API 11P – Specification for Packaged Reciprocating Compressors for

AND GAS PRODUCTION SERVICES [6]

This standard has actually become obsolete but is still widely referred to. It is replaced by ISO 13631 (which appears to contain very similar text). Outside of what is covered in its Section 11 “Skids,” API 11P briefly covers a number of topics loosely related to mounting, as well as mechanical integrity, safety and basic performance, and the following bulleted list summarizes these (details are paraphrased in places—section number indicated should be consulted for specific language):

1.7.1.1 Summary of API 11P Line Items Related to Mounting

When specified by the purchaser, compressor manufacturer shall furnish values for unbalanced primary and secondary forces and moments in horizontal and vertical directions (2.1.4).

Purchaser may specify maximum allowable piston speed and maximum allowable RPM (2.2).

Maximum discharge temperature to be below 350°F, and compressor must have enough stages for this unless otherwise specified by purchaser (2.3).

Maximum rod load shall be below allowable (2.4.1).

Rod loading shall reverse enough to ensure adequate lubrication (2.4.2).

Cylinder support shall be designed to avoid misalignment or excessive rod run-out (2.5.2.1).

A compressor frame oil level device shall be provided by the packager (2.11.6).

Materials, casting factors, weld quality to be up to ASME Code Section VIII, Div. I (2.13.1.4).

When required, inspection shall be according to ASME Code Section VIII (2.13.4.2).

Capacity control may be by speed variation, clearance variation, bypass, single acting, valve unloaders, Ps control, or any combination (3.2).

Bypass capacity control shall be of cold gas downstream of cooler (3.2.3.2).

Starting system shall be provided (air, gas, or electric) (4.2.3).

Rated BHP requirements (NB…treated differently for motor and engine) (4.2.1).

Electrical installations according to NFPA70 (1.7).

Packager will assume responsibility for a torsionally sound system (1.9).

Flywheels, sheaves, belts, shafts, and couplings shall have removable safety guards that meet OSHA standards (2.14.5).

Safety guards shall protect to within ½-inch of stationary housings and shall be stiff enough to withstand deflection and prevent rubbing as a result of bodily contact (2.14.5.1).

Engines to be equipped with the standard lubrication system (4.2.1).

Crankcase explosion-proof doors shall be furnished when specified by the purchaser (5.2).

Engine cooling systems to be provided for lube oil, turbo air (aftercooler), and engine water jacket (5.2).

Compressor cooling systems to be provided for cylinder jackets, rod packing, frame lube oil, and compressed gas (5.3).

Pressure vessels for compressed gas shall be in accordance with ASME pressure vessel code Section VIII, Div. 1 (construction, materials) (6.1).

Pulsation control and pulsation studies will be as specified by the purchaser and will be quoted separately by the packager (6.3.1).

Reinforcement pads shall be at least equal to the cut-away area (6.3.7).

Extent of gas piping to be supplied by the packager is to be specified by the purchaser (7.1.4).

When specified, the purchaser shall review the arrangements and drawings of all piping and appurtenances immediately upstream and downstream of the compressor prior to fabrication (7.1.5).

Connections 1.5 inches and smaller shall be designed to minimize overhung weight and shall be braced back to the main pipe in at least two planes to avoid breakage due to vibration; bracing shall be arranged to occupy minimum space (7.2).

Piping design shall accomplish: (7.3):

• Proper support and protection to prevent damage from vibration shipment, operation, and maintenance (7.3.1).

• Proper flexibility and normal accessibility for O&M and thorough cleaning (7.3.2).

• Installation in a neat and orderly arrangement adapted to machine contour and not obstructing access openings (7.3.3).

• Eliminate air pockets; complete drainage; and eliminate low points that could trap liquid (7.3.4, 7.3.5, 7.3.6).

• Utilize pipe clamps on any piping two inches and larger (7.3.7).

• Do not weld supports direct to piping (7.3.8).

Materials (for piping) shall be ASTM A-53 Grade B or A-106 Grade B or purchaser approved equivalent (7.1).

1.7.1.2 Instruments and Controls in API 11P

It should be noted that API 11P states that instruments and controls and electrical systems will not be addressed by the guidelines.

However, a few instruments are mentioned (discharge temperature measurement to be provided on each discharge nozzle; vibration shutdowns to be provided on cooler and at crankshaft level on prime mover and compressor). It is good to see all these included—

discharge temperature provides a sensitive basis for condition monitoring. Protection monitoring against excessive vibration at compressor and engine frames will catch and draw attention to any unexpected high vibrations.

1.7.1.3 Observations from Review of API 11P

The above list of topics is provided in some detail to provide the reader with a sense of the tone of the API 11P standard, to make the reader keenly aware of the purchasers’

responsibilities for specifying items, and to recognize that what API 11P does explicitly specify is generally no more than what would be reasonably expected as standard scope of supply.

