By Joseph Hickson, Steve Neher and Norm Koontz, WorleyParsons
In late 2001, Santee Cooper began a project to add a third 600 MW unit to its Cross Generating Station in Cross, S.C. Plans also included a fourth unit to be added later. The engineering, procurement and construction of Units 3 and 4 would eventually span almost seven years. The Cross Project demonstrates how Santee Cooper empowered its EPCM contractor to manage for change and how a well conceived plan and thoroughly developed schedule provide the necessary structure and flexibility to successfully do so. The Cross Project experience reinforces the idea that for large projects an EPCM arrangement provides the agility necessary to manage change and the means to manage risk.
Santee Cooper long ago determined that direct competitive procurement of major plant equipment provides savings in supplier pricing and elimination of contractor markup. Procurement management of the EPCM arrangement allows facile integration and coordination of purchasing scopes and schedules to match the evolution of the integrated project schedule. The EPCM format as executed at Santee Cooper’s Cross projects over the last 25 years consists of a close owner-engineer team, where the engineer is also the procurement, construction and startup manager. In that capacity, the engineer provides the overall project schedule and then dictates and integrates the schedules for all of the fixed-price, lump sum supply and erection contracts. The engineer develops all contract packages, bids, evaluates and recommends contract awards to the owner. The owner issues all purchase orders on its paper and assumes the contract risks (which are mitigated by careful early planning, timing and selection of contract scopes) and 80 percent engineering completion at erection contract bid request. The design, furnish and erect contracts (boiler/selective catalytic reduction, precipitator, flue gas desulphurization, cooling tower and chimney) were performance based contracts executed early to firm up the plant design and layout.
Project Development and Background
For EPCM to work, Santee Cooper and WorleyParsons are organized and operate as one coordinated team in all development, analysis and execution phases of the project. This was central to all that followed.
Santee Cooper is a knowledgeable client whose executive management and project staff both have extensive experience in project development, engineering, construction, startup and operations garnered from projects which began in the 1970’s. WorleyParsons’ offices in Reading, Penn. evolved from legacy companies Gilbert Associates, Gilbert Commonwealth and CT Main.
After Unit 3 boiler hydro work, major material movements would cease and the ringer crane could be removed. The Unit 4 foundations could then be released for steel erection. Photo courtesy WorleyParsons. Click here to enlarge image
When site excavation began, the Santee Cooper project manager and staff relocated to the Cross site office with the first WorleyParsons construction staff. Weekly team coordination meetings between engineering offices in Pennsylvania and the Santee Cooper offices in South Carolina began with video conferencing in lieu of face to face meetings. In 2002, that evolved to digital collaboration, as normal practice for scheduling, procurement, engineering and 3D design model reviews via a direct high band width dedicated data line. Project document management used WorleyParsons’ Encompass system. All documents were accessible in both locations over dedicated data lines. Project procedures capitalized on electronic transmission and review processes for all documents coordinating engineering reviews in Reading and constructability reviews in Cross.
Each of the 69 Unit 3 contracts and 59 Unit 4 contracts were assigned to a responsible engineer and procurement member from each organization. Those individuals were personally responsible for managing all commercial and technical elements of their respective contracts.
The project used one master CPM schedule comprising engineering, procurement, construction and startup. Initial Level I and Level II schedule development was based on the client’s target completion date. As part of request for proposal for initial major contracts, engineering deliverables, construction and start-up schedule requirements were included based on the project CPM schedule. As the boiler, turbine, precipitator and scrubber were being purchased, proposal schedules were analyzed for compliance with the initial schedule. To determine lead times for vendor engineering deliverables, fabrication and delivery of other key equipment market inquiries were developed. The information obtained from these and the initial major contract proposals were used in finalizing the Level III CPM schedule. As a starting target, the initial project schedule had been shortened by six months early in the project planning stage. After factoring in vendor design deliverables, market lead times for major equipment and commodities, site layout, master construction plan, and startup systems sequencing, the target completion date was extended by eight months for a net increase of two months over the original schedule.
The first six months of the project were dedicated to preliminary engineering and determining major plant configuration. Studies evaluated sub- and supercritical boiler cycles, steam path alloys, FGD process alternatives, bag house/precipitator, foundations concept and so on. As a result, Cross Units 3 and 4 comprise pulverized coal fired drum boilers, single reheat steam turbines, dual pressure water cooled condensers, electrostatic precipitators, wet limestone flue gas desulphurization and concrete circular mechanical draft cooling towers.
The first challenge to the project plan involved impacts to insurance and financial securities following Sept. 11, 2001 events. This translated into increased schedule durations for contract awards. The next challenge followed shortly after design work began, when the state of South Carolina promulgated a law mandating immediate implementation of the new international building code, IBC 2000. Cross Station is in a seismic zone 1 and is an area frequently and recently affected by hurricanes. Research determined that IBC 2000 mandated design changes for both cases. Higher hurricane wind design speeds affected structural design, but not schedule.
