Steam Path Audits

Mechanical efficiency loss inside the steam turbine can be attributed to two primary causes: leakage and surface roughness. Leakage refers to steam flowing unintentionally anywhere other than through the blades. Excessive seal clearance, damaged seals, and poor sealing surface joint condition are all forms of leakage loss.

Surface roughness is exactly as it sounds. Increased roughness corresponds to increased friction, and increased friction consumes energy that becomes unavailable for conversion to shaft rotational energy. Increased steam path surface roughness can be caused by deposits, corrosion, erosion, and object impact. For example, research has shown that deposit thickness of only a few thousandths of an inch (<0.1 mm) on stator and rotor blades can cause an efficiency loss of 3 to 4% and a flow capacity reduction of 1%.

Macek Power steam path audits evaluate steam path components for structural integrity and efficiency loss, then recommend an optimum course of action to take while the unit is open.

Options for each damaged or degraded steam path component include:

1. Accept “as is”
2. Repair
3. Refurbish
4. Scrap and replace

Factors such as cost, available time, reliability, capacity factor, service factor, and potential for efficiency improvement influence maintenance budget decisions. Macek Power considers these variables and optimizes the decision making process by computing benefit to cost ratios, which are presented in the steam path audit report. Presuming there are no structural (reliability) issues with any of the components, the report provides the equipment owner with the basis needed to optimize the use of the maintenance budget. Component replacement that provides the highest return on investment is prioritized and unnecessary or low return rate component replacement is avoided.

The usual steam path audit process includes computer model development prior to the site visit. This is followed by the site visit when the unit is open and “as found” clearance measurements are available. Upon arrival to site, visual inspection (for structural integrity) and a variety of dimensional measurements are taken along with a review of the clearance measurement data provided by the service provider. Preliminary “opening” observations can be provided prior to site departure to guide refurbishment efforts. Some customers additionally opt for a closing audit to compare and contrast “as found” with “as left” conditions.

Macek Power is a highly experienced steam path audit service provider.  The cost of the steam path audit is almost always insignificant given the recovered efficiency and consequent reduced annual operating cost, both of which are the products of the audit process.