• be_ixf; php_sdk; php_sdk_1.4.11
  • 15 ms
  • iy_2023; im_12; id_04; ih_09; imh_08; i_epoch:1.70170971305E+12
  • ixf-compiler; ixf-compiler_1.0.0.0
  • py_2018; pm_11; pd_14; ph_12; pmh_14; p_epoch:1.54222645072E+12
  • link-block; link-block_link-block; bodystr
  • pn_tstr:Wed Nov 14 12:14:10 PST 2018; pn_epoch:1.54222645072E+12
  • 0 ms
  • be_ixf; php_sdk; php_sdk_1.4.11
  • https://www.naes.com/news/leak-testing-with-helium-helps-eliminate-degradation-of-gas-turbine-performance/
  • https://www.naes.com/news/leak-testing-with-helium-helps-eliminate-degradation-of-gas-turbine-performance/
Skip to content
NAES
  • Twitter
  • LinkedIn
  • Services
    • Power Services
    • Compliance & Fleet Services
      • Engineering
      • E3 Consulting
      • O&M Services
      • Regulatory Compliance Services
      • Maximo Services
      • Field Engineering and Research
    • Fabrication, Maintenance, & Construction
    • Staffing Services
  • About Us
    • Subsidiaries
    • Leadership
  • Communications
    • News
    • Case Studies
    • Press Releases
  • Careers
  • Contact
    • Contact a Location
    • NAES Login Center
Solar Panels

In the News

Home Communications In the News Leak-Testing with Helium Helps Eliminate Degradation of Gas Turbine Performance

7.15.2019

Leak-Testing with Helium Helps Eliminate Degradation of Gas Turbine Performance

by Hugo Ordoñez Ruiz and Henry Barrios García – Plant Manager and Plant Engineer, Nuevo Pemex Cogeneration Facility

The Challenge

The Nuevo Pemex cogeneration facility, located in the State of Tabasco, Mexico, is equipped with two GE
MS7001FA combustion turbines, each with a single-stage pressure HRSG. In cogeneration mode, the plant
generates 277 MW and 1.76 million lbs/hr of steam.

Photo of Henry and Hugo – Plant Manager Hugo Ordonez Ruiz (right) and Plant Engineer Henry Barrios
Garcia: ‘Using the helium-spray method provides a high level of sensitivity as well as quantifiable and
reliable results.’

Maintaining the performance of gas turbines in accordance with OEM specifications as well as estimated
life-cycle degradation is vital for proper plant operation. Scheduling regular maintenance to identify and
repair air leaks in the air intake duct prevents fouling of the axial compressor turbine, erosion effects and
deposits in the compressor rotor – all of which degrade performance (figure 1).

Figure 1 – Severe gas turbine compressor fouling

Leaks can be caused by several factors, including defective expansion joints or manhole seals, defective
welds and faulty component assembly. Several household items can be used to test informally for vacuum
leaks: tissue paper, plastic wrap, soap foam, smoke and shaving cream. However, more sophisticated
technologies deliver more precise, quantifiable results:

  • Ultrasonic measurement (UT)
  • Vacuum decay test or pressure rise test
  • Helium sniff
  • Helium spray

Each of these has its pros and cons. For example, ultrasonic emits a sound that can be higher or lower,
depending on the size and frequency of the leak. Very small leaks emit a very high frequency sound that is
beyond our hearing range. This method is not reliable in complex systems where ultrasonic sounds can be
produced by multiple leaks as well as other sources. In addition, the leak rate can only be estimated – not
accurately measured. With a typical sensitivity of only 10-2 mbar·liter/second, ultrasonic instruments are
suitable for finding large leaks but not the fine ones typically found in a combustion turbine.

Using the helium spray method, on the other hand, provides a high level of sensitivity as well as
quantifiable and reliable results. Helium gas is introduced into the turbine’s air intake, where it mixes with
ambient air. A mass spectrometer probe is used to detect any helium present at the ninth compression
stage. This technology is sensitive enough to detect leaks that traditional methods such as pressure decay
and bubble-testing won’t find.

