Frequently Asked Questions

  • Which lifetime do Krah pipes promise?

    Krah pipes are produced with high quality Polyethylene with a live service time of more than 100 years, this meets the client’s requirements perfectly.

  • What is the stiffness of Krah pipes?

    Any needed stiffnesses and stiffness classes can be produced. Stiffnesses from SN2-SN16 acc. to ISO9969 are possible, as well as ring stiffnesses of SR2-SR164 acc. to DIN 16961. The wall structure is designed acc. to local requirements. 

  • What is the delivery length of Krah pipes?

    Usually Krah pipes are produced and delivered in a length of 6m, but in accordance to site conditions also any shorter length can be manufactured. Furthermore, prefabricated pipe lengths of 18 m can be shipped to construction site to shorten the already short installation time.

  • What is the dimension range?

    Krah pipes can be produced in all inside diameters from DN/ID 400 until DN/ID 5000 mm, in steps of 100 mm. Other non-metric sizes are also available on request.

  • How important is the eSDR in the Krah pipe production?

    eSDR means “equivalent SDR (Standard Dimension Ratio)” and allows a simple comparison to axial extruded pipes with the same stiffness. Often you find in tender texts a SDR class mentioned, even if no pressure pipe is requested – only because of the related stiffness.  A Krah pipe with e.g. eSDR11 provides the exact same stiffness as an axial extruded pipe with SDR 11 – but at a much lower price!

  • What about the bending angle?

    Krah pipes can be bent in a radius of 50x pipe diameter. Due to the flexibility of Krah pipes, often additional fittings (bends, elbows) can be avoided.

  • How long can Krah pipes be stored?

    The outside storage period depends on environmental conditions. At site we recommend 1 year as maximum storage time. At a factory under perfect conditions there is no limited storage time. 

  • How is the earthquake stability of Krah pipes?

    Krah pipes jointed by E-fusion (or any other welding system) are flexibly designed and homogenously jointed. That provides the best possible safety against soil movements and earthquakes. 

  • How do I connect Krah pipes? What do I need for it?

    Usually Krah pipes get jointed by integrated E-Fusion, the socket is already homogenously formed at the pipe end, the other pipe end is equipped with a solid wall spigot. But also jointing by butt-fusion, extrusion welding or simply by rubber gasket is possible. Your local Krah factory can provide you with all solutions.

  • How about chemical resistance?

    Polyethylene and Polypropylene are very resistant against many chemicals at certain temperatures. A brochure about this topic is for download available: “Chemical resistance of Krah pipes”

  • What is the stiffness of Krah manholes?

    The minimum stiffness is defined as SN2 in EN13598. Furthermore, all other stiffness classes can be manufactured if required and necessary.

  • What kind of fittings does the Krah system provide?

    Krah fittings are manufactured in the Krah factory. All necessary fittings and even customized design can be manufactured: bend, elbow, stub-end, flanges, reducers, T-branches, Y-branches etc. 

  • Is the load capacity of buckling pressure and inner pressure the same?

    No, it isn’t comparable! The inner pressure capacity mainly depends on waterway wall thickness and material strength. The buckling pressure capacity mainly depends on geometry (moment of inertia) and the flexural modulus.

  • Can Krah pipes resist inner pressure?

    Yes, due to the tailormade design any Krah pipe provides a certain solid waterway wall-thickness for the requested inside pressure.

  • How high is the vacuum / buckling pressure resistance of Krah pipes?

    Krah pipes provide a very high buckling pressure resistance due to their structured wall design. The bigger the pipe stiffness, the higher the buckling pressure resistance.

  • What is the most efficient manhole design for larger pipe diameters?

    The most efficient manhole design is the tangential manhole – its design is becoming more and more popular because it considers all the advantages in fabrication of Thermoplastics and helps to save costs!

  • What is the maximum size and height for Krah manholes?

    Typical Krah manholes are used in a maximum depth of 10-12 m. For bigger depths Krah recommends the telescopic manhole design which is used for landfill application as well. The biggest manhole diameter is DN/ID 5000 mm.

  • What is the installation speed of a Krah pipe?

    The installation speed of a Krah pipe is very high and a big cost-advantage for the contractor. Because of the Krah Electrofusion system the pipe strings can be installed in final position and be parallelly or later welded. That guarantees no time loss!

  • What is the welding time of Krah pipe Electrofusion?

    Krah designed the Electrofusion process to guarantee maximum quality at minimum of welding time. The welding time of Krah Electrofusion Joint is not more than ca. 20 minutes or any diameter.

  • Is it possible to recycle Krah pipes after usage?

    Krah pipes are made of Polyethylene (PE) or Polypropylene (PP) and can be recycled!  Important is cleaning and separation of the contents. Multitude of professional recycling companies are established world­wide. PE and PP are also after their first product life valuable resources.