1.7.1.4 Apparent Gaps in API 11P for Pipeline Applications

It is pointed out that there is no statement about post weld heat treatment in the API 11P section on piping (Section 7). There are no explicit requirements for piping weld inspection in Section 7, although reference is made in Section 2 to ASME Section VIII, which has inspection requirements. The purchaser should assure that this need is clearly understood—since examples of poor weld quality, which would not have passed such an inspection have come to light in some packages after installation and operation. There is a statement that threaded joints can be used for piping less than 2 inches in diameter. In an environment with potential for high vibration, it is recommended that all joints should be welded or flanged. There does not appear to be an explicit statement about piping for interstate pipeline compressor stations needing to meet ASME B31.8 [15] requirements for thermal flexibility (just the comment above about

“Proper Flexibility”). Material test reports (MTRs) and numerous other DOT requirements are also not addressed in API 11P.

In general, it should be recognized that when API 11P was written (pre-1995), the pipeline industry was not a target market for skid-mounted compressors; most of these units were used in the upstream gas industry.

1.7.1.5 API 11P: Section 11 “Skids”

All line items and subsections of API 11P Section 11 are covered below; slight paraphrasing has been used, so API 11P or ISO 13631 should be reviewed for specific language:

11.1 General. Structural steel, concrete, or concrete-filled steel skids shall be strong enough for transportation and installation, and transmit forces and couples to the purchaser’s foundation.

11.2 Design

11.2.1 Lifting — Skids shall have provision for winching or lifting.

11.2.2 Members — Load bearing components shall be full depth members, strong enough to prevent excess deflection that would damage installed equipment during transportation or installation

11.2.3 Mechanical Equipment — Compressor and driver to be mounted on full depth load bearing members and secured by bolting, grouting, or sole plate mounting. Horizontal jackscrews shall be provided. All bolts and nuts shall be accessible for maintenance with standard tooling.

11.2.4 Shims — Provision for shims to be provided where alignment is critical.

Shims to be of corrosion resistant material (e.g., stainless steel).

Provision for vertical alignment in the field of 0.125 inches.

11.2.5 Size — Skid to be wide and long enough for installation of equipment.

11.2.6 Screws and Bolts — On non-concrete-filled steel skids, leveling screws and anchor bolt holes are to be provided—minimum 3 per side, with a sufficient number of leveling screws to support the total weight of the skid and equipment.

11.2.7 Floor Plates — Open areas on skid shall be covered with at least 3/16-inch solid raised pattern floor plate welded or bolted in place.

Provisions shall be made to facilitate grout placement. Floor plate is not required on concrete or concrete-filled steel skids.

11.2.8 Braces — Supports and braces shall not be attached to unsupported floor plate.

11.2.9 Scrubbers — On steel skids, scrubbers shall be supported by full depth skid members and not the floor plate. They shall be welded or bolted to the members as specified by purchaser.

11.3 Construction — Structural steel skids shall be of welded construction. Abutting beams shall be welded on both sides. Splicing flanges of load bearing members is not acceptable. Contact between webs at perpendicular joints shall be a minimum of one-third of the depth of the smallest member.

11.4 Walkways, Stairs, and Platforms —Walkways, stairs and platforms, when specified by the purchaser, shall be provided with handrails on both sides except that they are required on only one side when the walkways and platforms are within two feet of grade or when one side is bounded by equipment not presenting a safety hazard. Handrails shall be complete with mid-rail and toe-plates.

The above items in Section 11 of API 11P are generally important, but clearly need substantial supplementing and refinement by the purchaser of a skid mounted pipeline compressor beyond the areas of specification highlighted in bold italics. In general, what is specified here just provides explicit language to ensure the purchaser gets what would reasonably be expected. (Clearly, it is important to be able to safely lift and install the skid, that loads be carried by full depth beams, that the equipment be attached to full depth members, that the skid be big enough for the mounted equipment, with horizontal jacking screws, that shimming for alignment should be possible with stainless steel shims, that there should be at least three skid anchor bolt holes per side, and that the skid vertical jacking screws should be able to carry the

total load of skid and equipment. Floor plate should cover open spaces, and nothing should be attached to or supported from the floor plates.)

Section 4 of these guidelines provides the needed supplement to address issues of dynamics and integrity incompletely addressed in API 11P for pipeline applications.

API 11P sections not discussed further are on painting, shipping, marking, corrosive gases, offshore, and marine.

API 11P Appendices

API 11P also has five appendices, which are not discussed further in these guidelines:

A Excerpts from GPSA Engineering Data Book B List of API Authorized Packagers

C About the API Monogram

D Data Sheets Provided by Purchaser to Packager E Data Sheets for the Packager’s Design