Seismic requirements, however, caused impacts to engineering/design, construction planning and schedule. In a departure from prior designs, a plan was engineered to install densely driven concrete piles and thick slab foundations. This plan generated reduction in construction schedule of two months and cost savings exceeding $6 million.
Excavation and dewatering began in October 2002, piling in November and foundations in 2003. Construction was suspended in June 2003 until permit details could be finalized. When construction resumed with foundation work for Unit 3, Santee Cooper directed the team to evaluate proceeding with parallel construction of Unit 4. A construction plan and schedule were developed based upon temporarily relocating Unit 3 construction access and accelerated installation of Unit 4 foundations to be completed and covered prior to Unit 3 drum transport for lift. Later during construction, that plan and schedule were further accelerated.
Unit 3 Construction Plan
Unit 3 construction started in the fall of 2002 with the preparation of the site facilities. This contract included clearing 35 acres of woodlands for additional laydown space, building and stoning access roads, installation of construction power systems, phones, and potable water and site fencing and reconfiguration. The site was deliberately arranged to separate the on-going plant operations and traffic from the construction site.
Work on the turbine building structure had to wait until the coal silo bay was completely erected and the crane removed. Photo courtesy WorleyParsons. Click here to enlarge image
In November 2002, the piling contractor mobilized and started with the chimney foundation and then the boiler areas. The piling contractor’s work was divided into areas sequenced to support the project’s critical paths (chimney, boiler, turbine, precipitator and FGD). Eventually, some 12,000 piles were driven for the Unit 3 powerblock area. The chimney foundation is 15 feet thick and its bottom is 19 feet below grade. It had to be completed early to allow construction of the FGD area to proceed, so a separate contract was awarded for just that foundation, an example of the flexibility that EPCM allows.
In early 2003, the powerblock foundation contractor mobilized and began to install the majority of both the Unit 3 and Unit 4 buried concrete 120-inch circulating water piping that transits the site. This involved digging a trench 80 feet wide and 15 feet deep that also required a dewatering system. For access reasons this had to be completed and backfilled before construction efforts and manning accelerated with the start of the structures. The EPCM arrangement allowed flexibility to assign scope and issue drawings for construction accordingly.
The foundations contractor followed closely behind the piling contractor with the boiler/selective catalytic reduction/coal silo bay and turbine building foundations. The boiler/SCR/coal silo bay foundation is a single eight-foot thick structural mat and was planned to be constructed and poured in 15 blocks averaging about 1,000 cubic yards each. The contractor had started forming some of the foundation pours when, in June 2003, Santee Cooper suspended construction work except for limited areas. At that time, piles and mud mats were completed and rebar and form work had just started on the Unit 3 boiler, coal silo bay, turbine building, and on the turbine generator foundations.
During the work suspension period, which lasted nine months, the entire Unit 3 boiler and boiler structure continued to be received and stored on site. This required developing an additional 13 acres of laydown space, located in the coal yard. Between June 2003 and February 2004, numerous schedules were developed as projected restart dates changed. In early March 2004, Unit 3 construction restarted and Santee Cooper decided to build Unit 4 as soon as possible.
Unit 4 Conceptual Plan
At the time Unit 3 construction restarted, Santee Cooper was desperate for the generation promised by its completion. Completing that unit on time became the highest priority and could not be jeopardized. Generation from Unit 4 still had to be expedited to meet projected growth in the not-too-distant future.
The project team had to minimize the time Unit 4 trailed Unit 3, but in the same breath could not delay Unit 3 even a day. The Unit 4 location is adjacent to the west side of Unit 3 and would have blocked access to Unit 3. These accesses were physically limited and had been denied to minimize affecting the existing operating Unit 2. The major critical paths for both units were the boiler/SCR followed closely by the coal silo bay and the turbine and turbine building.
Holding off the start of Unit 4 construction until Unit 3 was nearly done would have placed Unit 4 completion almost three years behind Unit 3. A plan was proposed that made possible a projected completion date just 22 months following Unit 3, without impact.
The WorleyParsons construction management team developed a sequence to minimize the time between unit completions by taking advantage of the relatively minimal access required to feed material for the piece-by-piece erection of the Unit 3 boiler structure.
The sequences set the timing for the remainder of the Unit 4 schedule, all hinged on the start of boiler steel erection. From that point on, the schedule was largely a replication of Unit 3’s plan. Erection sequencing throughout the contracts was generally east to west for both units, dictated by the two existing operating units and the shared coal handling systems.
One Unit 3 structure that had to be carefully orchestrated was the boiler sump. It is 18 feet deep, immediately adjacent to other structures and is 13 feet below ground water levels. It would have required a large excavation and would have extended the critical path had it not been designed and contracted as a sheet pile cofferdam. Sheet piles were driven to a top elevation at the bottom of the boiler foundation mat and later abandoned in place. The bottom mat was poured against the sheet pile and the sump walls were backfilled with flow fill, both operations saving considerable time.
