- Published on Tuesday, 15 April 2008 20:51
- Written by Ty L. Potter
In today’s environment of shorter outage windows and shrinking maintenance budgets, the maintenance team should explore all available options when faced with a decision to repair or replace a valve.
As an example, let’s consider the choices when a damaged seat is discovered in a large bore, high-pressure swing check and/or reverse current valve in a typical steam system. Due to the difficulty in making a successful seat repair on this type of valve, the traditional approach has been to “limp” along until a replacement valve is available and an extended outage window is planned to allow the project.
The valve replacement approach is typically very costly because:
- the new valve is expensive and usually has a long lead time
- removal of the existing valve and installation labor and equipment is costly
- the replacement process usually requires civil engineering to establish a rigging plan, restraint system and overall safe removal of existing valve and installation of the new one
- the replacement process will more than likely require quality control management of extensive nondestructive examination and pre/post-weld heat treatment.
Most check valves are designed with a welded, integral seat located in a narrow valve throat and typically set at a 30-degree angle. This design makes repair of the seating surface virtually impossible using “off the shelf” machines and tooling. The lack of equipment to adequately make this repair has in the past left the end-user with one option to restore the integrity of the system—valve removal and replacement.
To remove and replace check valve seats reliably and in a cost-effective manner, the valve repair vendor must utilize custom tooling, procedures and techniques.
Utilizing this special tooling, craft personnel have performed numerous successful seat replacements on check valves, ranging in size from 12-inch NPS to 50-inch NPS. In this repair process personnel typically:
- document “as-found” condition and dimensions
- perform liquid penetrant testing (LPT) of the existing seating surface
- machine-remove the existing alloy 21 hardfacing
- perform LPT of the base metal (valve body)
- perform base metal repairs if needed
- install new alloy 21 hardfacing
- machine a new seating surface to OEM specifications
- perform liquid penetrant testing of the new seating surface
- re-assemble the valve and “blue check” the seating surface to ensure 100% contact
- document the “as repaired” critical valve dimensions.
These new techniques, along with the traditional valve repair procedures, provide the end-user with a refurbished component, restored to OEM specifications, in this critical application—without the time and expense required for a full valve replacement.
As with all mechanical components, routine maintenance and inspection is critical to keeping these types of valves in proper working order. Most end-users follow a carefully planned maintenance schedule; however, it is worthwhile to recap the elements of a successful program:
- Schedule routine inspection and documentation of valve condition.
- Perform non-destructive examination of valve seating surfaces and base metal pressure-containing components.
- Maintain seating surface condition through a repair process such as the one described in this article.
- Refurbish or replace worn valve components discovered during the inspection process.
If replacement of these types of valves does become necessary, contact an OEM to assist in the selection of the best valve for the application; make allowances for rigging and restraining the existing piping prior to valve removal; and take the opportunity to make any configuration changes needed to improve valve maintenance accessibility.
TY L. POTTER is Vice President of Operations, Southeast Valve, Inc. located in Charlotte, NC. Reach the author at 704.588.0973.