Cameron’s SUPERIOR high speed reciprocating compressors and engines are well known for their high quality and high reliability. Industries that may require such reciprocating compression equipment to meet API 618 minimum standards such as Petroleum, Chemical and Gas can now partner with Cameron. The API 618 standard referenced here is the 5th edition, issued December 2007.
When recently approached to provide a high speed reciprocating compressor for an API 618 process application, Cameron quickly found that most specification requirements were already in the SUPERIOR product offering. The main reason for this is that both API and Cameron have the same objective when considering minimum requirements for compressors: high reliability that minimizes down time.
A general requirement of the equipment covered by the API 618 standard is that it is to be designed and constructed for a minimum service life of 20 years and at least 3 years of uninterrupted operation with some exceptions for wearing parts. This design standard requires the equipment manufacturer to be committed to long term quality standards. SUPERIOR has met this standard over and over again, with hundreds of compressors in the field that have been running for decades.
Certain process applications require non-lubricated cylinders to prevent oil from contaminating the gas. Non-lubricated cylinders eliminate the cost of replacing the lubrication fluid regularly, but consideration must be made for the wear on the cylinder and piston rings. SUPERIOR’s solution is a Teflon® coated running bore to extend the life of the piston rings. API 618 sets a predicted discharge temperature not to exceed 275oF (135oC) for these non-lubricated cylinders, and the standard maximum discharge temperature for lubricated cylinders is 300oF (150oC). SUPERIOR has a full line of both lubricated and non-lubricated cylinders that meet the API 618 specifications for temperature in sizes that range from diameters of 3.125” (80mm) to26.5” (648mm).
Cylinder standards set by API 618 specify that each cylinder must have a replaceable dry-type liner and be designed to enhance heat transfer and dimensional stability. SUPERIOR has a full line of lined cylinders to meet this minimum requirement and adds adds Teflon® to the cylinder liner to enhance the performance and durability of cylinder liner.
API 618 specifies water cooling systems as a minimum requirement. The advantage of water cooled cylinders is the ability to lower operating temperatures preventing overheating of the piston seals and increasing the packing life. SUPERIOR has a full line of water cooled cylinders that meet these core requirements but also offers a full line of air cooled cylinders.
The current API 618 specifications for the piston rods require that all piston rods, regardless of base material, be coated with a wear resistant material. The purpose of this is to reduce rod surface wear and extend the pressure packing life. SUPERIOR’s standard is a Tungsten Carbide coating, and as specified in API 618, the piston rods are continuously coated from the piston rod packing through the oil wiper travel areas.
API 618 requires that base material for piston rods be in compliance with NACE MR0175 when used in H2S applications. SUPERIOR components are in compliance with NACE to handle H2S and CO2. These quality parts are resistant to corrosion from sour gas without special trim, which is often required in process gas applications.
Double-acting cylinders are preferred by API 618 as the most efficient with compression occurring on both sides of the piston during both the advancing and retreating stroke. If accepted by the customer, single acting, step piston or tandem cylinder arrangements may be provided, but special care must be given to ensure rod load reversals are as specified in API 618. SUPERIOR offers double-acting cylinders as standard equipment and also has an extensive variety of cylinders available to fit any application.
Construction of wear rings must be designed to prevent underside pressurization (acting similarly to piston rings). They also need to be segmented to facilitate installation and be made from wear resistant material. API 618 further specifies that for non-lubricated horizontal cylinders, the bearing load calculated from the equation below on nonmetallic wear rings shall not exceed 5 lbf/in2 (0.035 N/mm2) based on the mass of the entire piston assembly plus half the mass of the rod divided by the projected area of a 120o arc of all wear rings. SUPERIOR cylinder double rider rings meet API 618 maximum contact pressure.
LB = (MPA + (MR/2)) / (0.866 x D x W)
where,
- LB is the bearing load on wear rings in 5 lbf/in2 (0.035 N/mm2)
- MPA is the weight of the piston assembly lbf (N)
- MR is the weight of the piston rod lbf (N)
- D is the cylinder bore diameter in in. (mm);
- W is the total width of all wear rings in in. (mm);
There are many API 618 specifications that must be considered for a compressor in a process application. Several have been pointed out in this article with the objective of highlighting the benefits to the end user. When API 618 requirements are met, reliability, longevity and reduced down time will result, saving the end user money over the life of the compressor. SUPERIOR reciprocating compressors are designed with such quality and reliability making them is a perfect fit for process applications requiring API 618 specifications.
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