Next to the boiler, the condenser is the next most important heat exchanger in the power plant. It is the primary source of feedwater contamination and has a direct impact on unit capacity and heat rate. Most condensers in service for 10 to 15 years experience severe capacity reduction caused by high tube failure rates. Factors contributing to tube failure are: outside-diameter metal loss from steam impingement, pitting and grooving caused by galvanic or ammonia attack. And wear and tear from tube vibration at supports plates. Still other waterside conditions can lead to tube plugging which undermines condenser performance. When problems such as these are encountered, the advice of a full service company such as American Power Services is highly recommended. We can perform eddy current testing, hydrostatic tube testing and tube sample removal for various analyses. From this testing, we can advise as to whether a full or partial retubing or other repairs are necessary. The report should include maps of all tubesheets, eddy-current strip charts, and repair recommendations.
Early planning: Once the decision has been made to either partially or fully retube your condenser, the following questions need to be answered:
- How much money should be budgeted for the project?
- What are the qualifications of all prospective contractors?
- Which contractors have the capability to assist writing the project specifications and in planning/scheduling?
Sometimes the user may decide to write their own specification (see comments below). After a list of qualified contractors has been compiled and a preliminary specification has been written, the user can conduct a pre-bid meeting and walk through in order to review the jobsite and specification as well as answer any questions that any prospective bidder may have. Bid evaluation is the final step, with the contract awarded to the specialized retubing contractor who offers the most complete and accurate proposal as well as provides the best value.
Answers to the following questions will help immeasurably in writing specifications for the condenser retubing project:
- Make and model of the condenser.
- Condenser design and configuration.
- Age, condition and deterioration of the tubes.
- Has the condenser ever been retubed before and why?
- Quantity, OD, wall thickness, length and alloy of existing tubes.
- New tube availability and cost?
- Are other projects scheduled to take place in the vicinity of the condenser retubing? If so, how will those project(s) impact the condenser retubing?
- Will weather be a factor in the retubing process?
- Is there sufficient access for the removal, storage and installation of the condenser tubes?
- Can the tubes be removed and installed from either condenser end?
- Are there major interferences that must be removed in order to facilitate the retubing process?
- Are there utilities in the general work area?
- Will the condenser require blocking of spring supports?
- Is structural support sufficient for moving the waterboxes or must the turbine room crane be used?
- What are the waterbox dimensions?
- Is there adequate storage for the waterboxes once they are removed?
- Are there circulating water pipes, expansion joints, or other items to be removed, supported or replaced during the retubing process?
- Does the condenser have any coating applied?
- Who provides the replacement gaskets and associated hardware?
- Is there access to both waterboxes and the condenser shell?
- Number and type of tube plugs.
- Are the tubes seal welded to the tubesheet?
- Are the tubes flared?
- Are the tubesheet holes serrated?
- Do the tubes have inlet ferrules/inserts?
- Are the tube ends flush with the tubesheet?
- Are the tube ends expanded or packed into the tubesheet holes?
- How thick are the tubesheets and what is the tubesheet material?
- Are tubesheet holes or ligaments damaged? If so, what type of repair should be considered?
- Does the condenser have an expansion joint? If so, what condition is it in?
- Have the existing tube ends been over expanded or work hardened?
- How will the tubesheet and support plate holes be cleaned? How many support plates does the condenser have?
- Procedure to follow should the tubes break during the extraction process and require removal by hand?
- How many tubes should the contractor anticipate will break during the retubing process?
- Chop old tubes into 6" sections for disposal.
- Who will dispose of the scrap tubing?
- Is there any internal damages or misalignment of the tube supports?
- Are there any internal shrouds?
- Where are the new tubes to be stored?
- What roller expansion method should be utilized during the tube end expansion process?
- Will a standing hydro be required?
- How are the new tubes to be handled in order to prevent damage to the replacement tubes?