API Spec 16C - Specification for Choke and Kill Systems

Last update: July 22, 2021

Standard Ed Section Question Answer
Spec 16C 2nd 4.2 Question 1: Do drilling chokes manufactured in accordance to API 16C have to Response 1: Yes. Drilling Chokes are covered in API 16C with specific requirements for choke
satisfy the requirement per section 4.2 ? (i.e is PSL-3 or higher and a material class and kill; chokes for general use - production, drilling, or other use - are covered in API 6A.
of DD/EE/FF/HH with H2S partial pressure rating of 1.5 or higher) if yes,
Question 2: do they have to be marked (with PSL & PR levels) as specified in API 6A Response 2: No, unless specifically referenced in16C for drilling chokes.
? Question 3: what will be the acceptance criteria for quality control
requirements in this case ? (i.e. section 7 of API 16C or relevant section in API 6A Response 3: Drilling chokes must meet the requirements of 16C, which may include some 6A
appropriate to PSL)? requirements by reference.
Spec 16C 2nd 4.2 Question 1: Does the specification differentiate between Chokes (monogrammed to Reponse 1: No
API 6A) & Drilling Chokes (monogrammed to API 16C) ?
Question 2: Do the requirements of section 4.2 apply to drilling chokes Response 2: Yes
(monogrammed to API 16C)?
Spec 16C 2nd 5.8.4.2 Question: 5.8.4.2 Tensile and impact specimens shall be recovered from the QTC Response: Yes. The Keel Block Configuration in 16C is in error. Please reference the keel block
such that their longitudinal center line axis is wholly within the center core 1/4T configuration in API 6A. This will be corrected in the 3rd edition.
envelope for a solid QTC or within 1/8 in. (3.2 mm) of the mid-thickness of the
thickest section of a hollow QTC, reference Figure 1, Figure 2, and Figure 3. In Figure
3—Keel Block Configuration, there is "1/4T" but "0.25R (ER = 2.3R)". I think there is
a error in the figure. "0.25R " shall is "1/4T". This will make the indication in the
figure consistent with the standard content.
Spec 16C 2nd 6.3.5.2 Question 1. Does the charpy location meet the requirement of 6.3.5.2? Response: Section 6 was not descriptive enough to provide adequate guidance for the
Question 2. The paragraph does not contain any details of what part of the charpy performance of charpy impact testing. The testing location is intended to pass through the
should be located at the 1/4 thickness location. Is the paragraph describing an base material HAZ and the weld material. The API SC16/Task Group 3 for Spec 16C has
envelope in which the charpy bar is to be located or does it require a specific part of addressed this issue, resulting in new guidance that will be included in the new 3rd Edition of
the charpy located at the exact 1/4 thickness? Spec 16C.
Question 3. If the base material is only 1/2" thick, can a full size specimen be
used and still meet the requirement?
Question 4. It is the opinion of the requestor that this paragraph only requires that
some part of the charpy bar is required to be placed in the 1/4 thickness location
(envelope). The paragraph contains no specific details on how to locate the charpy
specimen or whether or not a full size of subsize specimen is required for different
thickness of materials. It is requested that this section be reviewed to provide more
clarity to the exact location requirement of the charpy. It is suggested to consider
reviewing Paragraph 7.3.4.6 of API 6A 21st Edition and possibly adopting the
language in that paragraph.
Spec 16C 2nd 6.4.1 Question: Here, "drilling riser choke, kill" is "drilling riser choke and kill lines". Is it Response: Yes. "Drilling riser choke and kill lines" is correct.
right?
Spec 16C 2nd 6.5.4.4 Question: Some manufacturers of riser require all metal testing for overlay materials Response: Here is how API 16C, paragraph 6.5.4 (including 6.5.4.1, 6.5.4.2, 6.5.4.3, 6.5.4.4, 6.5.4.6, and
and some do not. As a buyer we do. We have a manufacturer that says it is not 6.5.4.7) needs to be interpreted when any part of an overly clad is included in the design calculations
required. Therefore the question below. Our justification for requiring it is as (see ASME BPVC, Section IX, QW-217):
1)API 16C, paragraph 6.5.4.1 states that “Qualifica on SHALL be in accordance with ASME BPVC, Sec on
follows: a) Paragraph QW-214 from ASME BPVC Section IX, states the requirements
IX, Article II and Article III, for weld overlay, hard facing, or other types of overlay as applicable.”
for corrosion-resistant weld metal overlay. This section does not include when any
Therefore – The Buyer’s interpretation “we use ASME BPVC as a guide” is not acceptable.
