PTQ Q4 2022 Issue

Piperacks Steel piperacks are used in the sulphur recovery unit to support piping, electrical cable trays, and mechanical equipment. Figure 7a shows a structural plan of the pri- mary steel members. The hatched areas represent the plat- forms required for the maintenance crew. Figure 2b shows the structural elevation ‘A-A’ between gridlines 1-9. The piperack segments are connected by platforms at elevation (z =6m,15m). The piperack was divided into four prefab- ricated modules (M1 to M4). Pipes and cable trays were installed in the fabrication yard in these modules and trans- ported to the site using trailers. The envelopes of these modules are identified by the dashed rectangles, as shown in Figure 7b . Note that the width of all modules is fixed (at W=6m). The height of the stick-built part is 7m. The V-bracing pattern is altered on the first level to maximise the access area required for maintenance vehicles. The piperack modules were designed for erection, opera- tion, testing, and transportation load conditions. Equipment dead loads included equipment weight, insulation, fireproof - ing, permanent fixtures, and attachments. Cable tray weight was approximated using linear load distribution along sup - porting beam spans. The piperack was modelled using 992 beam elements with total degrees of freedom (DOF = 3,420). The maximum beam vertical and horizontal reactions were computed as (B V =720 kN) and (B H =224 kN). The maximum beam vertical deflections were computed as ( δ max = 19mm). The allowable beam vertical deflection was ( δ v =20 mm), with the maximum piperack sway deflection at ( δ H =76 mm). The sway deflection was limited to 100 mm. The maximum SLS utilisation ratio was found as (UI SLS =0.74) and (UI ULS = 0.68). The maximum SLS column reaction for the piperack was found as (P max =762 kN), maximum shear reaction (Q max =145 kN) and (T max =160 kN) maximum tensile force. The maximum ULS column reactions are (P max =925 kN), (Q max =224 kN) and (T max =200 kN). The piperack columns were supported using 18 isolated piles. Circular concrete pedestals were projected from the pile cut-off elevation to the column base plates. Conclusions Existing methodologies overlook critical structural issues and focus on the process and mechanical design aspects. This article provided economical structural strategies that can be used to design sulphur recovery units (SRU). Simplified structural models are proposed to approximate load transfer in the support system.

Hot gas inlet

Cold gas outlet

Sliding saddle

Fixed saddle

Boiler feed water

(a) Elevation

AS1

AS2

Saddle wall

AS3

(b) Section B-B

AS4

Figure 6 ISS geometric details

tube bundle is used in this model. The boiler feedwater inlets are located at the lower portion of the vessel. The hot gas inlet is located at the rear end, and the cold gas outlet is located at the front end. The vessel is installed at a 1% slope toward the outlet to facilitate sulphur drainage. In this model, the fixed saddle is anchored to the con - crete wall support using four anchor rods. Teflon coating is bonded on the rear side of the sliding base plate to reduce the friction forces during operation. Figure 6 shows details of section B-B as a support base for the walls. Each wall is supported independently using rectangular pile-caps, shown as hatched rectangles. The saddle walls using this model are centred with the pile cap. Service ladders and platforms are connected to the ves- sel to support piping, electrical cable trays, and mechanical equipment. During operation, the vessel undergoes in- plane translation and rotation around the vertical axis. As a result, the rear support restrains the motion, while the front support allows the vessel to slide.

Frame support (FS)

5 6 7

5 m

PF4

PF3

4 m

4 m 6 m

6m 6m 6m 6m

6 m

PF4 PF4

PF3 PF5

5 m

PF3

PF4

6 m

PF2

Stick built

PF1

6 m

Segment (1)

Segment (2)

(a) Plan

(b) Elevation

Figure 7 Structural model of piperack

PTQ Q4 2022