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Normally PE pipes according EN 253: 2009 and installed according this standard fulfil these requirements

6.4.6 Limit states for valves

Valves shall withstand the bending moments and axial forces occurring under normal operation conditions:

• From thermal expansion

• From soil settlements

The calculated values shall not exceed Table B.1 of prEN 488.

E) In expansion sections, bending moments can also occur in the stem or stem extension of the valve, if no special provisions are made. This is not acceptable. Due provisions to allow for the calculated displacement, such as casing pipes, foam cushions, etc. shall be applied as to prevent or minimize those bending moments, since the stem extensions of the valves are neither designed nor tested to withstand such bending moments.

Application rule

Installation of valves in expansion sections shall be avoided. However circumstances (e.g. installation in urban areas with intense underground infrastructure and limited space) may be such that installation in these sections cannot be avoided.

7 Installation

The installation shall be done:

1. in accordance with the installation plan and the system manufacturers' instructions,

2. in accordance with the design documentation so to ensure the adequate safety of fitters and other personnel on site as well as any third persons,

3. so that installation and operation do not harm to other structures or installations, e.g. roads; conversely, those structures and installations shall not be able to cause damage to the pipe system.

According to 4.4, project classes have been determined, thus also the required design documentation.

For the installation and assembly of pipes and components only materials and methods, which meet the specified instructions, regulations, and standards shall be used

Application rule:

Pipeline sections, which cannot be installed in compliance with this standard such as other than preinsulated pipe sections, e.g. bridge crossings, water course crossings, casing pipes should be installed by skilled personnel according to the project drawings and corresponding other standards, codes and regulations.

If changes are made during installation the design documentation shall be changed accordingly. The constructive and static consequences of any changes that may become necessary shall be examined.

Handling, transportation and storage of pipes and fittings, etc., shall take account of the properties of the different materials, the special instructions given by the manufacturer of this material and current external conditions in order to avoid that subjecting the components to harmful impacts and in order to avoid impurities, etc., in pipes and fittings.

Precautions shall be taken to avoid scratches and notches. The special conditions for PE casing pipes shall be taken into account during transportation and storage.

Adequately wide straps, according to the dimension in question, shall be used as lifting tools as well as adequate supports.

Application rule:

Steel pipe ends should remain sealed by means of end caps.

PUR foam should be protected against moisture e.g. by foam skin.

Due to the risk of brittle fracture, precautionary measures should be taken in the case of temperatures below 10 °С.

The pipe trench shall be excavated in accordance with the specifications for line routing and depth.

The width of the excavation is, among other things, determined by the requirement for sufficient room during the installation phase, e.g. welding chambers, manholes but also the possibility of compacting the backfill material around the system.

In soft soil areas (organic material and the like) special attention shall be paid to adapting the pipe excavation to a possible need for additional foundation.

Prior to installation and during the installation stage the floor of the trench shall be made level and the trench shall also be checked on position, height, width. Impurities, stones, etc., shall be removed.

Special attention shall be given to the installation of pipes and components room for movements in the trench enlargements shall be given to expansion legs, branches, etc.

Whenever pipes and components are handled, precautions shall be taken to avoid damaging the PE casing.

The pipes shall be placed on a sand layer or corresponding foundation, see 7.8.

Application rule:

Sand sacks, styrene supports or sleepers can be used. If sleepers are used, attention shall be paid to any unallowable surface pressure on the PE casing pipe. Sleepers shall be removed prior to pre-stressing of the pipeline and backfilling.

If pipes are to be cut, this shall usually be done perpendicular to the pipe axis. Preinsulated fittings shall be shortened only according to manufacturers' instructions.

The distance between the casing pipes, of parallel laying pipes, shall be minimum 0,15 m or in accordance with the installation plans.

Steel pipes shall be assembled and steel welds tested according to 7.5, and the pressure test and/or tightness test of the pipeline shall be performed according to 7.6.

The joint installation shall be performed in accordance with the specifications given in 7.7.

Branches, compensators, valves, venting and draining arrangements and special components shall be installed according to their specifications.

