Pressure class differences

Except for the incompatability of the bolt patterns on flanged fittings of various pressure ratings, there is no problem with mixing components from various pressure classifications together as long as the highest pressure to be encountered does not exceed the lowest pressure rating of the system's components.

In screwed steam condensate piping it is very common to use fittings of a higher pressure rating that might errode (such as elbows or tees) faster than the rest of the components. This extends the time between failures and reduces the overall operating cost of the system. Systems usually don't make money when they are not working due to making repairs.

If you have a 300# rated valve it will fit well in a 150# system especially if you have a pipe fitter sitting there waiting for a 150# valve to come in the next day.

When working with welded pipe and fittings it is not unusual to mix components or various ratings just so long as the lowest rated component is still above the highest pressure of the system. When costing a project the simplified cost is material + Labor. Idle labor is extrememly expensive for the bottom line.

For flanged systems it is not unusual to make a spool piece with one flange of one pressure rating and a flange of another pressure rating for use as an adapter to accept components of different flange configurations due to different pressure rating. Often times components are only made with flanges of a higher pressure rating and the system will be working at a much lower pressure range and it is cheaper to fabricate the system with flanges of the lower rating. For example using a 300# valve in a system with other components having 150# flanges with a max operating pressure of 90-100 psi

Hi no it is not acceptible on PROCESS PIPING gasket size, pcd, bolt diameter all different on 150# to 300#

Best regards, John.

Process piping is not exclusively flanged piping. Also I used the statement-

"Except for the incompatability of the bolt patterns on flanged fittings of various pressure ratings, there is no problem with mixing components from various pressure classifications together as long as the highest pressure to be encountered does not exceed the lowest pressure rating of the system's components."

It is common knowledge that a compatible gasket and compatible bolts must be used with the flange set used if the joint is flanged. Mechanically flanges of different pressure rating will not match up to each other but that does not mean that components of various joining methods and various pressure ratings can not be used within the same PROCESS PIPING SYSTEM.

PROCESS PIPING SYSTEM covers a very broad spectrum of piping. Things that are right for one application may not be correct for another system, in fact they might be deadly in the other system.

Also if a system has the potential for needing to be taken apart in the future it is quite acceptable and preferred to install sets of flanges at appropriate locations to allow the insertion of blanks, removal of spool pieces or to facilitate the removal of a section of piping/components for repair or modification. Removal of a flanged section of piping and attaching blind flanges to the remaining piping flanges is the most preferred and best method of blanking/blinding for the removal of chemical or potential energy hazards. See OSHA removal of potential energy sources in piping.

In over a 40+ year career in the chemical industry handling many facets of engineering, operations, maintenance and safety therein, I have seen many instances where the mixing of various pressure rated componets and componets of various methods of joining are preferred. It can be an advantage with respect to installation, operations, ease of repair and also for safety considerations.

i think it will cause u alot of problems

if the service pressure is according to 300lb gate valve's flange then the 150lb flange will be failed e.g. leakage can be occured.

Also there will be a difference in sizes of 300lb flange n 150lb flange, e.g. wall thickness, which may cause problem for fluid flow.

u can use reducing flanges if they comply the standards, according to ur service pressure.