  • How is the axial load capacity for Krah manholes?

    The axial load capacity has the same importance for the design of manholes as the stiffness.   Axial loads by direct load induction from the top or down drag forces get transferred and absorbed by the solid wall thickness. Krah manholes can be produced with any required solid wall thickness to fulfil a maximum of axial load capacity.

  • How is the fitness of purpose for potable water applications?

    Krah Pipes can be made of approved raw material for potable water application and fulfil all requirements. The high pressure-capacity and the homogeneously jointing method complete the fitness.

  • Why is the nominal diameter of Krah pipes an inner diameter and not outer diameter like with PE pipes?

    Krah pipes are calibrated to an inner diameter. The inner diameter is the important diameter for hydraulic aspects and general planning. The stiffness and pressure capacity can be adjusted without any change of the inner diameter.

  • Can Krah pipes be used for outfall and intake pipelines?

    Yes, Krah pipes are 100% applicable for marine applications and have a multitude of successful reference projects worldwide. Both Krah profiled wall pipes and Krah solid wall pipes can be used for outfall and intake pipelines. However, the profiled wall in combination with the Krah Electrofusion technology is mostly used.

    Notice: The Krah marine pipe profile provides a higher stiffness and buckling stability than normal solid walls. And also an axial strength is excellently given by using this special Krah profile!

  • Will Krah pipes float in the water?

    Yes, Krah pipes are made of Polyethylene and Polypropylene, and due to being slightly less dense than water, they will float even when they are full of water.

    For underwater anchored pipeline installations, it is important to specify the proper weights and distance of the weights. Whenever possible, an underwater pipeline should be installed in a trench with a protective crushed rock cover.

    Notice: Krah can support you with designing marine pipes!

  • Will sunlight adversely affect Krah pipes?

    Sunlight is not a concern if black PEHD material is used. Carbon black, utilized for black compounds, is the most effective ultraviolet stabilizer. Therefore, black is the recommended pipe colour for an exposed long-term service or storage. Krah pipes, made of a black PE pipe compound will provide decades of outdoor use!

  • How is the chemical resistance of Krah pipes against acid and lyes?

    Krah pipes and Polyethylene products in general have been successfully used for decades in the chemical industry for transport of chemicals as well as for storage tanks.

    Notice: Polyethylene has a very good chemical resistance against most acids and lyes!

  • What is the maximum recommended flow velocity for possible fluids going through Krah pipes?

    In a pumped system the maximum operating velocity is limited by the surge pressure capacity of the Krah pipe. If surge is not a consideration, water flow velocities exceeding 7,5 meters per second may be acceptable. This number can also be used as a maximum for gravity applications.

  • Some applications require explosion protection, especially in explosive gas atmosphere – how can Krah pipes avoid a static charge?

    Krah pipes can be made of electrical conductive Polyethylene for an anti-static behaviour. Mostly it is sufficient to produce the co-extruded inner or outer layer with electrical conductive Polyethylene!

  • Are Krah pipes applicable for landfill technology?

    Yes, Krah pipes provide a perfect chemical resistance against almost all hazardous media you will find in landfill application. Krah pipes are used for leachate drainage pipes, telescopic shafts for manholes, gas collectors etc.

  • Is thermal expansion and contraction of Krah pipes a problem?

    No. All pipes expand and contract with change of temperature. The key is the management of the resultant thermal strain. As with all materials, expansion and contraction must be taken into consideration when designing a HDPE piping system. However, for above ground applications thermal effects must be considered - the unrestrained coefficient of thermal expansion for HDPE pipe is 0,18 mm per meter and degree temperature change (mm/mK).

    Notice: Buried pipelines usually do not move due to soil friction, especially in the case of a Krah profiled wall structure!

  • Can Krah pipes also be used as tank shell for vertical installation?

    Yes, we make a difference between vertical and horizontal tank applications. Vertical tanks are mostly used for an industrial application like a storage tank for water or chemicals. For the design we provide the static software “PROFITank” which considers all load case scenarios (wind, sun, earthquake etc.). Horizontal tanks made of Krah pipes are either buried in the ground or installed on saddles!

  • Systematic drainage is important to avoid flooding and soil stabilization! How can Krah pipes be used for drainage?

    Krah Pipes for drainage application have already been used for decades. According to project requirements either slots or holes are implemented in the wall structure between the profiles. The holes/slots can be implemented at fully or partially circumference and can be covered by Geotextile ex work. Krah drainage pipes and manholes are available in all stiffness classes from DN/ID 300 until DN/ID 5000 mm.

Contact Us

  • Krah Group
  • +49 (27 41) - 97 64 0
  • info@krah.net
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