When a feedwater heater is replaced, many companies choose to replace “in-kind.” While this might be a convenient option, the utility is not taking advantage of improvements in heat exchanger technology or utilizing state of the art designs. Often, a better option is to write a new specification that reflects the current and potential operating conditions, and then allow the Feedwater Heater Vendor to come up with a new, robust design. Regardless of the method of procurement, the Purchaser should not assume that their responsibility ends once the Vendor has been selected and a delivery date agreed on. Obviously, the Purchaser is responsible for reviewing and approving the drawings prior to fabrication. If no one is familiar with heat exchanger designs or deciphering detail drawings, it might be difficult to discern whether the Vendor’s design has actually met the requirements of the specification.
One of the most overlooked portions of the replacement feedwater heater procurement process is the need to conduct Quality Assurance (QA) inspections at the Vendor’s
A replacement feedwater heater can cost a utility anywhere from $300,000 up to $1 million, especially when installation costs are considered. However, often in a feedwater heater replacement project, the utility forgets to budget or is reluctant to spend additional funds to conduct inspections at the Vendor’s facilities to ensure that they are getting the quality they need for the money spent.
Most likely, the additional cost of performing these Quality Assurance inspections is just a small part of the overall cost to replace the heater, but it is money well spent in order to protect the investment. If you also consider the cost of taking the heater out of service in order to repair a tube leak, or to correct a deficiency that could have been identified during fabrication, the cost of the inspections generally pale in comparison. Additionally, documented inspections of “as built” conditions can assist in troubleshooting or eliminate potential variables when conducting failure cause analysis of future problems.
As part of the specification, the Purchaser should reserve the right to inspect the manufacturing facilities and equipment at any time during working hours. Several fabrication processes of concern should be monitored by the Purchaser’s representatives and listed in the specification as required witness points. The Purchaser might decide to waive a certain witness point in order to allow fabrication to continue, but a later dimensional/visual examination or a record review should be conducted. The following major components are recommended for Purchaser inspection/verification during fabrication.
The fabrication of tubing is generally subcontracted by the Feedwater Heater Vendor. However, the tube mill also should be available for inspection by the Purchaser’s representative, especially when you consider that the tubing of the heater is the single biggest material cost of the heater and is the most likely component to fail in operation.
Ideally, the inspectors should visit the tube mill while the tubes that will be used in the heater are in fabrication. The inspection should include any or all of the following:
- Dimensional Verification
- Witness of any required non-destructive examinations (NDE), such as eddy current tests or ultrasonic tests
- Witness of tube bending and stress relieving
- Witness of hydrostatic tests
- Witness or review of mechanical tests
- Final tube cleanliness and dryness prior to packaging.