Expansion cushions, if specified, shall be installed as prescribed.

In case the pipe system is thermally pre-stressed, temperature and expansion movements shall be checked.

The pre-stressing temperature shall be maintained until the trench has been completely backfilled unless otherwise specified. The design temperature shall not be exceeded during pre-stressing in order to avoid damage to the PUR foam.

It shall be ensured that the mechanical forces do not damage the pipe parts during mechanical pre-stressing.

This clause defines the minimum requirements for welding and testing of steel pipe joints used in district heating systems related to the 3 project classes.

Application rule:

Additional requirements may be specified in the installation plan when any of the following are considered critical:

• the strain on pipelines and systems,

• the line routing,

• the design or the welding technique,

• the materials.

The steel pipe standards specified in EN 253 are EN 10216-2, EN 10217-2 and EN 10217-5. The steel grades in these standards are in Group 1 of ISO/TR 15608:2000 for welding purposes. Other material groups may be used, but the requirements will need to be changed accordingly.

Fittings and other steel components should be made of steels grades that are compatible with the straight pipe and for welding should be in Group 1 of ISO/TR 15608:2000.

The welding contractor as mentioned in 7.5.2 can be a contractor, a welder, the owner or any organisation or person responsible for the welding part of a project.

The relation between project classes and quality demands is provided in Table 9; the table gives an overview, more details can be found in the text.

Application rule:

The quality requirements include the following aspects in the construction of the systems:

1. The contractor’s organisation/ personnel:

1. welder(s),

2. supervisor personnel,

3. testing personnel.

2. Welding procedures:

1. specification,

2. welding method,

3. material,

4. consumables,

5. execution of the work.

3. Level of testing:

1. percentage of non destructive testing,

2. destructive testing or other tests.

The quality requirements to be fulfilled by the contractors depend on project class applying to the project under construction. The quality level with specific areas of activity assigned to each class can be seen in Table 9, Section 1. Each quality level category includes the requirements of the lower one(s), as applicable.

Table 9 — Relation project classes and quality

X Requirement R Recommended

The use of particular method of a welding procedure is often a mandatory requirement of an application standard. In absence of such a requirement the method of approval shall be agreed between the contracting parties at inquiry or at the order stage.

The welders shall be qualified in accordance with EN 287-1 for the techniques, material groups, dimension ranges and welding position concerned. Welding personnel operating mechanised welding equipment shall be qualified in accordance with EN 1418.

Application rule:

Welders should always have a valid certificate according to EN 287-1.

Welding co-ordination personnel shall be responsible for all welding and testing. Depending on the project class, these persons shall possess a qualification to EN ISO 14731:2006 appropriate to the relevant quality requirement of EN ISO 3834 as shown in Table 9 section 1 and 2.

Destructive testing and non-destructive examination personnel shall be employed either by the pipeline contractor or by the pipeline operator or by an independent testing company. It is assumed that all NDT testing are performed by qualified and capable personnel.

Application rule:

In order to prove this qualification, it is recommended to certify the personnel in accordance with EN 473.

Welding procedure shall be specified in accordance with Subclause 4 of EN ISO 15607:2003 and approved in accordance with 4.1.1 of EN ISO 15607:2003 and the Table 9.

All types of fusion welding are acceptable, but for pipes with t > 3 mm arc welding with covered electrodes and gas shielded metal-arc welding are preferred.

Welding consumables shall be of such a quality that the welds have mechanical characteristics at least equivalent with the parent metal.

Welding consumables have to fit the basic material, the welding procedure and welding conditions.

Electrodes shall be in accordance with the relevant European Standard and be accompanied by a document E) type 3.1 <3 in accordance with EN 10204.

After electrodes have been removed from their original package, they shall be protected or stored in accordance with the manufacturer's requirements so that their characteristics or welding properties are not affected.

Weld joints, in particular tie-ins, shall be arranged and designed in a way suited to the planned welding and testing technique. The placement of tie-in welds is particularly important.

The choice of joint configuration shall take into account the welding technique, the welding position and the accessibility of the weld seam.