portion of the overlay cladding thickness is included in the design calculations. The 2)For cladding that is included in the design calcula ons, the Buyer’s interpreta on of tes ng “a ‘dog
closest paragraph in ASME Section IX that discusses how to qualify a clad thickness bone’ flat tensile specimen needs to be machined from the full clad thickness of the weld test coupon,
that is included in the design calculations is QW-217, “Joining of Composite (Clad and should not include any of the base metal heat affected zone.” is also not acceptable. ASME BPVC,
Metals). This section requires part (a) to be followed when qualifying the clad metal Section IX, QW-217(a) states “Tensile and bend tests required in QW-451 for groove welds, shall be
for strength. Part (a) of QW-217 states that tensile and bend tests shall be made, made, and they shall contain the full thickness of cladding through the reduced section of the
and they shall contain the full thickness of cladding through the reduced section of specimen.” Therefore, the proper interpretation would be to perform a procedure qualification test
the specimen. Additionally if welded by a fusion welding process, the side bends coupon using the same P-Number base metal, cladding, and welding process, and filler metal
require the base metal/HAZ/fusion line and clad thickness to be tested in a side combination to be used in production welding. A groove weld joining two pieces of base material (or
one thick piece of base material with a groove machined into the material), weld using the clad filler
bend specimen. The Buyers interpretation of this section in API 16C, paragraph
metal, up to a minimum clad thickness based on a chemical analysis performed in accordance with
6.5.4.4 is as follows: b) When mechanical testing of a weld metal shall be
Table QW-453. The actual weld clad thickness shall also require two transverse groove weld tension
performed, we use ASME BPVC Section IX as a guide. This document requires tensile specimens containing the full clad thickness tested, and meet Figure QW-46.1(a) for plate, or QW-
and bend tests of any and all fusion welding processes to be done for mechanical 462.1(b) for pipe. Each tensile specimens shall include the Base Metal/HAZ/Clad Weld Metal/HAZ/Base
testing of a weld qualification . Therefore, a ‘dog bone’ flat tensile specimen needs Metal.
to be machined from the full clad thickness of the weld test coupon, and should not 3)For cladding that is included in the design calcula ons, the base material shall be a minimum of 3/8”
include any of the base metal heat affected zone. We would find it reasonable to thickness, therefore allowing 4 side bend specimens to be taken. Two of the side bend specimens will be
machine 0.25mm (0.010”) from both sides of the clad metal (near the fusion line centered in the middle of the Vee-Groove or machined clad area. Each of the other two side bend
and the top of the cladding) in the reduced section area only of the tensile specimens shall be centered, one on each fusion line between the clad and the base material. The side
specimen. In this way the vast majority of the clad thickness, including most of the bends are used to verify the soundness of the clad deposit and that the strength and ductility at the
fusion line (partially mixed zone) has both soundness and that no deleterious phases or hardened zones
base metal diluted chemistry in the cladding will be part of the tensile specimen. As
have formed using the stated welding procedure variables. It is recommended that the Guided-Bend
a result, the mechanical strength of the clad will now be defined. c) Additionally the
Wrap Around Jig, in Figure QW-466.3, be used to center all 4 bend specimens at their required
4 standard side bends required by a Section IX qualification, will show the locations.
soundness of the clad deposited on the base metal, and (whether a PWHT was 4)When overlay cladding is performed as iden fied above. The sa sfactory qualifica on results may be
performed or not) the resulting ductility of the base metal’s Heat Affected Zone. used for either when the clad thickness is or is not used in the design calculations.

Spec 16C 2nd 7.5.4.4 Question 1: Test results shall be acceptable if there is no visible leakage during the Response 1: Yes. This is acceptable as long as the test pressure remains at or above 7,500 psi
hold periods. Pressure shall remain within 5 % of the testing pressure or 500 psi throughout the hold period and there can be no visible leakage.
(3.45MPa), whichever is less, during the entire hold period and shall not drop below Response 2: Acceptance criteria are that the pressure drop can be no more than 250 psi,
the rated test pressure. As per the above clause 5% of the testing pressure or 500 there can be no visible leakage and the pressure remains at or above the test pressure, i.e.
PSI, whichever less is acceptable. But pressure drop is not acceptable during entire 5,000 psi.
hold period of rated working pressure. Scenario number 1: equipment is tested @
test pressure 7500 PSI, drops 37.5 PSI and there is no visual leak, is it acceptable?
Question 2: Scenario number 2: When we do rated working pressure test for
complete assembled choke and kill manifold i. e. 5,000 PSI what is acceptance
tolerance.
