitable in all types of soil and even at elevated temperatures. Further information about our coating and lining systems can be found on the respective pages for oil & gas as well as water line pipe.


8. What is a fiber cement mortar (FCM) coating?
FCM coating

A fiber cement mortar (FCM) coating provides added protection to a plastic-coated steel line pipe. It consists of a mixture of sand, cement, fibers, water and other aggregates and is applied in a helical motion around the pipe; at the same time, it is reinforced with a fabric tape that is worked into the mortar. Fiber cement mortar coating is used wherever the plastic coating is exposed to increased mechanical stresses either during pipe-laying or under pipeline service conditions, i.e. in stony and rocky soils or during trenchless pipe-laying.

FCM coatings are also used for protection against buoyancy on offshore pipelines (or river crossings). The mill-applied FCM coating can be built up to a thickness of 50 mm. For further information can be found here.


9. What linings are available for steel line pipe?
CM lining

Pipe for the transportation of gaseous media can be provided with an epoxy flow lining for reduced friction resistance. This lining complies with the internationally acknowledged requirements specified in API RP 5L2 or EN 10311. Further information on epoxy flow coat can be found here.

Drinking water and sewer pipes are lined to protect the inside surface against corrosion caused by contact with the aqueous media. Usually, water pipes are lined with cement mortar as per EN 10298, although the final decision regarding the lining material depends on the medium to be transported.

 

In water pipelines or sewer pipes, lime-dissolving or very soft (demineralized) water may react with the lining. This could result in an undesirable increase in the pH value. In such cases, Salzgitter Mannesmann Line Pipe assesses the water quality in order to determine the best-suited lining material. Where drinking water pipelines are concerned, this will usually be a cement mortar lining mix based on Portland cement (new designation: CEM I), which can be given a special aftertreatment if necessary.

The lining can be used with all wastewaters subject to the requirements and limits of ATV-A 115. If specific limits are exceeded or the intended application involves special operating conditions, Salzgitter Mannesmann Line Pipe should be consulted when selecting the lining material.

Depending on the wastewater composition, a blast-furnace cement mortar is normally used (new designation: CEM III/A or CEM III/B, according to the composition of the granulated blast furnace slag). Further information on cement mortar linings can be found here.


10. How are pipes joined on site?
Welding of pipes on the construction site

Gas and water line pipe are now generally welded using a manual metal arc process (vertical-down technique and cellulose electrode), which has proved to be most cost-effective and suitable for field welding. In individual cases and with smaller pipe sizes (but only gas line pipe, not cement mortar-lined water pipes), a gas welding process may also be used. Where special requirements have been specified for weld quality (e.g. in power plant construction), TIG welding is also used.

Plastic-coated pipes

After welding using mobile equipment, the weld area is field coated to complete the protection. This is done using cold or hot coating systems. Today, the use of PE wrappers, shrink-on tubes or collars is standard practice.

FCM-coated pipes

Field coating of the weld areas in FCM-coated pipes is done using either a casting mortar system or cement wrappers, with casting mortar being the most frequently used.

For trenchless pipe-laying, Mannesmann Salzgitter Line Pipe recommends its proprietary MAPUR, a sand-filled polyurethane-based casting resin. Alternatively, a GRP coating material can be used.

Lined pipes

It is standard practice for pipes intended for butt-welding to be lined only up to between three and five millimeters from the pipe end to allow problem-free field welding. This means a gap measuring 10 mm maximum is left in the lining after welding. However, since butt-welding is only used for drinking water pipes, field lining of this area is unnecessary as the gap will close completely due to the reaction of the lining with the drinking water once the pipeline is operational, thus reliably preventing any corrosion attack.

For sewer or waste water pipes, slip welding joints are normally used. With this joint type, a continuous cement lining is generated that protects the pipe inside from the aggressive medium.


11. What needs to be observed regarding pipe bedding?
Pipeline in the pipe trench

Pipe bedding or cushioning is a key factor governing the service life and operational safety of a pipeline. Optimum bedding ensures uniform support and cushioning of the pipeline. In most cases, sand of a suitable grain size is used for this purpose. For example, if compaction of the soil cover on a buried pipeline is intended, a grain size of 0/4 (min./max., unbroken) should be used. The suitability of 0/8 material must be checked for each individual case; it depends essentially on the material's grading curve. If no compaction of the soil cover is intended, material with a grain size of 0/8 to 0/16 may be used. Further information on Pipe trench & bedding can be found in our pipe-laying instructions.


12. What are short pipes?
Short pipes

As a rule, it is impossible to lay all the pipes for a given pipeline in the original mill length. There will always be sections where shorter lengths are needed. In such cases, pipes cut to length are used.

Generally, an abrasive cut-off wheel is used to shorten the pipe on the construction site. Plastic-coated pipe lengths must then be stripped of the coating over a defined length to allow the pipe end to be beveled. For this purpose, the pipe is heated (preferably from inside) to about 80 °C with a gas burner. Then an incision is made in the plastic coating around the circumference and along the length to be stripped. The plastic coating will now pull off easily and the pipe end can be beveled as required.

Further information on Field cutting can be found in our pipe-laying instructions.


13. How are pipelines laid along curves and bends?
Curvy pipeline route

Directional changes in a pipeline, i.e. deviations from the straight line, require the use of pipe bends. These can be ordered in various designs from a pipe bending plant.

Pipes can also be laid in curves covering lengthy distances. However, taking into account the properties of the pipe material, the curves must then have a relatively large radius. The minimum bend radius for welded steel water pipelines is calculated using the formula
Rmin = 500 *OD [m], where OD is the pipe outside diameter in meters.

The minimum bend radius for gas pipelines is governed by the operating pressure of the pipeline. For operating pressures up to 4 bar, it is calculated using the formula Rmin = 210*S/K*OD. The formula for operating pressures >4 bar up to 16 bar is Rmin= 206*S/K*OD (where S = safety coefficient, K = yield strength of the pipe materials, and OD = pipe outside diameter). Further information on Directional changes can be found in our pipe-laying instructions.


© Mannesmann Line Pipe GmbH
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