Application rule:

Attention should be paid to movement due to temperature changes during welding.

Joint edge preparations shall be selected from EN ISO 9692-2 except that for joints between sections of different wall thickness Figure 8 shall apply.

For the different values of the possible misalignment and difference in wall thickness Table 10 shall apply.

Minor differences in pipe end measurements are to be distributed evenly over the entire circumference by centring of the pipes.

Table 10 — Adaptation of misalignment and difference in wall thickness

For small axial angular deviations in the welding joint between straight pipeline elements such as pipes, reducers and tees the maximum allowable values of Table C.4 apply.

Application rule:

These angular deviations can be necessary in the field to adjust the pipe route without the use of prefabricated smooth bends pipes.

Before tack welding the pipe ends are to be centred with tools, which at the same time correct ovalities.

During welding the pipes must be guided to achieve the best possible alignment of the centre lines and inner surfaces.

Figure 8 — Misalignment, difference in wall thickness and joint end preparation

Pipes, pipeline parts and other components which require marking shall be re-stamped or remarked next to the cutting line prior to cutting.

Application rule:

Marking only applies to the higher project classes if full traceability is required.

The seam spacing shall be such that the heat-affected zones do not overlap or interact, the absolute minimum spacing is 3,5 times the wall thickness.

Application rule:

A spacing of 100 mm or more is recommended.

7.5.Є.4 Interaction of longitudinal seams

Longitudinal seams or spiral seams shall be staggered by a distance of 10 times the wall thickness with a minimum of 50 mm.

7.5.Є.5 Welds with more than one pass

There shall be a minimum distance of 30 mm between the start and the stop positions of the passes.

7.5.Є.6 Execution of the welding (welding action)

The area 50 mm back from the weld on both sides of the joint shall be kept free of dust, dirt, grease and water, and protected against wind and rain.

At temperatures below 5 °С and in the event of high air humidity, the weld seam areas shall be heated to avoid condensation.

Arc strikes on the pipe surface shall be avoided. If arc strikes occur repair shall be removed by grinding.

Application rule:

To avoid potentially damaging air movements within the pipe, at least one end of the pipe should be sealed off during welding in the open air.

7.5.6.7 Actions after welding

After the weld is completed, weld spatter shall be removed. The weld surface shall be cleaned of slag. The cooling process shall not be accelerated.

Application rule:

At air temperatures below 5°C, and if the pipeline owner requires it, the weld seam should be protected against excessively rapid cooling.

7.5.Є.8 Repair of weld failures (defects)

Weld seams, which do not meet the specified requirements, shall be repaired or cut out.

Repairs shall be carried out in accordance with an approved welding procedure.

When the defect is a crack this shall only be repaired if the cause of cracking is clearly established and can be shown to be repairable.

Before special procedures are carried out, the type and scope of the weld joint shall be specified. The testing technique used will depend on the type and accessibility of the weld joints.

Structural parts shall be attached using a continuous weld. Intermittent welds shall not be acceptable.

Welding work on pressurised pipelines and systems shall only be carried out according to safe and proven procedures to ensure the correct mechanical properties of the weld and the safety of the working crew.

Seam weld quality shall be checked using the systems and personnel in accordance with Table 9 and the standards in Table 11 to show compliance with the requirements in Table 12 and if required Table 13.

Welded joints are divided into inspection section is such a way that for joints in the same section there will be no circumstances which may cause differences in quality.

Application rule:

Examples of welded joints, which should be referred to different inspection sections, are welds with difference in base material, welding process, welder or weather conditions during welding.

NDT of welds in pipelines is generally done by radiography. Alternatively, when agreed by the owner and in particular cases where this method is unable to give adequate information on the quality of the weld, radiographic examination should be supplemented or replaced by ultrasonic examination.

Weld seam examination shall be carried out in accordance with one or more of the standards shown in Table 11 unless another NDT method is required dependent on the material, design and/or welding technique.

Table 11 — NDT weld seam examination

Table 12 — Inspection and test requirements for seam weld quality of site welds