Spec 16C 2nd 7.5.6.1.2 Question: 7.5.6.1.2 does not specify how long the test pressure should be held for. Response: No. The hold times are specified and no error exists. The hold periods are given in
7.5.4.2. Section 7.5.4 applies to all hydrostatic body shell tests of assembled equipment.
[However, this could be made clearer in future editions! We will consider this going forward]
Spec 16C 2nd 7.5.6.2 Question: 7.5.6.2 does not belong in this section as it applies to a choke with an Response: No. No change is required. The inquiry is incorrect, as shown in the section titles:
actuator, not an adjustable or positive choke. These requirements should be in 7.5.5 Hydrostatic Testing for Adjustable and Positive Drilling Chokes 7.5.6 Actuators for
section 7.5.7. Drilling Chokes 7.5.7 Functional Testing for Adjustable Drilling Choke and Choke/Actuator
Assemblies Section 7.5.6 applies to actuators, not adjustable and positive drilling chokes, and
7.5.6.2 belongs in the section. The preceding section 7.5.5 applies to adjustable and positive
drilling chokes. Section 7.5.7 applies to adjustable chokes assembled complete with an
actuator (manual or hydraulic), and does not include the actuator testing. The actuator
testing of 7.5.6, including 7.5.6.2, can be performed with the actuator alone, it need not be
installed on a choke. For that reason it is correctly located in 7.5.6, not 7.5.7.

Spec 16C 2nd 7.5.6.3 Question: Record retention requirements of 7.6.3 are specified as 5 years but in Response: No. No change is required. Section 4.10.4 applies to design documentation.
4.10.4 the requirement is 10 years. Section 7.6.3 applies to manufacturing and quality records. The retention requirements can
be different.
Spec 16C 2nd 7.5.13 Question: For manifolds assembled entirely with components that have been Response: Yes. The test pressure shall be rated working pressure, which would be the
subjected to a hydrostatic body test, can the test pressure for the manifold minimum.
assembly be 1.5X?
Spec 16C 2nd 10.8 Question: API Spec. 16C section 10.8 Table 28 lists flexible choke and kill line sizes Response: Although not defined in 16C, “inner diameter” is a straight line passing from side
and pressure ratings. For the size internal diameter (ID) is listed in inches and mm-s. to side through the center of the inside of the object. Not specified in 16C, the intent would
An ID tolerance or minimum requirement was not found in the specification. A be that the inner diameter reflects a uniform distance through the object. If not uniform, the
nominal 3,5” 5000 psi hose has been developed, with 3,5” (90 mm) actual ID in the inner diameter would be determined by the narrowest point. So using your example above,
hose body, and just under 3” (actually 75,3 mm, 2,96”) ID in a portion of the the expectation is that the ID mark would be identified as 3” if that is the narrowest point.
coupling. Is it allowed to use the above hose in 3,5” choke and kill service, and mark NOTE: API does not address the use of any equipment. “Use” is determined by the owner
the hose 3,5” ID, or the above hose can be used only in 3” service, and should be and/or manufacturer of the equipment. Response 2: Your question must be in the form such
marked 3” ID (as the minimum cross section is about 3”)?. Question 2: What is the that the answer is “yes” or “no”. However it is noted that Table 28 identifies the inner
requirement for the minimal ID, at its narrowest point, of a flexible pipe, if its diameter of flexible lines allowed for a given rated working pressure.
nominal ID is 2”, 2,5”, 3”, 3,5” or 4”?

Spec 16C 2nd 10.8.5 Question: Is it allowed to manufacture the kill line hose with straight machine Response: Yes.
threads on end termination?
Spec 16C 2nd 10.8.7 Question: Section 10.8.7 states that, “Flexible choke and kill lines shall be full bore, Response: No. There is currently no maximum value for the inner diameter defined for
with actual inside diameter not lower than 95% of their nominal inside diameter at flexible choke and kill lines.
their narrowest point, including end termination and end connector.” Does API
Spec16C, 2nd Edition include any requirement related to the maximum value for
the inner diameter of flexible choke and kill lines?
Spec 16C 2nd 10.11.2 Question: Section 10.11.2 states that, “The design pressure rating for the buffer Response: “New” is as-manufactured; prior to installation, field service, and any
chamber, new and cold, shall be clearly identified on the buffer chamber by means remanufacture. “Cold” means the baseline pressure rating (for -20 °F to 100 °F) in the
of a nameplate securely affixed to the buffer chamber itself.” we would like to get material-specific tables of Pressure-Temperature Ratings in ASME B16.5 (for ANSI flanges).
exact interpretation of "New and Cold" pressure rating got the buffer chamber. This used to be called the “cold working pressure” (CWP).