Helium gas makes an excellent tracer. It’s non-toxic, inert, non-explosive, with a particle size so small that it
flows freely through any pores or imperfections. Because the ambient atmosphere typically has a helium
concentration of only 5 ppm, it allows for greater sensitivity in the test. Before spraying, we measured the
amount of helium in the ambient air to establish a baseline. Any value that exceeded this zero point would
indicate a leak.

Figure 2 – Ninth-stage compressor line modification

The helium spray method is effective with equipment such as a turbine, which generates a vacuum during
operation. The gas in the turbine’s air intake duct has a lower differential pressure (relative to the
atmosphere). We sprayed helium on each of several areas considered to be susceptible to leaks. If the
helium-enriched air entered the axial compressor through a leak, it was detected in the air sample taken
from the ninth compression stage.
Since helium is a very light gas, it’s important to perform the test on the upper parts of the equipment. It
expands rapidly and tends to rise, so if sprayed in a lower area, it can potentially enter a different leakage
test point and thus register as a false point of leakage.

The Solution

During a planned outage prior to the air leak test, we modified a ninth-stage compressor water drain pipe
by adding a ‘figure 8’ blind flange downstream of the 2-inch shut-off ball valve. Between these two fixtures,
we installed a sampling port with a ¼-inch ball valve (figure 2). During the test, we opened the sampling
port, allowing continuous extraction of small amounts of air from the compressor. This enabled us to
position the helium probe so that it wouldn’t affect turbine operation (figure 3).

Figure 3 – ¼” sampling point in the water drain line

We then determined the time it takes helium to travel from the point of spray to the sampling point. To do
this, we sprayed the helium directly upstream of the first-stage filtration system. Travel time for the helium
was approximately two seconds, which we used as the reference period.
Sometimes when we injected helium in areas near air pre-filters – around an implosion door, for example –
and the detection time was greater than two seconds, we concluded that there was a leak. However, the
same air flow and turbulences suck air with helium concentration in the environment to the filtration
system. So when we obtained a reading that suggested the existence of a leak, we found it was necessary
to check the measured value against the reference value – which revealed a detection time of less than two
seconds.

Using a Pfeiffer HLT560 mass spectrometry leak detector, we tested the following locations:

  • Manhole registers (figure 4)
  • Instrumentation tubing and fittings
  • Expansion joints
  • Implosion door
  • IBH pipe flanges
  • Rainwater drain pipe between the pre-filters and fine filters
  • Thermocouples
  • Nozzles for offline washing system

The Results

We found no major leaks, but we did find small ones in the offline washing nozzles. These were sealed with
silicone until we could permanently repair them.
Note: We weren’t able to perform leak-testing on the online water wash nozzles due to high operating
temperatures. However, based on our findings with the offline nozzles, we sealed the online nozzles as well
during a subsequent planned outage. We found a few other small leaks in the differential-pressure
transmitter fittings, one in the manhole register and one in an expansion joint.
We achieved our main objective: optimizing air flow to the compressor. Because the leaks we encountered
and sealed were small both in size and number, we were not able to detect a measurable uptick in turbine
performance. However, performance improvements in facilities where significant leaks are detected and
repaired have been well documented.

Join the Conversation

  • Twitter
  • LinkedIn
NAES

© Copyright 2023 NAES. All rights reserved.

  • Privacy Policy
  • Terms of Use
  • Do Not Sell My Personal Information

Website design by Jordan Crown

  • Services
    • Power Services
    • Compliance & Fleet Services
      • Engineering
      • E3 Consulting
      • O&M Services
      • Regulatory Compliance Services
      • Maximo Services
      • Field Engineering and Research
    • Fabrication, Maintenance, & Construction
    • Staffing Services
  • About Us
    • Subsidiaries
    • Leadership
  • Communications
    • News
    • Case Studies
    • Press Releases
  • Careers
  • Contact
    • Contact a Location
    • NAES Login Center

‹ › ×
    Manage Cookie Consent
    We use cookies to optimize our website and our service.
    Functional cookies Always active
    The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.
    Preferences
    The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.
    Statistics
    The technical storage or access that is used exclusively for statistical purposes. The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.
    Marketing
    The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.
    Manage options Manage services Manage vendors Read more about these purposes
    View preferences
    {title} {title} {title}
    CAISO Generator Modeling Process and Data Requirements

    Don’t wait until the last minute. You should allow time for at least one iteration with CAISO so that you are complete and deemed compliant before your deadline.

