Ductile cast iron pipes must be installed in such way that the external protection is not damaged. Due to the socket design, the pipe joint represents a particularly sensitive area in this connection.

DVGW GW 321 [HDD-15] stipulates that, for the joint areas, heat-shrinking sleeves (shrinking material) according to DIN 30672 [HDD-333] (see (Pipe joints)) or rubber sleeves should be used as suitable external joint protection. In all cases, these external …

Against internal corrosion as a consequence of aggressive water and biogenic sulphuric acid corrosion (BSC, see [HDD-43]), ductile cast iron pipes and fittings are standard protected with factory-made cement mortar linings.

Furthermore, cement mortar lining serves the purpose of preventing an impact on the quality of drinking water by corrosion products [HDD-410].

For the inner surface of water pipelines, for example, the cement mortar lining according …

Ductile cast iron is a ductile iron-carbon material whose carbon content predominantly consists of graphite in free form. Ductile cast iron mainly differs from the grey cast iron, which is nowadays no longer used for buried supply and discharge lines, in the shape of graphite particles [HDD-379]. Grey cast iron contains lamellar graphite, whereas ductile cast iron contains graphite spheres or spheroidal graphite. The shape of graphite mainly influences …

Polyethylene (PE) belongs to the group of semi-crystalline thermoplastics (polyolefin). It is marked by a high degree of flexibility and ductility also at low temperatures [HDD-415] [HDD-416].

PE is resistant to acids, alkalis and weak solvents. It is not resistant to oxidising acids and halogens. Further information in this respect is contained in the Addendum to DIN 8075 [HDD-417].

For PE-pipes, which are used in HDD, the following standards apply:

For the connection of PE-pipes, generally the following welding techniques can be used:

• heated coil socket welding,
• extrusion welding,
• heated tool or butt fusion welding.

In heated coil socket welding, electric welding fittings with integrated resistance wires are used for creating a pipe joint. They are electrically charged during welding (Figure 238). Pulling-in the pipe string that is welded by means of heated coil sockets without causing destruction …

According to DVGW GW 321 [HDD-15] with reference to DVS 2207-1 [HDD-435] and/or ASTM D3261-03 [HDD-436] and ASTM D2657-03 [HDD-437], PE 80 and PE 100-pipes for use in HDD must be connected by heated tool or butt fusion welding (Figure 240) [HDD-438].

In this welding technique, the connection surfaces of the pipes to be welded are heated under pressure at the heating element and are connected after removing the heating element (Figure 239 and Figure …

The following devices and materials are necessary for heated tool or butt fusion welding (Figure 241) [HDD-439] [HDD-440]:

• welding slide,
• hydraulic power unit,
• insertion shoulders for different pipe diameters,
• facer,
• heating element with control unit,
• cleaning tissues and ethyl alcohol,
• data recording device with outside temperature sensor, pressure sensor, etc.

For heated tool or butt fusion welding, only trained staff with a valid welder …

The following preparatory works must be completed before starting the welding:

• checking the roundness of the pipes and adjusting if necessary,
• clamping the pipe ends axially into the welding slide,
• pipe ends are “faced” with a machining tool to establish clean, parallel mating surfaces, perpendicular to the centreline of each pipe,
• checking the plane parallelism and displaced joints and adjusting, if necessary,
• cleaning the heating element,
• …

The following working steps are necessary:

• adjusting (Figure 242a),
• heating (Figure 242b),
• relocating (Figure 242c),
• joining (Figure 242d).

The pressures and times that must be observed for the welding process must be taken from the information by the manufacturer (see e.g. Table 79).

(Table: Table 79: Guideline values for heated tool or butt fusion welding of PE-pipes and fittings at an atmospheric temperature of around 20 °C (68°F) and moderate …

(Image: Working steps for PE-welding with corresponding temperature diagram – Joining)Welding works must be monitored. The type and extent must be arranged between the contract partners. It is recommended to document the process data in welding protocols or on data storage media [HDD-435] [HDD-441].

The welding protocol must contain the following data (cf. also diagram in Figure 242 d):

• melting temperature,
• melting time,
• jointing pressure.

The developing outer and inner welding seams, also called welding beads, are removed with corresponding devices (Figure 243a and b), where required.

(Image: Testing the welding seam by means of nondestructive ultrasonic inspection using the example of detecting a lack of fusion in the joint gap section – Sketch) (Image: Testing the welding seam by means of nondestructive ultrasonic inspection using the example of detecting a lack of fusion in the …

According to DVGW GW 321 [HDD-15] with reference to DVS 2207-1 [HDD-435] and/or ASTM D3261-03 [HDD-436] and ASTM D2657-03 [HDD-437], PE 80 and PE 100-pipes for use in HDD must be connected by heated tool or butt fusion welding (Figure 240) [HDD-438].

