Slimline monoflanges for cold service

The slimline monoflange is ideally suited to liquified natural gas applications.

By David Sear

Mr Shillito, what exactly is cold service?

Traditionally within liquified natural gas (LNG) plants, there are ‘cold service’ applications and cryogenic. Cold service is typically between -29 °C and -50 °C. Valves used on cold service are required to be operable at -50 °C, that is, be able to be opened and closed and maintain leak tightness through the gland and across the seat at the valve design pressure.

The slimline monoflange you have developed for cold service appears to have a bonnet extension. Why is that?

Valving for cold service do not require cryogenic bonnet extensions, however, they often require smaller extensions to allow for the application of lagging. Lagging types and thicknesses vary from project to project and can be up to 50mm thick. The reason for using a bonnet extension with lagged valves is to move the top of the bonnet outside the lagging. Should the valve ever develop a gland leak, the produced fluid will not be trapped within the lagging and cause corrosion issues.

What types of valves are used in the monoflange?

Both our block & bleed and double block & bleed assemblies utilise an outside screw and yoke needle valve for primary isolation with an inside screw and yoke type needle valves for secondary isolation and bleed valve.

How were these valves validated?

To validate the two types of needle valves with extended bonnets, Oliver have utilised the rigorous testing requirements called for within the Shell specification 77/300. Unlike some specifications which only deal with purely the ability of the gland seal to perform at the low temperatures, the Shell specification reviews both the gland seal and the seat seal. Oliver has performed the 77/300 validation test within its R&D facility, on a 1∞” Class 2500 block & bleed slimline monoflange with extended bonnets. The performance of all the gland seals at -50 °C were well within leak rate BH and seat leaks were zero. Testing was performed at ASME pressure classes 600 and 2500. All the testing was witnessed by a third party.

What was the driver for Oliver to develop this new monoflange?

Following discussions with LNG project engineers, it became clear that whilst valve companies could provide compact needle valve block and bleed and also double block and bleed valves with a minimum design temperature of – 50 °C, they were unable to provide verification reports on the operational ability of these valves at the low temperature. In addition, any testing that had been performed was not with the necessary extensions to allow for lagging which is so often fitted to pipelines for cold service.

Looking ahead, where do you see potential for these slimline monoflanges?

The LNG industry! The sector is starting to come back following the pandemic and there has been a positive response from the engineers we have spoken to. The monoflange is ideally suited for pressure instruments. It allows for the safe isolation of the instrument from the pipeline in a compact assembly.