Spec 16C 2nd 10.12.4.3 Question: Is it a requirement of Section 10.12.4.3 or any other part of 16C that flow Response: No. There is no reference to API 14E within the API 16C document, either
analysis be performed to verify that the maximum flow velocity of 15 feet/second normatively or bibliographically. Therefore, there is no requirement of API 16C to determine
specified in API RP 14E Section 2.3 is satisfied within the choke and kill manifold maximum flow velocity in accordance with any requirements of API 14E
when in operation?
Spec 16C 2nd B.2 Question: B.2 states that the annex addresses the design validation procedures for ALL the Response: Your concern is duly noted. However, the interpretation, for the time being, must
products listed in section 1. With this paragraph written this way it would seem each style of be that C&K Manifold Assemblies require design validation since Annex B ties that
choke and kill manifold assembly would have to receive design validation testing, which requirement to the products listed in Section 1 (which includes C&K Manifold Assemblies).
include some large furnace that could contain a choke and kill manifold assembly so that low
With that said, this has been elevated to the chair of the 16C task group and he plans to make
and high temperature testing can be performed. This is an unnecessary burden to the
this a discussion point for an upcoming TG meeting to further discuss this requirement. • As
manufacturer and customer. Choke manifold assemblies are unique to the purchaser as they
change the configuration to meet their specific needs. The choke manifold assembly is made
an aside, there were a couple of assumptions you made in your inquiry that may reflect a
up of equipment from API 6A that meet API specification 6A PSL3 requirements. This means misunderstanding of API 6A. The applicable text is highlighted in yellow as follows “…each
the valves have already passed design validation testing required by API 6A Annex F. Why style of choke and kill manifold assembly would have to receive design validation testing,
would we be required to test everything again at temperature just because it was bolted which include some large furnace that could contain a choke and kill manifold assembly so
together into a choke manifold? I believe there was an attempt to blanket all items from API that low and high temperature testing can be performed…” Note that there is no universal
16C with design validation requirements, without regard to each specific equipment type requirement that design validation of any type of equipment requires testing at minimum
addressed by API 16C. Obviously drilling chokes, articulated choke and kill lines, drilling choke and maximum rated temperature.
actuators, flexible choke and kill lines, and swivel unions used in choke and kill equipment
have moving parts that also utilize elastomers which need testing at extreme temperatures.
• The choke manifold assembly is made up of equipment from API 6A that meet API
However buffer chambers, rigid choke and kill lines have no moving parts or elastomers and
specification 6A PSL3 requirements. This means the valves have already passed design
are made using connectors controlled by API 6A, not requiring validation. Why would they
need them for API 16C? We should at least be able to exempt assemblies made up of validation testing required by API 6A Annex F. This is commonly misunderstood but is not
equipment that have successfully passed individual design validation testing of API 6A and correct for the following reasons: (a) there is no required relationship between PSL and PR;
equipment having no moving parts, elastomers or constructed of equipment which the PSL 3 does not dictate PR2. (b) PR2 does not require testing in conformance with Annex F,
design utilizes only connectors controlled by API 6A. This is a very big concern because of the which is an informative, not normative annex. (c) API 16C Section 4.2 does not require PR2
cost involved with attempting to construct a testing facility that can heat and cool extremely for 6A equipment.
large choke manifold assemblies. API 16C 1st edition did not state that the design validation
applied to all equipment of section 1. Not specifying this allowed the user to perform design
validation only to the equipment specifically defined in section 9. What is API’s view point on
this?

Spec 16C 2nd B.11.8 Question: Sections B11.8.1 thru B11.8.6.2 do not mention the pressure applied by Response: No. Section B.11 makes reference to the choke and actuator assembly, and as
the choke. API 6A section F.2.5 states, “Test the actuator either on a valve/choke or such, any testing according to this entire section would be as actuator and choke together.
on a fixture that simulates the opening/closing dynamic force profile of a Furthermore, in Section B.11.2, the requirement is that the drilling choke with the actuator
valve/choke.” However, this verbiage is not present in API 16C second edition. assembled shall be installed in a fluid flow circuit or manifold. This requirement provides no
Additionally, the response for a previous interpretation on section 7.5.6.2 of 16C allowance for test stand or independent testing of the actuator assy. Also, Section B.11.3
stated, “The actuator testing of 7.5.6, including 7.5.6.2, can be performed with the discusses the capacity of the manifold apparatus and its ability to flow fluid across the choke;
actuator alone, it need not be installed on a choke.” For section B11.8 of API 16C, this defines the need for a choke in this testing sequence. Though Section B.11.8 does not call
2nd edition, can the choke actuator be tested alone, without the choke? out the choke, the preceding specifically speaks to choke and actuator to test the actuator.