    On August 1, 2018, CAISO introduced a revised Business Practice Manual for Transmission Planning Process (BPM), which includes new data requirements for interconnected generation resources within the ISO’s footprint. Section 10 of the BPM establishes revised data requirements and compliance procedures for all participating generators including non-NERC registered entities. While additional requirements have been placed on larger NERC registered facilities, these changes may pose an even greater burden to entities that have been exempt from NERC mandated modeling and protection requirements.

    New data requirements include voltage and frequency protection models, power flow models, and in some cases, sub-synchronous resonance models. These models must be verified using criteria listed in the BPM, which can only be performed by entities with modeling software and knowledge of modeling practices.

    NAES is prepared to assist entities with data aggregation, modeling, and testing to ensure compliance with CAISO’s data requests. The following links will allow entities to determine when to expect their individual data requests (phase) and what data will be required (category).

    Business Practice Manual (BPM)

    Entity Category and Phase Listing

    CAISO Transmission Planning Website

    TPL-007

    TPL-007 establishes planning criteria for induced currents caused by geomagnetic disturbances. The standard is applicable to facilities using transformer(s) with a high side, wye grounded winding operated above 200 kV and can require both submittal of general geomagnetic data (R2) and thermal impact assessments (R6) depending on results of Planning Coordinator analysis.

    VOLTAGE AND REACTIVE (VAR) STANDARDS

    VAR-501-WECC

    VAR-501-WECC requires applicable entities within the WECC region to confirm performance settings and characteristics of Power System Stabilizers (PSS). NAES provides physical testing and reporting services to address WECC’s specific PSS requirements.

    PERSONNEL PERFORMANCE, TRAINING AND QUALIFICATIONS

    PER-006

    PER-006 requires Generator Operators to provide training to personnel who are responsible for the Real-time control of a generator. NAES has developed specific protection system training materials suitable for compliance with the Standard and provides this training both on and off site

    PROTECTION AND CONTROL (PRC) STANDARDS

    PRC-001

    PRC-001 requires entities to coordinate protection system changes with other affected parties. NAES offers both procedural documentation and engineering services to establish the required coordination for both PRC-001 and PRC-027.

    PRC-002

    PRC-002 requires the installation and operation of disturbance monitoring equipment (DME) for applicable entities. NAES can assist with the design and installation of DME as well as ongoing compliance support.

    PRC-019

    PRC-019 requires applicable entities to show coordination between voltage regulating controls, limiters, equipment capabilities, and protection settings. NAES produces PRC-019 specific coordination studies for both traditional generators and renewable projects to establish compliance with the Standard.

    PRC-023

    PRC-023 requires load responsive protective relays be set according to criteria within the Standard to ensure settings do not limit transmission loadability. NAES provides full engineering analyses to maintain compliance with this Standard.

    PRC-024

    PRC-024 requires applicable entities to ensure generator protective relays do not trip within predefined frequency and voltage limits. NAES can complete protection settings analyses and provide compliance documentation that clearly identifies protection settings as they relate to NERC’s “no trip” zones.

    PRC-025

    PRC-025 establishes minimum settings requirements for load-responsive relays protecting generators, step up transformers, and auxiliary transformers. NAES utilizes predefined calculation options as well as simulations to determine a facility’s compliance status and development of new relay settings if required.

    PRC-026

    PRC-026 requires applicable entities to perform load responsive relay settings analyses based on criteria identified within the Standard. Entities are typically notified by the Planning Coordinator when an analysis is required. NAES performs all required studies to establish compliance.

    MODELING, DATA, AND ANALYSIS (MOD) STANDARDS

    MOD-025

    MOD-025 requires Real and Reactive Power capability testing for individual generating units over 20 MVA or facilities with over 75 MVA of generation capacity. NAES offers site specific test procedures and/or complete onsite testing services to meet the requirements of this standard.

    MOD-026

    MOD-026 requires verification of excitation or volt/var control dynamic models through utilization of either system disturbances or physical testing. NAES offers full testing and modeling services to meet the requirements of this standard.

    MOD-027

    MOD-027 requires verification of governor or active power/frequency control dynamic models through utilization of either system disturbances or physical testing. NAES offers full testing and modeling services to meet the requirements of this standard.