The Unit 3 boiler building foundation was completed in late May 2004 and boiler steel erection commenced immediately. While the Unit 4 boiler and precipitator foundation work proceeded, the Unit 3 boiler erector was allowed access for steel staging. As part of the negotiations for the Unit 4 precipitator contract, the contract schedule for Unit 3 precipitator was renegotiated to postpone the start of precipitator erection to enable the Unit 3 boiler erector laydown area to store and shake out the boiler building steel.
Unit 3 steel erection began less than three months after work on the project and foundations restarted. An acceleration of the steel erection by three weeks over the contract schedule (to drum lift) was negotiated with the boiler erector and was accomplished through dedicated overtime and additional tools and equipment.
Boiler erection was the critical path for the project, so once the new start dates and the foundation and steel erection schedule accelerations were committed, new project milestones were established and negotiated with six other existing major contracts. Those milestones became the basis of all future contracts.
Erection of the coal silo bay (CSB) was a major component in the planning, linking both of the major critical paths. The CSB consists of the six pulverizers at grade, with the coal feeder floor, six coal silos, tripper deck and the deaerator above that. For access reasons (both for the mills and the structure above) the pulverizers were to be rough set first by the boiler erector before the boiler steel or the CSB steel started. On Unit 3, the southernmost boiler foundation blocks were completed first and the boiler erector released to set the pulverizers, before the remainder of the boiler foundation was completed. On Unit 4 the boiler erector was directed to start the mill erection early enough to permit unfettered erection of the CSB structure by others.
The turbine building foundation mat was also built in blocks, with priority given to the turbine-generator mat to expedite completion of the turbine-generator pedestal, which was critical path to starting the building structure and then the turbine itself. The two condenser sections were assembled from shop-tubed modules outside the turbine building and coordinated with the building erection to be slid into place after the pedestal was completed, but before the structure was started.
The project and the contractors benefited from the learning curve of building a second identical unit. The work was accomplished more quickly and productively and with less schedule duress. That effect was seen on every contract where the same contractor performed the second unit work. Additionally, unique equipment problems were encountered on Unit 3 and fixed on the identical equipment on Unit 4 before they became a problem.
Along the way both the project team and the contractors learned better ways to do things and applied those lessons to Unit 4. Some examples:
- Cable tray scaffolding blocked access: Both sides of a unit have vertical cable tray runs outside the structure from bottom to top. These runs are scaffolded for tray installation and cable pulls. On Unit 3 the scaffold towers were founded on the concrete mat and impeded access for an extended period. On Unit 4 the CM had the contractor install temporary support platforms for the scaffold towers that eliminated the impediment and also allowed the towers to stay in place longer, aiding the productivity of the electrical subcontractor.
- Pressure part prefab: The boiler erector discovered during Unit 3 erection places in the laydown area where it could preassemble boiler subpanels into larger panels before lifting into place. This saved scaffolding and welding time on its critical path.
- More crane hooks: The boiler erector added a tower crane on Unit 4 to eliminate operations waiting for “hook time”
- Second construction elevator: The boiler erector was obligated by contract to provide one elevator, to be made available to all contractors. On Unit 4 the erector added a second construction elevator to eliminate wait times experienced at peak periods of the day.
- Subcontract welders: The labor market became tight for tube welders. Specialty contractors still had a permanent cadre of welders that could be brought in, while the building trades’ welders were absorbed by market demands.
Work on Unit 4 started in earnest with the boiler steel erection in early January 2006. The Unit 4 boiler building steel erection and subsequent installation of the steam drum was completed 10 days ahead of the planned schedule. That success was a result of both planning and learning curve from Unit 3. Steel erection was accelerated through selective overtime and focus.
The flexibility of the contracting approach allowed the CM to cost-effectively direct the efforts of other contractors to accelerate supporting work activities in order to help the (critical path) boiler erector to maintain its inertia. For example, the foundations contractor was directed to work shifts and overtime and to prefabricate forms and templates, to finish both the fan foundations and the bottom ash hopper foundations sooner. The fan erector was also accelerated to support getting the furnace ready earlier for air flow testing. Ultimately, Unit 4 was brought on line 54 days earlier than scheduled.
Throughout the planning for this project the owner/engineer/CM team sought opportunities to overlap critical path activities wherever possible to shorten the overall schedule without major expense.
The EPCM approach is adaptive to change, including capturing new opportunities as they arise. In addition to schedule management, the approach allows the team to manage costs closely. Unit 3 was completed at $1,125/kW. Unit 4 will finish at $1,258/kW.
Authors: Joseph Hickson is vice president and project manager for WorleyParsons. As project manager for Cross Generating Station Units 3 & 4, he was responsible for all design, procurement and construction management at the site.
Steve Neher was site manager for Cross Units 3 & 4, responsible for contract and construction planning, construction scheduling, constructability reviews and initial set-up of the plant site.
Norm Koontz was senior project controls manager for Cross Units 3 & 4, responsible for developing and updating the EPCM and start-up schedules. His role involved overseeing contract schedules, bid evaluations, analysis of schedule changes, preparation of alternative work plans and monthly schedule and cost reports.