PSV Maintenance Access

[MNV1]

This inquiry is looking for opinions on safe maintenance access for Safety Relief Valves.

Safety Relief Valve maintenance access has been primarily dictated by the operators design scope. These can be very minimal in description and typically refer to API. API only states that maintenance access should be easily accessed. Not much direction here.

Preparing a more descriptive definition in an effort to improve maintenance access and safety, standardize design layout principles, reduce fabrication and construction costs.

People will argue that safe maintenance access can be achieved off a scaffolding platform, and new designs are being done this way with that philosophy (valve 7 to 10 feet above platform). However is this practical and economical for a 20 to 40 year design plant, not to mention the access mess scaffolding creates for the operators and the increased safety hazard they can create. Do I want to force the operators to live in that environment for the life of the plant?

Considering all design concepts are directed by project scope requirements, defining a requirement for PSV access clarifies the requirements at the front end for structures access requirements.

The following is my minimum project scope description. Please comment opinions and points of view.

Safety Relief Valve Access
- Safety Relief Valves are category 1 access valves (this means easily accessible).
- Valve shall be located at a convenient work height for maintenance removal.
- Access platform for PSV shall be a permanent design.
- Large diameter piping will require the design of an independent platform around the PSV that allows for proper maintenance removal access.
- Platforms shall be accessed by ladder or stair.
- Isolation block valves for PSV do not need permanent access platforms (however nice to have), but must be accessible by manual and mobile methods.

 

[don1980]

It's good that you are considering maintenance accessibility because that's an important engineering design detail for all equipment that needs periodic maintenance, including PSVs.

Since PSVs are installed on a wide range of equipment and vessels, which are vastly different from one another, I wouldn't write a set of one-size-fits-all accessibility requirement. Doing so may result in costly civil overdesign and/or installations in which the PSVs functional integrity is inadvertently compromised for better accessibility.

Instead, I would simply add a P&ID note next to each PSV instructing the piping and civil designers to maximize accessibility to the PSVs. Then, during one of the early 3-D model reviews, include PSV accessibility as one of the review tasks for that meeting. Be sure to include a knowledgeable relief design engineer in that meeting because there are a lot of PSV design and installation constraints that others may not be aware of (e.g. no pockets in PSV piping, sloping of outlet line, the PSV's placement on the vessel, potential of personnel exposure from bonnet vent of bellows PSV or the tailpipe of any PSV, etc.). This can results in final design in which the variables (PSV functionality, costs, accessibility) are optimized without compromising the safety integrity of the PSV designs.

 

[georgeverghese]

All your requirements are typical of at least one supermajor oil-gas OpCo.

 

[LittleInch]

The problem normally is that the requirements of the valve ( top of a vessel, inlet sloping down etc, often lead to relief valves being the highest thing and hence the cost of the access platform for one valve to maintain every 5 years is seen as excessive and in places difficult to fit in.

It's a great wish list, but there is a balance here between CAPEX and OPEX which more times than not swings the way of CAPEX, especially for EPC contracts.

It's important to consider maintenance and operations access, but there will be times when it is not optimal. That's a simple fact of life when you don't have years to design a plant and space is tight. There will always be a few locations where the result of the discussion is "well if we ever need to get it out we'll install some scaffolding.

The key to efficient design is to get that balance right. Don 1980 says the same thing with more eloquence.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MNV1]

Thanks for all your comments, it is appreciated. I realize the PSV subject has many dictating design factors, however my objective here is to define a design scope description for maintenance access that must be adhered to during the plant design.

From my own experience with majors, their safety concerns for personnel is paramount, as is efficiency during maintenance operations. And as georgeverghese commented, my short list is what would be required as a minimum in the design scope from a typical major OpCo.

Stating that access must be permanent will cause more thought to resolve during the design stage.