In this welding technique, the connection surfaces of the pipes to be welded are heated under pressure at the heating element and are connected after removing the heating element (Figure 239 and Figure …

The destruction-free check of the welding seam can be carried out in three ways according to EN 13100 [HDD-442]:

• visual inspection,
• X-ray testing,
• ultra-sonic testing.

Visual inspection checks butt welds according to the following criteria (Figure 243 a):

• The welding beads have to be equally round and clearly visible.
• All beads are supposed to be of equal size approximately.
• The bead surfaces have to be smooth.
• The beads are supposed to be free …

For the connection of PE-pipes, generally the following welding techniques can be used:

• heated coil socket welding,
• extrusion welding,
• heated tool or butt fusion welding.

In heated coil socket welding, electric welding fittings with integrated resistance wires are used for creating a pipe joint. They are electrically charged during welding (Figure 238). Pulling-in the pipe string that is welded by means of heated coil sockets without causing destruction …

If, due to the soil conditions, impermissible mechanical stress of the pipes or damage to the pipe surface (e.g. scratches, point loads and grooves) is expected (which can always be assumed when directly pullingin the pipe string into the borehole) according to [HDD-15], an additional external pipe protection must be used for PE 80- and PE 100-pipes.

In order to ensure its protective effects, the outer protective layer must comprise at least 10% of …

(Image: PE 100-pipe with dimensionally added protective coating of minerally reinforced PP of the type egeplast SLM®2.0 (SLM – Safety-Line® host pipe))In order to produce pipes with dimensionally added protective coating, according to DIN 8074 [HDD-431] and DIN 8075 [HDD-417], standard pipes of PE 80 or PE 100 (so-called core pipes) are, in a second production step, separately coated with another material such as mineral reinforced polypropylene …

In pipes with dimensionally integrated protective layer (also called coextruded pipes), the PE-pipes are inseparably connected with a protective layer, e.g. silane cross-linked polyethylene (PEX-b), to improve the material properties (increased strength values by increases to the yield stress and reduction of the ultimate strain) so that the outer diameter to DIN 8074 [HDD-431] can be adhered to [HDD-445].

It is differentiated between coextruded two-…

If, due to the soil conditions, impermissible mechanical stress of the pipes or damage to the pipe surface (e.g. scratches, point loads and grooves) is expected (which can always be assumed when directly pullingin the pipe string into the borehole) according to [HDD-15], an additional external pipe protection must be used for PE 80- and PE 100-pipes.

In order to ensure its protective effects, the outer protective layer must comprise at least 10% of …

Polyethylene (PE) belongs to the group of semi-crystalline thermoplastics (polyolefin). It is marked by a high degree of flexibility and ductility also at low temperatures [HDD-415] [HDD-416].

PE is resistant to acids, alkalis and weak solvents. It is not resistant to oxidising acids and halogens. Further information in this respect is contained in the Addendum to DIN 8075 [HDD-417].

For PE-pipes, which are used in HDD, the following standards apply:

PVC-U (polyvinylchloride free of plasticizer or unplasticised) belongs to the thermoplastic group. It is a polymer of vinyl chloride, which is made of ethylene (crude oil or natural gas) and chlorine (of NaCl) and to which thermal stabilizers and lubricants are added for pipe production [HDD-429]. Besides the hardness and form stability, a characteristic property of PVC-U is the high degree of resistance to acids, alkalis, alcohols, oils, fats, aliphatic …

The restrained joint of PVC-U pipes can be achieved by means of a socket, weld or glued connection (see (Type and design of the joints)). The latter variant is not used for HDD applications, because professionally completed glued connections require around 12 hours to harden completely and to be able to reliably bear longitudinal forces resulting from the pulling-in of the pipe [HDD-465].

The restrained joint of PVC-U jacking pipes is achieved by means of a special, rigid or flexible plugin socket joint, in which a mechanism prevents the joint from being pulled apart.

The restrained joint in its rigid variant can be of two types, for example, with the manufacturer CertainTeed [HDD-469] (see (Restrained socket or spigot joints)):

• Joining of both plug-in ends with a coupling, where a milled groove each in the outer wall at the plug-in …

For creating welded joints with PVC-U pipes, heated tool or butt fusion welding is used (Figure 254a and b). The welding process principally resembles that of PE-pipes (see (Heated tool or butt fusion welding)), however, there are essential differences regarding welding temperature, jointing pressure and duration of the single steps [HDD-472].

(Image: Creation of a pipe joint for PVC-U-pipes (12’’, SDR-18, type Fusible C900™) by means of heated element …

The restrained joint of PVC-U pipes can be achieved by means of a socket, weld or glued connection (see (Type and design of the joints)). The latter variant is not used for HDD applications, because professionally completed glued connections require around 12 hours to harden completely and to be able to reliably bear longitudinal forces resulting from the pulling-in of the pipe [HDD-465].