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Engineering
Civil and Structural Engineering

Assessment of supporting structures of pipelines

Profile image of Attila VardaiAttila Vardai

2019, fib Symposium Proceedings- Krakow

Abstract

The paper introduces the assessment of almost 1 500 above-ground supporting structures of the largest district heating pipeline of Hungary. As most of the district heating system in Hungary (and in middle-Europe) was established nearly 50 years ago, the majority of current structural hazards are related to the age and actual condition of the system-components. Every single structure of the investigated pipeline has been individually assessed and evaluated within a recent project, in accordance with the national regulations for existing structures. The discovered, typical problems are introduced in this paper and also the recommendations for necessary actions to keep/improve the performance of the supports are presented. Based on the collected information of the one-by-one inspection of the structures the possible risks and mitigation measures have been identified as well and general recommendations have been established in order to define the necessary maintenance actions and to set up the schedule of regular inspections for future operation.

Figures (10)
The expert investigations, following the event discovered progressed corrosion of the embedded elements and especially of the welding of the anchoring steel bars. It was also concluded, that the actual throat thickness of the weld was significantly less than planned and therefore, after nearly a half century of operation the connection failed, and the steel beams fell off from their position, leading to the collapse of the entire pipe- -section. lt nh ee, fF a | 1.2. Accident
The expert investigations, following the event discovered progressed corrosion of the embedded elements and especially of the welding of the anchoring steel bars. It was also concluded, that the actual throat thickness of the weld was significantly less than planned and therefore, after nearly a half century of operation the connection failed, and the steel beams fell off from their position, leading to the collapse of the entire pipe- -section. lt nh ee, fF a | 1.2. Accident
Figure 2. Sketch of typical supporting structures.
Figure 2. Sketch of typical supporting structures.
The forces of the pipeline are highly influenced by the possible pipe-movements. Various types of pipe supports were used in the network to allow the axial (and lateral) displacement of the pipes (Fig. 3.). Figure 3. Sketch of typical pipe supports.
The forces of the pipeline are highly influenced by the possible pipe-movements. Various types of pipe supports were used in the network to allow the axial (and lateral) displacement of the pipes (Fig. 3.). Figure 3. Sketch of typical pipe supports.
Figure 4. Fractured welds and corroded steel sliding surface.
Figure 4. Fractured welds and corroded steel sliding surface.
It must be highlighted, that the small gaps of the ball-basket (and especially the gaps at guided supports) were commonly filled with dense dirt and created highly corrosive environment. Figure 5. Partially displaced and corroded ball-baskets. In TYPE-B supports, on steel balls normally only slight surface corrosion was visible; however, the steel ball-basket was often rusty and directly in contact with the pipe-shoe, or column-head. In extreme cases, the pipe-shoe was partially displaced from the supporting structure (Fig. 5.).
It must be highlighted, that the small gaps of the ball-basket (and especially the gaps at guided supports) were commonly filled with dense dirt and created highly corrosive environment. Figure 5. Partially displaced and corroded ball-baskets. In TYPE-B supports, on steel balls normally only slight surface corrosion was visible; however, the steel ball-basket was often rusty and directly in contact with the pipe-shoe, or column-head. In extreme cases, the pipe-shoe was partially displaced from the supporting structure (Fig. 5.).
The values of Veszelak (1985) represent the input data for the design of the investigated pipe- network. The displayed coefficients of Korach (1978) are based on the experiments of the Hungarian Steel Research Institute (Vasipari Kutat6é Intézet), in 1973. Table |. Friction-coefficients for sliding and roller connections.
The values of Veszelak (1985) represent the input data for the design of the investigated pipe- network. The displayed coefficients of Korach (1978) are based on the experiments of the Hungarian Steel Research Institute (Vasipari Kutat6é Intézet), in 1973. Table |. Friction-coefficients for sliding and roller connections.
The spring supports (TYPE-C) were almost in all cases highly corroded and significantly deformed (Fig. 6.). It can be concluded that the required elasticity (springs-stiffness) ) for the pipes is not available. Figure 6. Corroded spring supports.
The spring supports (TYPE-C) were almost in all cases highly corroded and significantly deformed (Fig. 6.). It can be concluded that the required elasticity (springs-stiffness) ) for the pipes is not available. Figure 6. Corroded spring supports.
Table 2. Computed bending moments of RC columns with good sliding properties (adequate SS sliding plate). Table 3. Computed bending moments of RC columns, assuming CS sliding plate.
Table 2. Computed bending moments of RC columns with good sliding properties (adequate SS sliding plate). Table 3. Computed bending moments of RC columns, assuming CS sliding plate.
Table 4. Computed bending moments of RC columns, assuming corroded CS sliding plate.
Table 4. Computed bending moments of RC columns, assuming corroded CS sliding plate.
The tables above clearly show, that in case of adequate frictional properties of the connections, all investigated cases can be considered acceptable. However, depending on the level of deterioration of connections (increasing frictional resistance) more calculation results shall be considered unacceptable. We must remark that in some cases notable difference in the friction (and horizontal force afterward)
The tables above clearly show, that in case of adequate frictional properties of the connections, all investigated cases can be considered acceptable. However, depending on the level of deterioration of connections (increasing frictional resistance) more calculation results shall be considered unacceptable. We must remark that in some cases notable difference in the friction (and horizontal force afterward)

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References (12)

  1. Span length-L 0 [m] Bending moments at column-foot-M Ed [kNm] References EN 1337-1:2002, Structural bearings-Part 1: General design rules. EN 13480-3:2018, Metallic industrial piping-Part 3: Design and calculation. e-UT 07.03.11:2003, Bridge Accessories 1: Bearings and Expansion Structures of Highway Bridges. (in Hungarian)
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