Spec 16C 2nd G.2.2 Question 1: I accept there is a requirement for the Manifold and a requirement for Response 1: Yes, as per the 2nd sentence of G.2.2.2 a 4:1 ratio shall be required.
the Console, however Annex G details both. In G2.1g), it references pressure
transmitters on the Manifold and advises that the transmitter should be rated equal Response 2: Yes, this 4:1 ratio was directed at the use of hydraulic systems. For electrical
to or greater that the Manifold. G2.2.1 through G2.2.4 provides further details on systems this requirement does not apply.
the piston isolator transmitter, G2.2.4 specifically advises that the isolator should
“continue to isolate the process fluid” This is clearly indicating that the transmitter
must be on the manifold to be able to isolate process fluid. If the console includes
Analogue Gauges and the source pressure is above 10,000psi those hydraulic lines /
hoses are required to be turn downed by a ratio of 4:1 Correct? Question 2: If the
console does not have Analogue Gauges ONLY Digital Indicators which require
electrical signals only there is no requirement to turn down the pressure source.
Correct?
Spec 16C 2nd G.2.3 Question: The API 16C standard states that the choke open/close time should be 30 Response: Yes. The assumption is correct. Given the variables that cannot be controlled by
seconds. It also states that an emergency back-up device be in place in event of the manufacturer of the hand pump; the time limits for choke response do not apply to this
failure of the air-hydraulic pump. Our choke and kill consoles do have a Primary specific case. .
airhydraulic pump, then as a back-up has a secondary air-hydraulic pump. The
console does have accumulator as well which has stored pressure/flow in case the
both the primary and secondary pump becomes inactive. In addition to all this,
there is also a hand pump. The hand pump in its design always puts out very small
flow and depends on the individual ability to pump as much strokes as possible
something different from air-hydraulic pump which are not human operated. Since
the hand pump is a back-up of back-up solution in place to pump pressure/flow for
emergency cases, is it safe to assume that this does not require any time limits to
open/close choke like the primary pumps do as API 16C does not state in its spec
regarding times for using something like hand pump?
Spec 16C 2nd G.2.3.1 It is clear from the content of the clause that “rig power” is not electrical, it is air. Response: Yes. The mandatory requirement is for the existence of connections and fittings
Our console would normally have an air driven pump, consequently we provide for an alternate power source. What follows in that clause with “such as…” is an example and
connections and valves for a nitrogen supply to replace the lost air supply. not mandatory.
Consequently we comply with this clause correct?
Spec 16C 2nd G.2.3.2 Our choke control system is hydraulically operated The clause is advising that there Response: No. The requirement (shall) is explicit and a hand pump (and related equipment)
should be a hand pump to permit manual operation of the choke control system in to permit manual operation is mandated. The use of an air driven pump does not meet this
the event of failure of the “main hydraulic pump”.. Our console does not rely on the requirement.
rig hydraulic supply it has its own self contained hydraulic reservoir which is
powered by an air driven pump. Since the air driven pump has a nitrogen back up as
required in G.2.3.1 and we are not connected / dependent upon the rig hydraulic
supply / main pump we believe there is no requirement to have a hand pump, is
this correct?
Spec 16C 2nd Annex B Question: Buffer chamber : We are in the design process of Buffer Chamber at rated Response: No. Only hydrostatic testing temperature performed at 1.5 times rated working
temperature K ( -75⁰ F to 180 ⁰ F) as per API 16 C We have selected the material as pressure is to be performed. The OEM defines the test temperature for these parts. Annex
per API 16 C requirements including chemical and mechanical. The Impact tests are A.12 states that design validation requirements for the choke and kill buffer chamber shall be
performed at -60⁰ C and the results are well above the requirements. All outlets satisfied by the hydrostatic test.
(Weld NEck Flanges have been made as per API 6A we have selected the material
and Hydrostatic tested as per requirements as per the same (API) specification
requirements, There were no other parts apart from the steel material as per
applicable API specification. Please clarify that the testing a minimum/maximum
Temperature are required as part of Design Validation If so please what are the
design validations are applicable as testing at these temperatures are nearly
impossible for all the products.
Spec 16C 2nd B.9.4.3.5 Question: Shall we repeat steps 1 through 13 five times or just once? Response: Repeat steps 1-13 just once.