Offshore Pipelines In Gas & Sour Service

Following the main body of the line pipe specification “Certification of Line-pipe for oil and gas service“. This article will address an additional requirements for Offshore Pipelines in Gas and Sour Services.

Requirements For Offshore Pipelines In Gas Service

Charpy impact toughness should be performed in accordance with SR 5A, SR 5B, and SR 19.
Charpy energy average value (based on three full size specimens) should be In accordance with API 5L, SR 19 except that the values in Table F-3 should be the average of each heat the minimum of any one specimen should be 75% of the average.
The average shear value should be according to API 5L, SR 5A.
For pipe larger than NPS 20 inches, grade higher than X-52, and thickness greater than 0.312 inches, a drop weight tear test should be performed in accordance with API 4L, SR 6 at a temperature of 32°F or the minimum service temperature of the line, whichever is lower.

Requirements For Offshore Pipelines In Sour Service

1.0 Chemical Properties and Tests

The chemical composition of seamless pipe should meet the following requirements:

ELEMENT	COMPOSITION
Carbon (C)	0.16% max.
Manganese (Mn)	Per API 5L 3.1 *
Phosphorus (P)	0.020% max.
Sulfur (S)	0.008% max.
Silicon (Si)	0.35% max.
Nickel (Ni)	0.20% max.
Chromium (Cr)	0.20% max.
Molybdenum (Mo)	0.20% max.
Copper (Cu)	0.35% max.
Aluminum (Al)	0.05% max.
Calcium (Ca)	0.006% max.
Nitrogen (N)	0.012% max.
Niobium (Nb)	0.08% max.
Titanium (Ti)	0.025% max.
Vanadium (V)	0.08% max.
Boron (B)	0.0005% max.
Nb + Ti + V	0.12% max.
Carbon equivalent (IIW)	0.38% max.

* The maximum allowable manganese content is that listed in Table 3.1 of API 5L Table 2B. Manganese content increases based on carbon content are not permitted.

The chemical composition of submerged arc welded or electric welded pipe should meet the requirements of Appendix I, Section A2.0.

For welded pipe products, the steelmaking practice should require “inclusion shape control” chemistry additions to avoid Type II Mn inclusions and silicate stringers in the finish product. Supplier should include a brief description of steelmaking practices with his quotation.

2.0 Mechanical Properties and Tests

For seamless pipe in grades of X-60 and higher, hardness tests should be taken on one quadrant on a ring sample from each 25 joints or one per heat, whichever is greater. Hardness traverses should be made at a distance of 1-2 millimeters from the O.D. and I.D. surfaces and at mid-wall. A Rockwell or Vickers test should be performed. The maximum hardness value should be HRC 22. If any hardness test fails, the pipe should be rejected and one retest should be taken on two other pipes from the heat in the lot that failed. If either or both tests fail, the entire heat should be rejected or reprocessed. If both tests pass, the entire heat may be accepted.

For welded submerged arc welded (LSAW) or electric welded pipe (ERW), one metallographic cross section of the weld should be cut from each pipe from which tensile test samples are cut. Each traverse should include readings at less than 1.0 millimeters intervals in the base metal, HAZ, and weld metal (at least 3 readings in each zone) on both sides of the weld. No values should exceed 250 VHN using a 10 kg load. If any hardness test fails, the pipe should be rejected and one retest should be taken on two other pipes from the heat in the lot that failed. If either or both tests fail, the entire heat should be rejected or reprocessed. If both tests pass, the entire heat may be accepted.

Unless waived by Buyer, a HIC test per NACE TM02-84 Solution A should be performed on one pipe of each of the first three heats produced, and then every tenth heat in sequence thereafter. The test results should meet the following requirements:

CSR	<1%
CLR	<10%
CTR	<3%

If a HIC test fails, one retest of the heat is permitted. If the retest fails, the heat should be rejected and all heats in the order made prior to that heat, backwards to the last successfully passed heat, should be tested. Any of these heats which fail the HIC test and the retest should be rejected.

If specified, a test for sulfide stress cracking (SSC) should be performed in accordance with NACE TM01-77 Test Method A for grades of X-60 and higher. The frequency should be one test per heat on the first five heats. A threshold stress of 97=5% SMYS is required. If a test fails, one retest is permitted. If the retest fails, the heat should be rejected and the test frequency should be extended to 100% or as agreed upon between Buyer and the Supplier.

3.0 Nondestructive Inspection

For submerged arc welded or electric welded pipe, plate or coil should be ultrasonically inspected for lamination. The Supplier should submit a standard procedure for this inspection. The acceptance criteria should be as follows:

CSR	<1%
CLR	<10%
CTR	<3%

If specified, a test for sulfide stress cracking (SSC) should be performed in accordance with NACE TM01-77 Test Method A for grades of X-60 and higher. The frequency should be one test per heat on the first five heats. A threshold stress of 97=5% SMYS is required. If a test fails, one retest is permitted. If the retest fails, the heat should be rejected and the test frequency should be extended to 100% or as agreed upon between Buyer and the Supplier.

3.0 Nondestructive Inspection

Maximum Individual Indication	Minimum Indication Size Considered	Maximum Population Density Number of Indications Smaller than the Max and Greater than the Min
Area, mm²	Area, mm²	Length, mm	Width,	mm
500	150	15	8	10(Per 500mm x 500mm)²

Note: The Supplier may submit alternative criteria for Buyer approval.

Full body rotary ultrasonic inspection of the finished pipe is acceptable in place of ultrasonic inspection of the plate or coil, if the Supplier demonstrates that the search pattern is equivalent.

For electric welded pipe, Appendix I, Paragraph A4.3.3 is amended to a 5% notch and a one-sixteenth inch drilled hole.