Haus Düsse

1. Which concrete tank was lined?

The secondary digester at the Haus Düsse biogas plant was lined. The cast-in-situ concrete tank has a working volume of 1,000 m³.

Tank data

Tank function

Secondary digester

Construction

Cast-in-situ concrete

Internal diameter

16 m

Wall height

6 m

Working volume

1,000 m³

Lined area

262 m²

The plant also includes a primary digester with a working volume of 1,000 m³ and a digestate storage tank with a capacity of 2,100 m³. Neither of these tanks was included in the work described here.

2. What work was required on the existing tank?

The existing concrete was to be protected from the aggressive conditions inside the tank by a continuous plastic lining. The work covered the wall surfaces and the interfaces with existing fittings.

Initial condition

Damage to the concrete surface was visible around some existing connections. Photo 08 shows the condition around a circular opening before the new connection panel was installed. Some adjacent penetrations were closely spaced and differed in size.

Technical requirements

The protective barrier had to remain continuous around openings, pipe penetrations and fixings. This required connection pieces tailored to the existing components and welded transitions to the wall lining.

3. Which areas were actually lined?

The lined area totals 262 m². The work covered wall surfaces and the associated connections around openings, pipe penetrations and existing fittings.

Lined surfaces

The sheets follow the curvature of the tank wall and are arranged in several rows. Photos 01 to 04 show the lining from four directions. A strip of exposed wall below the lining is visible in the photographs.

Connections and penetrations

The existing manhole opening and several other openings and pipe penetrations were integrated into the wall lining, particularly in the upper part of the wall. Individual connection panels were cut to fit the different shapes and dimensions.

4. How was the work prepared and carried out?

The lining was installed using 2 mm thick PP-H sheets and 1.5 mm thick FPP cover strips. It was cut to size, mechanically fixed and welded on site.

Preparation

Cleaning with a conventional pressure washer was sufficient to prepare the surface. No further treatment by high-pressure water jetting or sandblasting was required.

Installation sequence

The PP-H sheets were cut to suit the tank geometry and mechanically anchored to the concrete. The joints and fixing areas were covered with FPP strips, which were welded to the sheets. At existing openings and pipe penetrations, the fitted connection pieces were welded to the wall lining.

5. Fixings and connections

Mechanical anchorage secures the lining to the structure. Welded covers protect the fixings from the environment inside the tank.

Mechanical fixing

The plastic sheets were anchored to the existing concrete. The fixing points are located in areas that were subsequently covered with welded plastic strips.

Covering the metal components

The metal fixings for the lining are covered by thermoplastic strips. These were welded to the lining along their edges, isolating the fixings beneath them from the tank environment.

Special connection details

The manhole opening and existing pipe penetrations were integrated into the lining using fitted connection pieces. At the closely spaced openings in the upper wall, individual connection panels were installed first and then joined to the wall lining using welded cover strips.

6. Welded joints

The sheets, cover strips and connection pieces were welded together on site to form a continuous protective barrier.

Welding process used

[Insert documented procedures and materials.]

Inspection

Hot-gas overlap welding produces durable, leak-tight joints between the lining sheets, the covers over the fixings and the custom-fitted connection pieces.

DVS Technical Code 2207-3 (12/2019)

8. What does this case study demonstrate technically?

The project demonstrates how an existing concrete tank can be retrofitted with mechanically fixed and welded plastic sheets.

The installation was adapted to the existing tank geometry, the manhole opening and the different arrangements of penetrations. The detailed photographs show how the individual connection panels and the wall lining were joined to form a continuous protective barrier.

The project illustrates how an existing tank can be fitted with a separate protective lining without rebuilding the concrete structure.

9. What determines long-term protection?

The chemical resistance of the plastic sheets alone is not sufficient. The protective barrier must also remain continuous at welds, fixing points and connections.

Leaks at connections can allow aggressive liquids to penetrate behind the lining and attack the concrete and fixings. Covering the fixings and sealing the penetrations are therefore just as important as lining the wall surfaces.

If additional connections are installed or existing components are modified at a later date, the affected areas must be sealed and integrated back into the lining.